Highlights of the U.S. Global Change Research Program
Climate Science Special Report
The climate of the United States is strongly connected to the changing global climate. The statements
below highlight past, current, and projected climate changes for the United States and the globe.
Global annually averaged surface air temperature has increased by about 1.8°F (1.0°C) over the last 115
years (1901–2016). This period is now the warmest in the history of modern civilization. The last few
years have also seen record-breaking, climate-related weather extremes, and the last three years have
been the warmest years on record for the globe. These trends are expected to continue over climate
This assessment concludes, based on extensive evidence, that it is extremely likely that human activities,
especially emissions of greenhouse gases, are the dominant cause of the observed warming
since the mid-20th century. For the warming over the last century, there is no convincing alternative
explanation supported by the extent of the observational evidence.
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
For example, 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.