USGCRP Climate Science Special Report: 4th National Climate Assessment (NCA4) is published

The U.S. Global Change Research Program (USGCRP) Climate Science Special Report, an authoritative assessment of the science of climate change, with a focus on the United States, is now available online.

It represents the first of the two volumes of the 4th National Climate Assessment, mandated by the Global Change Research Act of 1990. It focuses on past, current, and projected climate changes for the United States and the globe.

Among the main highlights of the report are that "in addition to warming, many other aspects of global climate are changing, primarily in response to human activities. Thousands of studies conducted by researchers around the world have documented changes in surface, atmospheric, and oceanic temperatures; melting glaciers; diminishing snow cover; shrinking sea ice; rising sea levels; ocean acidification; and increasing atmospheric water vapor.

For instance, global average sea level has risen by about 7-8 inches since 1900, with almost half (about 3 inches) of that rise occurring since 1993. Human-caused climate change has made a substantial contribution to this rise since 1900, contributing to a rate of rise that is greater than during any preceding century in at least 2,800 years. Global sea level rise has already affected the United States; the incidence of daily tidal flooding is accelerating in more than 25 Atlantic and Gulf Coast cities.

Global average sea levels are expected to continue to rise-by at least several inches in the next 15 years and by 1-4 feet by 2100. A rise of as much as 8 feet by 2100 cannot be ruled out. Sea level rise will be higher than the global average on the East and Gulf Coasts of the United States.

Changes in the characteristics of extreme events are particularly important for human safety, infrastructure, agriculture, water quality and quantity, and natural ecosystems. Heavy rainfall is increasing in intensity and frequency across the United States and globally and is expected to continue to increase. The largest observed changes in the United States have occurred in the Northeast."

The chapters of the report concern:

  • Our Globally Changing Climate
  • Physical Drivers of Climate Change
  • Detection and Attribution of Climate Change
  • Climate Models, Scenarios, and Projections
  • Large-Scale Circulation and Climate Variability
  • Temperature Changes in the United States
  • Precipitation Change in the United States
  • Droughts, Floods, and Wildfire
  • Extreme Storms
  • Changes in Land Cover and Terrestrial Biogeochemistry
  • Arctic Changes and their Effects on Alaska and the Rest of the United States
  • Sea Level Rise
  • Ocean Acidification and Other Ocean Changes
  • Perspectives on Climate Change Mitigation
  • Potential Surprises: Compound Extremes and Tipping Elements

You can download the report here.