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Web End = Clim Dyn (2015) 45:10091023
DOI 10.1007/s00382-014-2342-y
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Web End = Received: 23 April 2014 / Accepted: 13 September 2014 / Published online: 25 September 2014 Springer-Verlag Berlin Heidelberg 2014
1 Introduction
The sensitivity of the Earths climate to increasing concentrations of carbon dioxide (CO2) is at the heart of the scientic debate on anthropogenic climate change. Climate sensitivity is a metric that is used to summarize the global surface temperature response to an externally imposed radiative forcing. The term equilibrium climate sensitivity (ECS) refers to the equilibrium change in surface temperature to a doubling of atmospheric CO2 concentration.
A shorter-term measure of sensitivity, transient climate response (TCR), represents the extent of global warming at the time of the CO2 doubling following a linear increase in CO2 forcing over a period of 70 years.
For three decades up to 2007, scientic assessments (including those by the Intergovernmental Panel on Climate ChangeIPCC) provided a range and, generally, a best estimate for equilibrium climate sensitivity that hardly changed. In most cases the uncertainty range had a lower bound of 1.5 K and an upper bound of 4.5 K and the best estimate was 3 K. The 2007 IPCC Fourth Assessment Working Group I Report (AR4) narrowed the range to between 2.0 and 4.5 K, quantied as likely (1783 % probability), inuenced largely by climate model simulations. Subsequently, several observationally-based studies gave best estimates of between 1.5 and 2 K, substantially lower than most earlier studies. The IPCC Fifth Assessment Working Group I Report (AR5), published in 2014, reduced the likely lower bound back to 1.5 K, making the range 1.54.5 K, reecting the lower estimates that had been published recently in the literature. Signicantly, the IPCC authors decided not to provide a best estimate for climate sensitivity in AR5.
The key issue faced in the AR5 assessment was interpreting the discrepancy between climate sensitivity
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Web End = The implications for climate sensitivity of AR5 forcing and heat uptake estimates
Nicholas Lewis Judith A. Curry
Abstract Energy budget estimates of equilibrium climate sensitivity (ECS) and transient climate response (TCR) are...