Applied and Computational Mathematics Seminar

Seminar Details

Speaker:
Ray Bates
Affiliation:
University College Dublin
Title:
Estimating climate sensitivity using a simple energy balance model and satellite observations
Time:
3PM Wednesday, January 25, 2017
Location:
Room 1.18, Agricultural and Food Science Centre

Abstract

The dominant method of estimating climate sensitivity (defined as the equilibrium global warming that would result from a doubling of the atmospheric CO 2 concentration) is to integrate global climate models (GCMs) to equilibrium under a 2×CO 2 forcing; alternatively, the GCMs can be integrated for a fixed period under this forcing and the sensitivity can be estimated by extrapolating to equilibrium a plot of annual global means of top-of-atmosphere radiative imbalance versus surface temperature increase. From the GCM results, the climate sensitivity is estimated as lying in the range 1.5°C - 4.5°C. There has been no narrowing of this GCM range of uncertainty over the past 35 years. In recent years, satellite observations have shown that the tropics are radiatively more stable (i.e., emit more energy to space for a given surface temperature increase) than indicated by the GCMs. This has led to an increased emphasis on obtaining climate sensitivity estimates using simple energy balance models of the climate system into which the satellite-observed radiative responses are directly inserted. In this seminar, the results of a study (Bates, 2016) lying in this category will be presented. The linear energy balance model used is a two-zone (tropical/extratropical) one, with separate radiative response coefficients in each zone and dynamical energy transport between the zones taken as proportional to the interzone temperature difference. The results of a stability and sensitivity analysis of the model, and the outcome of inserting the best observational estimates of its parameters, will be presented. The results indicate a climate sensitivity of ≈ 1°C, which lies below the GCM range. The plausibility of this result, given the observed evolution of the global mean surface temperature, will be discussed.

References

  1. Bates, J. R. (2016). Estimating climate sensitivity using two-zone energy balance models. Earth and Space Science, 3, 207-225.

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