Atmospheric research provides clear evidence of human-caused climate
change signal associated with CO2 increases
Claims that climate change is natural are inconsistent with atmospheric temperature trends

Date:
May 8, 2023
Source:
Woods Hole Oceanographic Institution
Summary:
New research provides clear evidence of a human 'fingerprint' on
climate change and shows that specific signals from human activities
have altered the temperature structure of Earth's atmosphere.


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FULL STORY ==========================================================================
New research provides clear evidence of a human "fingerprint" on climate
change and shows that specific signals from human activities have altered
the temperature structure of Earth's atmosphere.

Differences between tropospheric and lower stratospheric temperature
trends have long been recognized as a fingerprint of human effects on
climate. This fingerprint, however, neglected information from the mid
to upper stratosphere, 25 to 50 kilometers above the Earth's surface.

"Including this information improves the detectability of a human
fingerprint by a factor of five. Enhanced detectability occurs
because the mid to upper stratosphere has a large cooling signal from human-caused CO2 increases, small noise levels of natural internal
variability, and differing signal and noise patterns," according to
the journal article, "Exceptional stratospheric contribution to human fingerprints on atmospheric temperature," published in the Proceedings
of the National Academy of Sciences (PNAS). Noise in the troposphere
can include day-to-day weather, interannual variability arising from El
Nin~os and La Nin~as, and longer-term natural fluctuations in climate.

In the upper stratosphere, the noise of variability is smaller, and the
human- caused climate change signal is larger, so the signal can be much
more easily distinguished.

"Extending fingerprinting to the upper stratosphere with long temperature records and improved climate models means that it is now virtually
impossible for natural causes to explain satellite-measured trends in
the thermal structure of the Earth's atmosphere," the paper states.

"This is the clearest evidence there is of a human-caused climate change
signal associated with CO2 increases," according to lead author Benjamin Santer, an adjunct scientist in the Physical Oceanography Department at
the Woods Hole Oceanographic Institute (WHOI) in Massachusetts.

"This research undercuts and rebuts claims that recent atmospheric
and surface temperature changes are natural, whether due to the Sun or
due to internal cycles in the climate system. A natural explanation is virtually impossible in terms of what we are looking at here: changes in
the temperature structure of the atmosphere," added Santer, who has worked
on climate fingerprinting for more than 30 years. "This research puts to
rest incorrect claims that we don't need to treat climate change seriously because it is all natural." The research was motivated by earlier
work by Suki Manabe and Richard Wetherald, who in 1967 used a simple
climate model to study how CO2 from fossil fuel burning might change atmospheric temperature. Their modeling found a very distinctive feature:
an increase in CO2 levels led to more trapping of heat in the troposphere
(the lowest layer of Earth's atmosphere) and less heat escaping higher up
into the stratosphere (the layer above the troposphere), thus warming the troposphere and cooling the stratosphere. This prediction of tropospheric warming and stratospheric cooling in response to increasing CO2 has been confirmed many times by more complex models and verified by comparing
model results with global-mean atmospheric temperature observations from weather balloons and satellites.

Although these earlier studies considered global-mean temperature changes
in the middle and upper stratosphere, roughly 25 to 50 kilometers above
Earth's surface, they did not look at detailed patterns of climate change
in this layer. This region can be better studied now because of improved simulations and satellite data. The new research is the first to search
for human-caused climate change patterns -- also called "fingerprints"
-- in the middle and upper stratosphere.

"The human fingerprints in temperature changes in the mid to upper
stratosphere due to CO2 increases are truly exceptional because they are
so large and so different from temperature changes there due to internal variability and natural external forcing. These unique fingerprints
make it possible to detect the human impact on climate change due to
CO2 in a short period of time (~10 - - 15 years) with high confidence,"
stated co-author Qiang Fu, a professor in the Department of Atmospheric Sciences at the University of Washington.

"The world has been reeling under climate change, so being as confident
as possible of the role of carbon dioxide is critical," said co-author
Susan Solomon, Martin Professor of Environmental Studies at the
Massachusetts Institute of Technology. "The fact that observations
show not only a warming troposphere but also a strongly cooling upper stratosphere is unique tell-tale evidence that nails the dominant role
of carbon dioxide in climate change and greatly increases confidence."
Santer said that although it is intellectually gratifying to be able to
extend fingerprinting higher up into the atmosphere to test the prediction
by Manabe and Wetherald, it is also deeply concerning.

"As someone who tries to understand the kind of world that future
generations are going to inhabit, these results make me very worried. We
are fundamentally changing the thermal structure of Earth's atmosphere,
and there is no joy in recognizing that," Santer said.

"This study shows that the real world has changed in a way that
simply cannot be explained by natural causes," Santer added. "We now
face important decisions, in the United States and globally, on what
to do about climate change. I hope those decisions are based on our
best scientific understanding of the reality and seriousness of human
effects on climate." Funding for the study was provided by National
Science Foundation, National Oceanic and Atmospheric Administration,
U.S. Department of Energy, and the Francis E. Fowler IV Center for Ocean
and Climate at Woods Hole Oceanographic Institution.

* RELATED_TOPICS
o Earth_&_Climate
# Climate # Environmental_Awareness # Global_Warming
# Atmosphere # Environmental_Issues # Weather #
Environmental_Policy # Geoengineering
* RELATED_TERMS
o Attribution_of_recent_climate_change o
Consensus_of_scientists_regarding_global_warming
o Effects_of_global_warming o
Temperature_record_of_the_past_1000_years o Global_climate_model
o Global_warming o Global_warming_controversy o Water_resources

========================================================================== Story Source: Materials provided by
Woods_Hole_Oceanographic_Institution. Note: Content may be edited for
style and length.


========================================================================== Journal Reference:
1. Benjamin D. Santer, Stephen Po-Chedley, Lilong Zhao, Cheng-Zhi
Zou, Qiang
Fu, Susan Solomon, David W. J. Thompson, Carl Mears, Karl E. Taylor.

Exceptional stratospheric contribution to human fingerprints on
atmospheric temperature. Proceedings of the National Academy of
Sciences, 2023; 120 (20) DOI: 10.1073/pnas.2300758120 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/05/230508190601.htm

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