The Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) of the United Nations (report known as AR4 for its acronym in English 4th Assessment Report) is the fourth in a series of reports with the purpose of evaluating from scientific, technical and socioeconomic points of view the known information regarding climate change, its potential effects and alternatives for mitigation and adaptation to it. The report was the most extensive, detailed and up-to-date summary of the climate change situation to the date of its writing (2007). Around 500 main authors and 2,000 expert reviewers participated in its writing, including scientists, economists and politicians from around 120 countries.[1].
Information
The fourth evaluation report (AR4, 2007)[2] was published with the following four different parts:
• - Report of Working Group I (WGI or Working Group I): Climate Change 2007: The Physical Science Basis. In Spanish: Summary for policy makers, technical summary and frequently asked questions[3].
• - Report of working group II (WGII): Climate Change 2007: Impacts, Adaptation and Vulnerability. In Spanish: Summary for policy makers and technical summary[4].
• - Report of working group III (WGIII):[5] (Climate Change Mitigation). In Spanish: Summary for policy makers and Technical Summary[6].
For this last section, the IPCC published the main report and summary, known as the Summary for Policy Makers. The full report summaries have been published as summaries of each of the WGI, WGII and WG III working groups, plus the report synthesis.
Conclusions
Among its conclusions, the report establishes the following (in the Synthesis Report):
About observed changes in climate, and their effects:.
• - The warming of the climate system is unequivocal, as evidenced by the observed increases in the global average of air and ocean temperatures, the widespread melting of snow and ice, and the rise in the global average of sea level.
Optimistic scenario
Introduction
The Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) of the United Nations (report known as AR4 for its acronym in English 4th Assessment Report) is the fourth in a series of reports with the purpose of evaluating from scientific, technical and socioeconomic points of view the known information regarding climate change, its potential effects and alternatives for mitigation and adaptation to it. The report was the most extensive, detailed and up-to-date summary of the climate change situation to the date of its writing (2007). Around 500 main authors and 2,000 expert reviewers participated in its writing, including scientists, economists and politicians from around 120 countries.[1].
Information
The fourth evaluation report (AR4, 2007)[2] was published with the following four different parts:
• - Report of Working Group I (WGI or Working Group I): Climate Change 2007: The Physical Science Basis. In Spanish: Summary for policy makers, technical summary and frequently asked questions[3].
• - Report of working group II (WGII): Climate Change 2007: Impacts, Adaptation and Vulnerability. In Spanish: Summary for policy makers and technical summary[4].
• - Report of working group III (WGIII):[5] (Climate Change Mitigation). In Spanish: Summary for policy makers and Technical Summary[6].
For this last section, the IPCC published the main report and summary, known as the Summary for Policy Makers. The full report summaries have been published as summaries of each of the WGI, WGII and WG III working groups, plus the report synthesis.
Conclusions
Among its conclusions, the report establishes the following (in the Synthesis Report):
• - Observations made on all continents and in most oceans show that numerous natural systems are being affected by changes in the regional climate, particularly by an increase in temperature.
• - With a medium level of confidence, other effects of regional climate change on the natural and human environment are beginning to appear, although many of them are difficult to identify due to adaptation and other non-climatic sources.
About the causes of change:
• - Global greenhouse gas (GHG) emissions due to human activities have increased, since the pre-industrial era, by 70% between 1970 and 2004.
• - Global atmospheric concentrations of CO2, methane (CH4) and nitrous oxide (N2O) have increased markedly as a result of human activities since 1750, and are currently much higher than pre-industrial values, determined from ice cores spanning many millennia.
• - Most of the observed increase in global average temperature since mid-century is most likely due to the observed increase in anthropogenic GHG concentrations. It is likely that appreciable anthropogenic warming has occurred over the past fifty years, on average for each continent (except the Antarctic region).
• - Progress since the Third Assessment Report indicates that discernible human influences are not limited to average temperatures, but also encompass other aspects of climate.
• - Anthropogenic warming over the past three decades has likely exerted a globally discernible influence on observed changes in many physical and biological systems.
About projected climate change and its impacts:
• - There is a high level of agreement and abundant evidence that with current policies to mitigate the effects of climate change and the sustainable development practices that they entail, global GHG emissions will continue to increase in the coming decades.
• - If GHG emissions continue at a rate equal to or higher than the current one, warming would increase and the global climate system would experience numerous changes during the century, most likely greater than those observed during the century.
• - The current degree of confidence is higher than that of the Third Assessment Report regarding the projected patterns of warming and other regional-scale aspects, such as changes in wind or precipitation patterns, and certain aspects of extreme values and sea ice.
• - The studies carried out since the Third Assessment Report have made it possible to understand in a more systematic way the chronology and magnitude of the impacts linked to different magnitudes and rates of climate change.
• - The alteration in the frequency and intensity of extreme weather events, added to the rise in sea level, will foreseeably have extremely adverse effects on natural and human systems.
• - Anthropogenic warming and sea level rise will continue for centuries due to the magnitude of the time scales associated with climate processes and feedbacks, even if GHG concentrations stabilize.
• - Anthropogenic warming could produce abrupt or irreversible impacts, depending on the speed and magnitude of climate change.
On adaptation and mitigation options:
• - A great diversity of adaptation options is available, but even greater adaptation than the current one will be necessary to reduce vulnerability to climate change. There are obstacles, limits and costs that have not been sufficiently analyzed.
• - Adaptive capacity is closely related to social and economic development, although it is unevenly distributed both between and within societies.
• - Studies, from both a bottom-up and top-down perspective, indicate that there is a high level of agreement and abundant evidence that there is substantial economic potential to mitigate global GHG emissions in the coming decades, which could offset the projected growth in global emissions or reduce them below current levels. Although both types of studies agree at the global level, they exhibit considerable differences at the sectoral level.
• - Governments have a wide variety of policies and instruments to create incentives that prioritize mitigation measures. Its applicability will depend on national circumstances and the sectoral context.
• - There are multiple options to reduce global GHG emissions through international cooperation. There is a high level of agreement and abundant evidence that the establishment of a global response to climate change, the stimulation of a range of national policies and the creation of an international carbon market and new institutional mechanisms in this regard are notable achievements of the UNFCCC and its Kyoto Protocol that could provide the basis for future mitigation efforts. Progress has also been made in addressing adaptation within the UNFCCC and further international initiatives have been suggested.
• - In several sectors it is possible to implement response options to obtain synergies and to avoid conflicts with other dimensions of sustainable development. Decisions on macroeconomic and other non-climate policies can significantly affect emissions, adaptive capacity, and vulnerability.
About the long-term perspective.
• - Determining what is meant by “dangerous anthropogenic interference with the climate system” in relation to Article 2 of the UNFCCC involves value judgments. Science, in this regard, can help make informed decisions, in particular by providing criteria for deciding which vulnerabilities could be considered “key”.
• - The 'five areas of concern' identified in the Third Assessment Report continue to constitute a viable framework for the study of key vulnerabilities. In the present work, these 'aspects' are considered more worrying than in the TIE. Many of the risks are identified here with a higher degree of confidence. Some will be larger, according to projections, or will occur with smaller increases in temperature. The relationship between impacts (the basis for the TAR “issues of concern”) and vulnerability (including the ability to adapt to impacts) is now known in greater detail.
• - There is a high degree of confidence that neither adaptation nor mitigation alone will avoid all the impacts of climate change; They can, however, complement each other and, together, significantly reduce the risks of climate change.
• - Many of the impacts can be reduced, delayed or avoided through mitigation measures. Mitigation efforts and investments over the next two to three decades will largely determine the opportunities to achieve lower stabilization levels. The delay in reducing emissions will significantly reduce these opportunities, and will increase the risk of worsening the repercussions of climate change.
• - There is a high level of agreement and abundant evidence that all the stabilization levels studied can be achieved by implementing a series of technologies currently available or expected to be commercialized in the coming decades, assuming that there are appropriate and effective incentives for their development, acquisition, implementation and dissemination, and to address the corresponding obstacles.
• - The macroeconomic costs of mitigation tend to increase as the restrictive nature of the stabilization objective increases. For certain countries and sectors, costs will vary considerably from the global average.
• - The response to climate change involves an iterative risk management process that encompasses both adaptation and mitigation measures and takes into account harms, co-benefits, sustainability, equity and attitudes to risk in relation to climate change.
Working Group I (WGI): scientific and physical bases
Contenido
El resumen del Grupo de Trabajo I (WGI) para los responsables de políticas (del inglés SPM o Summary for Policymakers)[8] fue publicado el 2 de febrero de 2007 y revisado el 5 de febrero de 2007. El informe completo de WGI[9] fue publicado en marzo y actualizado el 5 de septiembre de 2007. Se ha hecho accesible la página 34 sobre preguntas frecuentes del documento.[10].
Cambio climático 2007: Las bases científico físicas, del informe WGI, “evalúa con el actual conocimiento científico los cambios naturales y antropomórficos de cambio climático, cambios observados en el clima, la fiabilidad de la ciencia actual, para atribuir los cambios a diferentes causas, y proyecciones para el futuro del cambio climático”.
El informe fue producido por 620 autores y editores de 40 países y revisado por más de 620 expertos y gobiernos. Antes de ser aceptado, el sumario fue revisado línea por línea por representantes de 113 gobiernos durante la Décima Sesión de WGI,[11] que tuvo lugar en París, Francia, entre 29 de enero y 1 de febrero de 2007.
Sobre la cuestión de calentamiento global y sus causas, el SPM estableció que:[8].
• - “el calentamiento de el sistema climático es inequívoco”.
• - “La mayoría del incremento observado de la temperatura desde mediados del siglo XX responde ´muy probablemente´ al incremento antropomórfico en los niveles de concentración de gases de efecto invernadero”.
La Nota al pie 6 en la página 3 del resumen indica que ´muy probablemente´ y ´probable´ significan “la posibilidad de evaluar, usando opiniones de expertos” con un nivel de confianza del 90% y del 66%, respectivamente.
Observations
The report shows many observed changes in Earth's climate and atmosphere composition, global measured temperatures, ocean conditions and other climate changes.
Carbon dioxide, methane and nitrous oxide are all long-lived greenhouse gases.
• - Carbon dioxide, methane, and nitrous oxide have increased markedly as a result of human activities since 1750 and are now far exceeding pre-industrial values.
• - The amount of atmospheric carbon dioxide was (379 ppm) in 2005, far exceeding the natural ranges of the last 650,000 years (180 to 300 ppm).
• - The amount of atmospheric methane is (1774 ppm for 2005 and greatly exceeds the natural ranges of the last 650,000 years (between 320 ppm and 790 ppm).
• - The primary source of the increase in carbon dioxide is the use of fossil fuels, but the use of land (for agriculture, livestock, etc.) also contributes to this increase.
• - The primary source of the increase in methane is the combination of agricultural activities and fossil fuels, although it is not well determined how much each contributes.
• - Nitrous oxide concentrations have increased from pre-industrial values of 270 ppm to 319 ppm in 2005. More than a third of this increase is due to human activity, primarily agriculture.
Cold days, cold nights, and events like frost have become less frequent. Warm days, warm nights, and heat waves are more frequent. Additionally:.
• - Ten of the eleven years of the period (1995-2006) were in the ranking of the 12 warmest years in the instrumental record (since 1850, towards the end of the Little Ice Age).
• - Warming in the last 100 years has caused an increase of 0.74 °C in global temperature. Being 0.6 °C the increase predicted in the previous IPCC Third Assessment Report.
• - The urban heat island effect has a negligible influence (less than 0.0006 °C per decade over land and 0 over oceans) on the measurements.
• - Observations since 1960 showed that the oceans have been absorbing 80% of the heat added to the climate system, and that the temperature in the oceans has increased to depths of 300 m (9,800 ft).
• - “Temperatures in the Arctic have increased twice as much as the global temperature rate in the last 100 years.”
• - It is likely that greenhouse gases have caused more warming than observed that could have been amalgamated by the cooling effect of volcanoes and aerosol gases emitted by humans. See Global Dimming.
• - Northern Hemisphere mean temperatures during the second half of the century were higher than any 50-year period in the previous 500 years and the highest of the last 1,300 years (including the Medieval Warm Period and the Little Ice Age).
The Summary for Policymakers (SPM) documents showed an increase in wind intensity, a reduction in permafrost cover, increases in both droughts and heavy rainfall. Additionally:.
• - “The surface of mountain glaciers and snow cover has decreased in both hemispheres.”
• - Losses in the Greenland and Antarctic ice sheets have probably contributed (>90%) to sea level rise between 1993-2003.
• - Warming oceans cause seawater to expand, contributing to sea level rise.
• - Sea level has increased at an average rate of 1.8 mm/year during the period 1961-1993. And during the period 1993-2003 the rate has increased to 3.1 mm/year. Although it is not clear if it is a long-term change or a temporary variability.
• - Antarctic sea ice shows that there is no significant general trend consistent with a lack of warming in the region.
• - The intensity of hurricanes in the North Atlantic has increased since the 1970s and this increase is correlated with the increase in water surface temperature.
• - The observed increase in hurricane intensity is greater than what climate models predict for the changes experienced in surface temperature.
• - There is no clear trend in the number of hurricanes.
• - Other regions also appear to have experienced an increase in hurricane intensity, but there are concerns about the quality of the data for these regions.
• - It is more likely that no more than (>50%) has a human relationship or contributions to the increase in hurricane intensity.
• - It is likely (>66%) that we will see an increase in the intensity of hurricanes in the century.
Factors that warm or cool the planet
AR4 describes the warming and cooling effects of the planet in items of radiative forcing – the rate of change of energy in the system, measured as power per unit area (in SI units, W/m²). The report shows in detail the individual contributions (positive forcing) of carbon dioxide, methane, nitrous oxide, organohalogens, and other human factors that produce warming, and warming effects due to the origin of solar activity. It also shows cooling effects (negative forcing) of aerosol, land use changes"), and other human activities. All values are shown as changes from pre-industrial conditions.
• - The total radiative forcing of the sum of all human activities is +1.6 watts/m².
• - The radiative forcing of the increase in solar radiation since 1750 is +0.2 watts/m².
• - The radiative forcing of carbon dioxide, methane, and nitrous oxide combined is most likely (>90%) increasing faster during the current era (1750-present) than at any other time in the last 10,000 years.
Climate sensitivity
Climate sensitivity is defined as the average amount of surface warming following a doubling of carbon dioxide concentrations. It is likely to be in the range of 2 to 4.5°C, with the best estimate at 3°C. This range of values is not a projection of the temperature rise we will see in the century, when future changes in carbon dioxide concentrations are not known, the factors behind carbon dioxide concentrations affect temperature.
Projections for the future based on the model
The model projections are based on the analysis of several computational models run in different SRESS scenarios. As a result, the predictions for the century, shown below.
• - Surface air temperature in the century:.
• - * Best estimates in the “low scenario”[15] is 1.8 °C with a probable range of 1.1 to 2.9 °C.
Best estimates for a “high scenario”[16] is 4.0 °C, with a probable range between 2.4 and 6.4 °C.
An increase in temperatures of 0.1 °C per decade is expected for the next two decades, even if concentrations of greenhouse gases and aerosols were maintained at 2000 levels.
A temperature increase of 0.2 °C per decade is projected in all SRES scenarios for the next two decades.
Confidence in these short-term protections is strengthened by the relationship between the old models and the observed temperature increase.
• - It is estimated that the rise in sea level, based on multiple models that all exclude the flow of ice sheets") due to lack of basis in scientific publications,[17] will be:
on the low stage[15] from 18 to 38 cm
on the high stage[16] from 26 to 59 cm.
• - It is very likely that there will be an increase in hot periods, heat waves and heavy rain events.
• - There is likely to be an increase in areas affected by drought, the intensity of tropical cyclones (including hurricanes and typhoons), and the occurrence of large tides.
• - “The Arctic ice cap is estimated to shrink in both the Arctic and Antarctic... In some projections, the Arctic ice sheet will disappear almost entirely during the summer by the latter part of the 21st century.”
Projections for specific scenarios are based on multiple analyzes running many climate models and using various SRES scenarios. The “low scenarios” refer to B1, and are the most optimistic family of scenarios. “High scenarios” refer to A1F1, the most pessimistic family of scenarios.
There are six SRES scenario families, and AR4 includes projected temperatures and sea level rise (excluding future rapid changes in ice flow dynamics[18]) for each scenario family.
• - Scenario B1
Best estimates of temperature increase of 1.8°C with a likely range of 1.1 to 2.9°C.
Sea level rise with a probable range of [18 to 38 cm].
• - A1T Scenario
Best estimates of temperature rise of 2.4°C with a likely range of 1.4 to 3.8°C.
Sea level rise with a probable range of [20 to 45 cm].
Selected quotes from the Summary for Policymakers of Working Group I
“Both past and future anthropogenic carbon dioxide emissions will continue to contribute to warming and sea level rise for more than a millennium, due to the time scale required to remove this gas from the atmosphere.”
Reactions to the content of the report of Working Group I (WGI)
In the weeks before the first report was published, controversy erupted over projections of sea level change, which in the new report was estimated lower than in previous estimates. The text now published gives a warning that new estimates of sea level rise may be low. ”Dynamic processes related to ice flow not included in current models but suggested by recent observations may increase the vulnerability of ice sheets to warming, increasing future sea level rise.” The midpoint of sea level rise is estimated to be within ±10% of those announced in TAR; but the range has been reduced.
Martin Rees, the president of the Royal Society, said, "This report makes it clear, more convincingly than before, that human actions are largely written into the changes we are seeing, and will see, in the climate. The IPCC strongly emphasizes that substantial climate changes are inevitable, and that we will have to adapt to them. This should compel all of us – world leaders, businesses and individuals – towards action rather than paralysis by fear. We need to reduce our greenhouse gas emissions and prepare us for the impacts of climate change. Those who want to claim otherwise can no longer continue using science as the basis of their arguments.[19]"
United States Secretary of Energy Samuel Bodman said at a conference on the report that it had “solid scientific foundations” and that “as the president has said, and this report makes clear, human activity is contributing to changes in our earth's climate and this point is no longer up for debate.” [20] Kurt Volker, Principal Deputy Assistant Secretary for European and Eurasian Affairs, said “We support the recent IPCC report, in which scientists Americans played an important role.”[21].
Based on the report, 46 countries made the "Paris call to action" statement, read by French President Jacques Chirac, calling for the creation of a United Nations Environment Organization (UNEO), which would have more capacity than the current United Nations Environment Program (UNEP), and would follow the model of the more powerful World Health Organization. The 46 countries included the nations of the European Union, but notably did not include the US, China, Russia, and India, the four largest emitters of greenhouse gases.[22].
Working Group II (WGII): Impacts, adaptation and vulnerability
El Resumen para Responsables de Políticas del Grupo de Trabajo II[23] fue publicado el 6 de abril de 2007. El informe completo[24] fue publicado el 18 de septiembre de 2007.
El WGII estableció que “evidencia de todos los continentes y la mayoría de los océanos muestra que muchos sistemas naturales han sido afectados por cambios climáticos regionales, particularmente incrementos en la temperatura.”.
Some changes have been associated with climate changes at different confidence levels.
With high confidence (about 80% chance of being correct) the WGII states that climate change has led to:
• - More and larger glacial lakes.
• - Increase in soil instability in permafrost regions.
• - Increase in rock avalanches in mountainous regions.
• - Changes in some Arctic and Antarctic ecosystems.
• - Increased runoff and an early spring discharge peak in glacier- or snow-fed rivers.
• - Changes that affect algae, plankton, fish and zooplankton due to increases in water temperature and changes in:
ice coverage
salinity
oxygen levels
water circulation.
With high confidence (around 90% chance of being correct) the WGII states that climate change is affecting biological systems in these aspects:
• - Spring events such as leaf opening, egg laying, and migrations are occurring earlier.
• - Towards the poles and towards higher latitudes, there are changes in the variability of plant and animal species.
Attribution of changes
The WGII recognizes the difficulty of attributing specific changes to human-caused global warming, stating that “Limitations and gaps prevent attribution of causes to observed systems rather than to anthropomorphic warming” but found that the agreement between observed and projected changes was “However…sufficient to conclude with great confidence that anthropomorphic warming over the past three decades has had a discernible influence on many physical and biological systems.”
Projections
The WGII outlines some of what it forecasts for the coming century, based on studies and model projections.
It is projected with a high level of confidence that:.
• - dry regions become drier, and humid regions become wetter. “By mid-century, average annual river runoff and water availability are projected to increase by 10 – 40% in high latitudes and some tropical areas, and decrease by 10 – 30% over some arid regions in mid-latitudes and in the dry tropics…”.
• - Drought-affected areas will become larger.
• - Heavy rainfall events are very likely to become common and the risk of flooding will increase.
• - Water supplies stored in glaciers and snow cover will be reduced over the course of the century.
It is projected with a great level of confidence that:.
• - The resilience "Resilience (ecology)") of many ecosystems is likely to be exceeded in this century by the combination of global warming and other causes of stress.
• - la remoción de carbono por los ecosistemas terrestres es probable que llegue a un pico antes de mitad de centuria y a continuación se debilitara o revertirá. This will amplify climate change.
The Working Group III projection, with medium confidence (about 5 in 10 chances of being correct), is that globally, food production potential will increase with a temperature increase of 1 – 3 °C, but will decrease at higher temperature ranges.
It is projected with a great level of confidence that:.
• - coasts will be exposed to increased risk such as coastal erosion due to climate change and sea level rise.
• - “increases in sea surface temperature of 1–3 °C, resulting in more frequent coral bleaching events and general mortality, unless there is adaptation to temperature change or acclimatization of the corals.”
• - that “many millions of people” will be subject to flooding every year due to rising sea levels by the 2080s.”
Objections to the original text of the WGII
U.S. negotiators managed to remove text calling for eliminating greenhouse gas emissions, according to Patricia Romero Lankao, one of the authors from the National Center for Atmospheric Research (NCAR). The original draft said “However, adaptation alone is not expected to address all the projected effects of climate change, and especially not in the long term as most impacts increase in magnitude, {Mitigation measures will also be necessary.” The second sentence of the text does not appear in the final version of the report.[25].
China objected to the wording and says that “based on observed evidence, there is high confidence that many natural systems, on all continents and most oceans, are affected by regional climate changes, particularly temperature increases.” When China asked whether the word “very” could be affected, three scientific authors resisted, and the deadlock was broken only by a commitment to delete any reference to confidence levels.[25].
Working Group III (WGIII): Climate change mitigation
El Grupo de Trabajo III[26] Resumen para Responsables de Políticas (SPM)[27] fue publicado el 4 de mayo de 2007 en la 26th sesión del IPCC.[28] El informe completo WGIII fue publicado en línea en septiembre del 2007.[29].
El IPCC combino en Bangkok en 30 de abril para empezar la discusión en el resumen del proyecto, con la participación de 400 científicos y expertos de 120 países.[30] En el completo encuentro del IPCC el 4 de mayo, se llegó a un acuerdo en una reunión más grande de cerca de 2000 delegados. Una de las claves del debate fue la concerniente al propuesto límite en las concentraciones de gas de invernadero en la atmósfera de entre 445 partes por millón y 650 partes por millón para evadir cambio un climático peligroso"), con presiones sobre los países en vías de desarrollo para bajar sus emisiones a los límites más bajos. A pesar de esto, las figuras de la propuesta original fueron incorporadas al Resumen para Responsables de Políticas.[31] El resumen concluye que la estabilización de las concentraciones de gases de efecto invernadero es posible a un costo razonable, con una estabilización de 445 ppm y 535 ppm costando menos que un 3% del PBI.[32].
El WGIII del informen analiza la opciones de mitigación para los sectores principales en el cercano plazo, abordando también cuestiones intersectoriales como sinergias, co-beneficiarios, y compensaciones. También provee información en estrategias de mitigación en el largo plazo para varios niveles de estabilización, prestando especial atención a las implicaciones de estrategias a corto plazo para el logro de los objetivos a largo plazo.[33].
Mitigation in the short and medium term (before 2030)
The Summary for Policymakers concludes that there were high levels of agreement and much evidence that 'there are substantial economic potentials for mitigating global greenhouse gas emissions over the coming decades, which could offset global emissions growth or reduce emissions below current levels',[34] taking into account financial and social costs and benefits.[35] Technologies with the best economic potentials within this time scale are:[36].
The IPCC estimates that stabilizing greenhouse gases between 445-535 ppm (carbon dioxide equivalent) would result in a reduction in average annual GDP growth to ranges of less than 0.12%. Stabilizing at 535 to 590 ppm would reduce average annual GDP growth to a range of 0.1%, while stabilization of 590 to 710 ppm will reduce the annual average to ranges of 0.06%.[37] There is wide agreement and much evidence that a substantial fraction of these mitigation costs are offset by health benefits as a result of reduced air pollution, and there will be future cost savings from other benefits such as increased energy security, increased agricultural production, reduced pressure on natural ecosystems as well, in certain countries, improvements in trade balances, modern energy bans to rural areas and employment.[38].
The IPCC considers that achieving these reductions will require 'a major change in the investment pattern, although the net additional investment required ranges from negligible to 5-10%'. They conclude that it is more cost-effective to invest in improving energy efficiency use than to increase energy supply.[39].
In terms of electricity generation, the IPCC predicts that renewable energy can provide 30 to 35% of 2030 electricity (increasing from 18% in 2005) at a carbon price of more than US$50/t, and nuclear energy can increase to 16% to 18%. They also warn that high oil prices may lead to the exploitation of high-carbon alternatives such as oil sands, oil shale, heavy crude oil, and synthetic fuel derived from coal or natural gas, leading to increased emissions, unless carbon capture and storage technologies are used.[40].
In the transportation sector there has been moderate agreement and evidence that multiple mitigation options can be offset by increased use. And that there have been many barriers and lack of frameworks in government policies.[41].
There is widespread agreement and much evidence that, despite many barriers (particularly in developing countries), new and existing construction can reduce emissions considerably, and that this will also provide other benefits in terms of improvements in air quality, social well-being and energy security.[42].
Long-term mitigation (beyond 2030)
The IPCC reported that the effectiveness of mitigation efforts over the coming two to three decades will have a large impact on the ability to stabilize greenhouse gases at low levels, and the lowest level of stabilization, the sooner emissions peak and begin to decline.[43] For example, to stabilize between 445 and 490 ppm (resulting in a temperature estimate of 2 to 2.4 °C above the preindustrial average) the Peak emissions must be before 2015, with a reduction of 50 to 85% from 2000 levels by 2050.[44].
There is great agreement and much evidence that stabilization could be achieved by 2050 using current technologies, providing appropriate and effective incentives were put in place for their development, acquisition, development and dissemination, and those barriers were removed.[45] For stabilization at low levels the IPCC agrees on the necessary improvements in emissions intensity "to be done faster than they have done in the past, and a great effort will be needed in public and private efficiency in research, development & demonstration") and investment in new technologies over the coming decades.[46] The IPCC notes that governments have been funding energy programs less and less over the past 20 years, and now at half of 1980 levels.[47] Delays in cutting emissions will result in higher emissions stabilization increasing the risk of more severe impacts of climate change, the more high-emissions technologies have been deployed.[48].
Among the measurements that can be used, there is great agreement and much evidence that policies that put a cost on carbon emissions could incentivize consumers and producers. Carbon prices of 5 to 65 US$/tCO in 2030 and 15 to 130 US$/tCO by 2050 are expected to stabilize at 550 ppm by 2100.[49].
Summary of the AR4 Report
Una versión preliminar de la Síntesis del Informe AR4, , “Sin perjuicio de corrección de estilo final”, fue publicado el 16 de noviembre de 2007.
Los seis temas[50][51] de dirección del Informe de Síntesis son:.
Cambios observados en el clima y sus efectos (Grupos de Trabajo 1-2).
Causas del cambio (Grupos de Trabajo 1, 3).
Cambio climático y sus impactos en el corto y largo plazo bajo diferentes escenarios (Grupos de Trabajo 1, 3).
Opciones de adaptación y mitigación y respuestas, y las interrelaciones con el desarrollo sostenible, a nivel global y regional. (Grupos de Trabajo 2, 3).
Perspectivas a largo plazo: aspectos científico y socioeconómico relevantes y adaptación y mitigación, consistente con los objetivos y disposiciones de la Convención [sic], y en el contexto de desarrollo sostenible (Grupos de Trabajo 1, 3).
Conclusiones sólidas, las principales incertidumbres (Grupos de Trabajo 1, 3).
La “Convención” mencionada en el tópico 5 es la Convención Marco de las Naciones Unidas sobre el Cambio Climático (CMNUCC).
Las principales conclusiones del Informe de Síntesis del AR4 fueron discutidos el miércoles 13 de diciembre de 2007[52] en la Conferencia de Naciones Unidas sobre Cambio Climático (CMNUCC COP 13-CMP 3) en Bali, Indonesia, que tuvo lugar el 3-14 de diciembre de 2007 (ver sitio Web de CMNUCC[53]).
Anthropomorphic warming could lead to some impacts that are abrupt or irreversible
The SPM states that “Anthropomorphic warming could lead to some impacts that are abrupt or irreversible, depending on the speed and magnitude of climate change.”
• - "There is a medium confidence of approximately 20-30% of species assessed so far are likely to increase the risk of extinction if average global warming increases by exceeding 1.5-2.5 °C (relative to 1980-1999). If global average temperature exceeds 3.5 °C, projection models suggest significant extinctions (40-70% of species assessed) worldwide."
• - "Partial losses of ice sheets on polar land imply sea level rise in meters, large changes in coastlines and flooding of low-lying areas, with large effects on river deltas and low-lying islands. These changes are projected to occur on the time scale of a millennium, but a rapid rise in sea level in this century cannot be excluded."
Reviews
The Fourth evaluation report has been subject to criticism. Skeptics of anthropomorphic global warming say their claims were not sufficiently incorporated into the report. Others see the IPCC as very conservative in its estimates of the potential damages of climate change. The report has also been criticized for concluding erroneous data on the collapse of Himalayan glaciers.
Related to the issue of global warming in general, the IPCC's Fourth Assessment Report has been discussed by many bodies including government officials, interested task forces and scientific organizations; See the article Politics of Global Warming for a full discussion of the policies surrounding the phenomenon, and the positions of the parties involved.
The United Nations pointed to the independence of the group of scientists to “review the work of the world's main panel of climate scientists” who reported it in September 2010.[54].
• - IPCC First Assessment Report.
• - IPCC Second Assessment Report.
• - IPCC Third Assessment Report.
• - IPCC Fifth Assessment Report.
• - IPCC Sixth Assessment Report.
• - Avoid dangerous climate change.
• - Individual and political action on climate change").
• - Business action on climate change.
• - Energy policy.
• - Energy efficiency.
• - General circulation models.
• - Post-Kyoto Protocol negotiations on greenhouse gas emissions").
• - Precautionary principle.
• - Renewable Energy Sources and Climate Change Mitigation").
• - Consumption and energy resources worldwide.
• - Intergovernmental Panel on Climate Change home page.
• - Text in English from the IPCC (Fifth Synthesis Report November 2014).
• - Ten-webpage summary of the Fourth Assessment Report SPMs by GreenFacts"); the webpages as a self-contained.
• - Commentary on the Working Group I Report:
The Guardian Article on US political pressure on WGI Report, 27 January 2007
*UNEP.org Archived December 22, 2010 at the Wayback Machine. Press release: Evidence of Human-caused Global Warming “Unequivocal”, says IPCC, 2 February 2007
RealClimate") blog — Commentary on Working Group I Summary for Policymakers, 2 February 2007.
• - Videos:
From Science to Assessment: Overview of the IPCC AR4 Working Group I Report. A lecture given at Princeton University by Ronald Stouffer, Senior Research Meteorologist, Geophysical Fluid Dynamics Laboratory") (GFDL), 11 March 2008
Lessons from the Climate Wars: The Future of the IPCC. A lecture given at Princeton University by Gary Yohe"), Woodhouse/Sysco Professor of economics at Wesleyan University and Director of the John E. Andrus Public Affairs Center at Wesleyan, 7 May 2008
Emissions Mitigation and Climate Stabilization. A lecture given at Princeton University by Jae Edmonds, Chief Scientist, Joint Global Change Research Institute, Pacific Northwest National Laboratory"), April 22, 2008
How Would Climate Change Influence Society in the 21st Century? A lecture given at MIT by Rajendra Pachauri, January 29, 2008.
[15] ↑ a b "... a convergent world with the same global population, that peaks in mid-century and declines thereafter,... but with rapid change in economic structures toward a service and information economy, with reductions in material intensity and the introduction of clean and resource efficient technologies. The emphasis is on global solutions to economic, social and environmental sustainability, including improved equity, but without additional climate initiatives.".
[16] ↑ a b "... a future world of very rapid economic growth, global population that peaks in mid-century and declines thereafter, and the rapid introduction of new and more efficient technologies. Major underlying themes are convergence among regions, capacity building and increased cultural and social interactions, with a substantial reduction in regional differences in per capita income.... technological emphasis: fossil intensive".
[17] ↑ This contrasts with the TAR, which included these ice dynamics, and had a higher top end sea level rise estimate. The report states that recent observations suggest that ice flow dynamics could lead to additional rise: "Dynamical processes related to ice flow not included in current models but suggested by recent observations could increase the vulnerability of the ice sheets to warming, increasing future sea level rise. Understanding of these processes is limited and there is no consensus on their magnitude.".
[31] ↑ «Deal reached on climate change report». CNN. 4 de mayo de 2007. Consultado el 4 de mayo de 2007. (enlace roto disponible en Internet Archive; véase el [http://edition.cnn.com/2007/TECH/science/05/03/climate.report.ap/index.html?eref=rss_world «Deal reached on climate change report». CNN. 4 de mayo de 2007. Consultado el 4 de mayo de 2007. historial], la [http://edition.cnn.com/2007/TECH/science/05/03/climate.report.ap/index.html?eref=rss_world «Deal reached on climate change report». CNN. 4 de mayo de 2007. Consultado el 4 de mayo de 2007. primera versión] y la [http://edition.cnn.com/2007/TECH/science/05/03/climate.report.ap/index.html?eref=rss_world «Deal reached on climate change report». CNN. 4 de mayo de 2007. Consultado el 4 de mayo de 2007. última]).: http://edition.cnn.com/2007/TECH/science/05/03/climate.report.ap/index.html?eref=rss_world
About observed changes in climate, and their effects:.
• - The warming of the climate system is unequivocal, as evidenced by the observed increases in the global average of air and ocean temperatures, the widespread melting of snow and ice, and the rise in the global average of sea level.
• - Observations made on all continents and in most oceans show that numerous natural systems are being affected by changes in the regional climate, particularly by an increase in temperature.
• - With a medium level of confidence, other effects of regional climate change on the natural and human environment are beginning to appear, although many of them are difficult to identify due to adaptation and other non-climatic sources.
About the causes of change:
• - Global greenhouse gas (GHG) emissions due to human activities have increased, since the pre-industrial era, by 70% between 1970 and 2004.
• - Global atmospheric concentrations of CO2, methane (CH4) and nitrous oxide (N2O) have increased markedly as a result of human activities since 1750, and are currently much higher than pre-industrial values, determined from ice cores spanning many millennia.
• - Most of the observed increase in global average temperature since mid-century is most likely due to the observed increase in anthropogenic GHG concentrations. It is likely that appreciable anthropogenic warming has occurred over the past fifty years, on average for each continent (except the Antarctic region).
• - Progress since the Third Assessment Report indicates that discernible human influences are not limited to average temperatures, but also encompass other aspects of climate.
• - Anthropogenic warming over the past three decades has likely exerted a globally discernible influence on observed changes in many physical and biological systems.
About projected climate change and its impacts:
• - There is a high level of agreement and abundant evidence that with current policies to mitigate the effects of climate change and the sustainable development practices that they entail, global GHG emissions will continue to increase in the coming decades.
• - If GHG emissions continue at a rate equal to or higher than the current one, warming would increase and the global climate system would experience numerous changes during the century, most likely greater than those observed during the century.
• - The current degree of confidence is higher than that of the Third Assessment Report regarding the projected patterns of warming and other regional-scale aspects, such as changes in wind or precipitation patterns, and certain aspects of extreme values and sea ice.
• - The studies carried out since the Third Assessment Report have made it possible to understand in a more systematic way the chronology and magnitude of the impacts linked to different magnitudes and rates of climate change.
• - The alteration in the frequency and intensity of extreme weather events, added to the rise in sea level, will foreseeably have extremely adverse effects on natural and human systems.
• - Anthropogenic warming and sea level rise will continue for centuries due to the magnitude of the time scales associated with climate processes and feedbacks, even if GHG concentrations stabilize.
• - Anthropogenic warming could produce abrupt or irreversible impacts, depending on the speed and magnitude of climate change.
On adaptation and mitigation options:
• - A great diversity of adaptation options is available, but even greater adaptation than the current one will be necessary to reduce vulnerability to climate change. There are obstacles, limits and costs that have not been sufficiently analyzed.
• - Adaptive capacity is closely related to social and economic development, although it is unevenly distributed both between and within societies.
• - Studies, from both a bottom-up and top-down perspective, indicate that there is a high level of agreement and abundant evidence that there is substantial economic potential to mitigate global GHG emissions in the coming decades, which could offset the projected growth in global emissions or reduce them below current levels. Although both types of studies agree at the global level, they exhibit considerable differences at the sectoral level.
• - Governments have a wide variety of policies and instruments to create incentives that prioritize mitigation measures. Its applicability will depend on national circumstances and the sectoral context.
• - There are multiple options to reduce global GHG emissions through international cooperation. There is a high level of agreement and abundant evidence that the establishment of a global response to climate change, the stimulation of a range of national policies and the creation of an international carbon market and new institutional mechanisms in this regard are notable achievements of the UNFCCC and its Kyoto Protocol that could provide the basis for future mitigation efforts. Progress has also been made in addressing adaptation within the UNFCCC and further international initiatives have been suggested.
• - In several sectors it is possible to implement response options to obtain synergies and to avoid conflicts with other dimensions of sustainable development. Decisions on macroeconomic and other non-climate policies can significantly affect emissions, adaptive capacity, and vulnerability.
About the long-term perspective.
• - Determining what is meant by “dangerous anthropogenic interference with the climate system” in relation to Article 2 of the UNFCCC involves value judgments. Science, in this regard, can help make informed decisions, in particular by providing criteria for deciding which vulnerabilities could be considered “key”.
• - The 'five areas of concern' identified in the Third Assessment Report continue to constitute a viable framework for the study of key vulnerabilities. In the present work, these 'aspects' are considered more worrying than in the TIE. Many of the risks are identified here with a higher degree of confidence. Some will be larger, according to projections, or will occur with smaller increases in temperature. The relationship between impacts (the basis for the TAR “issues of concern”) and vulnerability (including the ability to adapt to impacts) is now known in greater detail.
• - There is a high degree of confidence that neither adaptation nor mitigation alone will avoid all the impacts of climate change; They can, however, complement each other and, together, significantly reduce the risks of climate change.
• - Many of the impacts can be reduced, delayed or avoided through mitigation measures. Mitigation efforts and investments over the next two to three decades will largely determine the opportunities to achieve lower stabilization levels. The delay in reducing emissions will significantly reduce these opportunities, and will increase the risk of worsening the repercussions of climate change.
• - There is a high level of agreement and abundant evidence that all the stabilization levels studied can be achieved by implementing a series of technologies currently available or expected to be commercialized in the coming decades, assuming that there are appropriate and effective incentives for their development, acquisition, implementation and dissemination, and to address the corresponding obstacles.
• - The macroeconomic costs of mitigation tend to increase as the restrictive nature of the stabilization objective increases. For certain countries and sectors, costs will vary considerably from the global average.
• - The response to climate change involves an iterative risk management process that encompasses both adaptation and mitigation measures and takes into account harms, co-benefits, sustainability, equity and attitudes to risk in relation to climate change.
Working Group I (WGI): scientific and physical bases
Contenido
El resumen del Grupo de Trabajo I (WGI) para los responsables de políticas (del inglés SPM o Summary for Policymakers)[8] fue publicado el 2 de febrero de 2007 y revisado el 5 de febrero de 2007. El informe completo de WGI[9] fue publicado en marzo y actualizado el 5 de septiembre de 2007. Se ha hecho accesible la página 34 sobre preguntas frecuentes del documento.[10].
Cambio climático 2007: Las bases científico físicas, del informe WGI, “evalúa con el actual conocimiento científico los cambios naturales y antropomórficos de cambio climático, cambios observados en el clima, la fiabilidad de la ciencia actual, para atribuir los cambios a diferentes causas, y proyecciones para el futuro del cambio climático”.
El informe fue producido por 620 autores y editores de 40 países y revisado por más de 620 expertos y gobiernos. Antes de ser aceptado, el sumario fue revisado línea por línea por representantes de 113 gobiernos durante la Décima Sesión de WGI,[11] que tuvo lugar en París, Francia, entre 29 de enero y 1 de febrero de 2007.
Sobre la cuestión de calentamiento global y sus causas, el SPM estableció que:[8].
• - “el calentamiento de el sistema climático es inequívoco”.
• - “La mayoría del incremento observado de la temperatura desde mediados del siglo XX responde ´muy probablemente´ al incremento antropomórfico en los niveles de concentración de gases de efecto invernadero”.
La Nota al pie 6 en la página 3 del resumen indica que ´muy probablemente´ y ´probable´ significan “la posibilidad de evaluar, usando opiniones de expertos” con un nivel de confianza del 90% y del 66%, respectivamente.
Observations
The report shows many observed changes in Earth's climate and atmosphere composition, global measured temperatures, ocean conditions and other climate changes.
Carbon dioxide, methane and nitrous oxide are all long-lived greenhouse gases.
• - Carbon dioxide, methane, and nitrous oxide have increased markedly as a result of human activities since 1750 and are now far exceeding pre-industrial values.
• - The amount of atmospheric carbon dioxide was (379 ppm) in 2005, far exceeding the natural ranges of the last 650,000 years (180 to 300 ppm).
• - The amount of atmospheric methane is (1774 ppm for 2005 and greatly exceeds the natural ranges of the last 650,000 years (between 320 ppm and 790 ppm).
• - The primary source of the increase in carbon dioxide is the use of fossil fuels, but the use of land (for agriculture, livestock, etc.) also contributes to this increase.
• - The primary source of the increase in methane is the combination of agricultural activities and fossil fuels, although it is not well determined how much each contributes.
• - Nitrous oxide concentrations have increased from pre-industrial values of 270 ppm to 319 ppm in 2005. More than a third of this increase is due to human activity, primarily agriculture.
Cold days, cold nights, and events like frost have become less frequent. Warm days, warm nights, and heat waves are more frequent. Additionally:.
• - Ten of the eleven years of the period (1995-2006) were in the ranking of the 12 warmest years in the instrumental record (since 1850, towards the end of the Little Ice Age).
• - Warming in the last 100 years has caused an increase of 0.74 °C in global temperature. Being 0.6 °C the increase predicted in the previous IPCC Third Assessment Report.
• - The urban heat island effect has a negligible influence (less than 0.0006 °C per decade over land and 0 over oceans) on the measurements.
• - Observations since 1960 showed that the oceans have been absorbing 80% of the heat added to the climate system, and that the temperature in the oceans has increased to depths of 300 m (9,800 ft).
• - “Temperatures in the Arctic have increased twice as much as the global temperature rate in the last 100 years.”
• - It is likely that greenhouse gases have caused more warming than observed that could have been amalgamated by the cooling effect of volcanoes and aerosol gases emitted by humans. See Global Dimming.
• - Northern Hemisphere mean temperatures during the second half of the century were higher than any 50-year period in the previous 500 years and the highest of the last 1,300 years (including the Medieval Warm Period and the Little Ice Age).
The Summary for Policymakers (SPM) documents showed an increase in wind intensity, a reduction in permafrost cover, increases in both droughts and heavy rainfall. Additionally:.
• - “The surface of mountain glaciers and snow cover has decreased in both hemispheres.”
• - Losses in the Greenland and Antarctic ice sheets have probably contributed (>90%) to sea level rise between 1993-2003.
• - Warming oceans cause seawater to expand, contributing to sea level rise.
• - Sea level has increased at an average rate of 1.8 mm/year during the period 1961-1993. And during the period 1993-2003 the rate has increased to 3.1 mm/year. Although it is not clear if it is a long-term change or a temporary variability.
• - Antarctic sea ice shows that there is no significant general trend consistent with a lack of warming in the region.
• - The intensity of hurricanes in the North Atlantic has increased since the 1970s and this increase is correlated with the increase in water surface temperature.
• - The observed increase in hurricane intensity is greater than what climate models predict for the changes experienced in surface temperature.
• - There is no clear trend in the number of hurricanes.
• - Other regions also appear to have experienced an increase in hurricane intensity, but there are concerns about the quality of the data for these regions.
• - It is more likely that no more than (>50%) has a human relationship or contributions to the increase in hurricane intensity.
• - It is likely (>66%) that we will see an increase in the intensity of hurricanes in the century.
Factors that warm or cool the planet
AR4 describes the warming and cooling effects of the planet in items of radiative forcing – the rate of change of energy in the system, measured as power per unit area (in SI units, W/m²). The report shows in detail the individual contributions (positive forcing) of carbon dioxide, methane, nitrous oxide, organohalogens, and other human factors that produce warming, and warming effects due to the origin of solar activity. It also shows cooling effects (negative forcing) of aerosol, land use changes"), and other human activities. All values are shown as changes from pre-industrial conditions.
• - The total radiative forcing of the sum of all human activities is +1.6 watts/m².
• - The radiative forcing of the increase in solar radiation since 1750 is +0.2 watts/m².
• - The radiative forcing of carbon dioxide, methane, and nitrous oxide combined is most likely (>90%) increasing faster during the current era (1750-present) than at any other time in the last 10,000 years.
Climate sensitivity
Climate sensitivity is defined as the average amount of surface warming following a doubling of carbon dioxide concentrations. It is likely to be in the range of 2 to 4.5°C, with the best estimate at 3°C. This range of values is not a projection of the temperature rise we will see in the century, when future changes in carbon dioxide concentrations are not known, the factors behind carbon dioxide concentrations affect temperature.
Projections for the future based on the model
The model projections are based on the analysis of several computational models run in different SRESS scenarios. As a result, the predictions for the century, shown below.
• - Surface air temperature in the century:.
• - * Best estimates in the “low scenario”[15] is 1.8 °C with a probable range of 1.1 to 2.9 °C.
Best estimates for a “high scenario”[16] is 4.0 °C, with a probable range between 2.4 and 6.4 °C.
An increase in temperatures of 0.1 °C per decade is expected for the next two decades, even if concentrations of greenhouse gases and aerosols were maintained at 2000 levels.
A temperature increase of 0.2 °C per decade is projected in all SRES scenarios for the next two decades.
Confidence in these short-term protections is strengthened by the relationship between the old models and the observed temperature increase.
• - It is estimated that the rise in sea level, based on multiple models that all exclude the flow of ice sheets") due to lack of basis in scientific publications,[17] will be:
on the low stage[15] from 18 to 38 cm
on the high stage[16] from 26 to 59 cm.
• - It is very likely that there will be an increase in hot periods, heat waves and heavy rain events.
• - There is likely to be an increase in areas affected by drought, the intensity of tropical cyclones (including hurricanes and typhoons), and the occurrence of large tides.
• - “The Arctic ice cap is estimated to shrink in both the Arctic and Antarctic... In some projections, the Arctic ice sheet will disappear almost entirely during the summer by the latter part of the 21st century.”
Projections for specific scenarios are based on multiple analyzes running many climate models and using various SRES scenarios. The “low scenarios” refer to B1, and are the most optimistic family of scenarios. “High scenarios” refer to A1F1, the most pessimistic family of scenarios.
There are six SRES scenario families, and AR4 includes projected temperatures and sea level rise (excluding future rapid changes in ice flow dynamics[18]) for each scenario family.
• - Scenario B1
Best estimates of temperature increase of 1.8°C with a likely range of 1.1 to 2.9°C.
Sea level rise with a probable range of [18 to 38 cm].
• - A1T Scenario
Best estimates of temperature rise of 2.4°C with a likely range of 1.4 to 3.8°C.
Sea level rise with a probable range of [20 to 45 cm].
Selected quotes from the Summary for Policymakers of Working Group I
“Both past and future anthropogenic carbon dioxide emissions will continue to contribute to warming and sea level rise for more than a millennium, due to the time scale required to remove this gas from the atmosphere.”
Reactions to the content of the report of Working Group I (WGI)
In the weeks before the first report was published, controversy erupted over projections of sea level change, which in the new report was estimated lower than in previous estimates. The text now published gives a warning that new estimates of sea level rise may be low. ”Dynamic processes related to ice flow not included in current models but suggested by recent observations may increase the vulnerability of ice sheets to warming, increasing future sea level rise.” The midpoint of sea level rise is estimated to be within ±10% of those announced in TAR; but the range has been reduced.
Martin Rees, the president of the Royal Society, said, "This report makes it clear, more convincingly than before, that human actions are largely written into the changes we are seeing, and will see, in the climate. The IPCC strongly emphasizes that substantial climate changes are inevitable, and that we will have to adapt to them. This should compel all of us – world leaders, businesses and individuals – towards action rather than paralysis by fear. We need to reduce our greenhouse gas emissions and prepare us for the impacts of climate change. Those who want to claim otherwise can no longer continue using science as the basis of their arguments.[19]"
United States Secretary of Energy Samuel Bodman said at a conference on the report that it had “solid scientific foundations” and that “as the president has said, and this report makes clear, human activity is contributing to changes in our earth's climate and this point is no longer up for debate.” [20] Kurt Volker, Principal Deputy Assistant Secretary for European and Eurasian Affairs, said “We support the recent IPCC report, in which scientists Americans played an important role.”[21].
Based on the report, 46 countries made the "Paris call to action" statement, read by French President Jacques Chirac, calling for the creation of a United Nations Environment Organization (UNEO), which would have more capacity than the current United Nations Environment Program (UNEP), and would follow the model of the more powerful World Health Organization. The 46 countries included the nations of the European Union, but notably did not include the US, China, Russia, and India, the four largest emitters of greenhouse gases.[22].
Working Group II (WGII): Impacts, adaptation and vulnerability
El Resumen para Responsables de Políticas del Grupo de Trabajo II[23] fue publicado el 6 de abril de 2007. El informe completo[24] fue publicado el 18 de septiembre de 2007.
El WGII estableció que “evidencia de todos los continentes y la mayoría de los océanos muestra que muchos sistemas naturales han sido afectados por cambios climáticos regionales, particularmente incrementos en la temperatura.”.
Some changes have been associated with climate changes at different confidence levels.
With high confidence (about 80% chance of being correct) the WGII states that climate change has led to:
• - More and larger glacial lakes.
• - Increase in soil instability in permafrost regions.
• - Increase in rock avalanches in mountainous regions.
• - Changes in some Arctic and Antarctic ecosystems.
• - Increased runoff and an early spring discharge peak in glacier- or snow-fed rivers.
• - Changes that affect algae, plankton, fish and zooplankton due to increases in water temperature and changes in:
ice coverage
salinity
oxygen levels
water circulation.
With high confidence (around 90% chance of being correct) the WGII states that climate change is affecting biological systems in these aspects:
• - Spring events such as leaf opening, egg laying, and migrations are occurring earlier.
• - Towards the poles and towards higher latitudes, there are changes in the variability of plant and animal species.
Attribution of changes
The WGII recognizes the difficulty of attributing specific changes to human-caused global warming, stating that “Limitations and gaps prevent attribution of causes to observed systems rather than to anthropomorphic warming” but found that the agreement between observed and projected changes was “However…sufficient to conclude with great confidence that anthropomorphic warming over the past three decades has had a discernible influence on many physical and biological systems.”
Projections
The WGII outlines some of what it forecasts for the coming century, based on studies and model projections.
It is projected with a high level of confidence that:.
• - dry regions become drier, and humid regions become wetter. “By mid-century, average annual river runoff and water availability are projected to increase by 10 – 40% in high latitudes and some tropical areas, and decrease by 10 – 30% over some arid regions in mid-latitudes and in the dry tropics…”.
• - Drought-affected areas will become larger.
• - Heavy rainfall events are very likely to become common and the risk of flooding will increase.
• - Water supplies stored in glaciers and snow cover will be reduced over the course of the century.
It is projected with a great level of confidence that:.
• - The resilience "Resilience (ecology)") of many ecosystems is likely to be exceeded in this century by the combination of global warming and other causes of stress.
• - la remoción de carbono por los ecosistemas terrestres es probable que llegue a un pico antes de mitad de centuria y a continuación se debilitara o revertirá. This will amplify climate change.
The Working Group III projection, with medium confidence (about 5 in 10 chances of being correct), is that globally, food production potential will increase with a temperature increase of 1 – 3 °C, but will decrease at higher temperature ranges.
It is projected with a great level of confidence that:.
• - coasts will be exposed to increased risk such as coastal erosion due to climate change and sea level rise.
• - “increases in sea surface temperature of 1–3 °C, resulting in more frequent coral bleaching events and general mortality, unless there is adaptation to temperature change or acclimatization of the corals.”
• - that “many millions of people” will be subject to flooding every year due to rising sea levels by the 2080s.”
Objections to the original text of the WGII
U.S. negotiators managed to remove text calling for eliminating greenhouse gas emissions, according to Patricia Romero Lankao, one of the authors from the National Center for Atmospheric Research (NCAR). The original draft said “However, adaptation alone is not expected to address all the projected effects of climate change, and especially not in the long term as most impacts increase in magnitude, {Mitigation measures will also be necessary.” The second sentence of the text does not appear in the final version of the report.[25].
China objected to the wording and says that “based on observed evidence, there is high confidence that many natural systems, on all continents and most oceans, are affected by regional climate changes, particularly temperature increases.” When China asked whether the word “very” could be affected, three scientific authors resisted, and the deadlock was broken only by a commitment to delete any reference to confidence levels.[25].
Working Group III (WGIII): Climate change mitigation
El Grupo de Trabajo III[26] Resumen para Responsables de Políticas (SPM)[27] fue publicado el 4 de mayo de 2007 en la 26th sesión del IPCC.[28] El informe completo WGIII fue publicado en línea en septiembre del 2007.[29].
El IPCC combino en Bangkok en 30 de abril para empezar la discusión en el resumen del proyecto, con la participación de 400 científicos y expertos de 120 países.[30] En el completo encuentro del IPCC el 4 de mayo, se llegó a un acuerdo en una reunión más grande de cerca de 2000 delegados. Una de las claves del debate fue la concerniente al propuesto límite en las concentraciones de gas de invernadero en la atmósfera de entre 445 partes por millón y 650 partes por millón para evadir cambio un climático peligroso"), con presiones sobre los países en vías de desarrollo para bajar sus emisiones a los límites más bajos. A pesar de esto, las figuras de la propuesta original fueron incorporadas al Resumen para Responsables de Políticas.[31] El resumen concluye que la estabilización de las concentraciones de gases de efecto invernadero es posible a un costo razonable, con una estabilización de 445 ppm y 535 ppm costando menos que un 3% del PBI.[32].
El WGIII del informen analiza la opciones de mitigación para los sectores principales en el cercano plazo, abordando también cuestiones intersectoriales como sinergias, co-beneficiarios, y compensaciones. También provee información en estrategias de mitigación en el largo plazo para varios niveles de estabilización, prestando especial atención a las implicaciones de estrategias a corto plazo para el logro de los objetivos a largo plazo.[33].
Mitigation in the short and medium term (before 2030)
The Summary for Policymakers concludes that there were high levels of agreement and much evidence that 'there are substantial economic potentials for mitigating global greenhouse gas emissions over the coming decades, which could offset global emissions growth or reduce emissions below current levels',[34] taking into account financial and social costs and benefits.[35] Technologies with the best economic potentials within this time scale are:[36].
The IPCC estimates that stabilizing greenhouse gases between 445-535 ppm (carbon dioxide equivalent) would result in a reduction in average annual GDP growth to ranges of less than 0.12%. Stabilizing at 535 to 590 ppm would reduce average annual GDP growth to a range of 0.1%, while stabilization of 590 to 710 ppm will reduce the annual average to ranges of 0.06%.[37] There is wide agreement and much evidence that a substantial fraction of these mitigation costs are offset by health benefits as a result of reduced air pollution, and there will be future cost savings from other benefits such as increased energy security, increased agricultural production, reduced pressure on natural ecosystems as well, in certain countries, improvements in trade balances, modern energy bans to rural areas and employment.[38].
The IPCC considers that achieving these reductions will require 'a major change in the investment pattern, although the net additional investment required ranges from negligible to 5-10%'. They conclude that it is more cost-effective to invest in improving energy efficiency use than to increase energy supply.[39].
In terms of electricity generation, the IPCC predicts that renewable energy can provide 30 to 35% of 2030 electricity (increasing from 18% in 2005) at a carbon price of more than US$50/t, and nuclear energy can increase to 16% to 18%. They also warn that high oil prices may lead to the exploitation of high-carbon alternatives such as oil sands, oil shale, heavy crude oil, and synthetic fuel derived from coal or natural gas, leading to increased emissions, unless carbon capture and storage technologies are used.[40].
In the transportation sector there has been moderate agreement and evidence that multiple mitigation options can be offset by increased use. And that there have been many barriers and lack of frameworks in government policies.[41].
There is widespread agreement and much evidence that, despite many barriers (particularly in developing countries), new and existing construction can reduce emissions considerably, and that this will also provide other benefits in terms of improvements in air quality, social well-being and energy security.[42].
Long-term mitigation (beyond 2030)
The IPCC reported that the effectiveness of mitigation efforts over the coming two to three decades will have a large impact on the ability to stabilize greenhouse gases at low levels, and the lowest level of stabilization, the sooner emissions peak and begin to decline.[43] For example, to stabilize between 445 and 490 ppm (resulting in a temperature estimate of 2 to 2.4 °C above the preindustrial average) the Peak emissions must be before 2015, with a reduction of 50 to 85% from 2000 levels by 2050.[44].
There is great agreement and much evidence that stabilization could be achieved by 2050 using current technologies, providing appropriate and effective incentives were put in place for their development, acquisition, development and dissemination, and those barriers were removed.[45] For stabilization at low levels the IPCC agrees on the necessary improvements in emissions intensity "to be done faster than they have done in the past, and a great effort will be needed in public and private efficiency in research, development & demonstration") and investment in new technologies over the coming decades.[46] The IPCC notes that governments have been funding energy programs less and less over the past 20 years, and now at half of 1980 levels.[47] Delays in cutting emissions will result in higher emissions stabilization increasing the risk of more severe impacts of climate change, the more high-emissions technologies have been deployed.[48].
Among the measurements that can be used, there is great agreement and much evidence that policies that put a cost on carbon emissions could incentivize consumers and producers. Carbon prices of 5 to 65 US$/tCO in 2030 and 15 to 130 US$/tCO by 2050 are expected to stabilize at 550 ppm by 2100.[49].
Summary of the AR4 Report
Una versión preliminar de la Síntesis del Informe AR4, , “Sin perjuicio de corrección de estilo final”, fue publicado el 16 de noviembre de 2007.
Los seis temas[50][51] de dirección del Informe de Síntesis son:.
Cambios observados en el clima y sus efectos (Grupos de Trabajo 1-2).
Causas del cambio (Grupos de Trabajo 1, 3).
Cambio climático y sus impactos en el corto y largo plazo bajo diferentes escenarios (Grupos de Trabajo 1, 3).
Opciones de adaptación y mitigación y respuestas, y las interrelaciones con el desarrollo sostenible, a nivel global y regional. (Grupos de Trabajo 2, 3).
Perspectivas a largo plazo: aspectos científico y socioeconómico relevantes y adaptación y mitigación, consistente con los objetivos y disposiciones de la Convención [sic], y en el contexto de desarrollo sostenible (Grupos de Trabajo 1, 3).
Conclusiones sólidas, las principales incertidumbres (Grupos de Trabajo 1, 3).
La “Convención” mencionada en el tópico 5 es la Convención Marco de las Naciones Unidas sobre el Cambio Climático (CMNUCC).
Las principales conclusiones del Informe de Síntesis del AR4 fueron discutidos el miércoles 13 de diciembre de 2007[52] en la Conferencia de Naciones Unidas sobre Cambio Climático (CMNUCC COP 13-CMP 3) en Bali, Indonesia, que tuvo lugar el 3-14 de diciembre de 2007 (ver sitio Web de CMNUCC[53]).
Anthropomorphic warming could lead to some impacts that are abrupt or irreversible
The SPM states that “Anthropomorphic warming could lead to some impacts that are abrupt or irreversible, depending on the speed and magnitude of climate change.”
• - "There is a medium confidence of approximately 20-30% of species assessed so far are likely to increase the risk of extinction if average global warming increases by exceeding 1.5-2.5 °C (relative to 1980-1999). If global average temperature exceeds 3.5 °C, projection models suggest significant extinctions (40-70% of species assessed) worldwide."
• - "Partial losses of ice sheets on polar land imply sea level rise in meters, large changes in coastlines and flooding of low-lying areas, with large effects on river deltas and low-lying islands. These changes are projected to occur on the time scale of a millennium, but a rapid rise in sea level in this century cannot be excluded."
Reviews
The Fourth evaluation report has been subject to criticism. Skeptics of anthropomorphic global warming say their claims were not sufficiently incorporated into the report. Others see the IPCC as very conservative in its estimates of the potential damages of climate change. The report has also been criticized for concluding erroneous data on the collapse of Himalayan glaciers.
Related to the issue of global warming in general, the IPCC's Fourth Assessment Report has been discussed by many bodies including government officials, interested task forces and scientific organizations; See the article Politics of Global Warming for a full discussion of the policies surrounding the phenomenon, and the positions of the parties involved.
The United Nations pointed to the independence of the group of scientists to “review the work of the world's main panel of climate scientists” who reported it in September 2010.[54].
• - IPCC First Assessment Report.
• - IPCC Second Assessment Report.
• - IPCC Third Assessment Report.
• - IPCC Fifth Assessment Report.
• - IPCC Sixth Assessment Report.
• - Avoid dangerous climate change.
• - Individual and political action on climate change").
• - Business action on climate change.
• - Energy policy.
• - Energy efficiency.
• - General circulation models.
• - Post-Kyoto Protocol negotiations on greenhouse gas emissions").
• - Precautionary principle.
• - Renewable Energy Sources and Climate Change Mitigation").
• - Consumption and energy resources worldwide.
• - Intergovernmental Panel on Climate Change home page.
• - Text in English from the IPCC (Fifth Synthesis Report November 2014).
• - Ten-webpage summary of the Fourth Assessment Report SPMs by GreenFacts"); the webpages as a self-contained.
• - Commentary on the Working Group I Report:
The Guardian Article on US political pressure on WGI Report, 27 January 2007
*UNEP.org Archived December 22, 2010 at the Wayback Machine. Press release: Evidence of Human-caused Global Warming “Unequivocal”, says IPCC, 2 February 2007
RealClimate") blog — Commentary on Working Group I Summary for Policymakers, 2 February 2007.
• - Videos:
From Science to Assessment: Overview of the IPCC AR4 Working Group I Report. A lecture given at Princeton University by Ronald Stouffer, Senior Research Meteorologist, Geophysical Fluid Dynamics Laboratory") (GFDL), 11 March 2008
Lessons from the Climate Wars: The Future of the IPCC. A lecture given at Princeton University by Gary Yohe"), Woodhouse/Sysco Professor of economics at Wesleyan University and Director of the John E. Andrus Public Affairs Center at Wesleyan, 7 May 2008
Emissions Mitigation and Climate Stabilization. A lecture given at Princeton University by Jae Edmonds, Chief Scientist, Joint Global Change Research Institute, Pacific Northwest National Laboratory"), April 22, 2008
How Would Climate Change Influence Society in the 21st Century? A lecture given at MIT by Rajendra Pachauri, January 29, 2008.
[15] ↑ a b "... a convergent world with the same global population, that peaks in mid-century and declines thereafter,... but with rapid change in economic structures toward a service and information economy, with reductions in material intensity and the introduction of clean and resource efficient technologies. The emphasis is on global solutions to economic, social and environmental sustainability, including improved equity, but without additional climate initiatives.".
[16] ↑ a b "... a future world of very rapid economic growth, global population that peaks in mid-century and declines thereafter, and the rapid introduction of new and more efficient technologies. Major underlying themes are convergence among regions, capacity building and increased cultural and social interactions, with a substantial reduction in regional differences in per capita income.... technological emphasis: fossil intensive".
[17] ↑ This contrasts with the TAR, which included these ice dynamics, and had a higher top end sea level rise estimate. The report states that recent observations suggest that ice flow dynamics could lead to additional rise: "Dynamical processes related to ice flow not included in current models but suggested by recent observations could increase the vulnerability of the ice sheets to warming, increasing future sea level rise. Understanding of these processes is limited and there is no consensus on their magnitude.".
[31] ↑ «Deal reached on climate change report». CNN. 4 de mayo de 2007. Consultado el 4 de mayo de 2007. (enlace roto disponible en Internet Archive; véase el [http://edition.cnn.com/2007/TECH/science/05/03/climate.report.ap/index.html?eref=rss_world «Deal reached on climate change report». CNN. 4 de mayo de 2007. Consultado el 4 de mayo de 2007. historial], la [http://edition.cnn.com/2007/TECH/science/05/03/climate.report.ap/index.html?eref=rss_world «Deal reached on climate change report». CNN. 4 de mayo de 2007. Consultado el 4 de mayo de 2007. primera versión] y la [http://edition.cnn.com/2007/TECH/science/05/03/climate.report.ap/index.html?eref=rss_world «Deal reached on climate change report». CNN. 4 de mayo de 2007. Consultado el 4 de mayo de 2007. última]).: http://edition.cnn.com/2007/TECH/science/05/03/climate.report.ap/index.html?eref=rss_world