Warming World: Impacts per Degree

Because carbon dioxide is long-lived in the atmosphere, increases in this gas can lock future generations into a range of impacts. The report uses the latest advances in science to project expected future impacts per degree of warming, which include: 5-10 percent changes in precipitation across many regions, 3-10 percent increases in the amount of rain falling during the heaviest precipitation events, 5-10 percent changes in stream flow across many river basins, 5-15 percent reductions in the yields of crops as currently grown, and 200-400 percent increases in the areas burned by wildfire in parts of the western United States. Policy choices informed by these recent advances in climate science could lead to emission reductions that have far reaching impacts for many future generations.

On April 25, 2011, the Environmental and Energy Study Institute (EESI) held a briefing on a new report from the National Research Council of the National Academy of Sciences (NAS) that details for the first time what the effects of climate change will be per degree of global temperature increase. Climate Stabilization Targets: Emissions, Concentrations and Impacts over Decades to Millennia details the impacts of human activities — particularly emissions of carbon dioxide, but also other greenhouse gas emissions — which are so vast they will largely control the future of the Earth’s climate system. A companion piece, Warming World: Impacts by Degree, highlights the main findings of the report. Two authors of the report discussed its findings and how the future could bring a relatively mild change in climate or an extreme change to entirely different climate conditions that will persist for many thousands of years. The briefing also included perspective on the value judgments that policymakers face when they deliberate on the risks of climate change.

• The traditional approach to determine climate change impacts had been to start with levels of greenhouse gas emissions, then estimate future concentrations, followed by computer models to simulate temperature increase and impacts. However, this produced large ranges of uncertainties due to variabilities in human activity, carbon cycles, climate sensitivities, and impact response.
• The more policy-relevant approach starts with assumed temperature changes (for example, 2°C of warming) and works backward to determine what greenhouse gas concentrations and emissions would need to be in order to limit warming to those targets. Scientists then work forward to determine impacts with much greater degrees of certainty.
• Climate change impacts that scale with temperature include sea ice, wildfires, food crop yields, hot summers, precipitation patterns, and streamflow. With each degree Celsius of warming (up to 4°C), the following impacts can be expected:

1. 5-10 percent less rainfall in the Mediterranean, southwestern North America, and southern Africa dry seasons
2. 5-10 percent more rainfall in Alaska and other high latitude northern hemisphere areas
3. 3-10 percent increase in amount of rain falling during heaviest precipitation events
4. 5-10 percent less streamflow in some river basins, including the Arkansas and Rio Grande
5. 5-15 percent reduced yield of U.S. corn, African corn, and Indian wheat
6. 15 percent reduction in the annual average of Arctic sea ice area and 25 percent reduction in the yearly minimum

• With each degree Celsius of warming (up to 2°C), a 200-400 percent increase in the area burned by wildfire in parts of the western United States is expected.
• With 3°C of warming, about 250,000 square kilometers of coastal land would be lost and many millions more people would be at risk of coastal flooding.
• The risk management approach to climate change policy has been incorporated into many planning frameworks, including the National Climate Assessment, the New York (City) Panel of Climate Change and Adaptation Task Force, and the Department of Defense. Scientists can say what is at risk, but not how much risk is acceptable. That is a judgment policymakers must make.
• An approach to link policy to science is to adopt an iterative process that can adapt to new scientific evidence and technological advancements. The stabilization targets outlined in the NAS study can form the basis of a “carbon budget”.
• Near-term mitigation should be thought of as an investment in reducing risk—lowering the likelihoods and/or consequences of climate disruption—or partial insurance. While this approach does not produce guarantees of avoided damages, we invest for similar reasons in Homeland Security.
• Delayed mitigation in the United States locks in carbon-intensive energy source investments both private and public and creates long-term inflexibilities. In addition, it creates a competitive disadvantage (e.g. to China) in new technology markets.
• As a respondent to the findings of the NAS study, Dr. MacCracken noted that the conventional approach to climate change policy is to calculate the net effect of emissions on a 100-year time scale. However, methane (CH4) is more potent in the short-term, with a global warming potential 72 times as high as carbon dioxide (CO2) over a 20-year time period (compared to 25 times as high over a 100-year time period).
• Dr. MacCracken suggested a three-part approach: limit CO2 emissions to limit long-term climate change, sharply reduce methane, black carbon, and ozone (O3) precursors (shorter-lived contributors to warming) to slow the rate of climate change over the next several decades, and sustain the effect that sulfates have had in offsetting the additional warming greenhouse gases would have caused through geo-engineering.

Related Media Coverage

'Climate Change Impacts' report forecasts sharp drop in corn yields by Jon H. Harsch, Agri-Pulse
Climate Change Research Council Report Calculates Effects Of Climate Change Per Degree of Warming by Andrew Childers, BNA (subscription required)

Background

Because carbon dioxide is long-lived in the atmosphere, increases in this gas can lock future generations into a range of impacts. The report uses the latest advances in science to project expected future impacts per degree of warming, which include: 5-10 percent changes in precipitation across many regions, 3-10 percent increases in the amount of rain falling during the heaviest precipitation events, 5-10 percent changes in stream flow across many river basins, 5-15 percent reductions in the yields of crops as currently grown, and 200-400 percent increases in the areas burned by wildfire in parts of the western United States. Policy choices informed by these recent advances in climate science could lead to emission reductions that have far reaching impacts for many future generations.