NCAS Science Highlight
Accelerating warming from
increasing carbon dioxide
Jonathan Gregory1,2, Timothy Andrews2, Peter Good2
1NCAS-Climate,
University of Reading
2Met
Office Hadley Centre
What are the new findings?
Burning fossil fuels (oil, gas and coal) produces carbon
dioxide (CO2). CO2 in the atmosphere is the most
important “greenhouse gas”, so called because it keeps
the climate warm, making it harder to lose heat to space
by insulating the Earth’s surface. This is the main process
involved in global warming. To study it, climate scientists
consider a simple scenario in which the atmospheric CO2
concentration goes up at 1% per year. It is assumed that
the climate would warm at a fairly steady rate in this
scenario, but we have discovered that the rate of
warming accelerates as time passes (see diagram).
Jonathan Gregory,
the lead author of
the study, has been
an NCAS-climate
senior scientist and
a Science Fellow at
the Met Office
since 2002.
2.7C
1.9C
Why are these findings important?
The size of global warming for a given CO2 increase can be
estimated by various methods, and it is customary to
compare the results using “benchmarks” (for example,
how much does the planet warm when atmospheric CO2
concentration is doubled), which are referred to in climate
policy negotiations. Our results imply these benchmarks
are a less reliable guide than sometimes assumed, and
could lead to underestimates of future warming.
How did we discover this?
We analysed 16 different sets of climate change
simulations produced by scientific research centres
worldwide in which atmospheric CO2 concentration was
increased by 1% each year. In these experiments, we
calculated the heating effect of adding more CO2 to the
atmosphere, the ability of the climate system to lose
more heat to space as it warms up, and the rate at which
extra heat is stored in the ocean. We found that all of
these three phenomena change as time passes in such a
way as to increase the rate of global warming.
This research was funded by the European Research
Council (an EU body), NCAS and the UK government.
Above: The red line shows the warming
predicted by climate simulations with
CO2 increasing at 1% per year. The rate of
warming grows as time passes, as can be
seen by comparison with the black line,
which shows a constant warming rate.
The warming in the second 70 years
(2.7C) is 40% larger than the warming in
the first 70 years (1.9C).
Find out more:
• See Jonathan Gregory’s webpage
• Email [email protected]
• Take a look at the journal article
http://dx.doi.org/10.1098/rsta.2014.0417
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