Author: Associated Press
Posted on: The Guardian | November 3rd, 2017
A comprehensive review by 13 US federal agencies concludes that evidence of global warming is stronger than ever and that more than 90% of it has been caused by humans.
The conclusion contradicts a favorite talking point of senior members of the Trump administration.
A 477-page report released on Friday said it was “extremely likely” – meaning with 95 to 100% certainty – that global warming is manmade, mostly from carbon dioxide through the burning of coal, oil and natural gas.
The energy secretary, Rick Perry, and Environmental Protection Agency chief, Scott Pruitt, have said carbon dioxide is not the primary contributor to global warming.
Despite fears by some scientists and environmental advocates, David Fahey of the National Oceanic and Atmospheric Administration (Noaa) and several authors said there was no political interference or censoring. It is the most comprehensive summary of climate science since 2013, showing a warming, worsening world.
“A lot of what we’ve been learning over the last four year suggests the possibility that things may have been more serious than we think,” said Robert Kopp of Rutgers University, one of the dozens of scientists inside and outside the government who wrote the studies.
Since 1900, the report says Earth has warmed by 1C and seas have risen by 8in. Heatwaves, downpours and wildfires have become more frequent.
Scientists calculated that human contribution to warming since 1950 is between 92% and 123%. 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, said study co-author Katharine Hayhoe of Texas Tech.
“This period is now the warmest in the history of modern civilization,” she said.
For the first time, scientists highlighted a dozen “tipping points” of potential dangers that could happen from warming, things that Hayhoe said “keep me up at night”.
They include the slowing down of the giant Atlantic Ocean circulation system that could dramatically warp weather worldwide, much stronger El Niños, major decreases in ice sheets in Greenland and Antarctica, which would spike sea level rise, and massive release of methane and carbon dioxide from thawing permafrost that could turbo-charge warming.
Researchers did not provide an estimate of how likely it was that tipping points would occur, but “there is certainly some chance of some of these things happening,” Fahey said.
The report also documented how different climate change-caused events can interact in a complex way to make life worse such as the California wildfires and Superstorm Sandy five years ago.
“It shows that if anything the findings of scientists have become more dire” since 2013, said University of California Berkeley climate scientist Zeke Hausfather, who was not part of the work.