It is “extremely likely” that humans are driving warming on Earth since the 1950s. That statement — which indicates a 95 to 100 percent confidence in the finding — came in a report released November 3 by the U.S. Global Change Research Program. This interagency effort was established in 1989 by presidential initiative to help inform national science policy.
The 2017 Climate Science Special Report, which lays out the current state of scientific knowledge on climate change, will be rolled into the fourth National Climate Assessment, set to be released in late 2018.
The last national climate assessment, released in 2014, also concluded that recent warming was mostly due to humans, but didn’t give a confidence level (SN Online: 5/6/14). Things haven’t gotten better. Ice sheet melting has accelerated, the 2017 report finds. As a result, projections of possible average global sea level rise by 2100 under a high greenhouse gas emissions scenario (in which emissions rise unabated throughout the 21st century) have increased from 2 meters to as much as 2.6 meters.
In addition, the report notes that three of the warmest years on record — 2014, 2015 and 2016 — occurred since the last report was released; those years also had record-low sea ice extent in the Arctic Ocean in the summer.
The report also notes some still-unresolved questions that have become increasingly active areas of research. One big one: How will climate change alter atmospheric circulation in the mid-latitude areas? Scientists are wrangling with whether and how these changes will affect storm patterns and contribute to extreme weather events, including blizzards and drought.