Hi All
Is ramping /down/ from 2 xCO2 to 4 x CO2 a misprint?
Stephen
Emeritus Professor of Engineering Design. School of Engineering,
University of Edinburgh, Mayfield Road, Edinburgh EH9 3JL, Scotland
[email protected], Tel +44 (0)131 650 5704, Cell 07795 203 195,
WWW.homepages.ed.ac.uk/shs, YouTube Jamie Taylor Power for Change
On 29/06/2015 14:21, Andrew Lockley wrote:
http://link.springer.com/article/10.1007/s00382-014-2302-6?wt_mc=alerts.TOCjournals
Climate Dynamics
August 2015, Volume 45, Issue 3-4, pp 745-754
26 Aug 2014
The reversibility of CO2 induced climate change
Peili Wu, Jeff Ridley, Anne Pardaens, Richard Levine, Jason Lowe
Abstract
This paper investigates the reversibility of CO2 induced climate
change and in particular the potential impacts of different rates of
CO2 reduction using a coupled climate model. Atmospheric CO2
concentration is ramped up by 0.5 %/year from the preindustrial value
to 4×CO2 and then ramped down from 2×CO2 to 4×CO2 with different
rates. How the response of the climate system is affected by the peak
atmospheric CO2 concentration and the rate of long term decline is
vital information for those considering hypothetical geoengineering
options to remove CO2. Major components of the climate system
including global mean surface air temperature and precipitation,
contribution of thermal expansion to global sea level rise, loss of
the Arctic sea ice, weakening of the Atlantic meridional overturning
circulation (AMOC) and the South Asia monsoon are analyzed. We have
found no ‘tipping points’ or thresholds beyond which CO2 induced
climate change in these components become irreversible within this
model under the specific scenarios. However, there are strong inertias
and path-dependent hysteresis in the climate system linked through
oceanic memory. Initially the strengthened global hydrological cycle
accelerates further in response to a CO2 ramp-down before weakening.
Thermal expansion of the oceans continues for many decades after CO2
concentration starts to decrease. A 0.5 %/year reduction from 4×CO2
could see a further 25 % sea level rise. The weakening of the AMOC is
reversible, but the build-up of highly saline subtropical waters
during global warming drives an overshoot of the AMOC after the CO2
ramp-down and extends the warming of the northern high latitudes by
many decades. The South Asia monsoon strengthens in response to a CO2
ramp-up marked by an increase in summer monsoon rainfall. This
increase reverses rapidly following a CO2 ramp-down, displaying an
undershoot in monsoon rainfall for rapid CO2 reductions.
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