Watts Up With That?

Global Warming as a Natural Response to Cloud Changes Associated with the Pacific Decadal Oscillation (PDO)

Reposted here from weatherquestions.com

UPDATED – 10/20/08 See discussion section 4

by Roy W. Spencer

(what follows is a simplified version of a paper I am preparing to submit GRL for publication, hopefully by the end of October 2008)

A simple climate model forced by satellite-observed changes in the Earth’s radiative budget associated with the Pacific Decadal Oscillation is shown to mimic the major features of global average temperature change during the 20th Century – including two-thirds of the warming trend. A mostly-natural source of global warming is also consistent with mounting observational evidence that the climate system is much less sensitive to carbon dioxide emissions than the IPCC’s climate models simulate.

1. Introduction

For those who have followed my writings and publications in the last 18 months (e.g. Spencer et al., 2007), you know that we are finding satellite evidence that the climate system could be much less sensitive to greenhouse gas emissions than the U.N.’s Intergovernmental Panel on Climate Change (IPCC, 2007) climate models suggest.

To show that we are not the only researchers who have documented evidence contradicting the IPCC models, I made the following figure to contrast the IPCC-projected warming from a doubling of atmospheric carbon dioxide with the warming that would result if the climate sensitivity is as low as implied by various kinds of observational evidence. The dashed line represents our recent apples-to-apples comparison between satellite-based feedback estimates and IPCC model-diagnosed feedbacks, all computed from 5-year periods (Spencer and Braswell, 2008a):

Fig. 1. Projected warming (assumed here to occur by 2100) from a doubling of atmospheric CO2 from the IPCC versus from various observational indicators. (click for larger image)

The discrepancy between the models and observations seen in Fig. 1 is stark. If the sensitivity of the climate system is as low as some of these observational results suggest, then the IPCC models are grossly in error, and we have little to fear from manmade global warming. Read the rest of this entry »