December 14, 2007

Tropical Trends Stir Warming Debate

Filed under: Surface, Temperature History

Over and over, we hear that the global warming debate is over, the science is settled, and it is time to move past the science and turn the focus onto the policy side of the issue. Anyone who suggests that the science is not settled and the debate is still alive is immediately accused of being heavily funded by industry and discredited by the mainstream scientific community. Who could forget the August 13, 2007 Newsweek issue with its cover suggesting “naysayers” are well-funded by industry and apparently unaware that the Earth is becoming the red planet.

Anyone who reads World Climate Report regularly is aware that the debate is very much alive and well in the major scientific journals related to global warming. We find numerous articles each year presenting results that are clearly at odds with the popular predictions and claims of the global warming advocates. A recent article has appeared in the prestigious International Journal of Climatology, and the last two sentences of the piece state “Yet the models are seen to disagree with the observations. We suggest, therefore, that projections of future climate based on these models be viewed with much caution.” To say the least, we wanted to examine this one in far more detail.

Basically, the problem at hand goes back to the issue of not whether the world warming, but where is it warming? We have known for several decades that climate models predict far more warming in the mid-to-high latitude land areas than other parts of the world due to decreased surface reflectivity should snow melt and the fact that the driest and coldest air masses would be more impacted by elevated carbon dioxide than warmer and more moist air masses. Adding greenhouse gases to a dry air mass greatly increases the odds of capturing outgoing infrared energy; in moist air masses, the water vapor tends to intercept most of the infrared energy, so adding greenhouse gases only slightly increases the odds of absorbing and redirecting the heat energy emitted from the surface.

There is another often overlooked component to the warming. Climate models predict that the greatest warming should occur above the surface, not at or near the surface where we live. In 2000, the National Research Council examined this issue of the differential warming in various layers of the atmosphere, they concluded that the surface was warming far more than the lower troposphere, this pattern is not consistent with model predictions, and no obvious explanation was apparent.

The latest paper is by four scientists from the University of Rochester, the University of Alabama in Huntsville, and the University of Virginia. Senior author David Douglass has written about the disparity between surface and lower tropospheric temperature trends in the past, and he has dared to conclude that model simulations are not consistent with observed patterns. The second author is noted satellite climatologist John Christy who despite his international reputation as one of the most prolific scientists of our day, he has been outspokenly skeptical about many elements of the global warming scare. The fourth author is S. Fred Singer who is certainly one of the elder icons in the skeptical camp and is the brains behind the controversial Science and Environmental Policy Project in Arlington, Virginia. The third author is an experienced researcher who has worked in association with David Douglass on many similar projects in the past.

The Douglass et al. team gathered output from models, surface observations, balloon records, and satellite records over the period 1979-2004 from which they calculated model-based and observed temperature trends at the surface and various altitudes in the tropical atmosphere. The focused on the tropics (20°N to 20°S) because “Much of the Earth’s global mean temperature variability originates in the tropics, which is also the place where the disparity between model results and observations is most apparent.”

Just as we suspected, trends from the models and observations agree at the surface but totally disagree from just above the surface to 14 km above the surface (Figure 1). The models all predict far more warming around 10 km up in the atmosphere than what is predicted at the surface, but all of the observational evidence shows no such pattern whatsoever.


Figure 1. Temperature trends for the satellite era (°C/decade). Relax – it is simple. HadCRUT, GHCN and GISS are various compilations of surface temperature observations. IGRA, RATPAC, HadAT2, and RAOBCORE are all balloon-based observations of the surface and lower troposphere. UAH, RSS, UMD are satellite-based data for various levels of the atmosphere. The 22-model average comes from an ensemble of 22 model simulations from the most widely used models from throughout the world. The light red lines are the +2 and -2 standard errors of the mean from the 22 models (from Douglass et al., 2007).

Douglass et al. conclude that “Model results and observed temperature trends are in disagreement in most of the tropical troposphere, being separated by more than twice the uncertainty of the model mean. In layers near 5 km, the modelled trend is 100 to 300% higher than observed, and, above 8 km, modelled and observed trends have opposite signs.” Even juicier, they state “On the whole, the evidence indicates that model trends in the troposphere are very likely inconsistent with observations that indicate that, since 1979, there is no significant long-term amplification factor relative to the surface. If these results continue to be supported, then future projections of temperature change, as depicted in the present suite of climate models, are likely too high.”

So, do you still think the “debate is over”?

Reference:

Douglass, D.H., J.R. Christy, B.D. Pearson, and S.F. Singer. 2007. A comparison of tropical temperature trends with model predictions. International Journal of Climatology, DOI: 10.1002/joc.1651.




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