Understanding Climate Change
Highlights from the IPCC Working Group II Summary for Policymakers of "Climate Change 2007: Impacts, Adaptation and Vulnerability"
Below are some of the key statements in the Summary for Policymakers from Working Group II of the 2007 IPCC Fourth Assessment Report. The summary was released on Friday, April 6, 2007, and is available on the IPCC Web site, along with the full working group and synthesis reports (see box at right).
The working group has assigned confidence
levels, either in the text or in parentheses, to many of its
findings. Spelling and punctuation have been adapted to Standard American
“Observational evidence from all continents and most oceans shows that many natural systems are being affected by regional climate changes, particularly temperature increases.”
“With regard to changes in snow, ice and frozen ground (including
permafrost) , there is high confidence that natural systems are affected.
“Based on growing evidence, there is
high confidence that the following types of hydrological systems are
being affected around the world:
“There is very high confidence, based on more
evidence from a wider range of species, that recent warming is strongly affecting
terrestrial biological systems, including such changes as:
What do we know about future impacts?
“Magnitudes of impact can now be estimated more systematically for a range of possible increases in global average temperature.”
“By mid-century, annual average river runoff and water availability are projected to increase by 10-40% at high latitudes and in some wet tropical areas, and decrease by 10-30% over some dry regions at mid-latitudes and in the dry tropics, some of which are presently water stressed areas. In some places and in particular seasons, changes differ from these annual figures (high confidence).”
“Drought-affected areas will likely increase in extent. Heavy precipitation events, which are very likely to increase in frequency, will augment flood risk (high confidence).”
“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 the world population currently lives (high confidence).”
“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) (high confidence). ”
“Approximately 20–30% 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.[2.7–4.5°F] (medium confidence).”
“Crop productivity is projected to increase slightly at mid to high latitudes for local mean temperature increases of up to 1–3°C [1.8–5.4°F] depending on the crop, and then decrease beyond that in some regions (medium confidence).”
“At lower latitudes, especially seasonally dry and tropical regions, crop productivity is expected to decrease for even small local temperature increases, (1–2°C [1.8–3.6°F]), which would increase risk of hunger (medium confidence).”
Coastal systems and low-lying areas:
“Increases in sea surface temperature of about 1 to 3°C [1.8 to 5.4°F] are projected to result in more frequent coral bleaching events and widespread mortality, unless there is thermal adaptation or acclimatization by corals (very high confidence).”
“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 (very high confidence).”
Industry, settlement and society
“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 (high confidence).”
“Poor communities can be especially vulnerable, in particular those concentrated in high-risk areas. They tend to have more limited adaptive capacities, and are more dependent on climate-sensitive resources such as local water and food supplies (high confidence).”
“Projected climate change-related exposures are likely to affect the
health status of millions of people, particularly those with low adaptive
“Climate change is expected to have some mixed effects, such as the decrease or increase of the range and transmission potential of malaria in Africa (high confidence).”
“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 (high confidence).”
For more information on projected impacts, sector-by-sector, see the table
detailing those impacts and their likelihood of occurrence in
Table SPM-2 on page 16 of the WG2
Summary for Policymakers (PDF).
What are the largest impacts that might happen, especially after 2100?
“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 millennia for a global average temperature increase of 1–4°C [1.8–7.2°F] (relative to 1990–2000), causing a contribution to sea-level rise of 4–6 meters [13–20 feet] or more.”
“Based on climate model results, it is very unlikely that the Meridional
Overturning Circulation (MOC) in the North Atlantic [known as the
ocean conveyor belt] will undergo a large abrupt transition during
the 21st century. Slowing of the MOC this century is very likely, but
temperatures over the Atlantic and Europe are projected to increase
nevertheless, due to global warming.”
What do we know about responding to climate change?
“Some adaptation is occurring now, to observed and projected future climate change, but on a limited basis.”
“Adaptation will be necessary to address impacts resulting from the warming which is already unavoidable due to past emissions.”
“However, 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.”
“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.”
“Vulnerability to climate change can be exacerbated by the presence of other stresses.”
“. . .[T]he 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.”
“A portfolio of adaptation and mitigation measures can further diminish the risks associated with climate change.”
“This Assessment makes it clear that the impacts of future climate change will be mixed across regions. For increases in global mean temperature of less than 1 to 3°C [1.8 to 5.4°F] 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 to 3°C [3.6 to 5.4°F].”
The University Corporation for Atmospheric Research manages the National Center for Atmospheric Research under sponsorship by the National Science Foundation. Any opinions, findings and conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.