Four degrees and beyond: the potential for a global ... - Amper

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Phil. Trans. R. Soc. A (2011) 369, 45–66
doi:10.1098/rsta.2010.0288
Cumulative carbon emissions, emissions floors
and short-term rates of warming: implications
for policy
BY NIEL H. A. BOWERMAN 1, *, DAVID J. FRAME 1,2 ,CHRIS HUNTINGFORD 3 ,
JASON A. LOWE 4 AND MYLES R. ALLEN 1
1 Atmospheric, Oceanic and Planetary Physics, Department of Physics,
University of Oxford, Oxford OX1 3PU, UK
2 Smith School of Enterprise and the Environment, University of Oxford,
Oxford OX1 2BQ, UK
3 Centre for Ecology and Hydrology, Wallingford OX10 8BB, UK
4 Department of Meteorology, Met Office Hadley Centre (Reading Unit),
University of Reading, Reading RG6 6BB, UK
A number of recent studies have found a strong link between peak human-induced global
warming and cumulative carbon emissions from the start of the industrial revolution,
while the link to emissions over shorter periods or in the years 2020 or 2050 is generally
weaker. However, cumulative targets appear to conflict with the concept of a ‘floor’ in
emissions caused by sectors such as food production. Here, we show that the introduction
of emissions floors does not reduce the importance of cumulative emissions, but may make
some warming targets unachievable. For pathways that give a most likely warming up to
about 4 ◦ C, cumulative emissions from pre-industrial times to year 2200 correlate strongly
with most likely resultant peak warming regardless of the shape of emissions floors used,
providing a more natural long-term policy horizon than 2050 or 2100. The maximum rate
of CO2-induced warming, which will affect the feasibility and cost of adapting to climate
change, is not determined by cumulative emissions but is tightly aligned with peak rates
of emissions. Hence, cumulative carbon emissions to 2200 and peak emission rates could
provide a clear and simple framework for CO2 mitigation policy.
Keywords: cumulative emissions; emissions floors; rate of warming; climate change
1. Introduction
A substantial fraction of the carbon dioxide (CO2) emitted into the atmosphere
by human activity remains there, in effect, for centuries to millennia. Changes
in ocean chemistry, which can be described through the Revelle buffer factor [1],
limit oceanic removal of CO2 [2], while the potential for terrestrial vegetation to
takeupCO2 is also predicted by some models to fall as the climate warms [3],
*Author for correspondence (bowerman@atm.ox.ac.uk).
One contribution of 13 to a Theme Issue ‘Four degrees and beyond: the potential for a global
temperature increase of four degrees and its implications’.
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