Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC, 2007) and Global Climate Change Impacts in the United States (USGCRP, 2009).

The overall conclusion of the National Academies report Advancing the Science of Climate Change was that climate change “poses significant risks for—and in many cases is already affecting—a broad range of human and natural systems” (NRC, 2010b, p. 1). The US Global Change Research Program, which coordinates and integrates federal climate change research, found (USGCRP, 2009, p. 9) that

Climate-related changes have already been observed globally and in the United States. These include increases in air and water temperatures, reduced frost days, increased frequency and intensity of heavy downpours, a rise in sea level, and reduced snow cover, glaciers, permafrost, and sea ice. A longer ice-free period on lakes and rivers, lengthening of the growing season, and increased water vapor in the atmosphere have also been observed. Over the past 30 years, temperatures have risen faster in winter than in any other season, with average winter temperatures in the Midwest and northern Great Plains increasing more than 7ºF. Some of the changes have been faster than previous assessments had suggested.

These climate-related changes are expected to continue while new ones develop. Likely future changes for the United States and surrounding coastal waters include more intense hurricanes with related increases in wind, rain, and storm surges (but not necessarily an increase in the number of these storms that make landfall), as well as drier conditions in the Southwest and Caribbean. These changes will affect human health, water supply, agriculture, coastal areas, and many other aspects of society and the natural environment.

Such findings are relevant to the committee’s work because conditions in the outdoor environment greatly influence conditions in the indoor environment.

Literature Regarding Observations of Climate Change

This report uses the term climate to refer to prevailing outdoor environmental conditions—including temperature, humidity, wind, precipitation, sea level, and other phenomena—and climate change to refer to modifications in those outdoor conditions that occur over an extended period of time. Observations of key climatic variables provide a rich historical record of how the climate has changed in the past and serve as a basis for assessing potential future change (IPCC, 2007; NRC, 2010b; USCCSP, 2008).

Measurements of global mean temperature indicate that the first decade of the 21st century was 0.8°C (1.4°F) warmer than the first decade of the

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