The scientific consensus that humans are causing global warming
is likely to have passed 99 percent, according to the lead author
of the most authoritative study on the subject, and could rise
further after separate research that clears up some of the
Three studies published in Nature and Nature Geoscience use
extensive historical data to show there has never been a period in
the last 2,000 years when temperature changes have been as fast and
extensive as in recent decades.
It had previously been thought that similarly dramatic peaks and
troughs might have occurred in the past, including in periods
dubbed the Little Ice Age and the Medieval Climate Anomaly. But the
three studies use reconstructions based on 700 proxy records of
temperature change, such as trees, ice, and sediment, from all
continents that indicate none of these shifts took place in more
than half the globe at any one time.
The Little Ice Age, for example, reached its extreme point in
the 15th century in the Pacific Ocean, the 17th century in Europe,
and the 19th century elsewhere, says one of the
studies. This localization is markedly different from the trend
since the late 20th century when records are being broken year
after year over almost the entire globe, including this summer’s
European heat wave.
Major temperature shifts in the distant past are also likely to
have been primarily caused by volcanic eruptions, according to
the studies, which helps to explain the strong global
fluctuations in the first half of the 18th century as the world
started to move from a volcanically cooled era to a climate warmed
by human emissions. This has become particularly pronounced since
the late 20th century, when temperature rises over two decades or
longer have been the most rapid in the past two millennia, notes
The authors say this highlights how unusual warming has become
in recent years as a result of industrial emissions.
“There is no doubt left — as has been shown extensively in
many other studies addressing many different aspects of the climate
system using different methods and data sets,” said Stefan
Brönnimann, from the University of Bern and the Pages 2K
consortium of climate scientists.
Commenting on the study, other scientists said it was an
important breakthrough in the “fingerprinting” task of proving
how human responsibility has changed the climate in ways not seen
in the past.
“This paper should finally stop climate change deniers
claiming that the recent observed coherent global warming is part
of a natural climate cycle. This paper shows the truly stark
difference between regional and localized changes in climate of the
past and the truly global effect of anthropogenic greenhouse
emissions,” said Mark Maslin, professor of climatology at
University College London.
Previous studies have shown near unanimity among climate
scientists that human factors — car exhausts, factory chimneys,
forest clearance, and other sources of greenhouse gases — are
responsible for the exceptional level of global warming.
A 2013 study in Environmental
Research Letters found 97 percent of climate scientists agreed
with this link in 12,000 academic papers that contained the words
“global warming” or “global climate change” from 1991 to
2011. Last week, that paper
1 million downloads, making it the most accessed paper ever
among the 80-plus journals published by the Institute of Physics,
according to the authors.
The pushback has been political rather than scientific. In the
U.S., the rightwing think tank the Competitive Enterprise Institute
is reportedly putting pressure on NASA to remove a reference to the
97 percent study from its webpage. The CEI has
received event funding from the American Fuel and Petrochemical
Manufacturers and Charles Koch Institute, which have much to lose
from a transition to a low-carbon economy.
But among academics who study the climate, the convergence of
opinion is probably strengthening, according to John Cook, the lead
author of the original consensus paper and a follow-up study on the
“consensus about consensus” that looked at a range of similar
estimates by other academics.
He said that at the end of his 20-year study period there was
more agreement than at the beginning: “There was 99 percent
scientific consensus in 2011 that humans are causing global
warming.” With ever stronger research since then and increasing
heat waves and extreme weather, Cook believes this is likely to
have risen further and is now working on an update.
“As expertise in climate science increases, so too does
agreement with human-caused global warming,” Cook
wrote on the Skeptical Science blog. “The good news is public
understanding of the scientific consensus is increasing. The bad
news is there is still a lot of work to do yet as climate deniers
continue to persistently attack the scientific consensus.”
This story was originally published by Grist with the headline
‘There’s no doubt left’ about scientific consensus on global
warming anymore on Jul 27, 2019.
Source: FS – All – Ecology – News 2
‘There’s no doubt left’ about scientific consensus on global warming anymore