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Last 30 years shows climate feedbacks are zero (at best)

Posted By Joanne Nova On April 9, 2012 @ 10:57 pm In Global Warming | Comments Disabled

Let’s be as generous as we can.

The IPCC say feedbacks amplify CO2′s warming by a factor of about three.

Without the amplification from positive feedback there is no crisis

So being nice people, let’s assume it’s warmed since 1979 and assume that it was all due to carbon dioxide. If so, that means feedbacks are …. zero. There goes that prediction of 3.3ºC.
Feedbacks are the name of the game. If carbon dioxide doesn’t trigger off powerful positive feedbacks, there was and is no crisis. Even James Hansen would agree — inasmuch as he himself said that CO2 would directly cause about 1.2ºC of warming if it doubled, without any feedbacks (Hansen 1984).

Consider the warming from1979 to 2007, when we measured temperatures using satellites and not corrupted and adjusted land thermometers. Douglass and Christy (2008) point out that, given how much CO2 levels increased in that time, the warming only amounts to what the IPCC scientists predict we should get from CO2 alone, from the direct effect of CO2, and not from the effect of CO2 plus positive feedbacks.

The warming trend expected from CO2 without any feedbacks at all is 0.07 ºC/decade. The trends from the UAH satellites are 0.06±0.01ºC/decade. Since the two figures are almost the same, no one needs a super-computer to tell them that this implies that the sum of all feedbacks (and the sum of all fears) is zip, nada, nothing.

Furthermore, this study likely overestimates the effect of CO2. There is clearly a 60 year cycle of warming and cooling due to the Pacific Decadal Oscillation, and the 28 year study period was the steepest part of that 60 year cycle. Hence, trends over longer periods are likely to be smaller, which implies that feedbacks are negative.

Thus the upper bound on climate sensitivity (the temperature rise when CO2 doubles) from the last three decades of warming is about 1°C, and that’s assuming all the warming is due to CO2 increases and not due to other factors like solar magnetic effects, cosmic radiation, ocean current oscillations, or geomagnetic forces. Which is much less than the IPCC median estimate of 3.3°C.

The Douglass and Christy paper of 2008 has a good discussion on why UAH is a better data source than RSS, and why both satellites are better than the surface measures. It also discusses why the pattern of warming of Earth does not fit the “fingerprint” expected of the planetwide heating that would be caused by a well mixed gas such as carbon dioxide:

  1. CO2 ought to warm at all latitudes, but the northern hemisphere outside the tropics is warming four times as fast as the tropics, and twice as fast as the globe. (So some other effect is warming the Northern Hemisphere.)
  2. The tropical warming appears to correlate well with ENSO effects but not with CO2.
  3. CO2 has risen in a linear fashion. There is not necessarily an underlying linear warming trend. Some analysis suggests the rise is a step change.


The global atmospheric temperature anomalies of Earth reached a maximum in 1998 which has not been exceeded during the subsequent 10 years. The global anomalies are calculated from the average of climate effects occurring in the tropical and the extratropical latitude bands. El Niño/La Niña effects in the tropical band are shown to explain the 1998 maximum while variations in the background of the global anomalies largely come from climate effects in the northern extratropics. These effects do not have the signature associated with CO2 climate forcing. However, the data show a small underlying positive trend that is consistent with CO2 climate forcing with no-feedback.

I wrote about feedbacks: The one flaw that wipes out the crisis in 2009. David Evans wrote about them in more detail The Skeptics Case. Thanks to Tony Cox for getting me back to the papers that matter.


Hansen J., A. Lacis, D. Rind, G. Russell, P. Stone, I. Fung, R. Ruedy and J. Lerner, (1984) Climate sensitivity: Analysis of feedback mechanisms. In Climate Processes and Climate Sensitivity, AGU Geophysical Monograph 29, Maurice Ewing Vol. 5. J.E. Hansen and T. Takahashi, Eds. American Geophysical Union, pp. 130-163 [Abstract]

Douglass, D.H., and  Christy, J.R.(2008): Limits on CO2 Climate Forcing from Recent Temperature Data of Earth. Energy and Environment, Vol 20, No 1.  [Abstract] [Discussion]


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