6 November 2017

Official US climate report attributes 92% of climate change to human activity

The US Government has released a special report which concludes that it is “extremely likely” human activities have been the main driver of global warming since the 1950s, contrary to what officials from the Trump Administration have argued so far.

The Climate Science Special Report is part of the 4th National Climate Assessment which is mandated by the Global Change Research Act of 1990 to be an authoritative assessment of the science behind climate change and help monitor climate risks for decision makers to make informed decisions about responses.

The report was overseen by the U.S. Global Change Research Program (USGCRP) and the research was conducted by scientists representing Federal agencies, national laboratories, universities and the private sector.

The report highlighted several potential dangers that could happen as a result of global warming, but did not provide an estimate of likelihood or time.

Negative effects include the slowing down of the giant Atlantic Ocean circulation system that can significantly warm weather conditions worldwide.

Stronger El Niños and sea-level rises due to melting ice sheets in Greenland and Antarctica are among the most prominent dangers of global warming. 

The 600-page report stresses that there is “no convincing alternative explanation” for the changing climate other than “human activities, especially emissions of greenhouse gases”.

"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”, the report said.

Co-author Katharine Hayhow of Texas Tech. said: “This period is now the warmest in the history of modern civilisation”.

The report argued that 92 to 123 percent of the observed 1951–2010 changes are likely attributed to human activity.

As Katherine Hayhow explained, it’s more than 100% on one end because some natural forces such as volcanoes and orbital cycle are working to cool Earth, but are being overwhelmed by the effects of greenhouse gases

Robert Kopp from Rutgers University said: “A lot of what we’ve been learning over the last four years suggests the possibility that things may have been more serious than we think”.

Rachel Licker, Senior Climate Scientist at the Union of Concerned Scientists said: “The draft NCA highlights the significant impacts climate change is already having around the country. Those impacts, including on our health and economy, will likely worsen unless we take strong steps to limit global warming emissions, and adequately prepare and protect communities”.

She added: “Unlike a physician, the climate assessment stops short of offering up a specific prescription or treatment plan. Instead, the American public must hold legislators and policy-makers accountable for taking action commensurate with the problem”.

The report will be finalised in 2018 after having been reviewed by hundreds of independent scientists and it will also incorporate public comments.

You can access the full Climate Science Special report here

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