Update To Andy Revkin’s Question In 2005: “Is Most Of The Observed Warming Over The Last 50 Years Likely To Have Been Due To The Increase In Greenhouse Gas Concentrations”?

In 2005, I posted an answer to Andy Revkin’s question on climate change;

Response to Andy Revkin’s Science Question of August 26, 2005

“Is most of the observed warming over the last 50 years likely to have been due to the increase in greenhouse gas concentrations”?

My answer in 2005 started with the text

On Global Warming:

There are natural explanations for global warming of which a change in the output of solar energy is a candidate. However, none of the published work has convinced me that this can explain much of the observed global warming over the last several decades. Volcanic emissions are another natural global forcing, and it is well known that they produce cooling, such as after the eruption of Mount Pintatubo, where in August of 1991 it was estimated as -4 Watts per meter squared. There have not been eruptions of that magnitude since, such that the absence of such major eruptions might permit greater absorbed solar radiation in the climate system than otherwise would occur. However, this absence of eruptions resulting in any positive radiative imbalance for a period of time well after a major volcanic emission has also not been shown to occur. This leaves anthropogenic emissions as a source for global warming.

There is new information, however, that prompts me to update my answer.

This is based on insight provided by Roy Spencer, as summarized in his post  of April 20 2010 titled

The Great Global Warming Blunder: How Mother Nature Fooled the World’s Top Climate Scientists

where he presented his new book with the same title published by Encounter Books.

The text in his April 20th post that provides this perspective of the natural climate system is

“The most obvious way for warming to be caused naturally is for small, natural fluctuations in the circulation patterns of the atmosphere and ocean to result in a 1% or 2% decrease in global cloud cover. Clouds are the Earth’s sunshade, and if cloud cover changes for any reason, you have global warming — or global cooling.

How could the experts have missed such a simple explanation? Because they have convinced themselves that only a temperature change can cause a cloud cover change, and not the other way around. The issue is one of causation. They have not accounted for cloud changes causing temperature changes.”

Other colleagues whose studies, in combination, have convinced me of a larger natural variability with respect to global warming and cooling, include as examples, the following papers, blogs and presentations

Baldwin, Mark P.   and Timothy J. Dunkerton, 2001: Stratospheric Harbingers of Anomalous Weather Regimes. Science 19 October 2001:Vol. 294. no. 5542, pp. 581 – 584 DOI: 10.1126/science.1063315

Posts by Joseph  D’Aleo on  http://www.icecap.us/ [see http://icecap.us/index.php/go/about-climate-change]

Compo, G. P., and P. D. Sardeshmukh, 2009: Oceanic influences on recent continental warming. Climate Dynamics, 32,333-342. [see my post on this paper in 2008]

 R.S. Lindzen, M.-D. Chou, and A.Y. Hou (2001) Does the Earth have an adaptive infrared iris? Bull. Amer. Met. Soc. 82, 417-432

W. M. Gray, 2009: Climate change: Driven by the ocean – not humans. The Steamboat Institute Conference, Steamboat Springs, Colorado, August 29, 2009.

Stephens, Graeme at the August 2009 GEWEX meeting in Melbourne Australia in a talk titled “Earth observations and moist processes”.

Sun, D.-Z., Y. Yu, and T. Zhang, 2007: Tropical Water Vapor and Cloud Feedbacks in Climate Models: A Further Assessment Using Coupled Simulations. J. Climate [a powerpoint talk of this research was completed for my class in 2007 Human Impacts on Weather and Climate(see Validating and Understanding Feedbacks in Climate Models).

Thompson, D. W. J. and J. M. Wallace, 1998: The Arctic Oscillation signature in the wintertime geopotential height and temperature fields. Geophys. Res. Lett., 25, 1297-1300.

Trenberth, K. E., D. P. Stepaniak, and J. M. Caron 2002: Interannual variations in the atmospheric heat budget J. Geophys. Res., 107, D8, 10.1029/2000JD000297.

A.A. Tsonis, K.L. Swanson, and S. Kravtsov, 2007: A new dynamical mechanism for major climate shifts. Geophys. Res. Lett., 34, L13705, doi:10.1029/ 2007GL030288.

A.A. Tsonis and K.L. Swanson, 2006: What do networks have to do with climate? Bull. Amer. Meteor. Soc. doi:10.1175/BAMS-87-5-585.

Marcia Wyatt, Ocean Heat, April 27 & May 4, 2007 in my class on Human Impacts on Weather and Climate [natural climate variability is currently her Ph.d. dissertation topic working with A. Tsonis and S. Kravtsov].

I am also further convinced based on the recognition that there is “missing heat” in the climate system (e.g. see the recent set of posts on this topic starting with this one). The long term variations in atmospheric and ocean circulation features, with resulting global average changes in radiative forcing, can explain at least part of the reason for this “missing heat”.

In 2005 I wrote a post

What is the Importance to Climate of Heterogeneous Spatial Trends in Tropospheric Temperatures?.

Roy’s perspective, bolstered by such colleagues as listed above, provides convincing further evidence that such variations in regional heating and cooling can alter significantly the global average heating more than has been indicated by the IPCC-type multi-decadal global climate model simulations.

The solar influence also appears to be larger than was understood in 2005, as illiustrated by these papers

Scafetta N., R. C. Willson (2009), ACRIM-gap and TSI trend issue resolved using a surface magnetic flux TSI proxy model, Geophys. Res. Lett., 36, L05701, doi:10.1029/2008GL036307.

Lean, J. L., and D. H. Rind (2009): How Will Earth’s Surface Temperature Change in Future Decades?,
Geophys. Res. Lett., doi:10.1029/2009GL038932, in press. (accepted 9 July 2009).

The 2010 answer to the question by Andy Revkin 

“Is most of the observed warming over the last 50 years likely to have been due to the increase in greenhouse gas concentrations”?

remains NO.

The added greenhouse gases from human activity clearly have a role in increasing the heat content of the climate system from what it otherwise would be. However, there are other equally or even more important significant human climate forcings, as I summarized in my 2005 post and in the 2009 article

Pielke Sr., R., K. Beven, G. Brasseur, J. Calvert, M. Chahine, R. Dickerson, D. Entekhabi, E. Foufoula-Georgiou, H. Gupta, V. Gupta, W. Krajewski, E. Philip Krider, W. K.M. Lau, J. McDonnell,  W. Rossow,  J. Schaake, J. Smith, S. Sorooshian,  and E. Wood, 2009: Climate change: The need to consider human forcings besides greenhouse gases. Eos, Vol. 90, No. 45, 10 November 2009, 413. Copyright (2009) American Geophysical Union.

We now know, however, that the natural variations of atmospheric and ocean circulation features within the climate system produces global average heat changes that are substantially larger than what was known in 2005. The IPCC models have failed to adequately simulate this effect. 

The answer to Andy’s question from 2005 is an even more clearly No.  That is,  a significant fraction of the observed warming over the last 50 years is NOT due to the increase in greenhouse gas concentrations”

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