FACT SHEET | May 17, 2007

Authoritative IPCC Report Confirms Existence, Consequences of Global Climate Change

The Intergovernmental Panel on Climate Change (IPCC) was established in 1988 by World Meteorological Organization (WMO) and United Nations Environment Program (UNEP) to assess scientific, technical and socio-economic information relevant for the understanding of climate change, its potential impacts and options for adaptation and mitigation. The IPCC does not carry out research nor does it monitor climate related data or other relevant parameters. Instead, the panel bases its assessment mainly on peer reviewed and published scientific/technical literature. The IPCC has released four comprehensive Assessment Reports: in 1990, 1995, 2001, and 2007.

 The IPCC Fourth Assessment Report (AR4), which was released in three installments from February through May 2007, reviewed all available scientific data through 2005 to examine the issue of climate change in three working groups, each of which produced a report on their findings:


1) the scientific aspects of the climate system and climate change; 

2) the vulnerability of socio-economic and natural systems to climate change, negative and positive consequences of climate change, and options for adapting to it; and 

3) options for limiting greenhouse gas emissions and otherwise mitigating climate change.


Over 2,500 scientific expert reviewers, 800 contributing authors, and 450 lead authors from more than 130 countries worked for six years on AR4.


The report uses specific phrases to describe the likelihood of an outcome or a result. 

  • Virtually certain > 99 percent probability of occurrence
  • Extremely likely > 95 percent probability
  • Very likely > 90 percent probability
  • Likely> 66 percent probability
  • More likely than not > 50 percent probability
  • Very unlikely < 10 percent probability
  • Extremely unlikely < 5 percent probability 

The report also uses specific language to describe the confidence in a statement.


·Very high confidence: At least 9 out of 10 chance of being correct

  • High confidence: About 8 out of 10 chance
  • Medium confidence: About 5 out of 10 chance
  • Low confidence: About 2 out of 10 chance
  • Very low confidence: Less than a 1 out of 10 chance


Key Findings from Working Group I

The first installment of the IPCC report focuses on the scientific aspects of the climate system and climate change. The following passages have been excerpted from the Summary for Policymakers of the Working Group I report: 

  • The global atmospheric concentration of carbon dioxide has increased from a pre-industrial value of about 280 parts per million (ppm) to 379 ppm in 2005. The atmospheric concentration of carbon dioxide in 2005 exceeds by far the natural range over the last 650,000 years (180 to 300 ppm). The annual carbon dioxide concentration growth rate was larger during the last 10 years than it has been since the beginning of continuous direct atmospheric measurements although there is year-to-year variability in growth rates. 
  • The primary source of the increased atmospheric concentration of carbon dioxide since the pre-industrial period results from fossil fuel use, with land-use change providing another significant but smaller contribution. 
  • The understanding of anthropogenic warming and cooling influences on climate has improved since the Third Assessment Report (TAR), leading to very high confidence that the global average net effect of human activities since 1750 has been one of warming.
  • Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level.
  • Eleven of the last twelve years (1995-2006) rank among the 12 warmest years in the instrumental record of global surface temperature (since 1850).
  • New data since the TAR now show that losses from the ice sheets of Greenland and Antactica have very likely contributed to sea level rise over 1993 to 2003.
  • At continental, regional and ocean basin scales, numerous long-term changes in climate have been observed. These include changes in arctic temperatures and ice, widespread changes in precipitation amounts, ocean salinity, wind patterns and aspects of extreme weather including droughts, heavy precipitation, heat waves and the intensity of tropical cyclones.
  • Palaeoclimatic information supports the interpretation that the warmth of the last half century is unusual in at least the previous 1,300 years. The last time the polar regions were significantly warmer than present for an exended period (about 125,000 years ago), reductions in polar ice volume led to 4 to 6 m of sea level rise.
  • Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations. This is an advance since the TAR’s conclusion that ‘most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations.’ Discernible human influences now extend to other aspects of climate, including ocean warming, continental-average temperatures, temperature extremes and wind patterns.
  • For the next two decades, a warming of about 0.2˚C per decade is projected for a range of emission scenarios. Even if the concentrations of all greenhouse gases and aerosols had been kept constant at year 2000 levels, a further warming of about 0.1˚C per decade would be expected…Current greenhouse gas emissions at or above current rates would cause further warming and induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century.
  • In some projections, arctic late-summer sea ice disappears almost entirely by the latter part of the 21st century.
  • Based on a range of models, it is likely that future tropical cyclones (typhoons and hurricanes) will become more intense, with larger peak wind speeds and more heavy precipitation assoiciated with ongoing increases of tropical sea surface temperatures. There is less conficence in projections of a global decrease in numbers of tropical cyclones. The apparent increase in the proportion of very intense storms since 1970 in some regions is much larger than simulated by current models for that period.
  • Anthropogenic warming and sea level rise would continue for centuries due to the time scales associated with climate processes and feedbacks, even if greenhouse gas concentrations were to be stabilised. 


Key Findings from Working Group II

The second installment of the IPCC report focuses on the vulnerability of socio-economic and natural systems to climate change, negative and positive consequences of climate change, and options for adapting to it. The following passages have been excerpted from the Summary for Policymakers of the Working Group II report:


The Vulnerability of Natural Systems

  • Observational evidence from all continents and most oceans shows that many natural systems are being affected by regional climate changes, particularly temperature increases.
  • A global assessment of data since 1970 has shown it is likely that anthropogenic warming has had a discernible influence on many physical and biological systems. 
  • Recent climate changes and climate variations are beginning to have effects on many other natural and human systems. However, based on the published literature, the impacts have not yet become established trends. Examples include…sea-level rise and human development are together contributing to losses of coastal wetlands and mangroves and increasing damage from coastal flooding in many areas. 
  • By mid-century, annual average river runoff and water availability are projected to increase by 10-40 percent at high latitudes and in some wet tropical areas, and decrease by 10-30 percent over some dry regions at mid-latitudes and in the dry tropics, some of which are presently water stressed areas. 
  • Drought-affected areas will likely increase in extent. Heavy precipitation events, which are very likely to increase in frequency will augment flood risk.
  • In the course of the century, water supplies stored in glaciers and snow cover are projected to decline, reducing water availability in regions supplied by meltwater from major mountain ranges, where more than one-sixth of th world population currently lives.
  • The resilience of many ecosystems is likely to be exceeded this century by an unprecedented combination of climate change, associated disturbances (e.g., flooding, drought, wildfire, insects, ocean acidification), and other global change drivers (e.g., land use change, pollution, over-exploitation of resources).
  • Over the course of this century, net carbon uptake by terrestrial ecosystems is likely to peak before mid-century and then weaken or even reverse, thus amplifying climate change.
  • Approximately 20-30 percent of plant and animal species assessed so far are likely to be at increased risk of extinction if increases in global average temperature exceed 1.5-2.5˚C.
  • For increases in global average temperature exceeding 1.5-2.5˚C and in concomitant atmospheric carbon dioxide concentrations, there are projected to be major changes in ecosystem structure and function, species’ ecological interactions, and species’ geographic ranges, with predominantly negative consequences for biodiversity, and ecosystem goods and services e.g., water and food supply.
  • The progressive acidification of oceans due to increasing atmospheric carbon dioxide is expected to have negative impacts on marine shell forming organisms (e.g., corals) and their dependent species.


Projected Impacts on Natural Systems in North America

  • Moderate climate change in the early decades of the century is projected to increase aggregate yields of rainfed agriculture by 5-20 percent, but with important variability among regions. Major challenges are projected for crops that are near the warm end of their suitable range or depend on highly utilised water resources. [high confidence]
  • Warming in western mountains is projected to cause decreased snowpack, more winter flooding, and reduced summer flows, exacerbating competition for over-allocated water resources.[very high confidence]
  • Disturbances from pests, diseases, and fire are projected to have increasing impacts on forests, with an extended period of high fire risk and large increases in area burned. [very high confidence]
  • Cities that currently experience heat waves are expected to be further challenged by an increased number, intensity and duration of heat waves during the course of the century, with potential for adverse health impacts. The growing number of the elderly population is most at risk.[very high confidence]
  • Coastal communities and habitats will be increasingly stressed by climate change impacts interacting with development and pollution. Population growth and the rising value of infrastructure in coastal areas increase vulnerability to climate variability and future climate change, with losses projected to increase if the intensity of tropical storms increases. Current adaptation is uneven and readiness for increased exposure is low.[very high confidence]


Vulnerability of Socio-Economic Systems

  • Crop productivity is projected to increase slightly at mid-to high latitudes for local mean temperature increases of up to 1-3˚C depending on the crop, and then decrease beyond that in some regions. At lower latitudes, especially seasonally dry and tropical regions, crop productivity is projected to decrease for even small local temperature increases (1-2˚C), which would increase risk of hunger.
  • Globally, the potential for food production is projected to increase with increases in local average temperature over a range of 1-3˚C, but above this is projected to decrease.
  • Increases in the frequency of droughts and floods are projected to affect local crop production negatively, especially in subsistence sectors at low latitudes.
  • Regional changes in the distribution and production of particular fish species are expected due to continued warming, with adverse effects projected for aquaculture and fisheries.
  • Coasts are projected to be exposed to increasing risks, including coastal erosion, due to climate change and sea-level rise. The effect will be exacerbated by increasing human-induced pressures on coastal areas.
  • Increases in sea surface temperature of about 1-3˚C are projected to result in more frequent coral bleaching events and widespread mortality, unless there is thermal adaptation or acclimatisation by corals.
  • Many millions more people are projected to be flooded every year due to sea-level rise by the 2080s. Those densely-populated and low-lying areas where adaptive capacity is relatively low, and which already face other challenges such as tropical storms or local coastal subsidence, are especially at risk. The numbers affected will be largest in the mega-deltas of Asia and Africa while small islands are especially vulnerable.
  • Costs and benefits of climate change for industry, settlement, and society will vary widely by location and scale. In the aggregate, however, net effects will tend to be more negative the larger the change in climate.
  • Projected climate change-related exposures are likely to affect the health status of millions of people, particularly those with low adaptive capacity, through:
  • Increases in malnutrition and consequent disorders, with implications for child growth and development;
  • Increased deaths, disease and injury due to heat waves, floods, storms, fires, and droughts;
  • The increased burden of diarrhoeal disease;
  • The increased frequency of cardio-respiratory diseases due to higher concentrations of ground level ozone related to climate change; and
  • The altered spatial distribution of some infectious disease vectors.
  • Studies in temperate areas have shown that climate change is projected to bring some benefits, such as fewer deaths from cold exposure. Overall it is expected that these benefits will be outweighed by the negative health effects of rising temperatures world-wide, especially in developing countries.
  • Very large sea-level rises that would result from widespread deglaciation of Greenland and West Antarctic ice sheets imply major changes in coastlines and ecosystems, and inundation of low-lying areas, with greatest effects in river deltas… There is medium confidence that at least partial deglaciation of the Greenland ice sheet, and possibly the West Antarctic ice sheet, would occur over a period of time ranging from centuries to millenia for a global average temperature increase of 1-4˚C (relative to 1990-2000), causing a contribution of 4-6m or more. The complete melting of the Greenland ice sheet and the West Antarctic ice sheet would lead to a contribution to sea-level rise of up to 7 m and about 5 m, respectively.
  • For increases in global mean temperature of less than 1-3˚C above 1990 levels, some impacts are projected to produce benefits in some places and some sectors, and produce costs in other places and other sectors. It is, however, projected that some low latitude and polar regions will experience net costs even for small increases in temperature. It is very likely that all regions will experience either declines in net benefits or increases in net costs for increases in temperature greater than about 2-3˚C. These observations confirm evidence reported in the TAR that, while developing countries are expected to experience larger percentage losses, global mean losses could be 1-5 percent GDP for 4˚C of warming.
  • It is virtually certain that aggregate estimates of costs mask significant differences in impacts across sectors, regions, countries, and populations. In some locations and amongst some groups of people with high exposure, high sensitivity, and/or low adaptive capacity, net costs will be significantly larger than the global aggregate.

Adapting to Climate Change

  • Adaptation will be necessary to address impacts resulting from the warming which is already unavoidable due to past emissions…A wide array of adaptation options is available, but more extensive adaptation than is currently occurring is required to reduce vulnerability to future climate change. There are barriers, limits and costs, but these are not fully understood.
  • Adaptation alone is not expected to cope with all the projected effects of climate change, and especially not over the long run as most impacts increase in magnitude.
  • An important advance since the TAR has been the completion of impacts studies for a range of different development pathways taking into account not only projected climate change but also projected social and economic changes… These studies show that the projected impacts of climate change can vary greatly due to the development pathway assumed. For example, there may be large differences in regional population, income and technological development under alternative scenarios, which are often a strong determinant of the level of vulnerability to climate change.
  • Sustainable development can reduce vulnerability to climate change by enhancing adaptive capacity and increasing resilience. At present, however, few plans for promoting sustainability have explicitly included either adapting to climate change impacts, or promoting adaptive capacity. On the other hand, it is very likely that climate change can slow the pace of progress toward sustainable development either directly through increased exposure to adverse impact or indirectly through erosion of the capacity to adapt.
  • Even the most stringent mitigation efforts cannot avoid further impacts of climate change in the next few decades, which makes adaptation essential, particularly in addressing near-term impacts. Unmitigated climate change would, in the long term, be likely to exceed the capacity of natural, managed and human systems to adapt. 

Sources: IPCC website, http://www.ipcc.ch/

Working Group I Summary for Policymakers, http://www.ipcc.ch/WG1_SPM_17Apr07.pdf

Working Group II Summary for Policymakers, http://www.ipcc.ch/SPM13apr07.pdf




  • Sara Mills (224-3232)


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