CO2e- the Zombie Climate Metric

Professor Raymond Pierrehumbert, University of Oxford

Thursday 13^th October (room C21, Pariser Building, Sackville Street) at 4.00pm.  Please note the change of venue from the usual Tyndall seminars room!

Anthropogenic greenhouse gases vary in the two dimensional space of atmospheric lifetime and radiative efficiency, but ever since the IPCC First Assessment Report, various metrics have come into use in a (largely fruitless) attempt to characterize the  mix of emitted gases by a single metric, generally phrased in terms of “equivalent CO2” or CO2e.  All of these metrics have serious shortcomings, but the flaws of the most widely used metric — CO2e based on Global Warming Potential — are particularly bad and lead to perverse incentives when incorporated in emissions targets, taxes or trading scheme. In particular, the metric severely overestimates the importance of mitigation of short-term climate pollution like methane or HFC.

In this talk, I will go through some case studies illustrating problems with CO2e, and point to better ways of evaluating the climate impact of a mix of gases.  I will also discuss the problems arising from the fact that most of the COP21 INDC targets were phrased in terms of CO2e, without further specification as to how the target would be achieved.  Generally speaking, so far as climate protection goes the only near term SLCP mitigation that needs to be encouraged are measures of very low or negative cost, but policy vehicles which incentivize such measures without displacing more important CO2 mitigation are very difficult to formulate.

The seminar will take place in room C21, in the Pariser Building on Sackville Street– number 12 on the map here-  http://www.manchester.ac.uk/discover/maps/interactive-map/?id=9