The National Climate Assessment: Measuring Domestic Climate Impacts

The Environmental and Energy Study Institute (EESI) held a briefing on the Third National Climate Assessment (NCA), which was released on May 6. Required by the Global Change Act of 1990, this report examines the current state of the climate in the United States, as well as its historic trends and potential future changes.

The Third National Climate Assessment covers regional impacts in the Northeast, Southeast, Northwest, Southwest, Midwest, Great Plains, Alaska and the Arctic, as well as Hawaii and the Pacific Islands. The report’s authors examined climate impacts to human health, water, energy, transportation, agriculture, forests, ecosystems, coastal areas, oceans and marine resources. Thirteen federal agencies collaborated to produce the report under the auspices of the Global Change Research Program (USGCRP). More than 240 scientists from academia, state, local and federal government, the private sector, and the nonprofit sector volunteered their time as authors.

In this briefing, NCA authors explored the risks inherent in the changes occurring in the United States, the latest findings highlighted in the report, and the science and scientific process informing the NCA’s conclusions.

Dr. Yohe and Dr. Wuebbles both hold leadership positions as part of the NCA and Development Advisory Committee, and have long been involved in climate science and impact assessments.

• Dr. Gary Yohe, Professor of Economics and Environmental Studies, Wesleyan University, said Congress’s current attitude toward climate change legislation is surprising when one considers that the Global Change Research Act of 1990 (which requires the National Climate Assessment) passed the House by voice vote, and passed the Senate 100-0. The Global Change Research Act requires that the National Climate Assessment reports are to be published not less than four years apart. The first was published in 2000; the second in 2009.
• The third National Climate Assessment, released on May 6, uses a risk-based framework for the first time. This recognizes that climate is another source of stress and possible change, not the only one. For example, climate is only one of multiple factors affecting water supply availability.
• New in-depth topics in the third assessment include oceans, coasts, urban areas, rural areas, and land-use. There are cross-sectoral chapters on issues such as the energy/water/land nexus. The report is also published in a completely interactive way, with digital products making it easy for everyone to access and manipulate the data. Because of several additional years of observed data and new technology, local climate change impacts can be shown in great detail and specificity for the first time.
• Dr. Yohe said one of the main differences between the report by the United Nations Intergovernmental Panel on Climate Change and the NCA, is that the IPCC covers continent, while the NCA looks only at the United States, dividing it into regions. This allows the authors to build a picture of what is happening from the bottom up.
• Dr. Yohe listed the four major results from the NCA: 1) human-induced climate change has moved into the present. It’s happening now, across the United States. 2) Impacts are apparent in every region and across important sectors, including health, water, agriculture, etc. Every person in the country has seen some of the effects of climate change. 3) Americans are already feeling the effects of climate change, as extreme weather becomes more prevalent and sea levels rise. 4) There are many actions we can take to mitigate climate change and its impacts, and to prepare for impacts we cannot avoid.
• Much of the report covers opportunities for people to respond to the risks from climate change. This includes adaptation and resilience.
• Dr. Wuebbles, Professor of Atmospheric Science, University of Illinois, discussed how climate change has always been the term preferred by the scientific community, rather than global warming, because the temperature rise worldwide has such complex impacts.
• The United States is observably warmer as a whole. While not every place has warmed (the Southeast, noticeably, has not), most places have warmed, and warmed exceptionally.
• Overall, precipitation has increased across the United States, particularly in the Northeast and Midwest, which have become considerably wetter. There are places, however, that have seen a decrease. That is due to the movement of tropical dry-zones northward, making the Southeast and Southwest of the United States drier.
• Extreme weather events are becoming more common, with the types of extreme events changing. For example, heat waves are increasing, and cold waves are decreasing. The unusually cold winter along the East Coast this year has been an exception to the general rule, but the last three decades have followed the underlying warming trend. There are increasing risks of floods in some regions, especially in the Northeast and Midwest; as well as an increase in droughts in the Southeast and Southwest.
• Texas heat waves and droughts are twice as likely due to climate change. Dr. Wuebbles said scientists were previously reluctant to attribute specific weather events to climate change, but are now more confident in their data and models.
• Dr. Wuebbles explained that researchers know climate change is not caused by the sun. He displayed a graph showing the 11-year sunspot cycle since 1976 compared to fluctuations of the Earth’s surface temperature (which has steadily increased in that period), showing that the sun’s sunspot cycle is not sufficient to explain rising temperatures on Earth. Indeed, there has actually been a slight decrease in the amount of energy the Earth is receiving from the sun.
• Human activity is the primary cause of climate change. As we continue to burn fossil fuels, the NCA projects a greater increase in temperatures. The NCA calculated low-emission and high-emission scenarios, and the impacts of their related temperature rises. Unfortunately, we are currently headed toward the high-emission scenario, based on current emission levels.
• There has been an 8-inch increase in sea levels over the last century, and over the next century they will probably rise by one to four feet. That’s enough to be quite disruptive to many locations: a three-foot change would put much of Miami in great danger. Storm surges then exacerbate these impacts, causing even greater damage unless effective adaptation measures are taken.
• The acidity of the oceans is increasing, as they absorb increased amounts of carbon dioxide. This is threatening marine life.
• Dr. Yohe concluded that the choices we make over the near term and slightly-longer term will have a large effect on which of those futures unfolds. The fundamental take-home message is that we must communicate these risks, and get businesses and the public to understand that they need to take climate into consideration as they make decisions.