Yesterday the Intergovernmental Panel on Climate Change (IPCC) released its second report of the year on global warming. Back in February, the IPCC explained the scientific consensus on human-caused climate change. This time, we learn the impacts.

For increases in global mean temperature of less than 1-3 degrees Celsius above 1990 levels, impacts may produce benefits in some places and some sectors, and produce costs in other places and sectors. However, some low latitude and polar regions of the world will see net costs rise even with only small increases in temperature. Once the average temperature increases more than 2-3 degrees Celsius in any region, however, it is “very likely” that we wil see declining benefits and instead see an increase in net costs.

The Summary for Policymakers of the Impacts, Adaptation, and Vulnerability reports the projected effects of climate change:

• 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.

• Crop productivity is projected to increase slightly at mid to high latitudes for local mean temperature increases of up to 1-3 degrees Celsius depending on the crop, and then decrease beyond that in some regions.

• 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.

• 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 degrees Celsius.

Each word of the report had to be agreed upon by consensus, but disputes between the scientific authors and diplomatic editors infuriated some scientists. They claim the predicted impacts have been watered down because of political interference. For example, a sentence that originally said scientists had “very high confidence” (greater than 90 percent) that many natural systems would be affected by rising temperatures was changed to “high confidence” (greater than 80 percent) at the insistence of delegates from China and Saudi Arabia.

The report goes on to say that global warming cannot be stopped at this point, only slowed down. However, the most catastrophic effects can still be avoided with swift and decisive global action. The IPCC recommends a combination of adaptation and mitigation measures:

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.

This suggests the value of a portfolio or mix of strategies that includes mitigation, adaptation, technological development (to enhance both adaptation and mitigation) and research (on climate science, impacts, adaptation and mitigation).

The full report will be released next week. It includes more than 2,500 scientists appointed by more than 130 countries.

The IPCC was created by the World Meteorological Organization and the United Nations Environment Programme to assess the scientific, technical, and socio-economic information relevant to understanding the scientific basis of risk for climate change, along with its potential impacts and options for adaptation and mitigation. Its assessments are based solely on peer reviewed and published scientific/technical literature.

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Impacts, Adaptation, and Vulnerability: Summary for Policymakers
Intergovernmental Panel on Climate Change