Official US climate science report confirms global climate trends
The U.S. Global Change Research Program has released the Climate Science Special Report as part of the Fourth National Climate Assessment (NCA4), providing an overview of current international scientific understanding of climate change, with a focus on the United States.
The U.S. Global Change Research Program (USGCRP), established by Presidential Initiative in 1989 and mandated by Congress in the Global Change Research Act (GCRA) of 1990, is administered by the National Oceanic and Atmospheric Administration (NOAA).
Some of the key findings of the Climate Science Special Report are:
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 timescales.
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.
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.
Global average sea level has risen by about 7–8 inches (17.78 - 20.32 cm) since 1900, with almost half (about 3 inches, or 7.6 cm) of that rise occurring since 1993. 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 (2.4m) by 2100 cannot be ruled out.
Over the next few decades (2021–2050), annual average temperatures are expected to rise by about 2.5°F for the United States, relative to the recent past (average from 1976–2005), under all plausible future climate scenarios.
The global atmospheric carbon dioxide (CO2) concentration has now passed 400 parts per million (ppm), a level that last occurred about 3 million years ago, when both global average temperature and sea level were significantly higher than today. Continued growth in CO2 emissions over this century and beyond would lead to an atmospheric concentration not experienced in tens to hundreds of millions of years.
In 2014 and 2015, emission growth rates slowed as economic growth became less carbon-intensive. Even if this slowing trend continues, however, it is not yet at a rate that would limit global average temperature change to well below 3.6°F (2°C) above preindustrial levels.
The US Global Change Research Program Climate Science Special Report is available here.