Monday, May 3, 2010

Dr. Lindzen's New Paper: 0.7°C temperature change from doubled CO2

Drs. Lindzen's & Choi's new draft paper has been submitted to the Journal of Geophysical Research. The paper updates and responds to criticisms of their 2009 paper, but arrives at essentially the same conclusions. They find on the basis of empirical satellite observations that the climate sensitivity to a doubling of CO2 levels is a mean of 0.7°C, implying net climate feedbacks from water vapor, clouds, etc. are negative, not positive as assumed by all IPCC models, and thus all IPCC models exaggerate warming due to increased CO2. This is in close agreement with other peer reviewed papers which have examined empirical satellite and radiosonde data.

From the abstract: "We again find that the outgoing radiation resulting from SST fluctuations exceeds the zero-feedback fluxes thus implying [net] negative feedback."

UPDATE: Full published paper available here

From p. 385:

"As a result, the climate sensitivity for a doubling of CO2 is estimated to be 0.7K (with the confidence interval 0.5K -1.3K at 99% levels). This observational result shows that model sensitivities indicated by the IPCC AR4 are likely greater than the possibilities estimated from the observations."

24 Abstract

25 To estimate climate sensitivity from observations, Lindzen and Choi [2009] used the
26 deseasonalized fluctuations in sea surface temperatures (SSTs) and the concurrent responses in
27 the top-of-atmosphere outgoing radiation from the ERBE satellite instrument. Distinct periods of
28 warming and cooling in the SST were used to evaluate feedbacks. This work was subject to
29 significant criticism by Trenberth et al. [2009], much of which was appropriate. The present
30 paper is an expansion of the earlier paper in which the various criticisms are addressed and
31 corrected. In this paper we supplement the ERBE data for 1985-1999 with data from CERES for
32 2000-2008. Our present analysis accounts for the 36 day precession period for the ERBE satellite
33 in a more appropriate manner than in the earlier paper which simply used what may have been
34 undue smoothing. The present analysis also distinguishes noise in the outgoing radiation as well
35 as radiation changes that are forcing SST changes from those radiation changes that constitute
36 feedbacks to changes in SST. Finally, a more reasonable approach to the zero-feedback flux is
37 taken here. We argue that feedbacks are largely concentrated in the tropics and extend the effect
38 of these feedbacks to the global climate. We again find that the outgoing radiation resulting from
39 SST fluctuations exceeds the zero-feedback fluxes thus implying negative feedback. In contrast
40 to this, the calculated outgoing radiation fluxes from 11 atmospheric GCMs forced by the
41 observed SST are less than the zero-feedback fluxes consistent with the positive feedbacks that
42 characterize these models. The observational analysis implies that the models are exaggerating
43 climate sensitivity.
45 1. Introduction

46 It is usually claimed that the heart of the global warming issue is so-called greenhouse
47 warming. This simply refers to the fact that the earth balances the heat received from the sun
48 (mostly in the visible spectrum) by radiating in the infrared portion of the spectrum back to
49 space. Gases that are relatively transparent to visible light but strongly absorbent in the infrared
50 (greenhouse gases) will interfere with the cooling of the planet, thus forcing it to become warmer
51 in order to emit sufficient infrared radiation to balance the net incoming sunlight. By the net
52 incoming sunlight, we mean that portion of the sun’s radiation that is not reflected back to space
53 by clouds and the earth’s surface. The issue then focuses on a particular greenhouse gas, carbon
54 dioxide. Although carbon dioxide is a relatively minor greenhouse gas, it has increased
55 significantly since the beginning of the industrial age from about 280 ppmv to about 390 ppmv,
56 and it is widely accepted that this increase is primarily due to man’s emissions. However, it is
57 also widely accepted that the warming from a doubling of carbon dioxide would only be about
58 1°C (based on simple Planck black body calculations; it is also the case that a doubling of any
59 concentration in ppmv produces the same warming because of the logarithmic dependence of
60 carbon dioxide’s absorption on the amount of carbon dioxide).
61 This amount of warming is not considered catastrophic, and, more importantly, this is much
62 less than current climate models suggest the warming from a doubling of carbon dioxide will be.
63 The usual claim from the models is that a doubling of carbon dioxide will lead to warming of
64 from 1.5°C to 5°C and even more. What then is really fundamental to ‘alarming’ predictions? It
65 is the ‘feedback’ within models from the more important greenhouse substances, water vapor and
66 clouds. Within all current climate models, water vapor increases with increasing temperature so
67 as to further inhibit infrared cooling. Clouds also change so that their net effect resulting from
68 both their infrared absorptivity and their visible reflectivity is to further reduce the net cooling of
69 the earth. These feedbacks are still acknowledged to be highly uncertain, but the fact that these
70 feedbacks are strongly positive in most models is considered to be a significant indication that
71 the result has to be basically correct. Methodologically, this is an unsatisfactory approach to
72 such an important issue. Ideally, one would seek an observational test of the issue. As it turns
73 out, it may be possible to test the issue with existing data from satellites and there has recently
74 been a paper [Lindzen and Choi, 2009] that has attempted this though, as we will show in this
75 paper, the details of that paper were, in important ways, incorrect. The present paper attempts to
76 correct the approach and arrives at similar conclusions.

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