Fourth National Climate Assessment: A Dire Forecast for US if Action is Not Taken

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The Fourth National Climate Assessment (NCA4) report was released rather inauspiciously last week on the day after Thanksgiving – a traditionally slow news day. Nevertheless, the report is out and it clearly states, “the evidence of human-caused climate change is overwhelming and continues to strengthen.”

The massive report, considered volume two of NCA4, builds on the Climate Science Special Report issued last year. It gives a detailed account of what the impacts will be across the country and how the worst effects could be avoided.

The U.S average temperature, according to the report, has increased by 1.8°F since 1901, and is projected to continue rising. Over the next few decades, temperatures are projected to rise another 2.5°F.  By the end of the century, our average temperature could soar by as much as 11.9°F if greenhouse gas emissions continue to increase unchecked.

The report also looks at the long-term economic impacts for the country as the average temperature continues to climb. Costs from rising sea levels could reach as high as $118 billion and the projected total for damaged infrastructure is $32 billion. This is in addition to the reduced agricultural productivity expected from high heat and extended drought events. Overall, the report warns that if significant steps are not taken, climate change could slash the US economy’s GDP by 10% by the end of the century.

Not all doom and gloom, the report’s authors emphasize, “These impacts are projected to intensify—but how much they intensify will depend on actions taken to reduce global greenhouse gas emissions and to adapt to the risks from climate change now and in the coming decades.”

While similar in theme to the IPCC report from the UN, this assessment focuses solely on the United States. Emphasizing the fact that rising temperatures will affect different parts of our vast country in different ways, the NCA breaks the nation down into specific regions. It details the current and future impacts of climate change in each one:

The report also includes a supplemental set of State Climate Summaries that give a clear idea of what to expect in each of the 50 states as well as the US territories.

Mandated by Congress under the Global Change Research Act, this exhaustive 1600 page peer-reviewed report was produced by 300 scientists from 13 different government agencies. Published every four years, it is considered this country’s most authoritative statement on climate change.

Annual average temperatures across the United States are projected to increase over this century, with greater changes at higher latitudes as compared to lower latitudes, and greater changes under a higher scenario (RCP8.5; right) than under a lower one (RCP4.5; left). This figure shows projected differences in annual average temperatures for mid-century (2036–2065; top) and end of century (2071–2100; bottom) relative to the near present (1986–2015). Image credit: Fourth NCA, Vol II, figure 2.4.