US and Swiss researchers have, for the first time, modeled a
climate system with extremely high carbon emissions in an attempt to test the
boundaries of the current computer simulation programs that inform us.
Published in Environmental
Research Letters, the study has revealed the potentially devastating
effects that high carbon emissions could have on our climate.
Little attention has previously been paid to the upper bound
range of future emissions which, as the researchers state, is imperative when
testing the outcomes of climate change simulations.
The A1F1 scenario, considered in the most recent report from
the Intergovernmental Panel on Climate Change (IPCC), represents the upper
bound of predicted carbon emissions.
The researchers, from the National
Center for Atmospheric Research, Colorado, and the Institute for Atmospheric and Climate
Science, Zurich,
created two hypothetical high carbon emission scenarios and compared their
effects to the existing emission scenarios.
The first scenario created, CurrentMix, assumed that global
energy behavior would remain constant but that the global population would rise
to 11 billion by 2100. The increase in carbon emissions envisaged in the A1F1
scenario would be doubled by the end of the century.
The second scenario, AllCoal, was designed as a thought
experiment to exceed all likely emissions for the remainder of the century.
This scenario assumed that the global population would
increase to 15 billion by 2100 and that demand for fuel sources would increase,
with more demand placed on coal—the fuel with the highest amount of carbon per
unit of energy. This would result in four times the increase in carbon
emissions envisaged in the A1F1 scenario.
According to the researchers’ computer simulations, the
major differences between each scenario would begin to materialize towards the
end of the 21st century.
By 2100, the AllCoal and CurrentMix scenarios would produce
a warming of over 12 K in the Arctic regions, with global sea levels rising by
33 cm and 27 cm respectively due to the thermal expansion of the oceans.
The A1F1 scenario showed a 21 cm increase in sea levels;
however the figures did not account for melting ice-sheets, which could
increase sea levels by large amounts. The AllCoal scenario projected a complete
loss of summer Arctic sea ice by 2070.
Each of the scenarios showed the typical pattern of
increased rainfall towards the poles and drying subtropics. For example, the
AllCoal scenario showed a 30 to 80% precipitation reduction in Southern Europe,
Central America, and Southern Australia, as well as increases of 50 to 200% in
the Arctic and Antarctic regions, Northern Canada, and Siberia.
The increase in most regions’ maximum temperatures went up
by a factor of two in the AllCoal scenario; however some regions showed a
considerably larger increase. In particular, the maximum summer temperatures in
Northern Europe increased by 6 to 7 K by 2100.
Lead author Professor Ben Sanderson says, “Our study
considered a future in which fossil fuel availability is completely
unrestricted and climate change is unmitigated, resulting in significant additional
warming above the entire range of scenarios considered in the Fourth Assessment
Report of the IPCC.”
“This study showed us that the model behaves on a global
scale largely as we would expect.”
