New observations and new research have increased our understanding of past, current, and
future climate change since the Third U.S. National Climate Assessment (NCA3) was
published in May 2014.
This Climate Science Special Report (CSSR) is designed to capture
that new information and build on the existing body of science in order to summarize the
current state of knowledge and provide the scientific foundation for the Fourth National
Climate Assessment (NCA4).
Since NCA3, stronger evidence has emerged for continuing, rapid, human-caused warming of
the global atmosphere and ocean.
For the warming over the last century, there is no convincing alternative explanation
supported by the extent of the observational evidence.”
The last few years have also seen record-breaking, climate-related weather extremes, the three
warmest years on record for the globe, and continued decline in arctic sea ice.
are expected to continue in the future over climate (multidecadal) timescales.
Since 1980, the cost
of extreme events for the United States has exceeded $1.1 trillion, therefore better
understanding of the frequency and severity of these events in the context of a changing
climate is warranted.
Periodically taking stock of the current state of knowledge about climate change and putting
new weather extremes, changes in sea ice, increases in ocean temperatures, and ocean
acidification into context ensures that rigorous, scientifically-based information is available to
inform dialogue and decisions at every level.
In this Executive Summary, green boxes present highlights of the main report.
are followed by related points and selected figures providing more scientific details.
summary material on each topic presents the most salient points of chapter findings and
therefore represents only a subset of the report’s content.
For more details, the reader is
referred to the individual chapters.
This report discusses climate trends and findings at several
scales: global, nationwide for the United States, and for ten specific U.S. regions (shown in
Figure 1 in the Guide to the Report)
A statement of scientific confidence also follows each
point in the Executive Summary.
The confidence scale is described in the Guide to the Report.
At the end of the Executive Summary and in Chapter 1: Our Globally Changing Climate, there is also a summary box highlighting the most notable advances and topics since NCA3 and since the 2013 Intergovernmental Panel on Climate Change (IPCC) report.
For full report press here: Climate Science Special Report