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New Paper Demonstrates Positive Feedback Bias in Climate Models
A new paper by Roy Spencer and William Braswell has now been published in the Journal of Climate. The paper is entitled: ‘Potential Biases in Feedback Diagnosis from Observational Data: A Simple Model Demonstration.’
The Abstract states:
Feedbacks are widely considered to be the largest source of uncertainty in determining the sensitivity of the climate system to increasing anthropogenic greenhouse gas concentrations, yet our ability to diagnose them from observations has remained controversial. Here we use a simple model to demonstrate that any non-feedback source of top-of-atmosphere radiative flux variations can cause temperature variability which then results in a positive bias in diagnosed feedbacks. We demonstrate this effect with daily random flux variations, as might be caused by stochastic fluctuations in low cloud cover. The daily noise in radiative flux then causes interannual and decadal temperature variations in the model’s 50 m deep swamp ocean. The amount of bias in the feedbacks diagnosed from time-averaged model output depends upon the size of the non-feedback flux variability relative to the surface temperature variability, as well as the sign and magnitude of the specified (true) feedback. For model runs producing monthly shortwave flux anomaly and temperature anomaly statistics similar to those measured by satellites, the diagnosed feedbacks have positive biases generally in the range of −0.3 to −0.8 W m−2 K−1. These results suggest that current observational diagnoses of cloud feedback – and possibly other feedbacks - could be significantly biased in the positive direction.
Excerpt from Discussion and Conclusions:
What we have demonstrated is directly related to Stephens’ (2005) emphasis on how we perceive the operation of the climate system when diagnosing feedbacks. Stephens noted the overly simplistic nature of the system that is implicitly invoked when feedbacks are diagnosed from the covariability between observed radiative fluxes and surface temperature. Since it is well known that the processes that control cloud formation and dissipation are myriad, complex, and in general not perfectly correlated with surface temperature variations (e.g., vertical temperature and water vapor profiles, horizontal temperature gradients), the existence of nonfeedback sources of cloud variability should not be unexpected.
While we have used here the example of daily random variability in radiative fluxes which might be expected from the stochastic component of cloud behavior, it should be noted that feedback estimates could also be corrupted by other nonfeedback sources of variability on longer time scales, for example, from any radiative effects resulting from a small change in the general circulation of the ocean–atmosphere system.
Our results hopefully provide some semiquantitative insight into previously expressed concerns about the validity of cloud feedbacks diagnosed from observational data. They also underscore the need for new methods of diagnosing cloud feedback, as was advocated by Stephens (2005), and one example of which is the methodology developed by Aires and Rossow (2003).
November 7th, 2008 at 9:16 am
Climate Change And More…
Can’t say you weren’t warned: Environmentalists
see high hopes for new Congress – WASHINGTON–Environmental officials said on Tuesday they expect major
legislative victories in the new Congress on climate control, chemical plant security, an……
November 7th, 2008 at 2:58 pm
[...] On November 3rd 2008, two technical papers that Dr Roy Spencer had recently submitted to the journal Geophysical Research Letters were outright rejected in back-to-back emails and on the same day all 78 reviews of his book ‘Climate Confusion’ on Amazon.com were removed from that website. Ironically, this coincides with the publication of his Journal of Climate paper, blogged by Climate Research News here. [...]
February 27th, 2010 at 8:43 pm
I can see that when temperature data is hidden, when sources of information are lost, we are using the “dog ate my homework” excuse.
The same excuses are used by corporations when asked for data on speed cameras and refusing to acknowledge inaccuracies in breathelisers. The truth becomes secondary when we allow this ti happen.
Off with their heads, anyone who supports these things! The list will be long, but it will bring justice back to the people.
When will the people have more justice than forever living corporations?