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In a stunning paper in Science, researchers claim to have reversed the impact of clouds on global climate. It has long been known that low level cloud cover creates a net cooling effect on climate. This new study, which concentrated on a restricted area of the Pacific Ocean, claims that warming oceans reduce low cloud cover letting in more sunlight that further warm the ocean and hence provide a positive feed back that adds to global warming. Based on a warming episode that started in 1978, the article claims that observational analysis showed that clouds act as a positive feedback in this region on decadal time scales. But a cometary on the article in the same issue of Science says that the analysis suggests—but falls short of proving—that clouds are strongly amplifying the warming. If it's true, then almost all climate models have got it wrong.

In a paper entitled “Observational and Model Evidence for Positive Low-Level Cloud Feedback,” authors Amy C. Clement, Robert Burgman, and Joel R. Norris claim to have found this previously unsuspected positive feedback between cloud cover and global warming by studying records for a patch of the Northeast Pacific Ocean between Hawaii and and Mexico. According to the paper: Our principal source of data is monthly mean gridded surface-based observations of total cloud cover from the Comprehensive Ocean Atmosphere Data Set (COADS) during 1952 to 2007. We supplement this with cloud-type information from COADS that has been compiled by Hahn and Warren for the period 1952 to 1997, and in particular, we examine the category of marine stratiform clouds (comprising ordinary stratocumulus, cumulus under stratocumulus, fair-weather stratus, and bad-weather stratus). Additional independent information on total cloud amount, low-level cloud amount, and surface radiative fluxes is provided by the International Satellite Cloud Climatology Project (ISCCP)... Here we examine long-term cloud variations in independent cloud data sets and analyze meteorological data to provide a physical framework for interpreting these variations.

The results of these analyses are shown in the figure below taken from the paper. Parts A and B show the total and low-level cloud cover averaged over the NE Pacific (115° to 145°W, 15° to 25°N) respectively. Both COADS and adjusted ISCCP data sets trend toward more total cloud cover in the late 1990s, with the increase primarily in low-level cloud cover in the adjusted ISCCP data (bars, in B). The longer COADS total cloud time series indicates that a reduction in cloud cover occurred in the mid-1970s, and this earlier shift was also dominated by marine stratiform clouds (bars, A).


Cloud cover and surface temperature from Science article

Other climate variables shown are sea surface temperature (SST, in C), sea-level pressure (SLP, in D) from the Hadley center data. As you can see, for these data the low cloud coverage appears to be in anti-phase with the variation in surface temperature. The researchers concluded that the changes in the area of the Pacific they studied are “part of a dominant mode of global cloud variability.” Taking their observations a step further they decided to evaluate cloud models for similar behavior.

“To address this question, we analyze the 20th-century climate simulation in 18 coupled ocean-atmosphere general circulation models with comprehensive output available from the World Climate Research Programme’s (WCRP’s) Coupled Model Intercomparison Project phase 3 (CMIP3) multimodel archive,” they state. After acknowledging that the cloud-meteorology correlation test alone is not a sufficient metric for global climate sensitivity, they found that the only model that passed the test simulated a reduction in cloud cover over much of the Pacific when greenhouse gases were increased. In other words, the model exhibited a positive low-level cloud feedback. “Evaluating cloud feedback with one model is, however, far from ideal,” the authors conclude. “This presents a clear challenge to develop a larger number of climate models that can pass these and other tests so that we may have greater confidence in the sign of the low-cloud feedback under future changes in greenhouse gas concentrations.”



Acknowledging that low-level clouds are of great climatic importance because of their net cooling effect on the global climate the authors admit, “at present, the sign of the low-level cloud feedback in climate change is unknown.” This has not stopped a number of climate change alarmists in citing this paper as proof that global warming is even worse than previously though. As usual, the climate catastrophe crowd is ignoring the limited scope of the study—performed over selected, relatively short time spans in a restricted patch of one ocean. The researchers themselves state that “clouds act as a positive feedback in this region on decadal time scales.”

According to Richard Kerr, “During a cooling event in the late 1990s, both data sets recorded just the opposite changes—exactly what would happen if the same amplifying process were operating in reverse.” In his commentary on the paper by Clement et al., “Clouds Appear to Be Big, Bad Player in Global Warming,” Kerr quoted climate researcher David Randall of Colorado State University. “There's been a gradual recognition that this rather boring type of [low-level] cloud is important in the climate system,” said Randall. “They make a good case that in [decadal] variability there is a positive feedback. The leap is that the same feedback would operate in global climate change.” The study indicates an important role for marine low clouds in amplifying global warming, he says, but it doesn't prove it.

As a mater of course, Clement et al. attributed the warming surface waters to the effects of rising CO2 levels, something that their observational analysis does not support. Rather, the plug for CO2 as the proximate cause comes from the computer models, whose sensitivity settings all hinge on rising carbon dioxide levels. If it were true that CO2 was the cause, and since CO2 levels have continued to rise, why have the SST levels fallen and not risen monotonically? Perhaps a better explanation for the changes in sea surface temperatures is the El Niño – Southern Oscillation (ENSO).

A paper in the July 2009 Journal of Geophysical Research by J. D. McLean et al. states the the ENSO accounted for 81% of the variance in tropospheric temperature anomalies in the tropics. According to that study: “Overall the results suggest that the Southern Oscillation exercises a consistently dominant influence on mean global temperature, with a maximum effect in the tropics, except for periods when equatorial volcanism causes ad hoc cooling. That mean global tropospheric temperature has for the last 50 years fallen and risen in close accord with the SOI of 5–7 months earlier shows the potential of natural forcing mechanisms to account for most of the temperature variation.” El Niño and its opposite La Niña are much more direct and influential climate forcings.


Pacific Ocean in April 2008 showing La Nina and Pacific Decadal Anomalies. NASA

Throw in the effects of the Pacific decadal oscillation (PDO), which affects surface waters in the Pacific Ocean, north of 20° N on a time scale of 20 to 30 years, and the interdecadal Pacific oscillation (IPO or ID), which displays similar sea-surface temperature (SST) and sea-level pressure (SLP) patterns on a cycle of 15–30 years, and there is little need to drag CO2 into the argument at all.

What does this new result mean? It means that there are still a lot of things to be figured out about how Earth's climate system works: in this case feedbacks unsuspected or wrongly calibrated. If the paper's result holds a lot of climate models will need to be revamped. Note that this doesn't make the dreaded global warming any worse or any better, it simply changes how factors in Earth's climate system interact. In fact, this report re-emphasizes the importance of low cloud cover as a cause of cooling on climate. It also shows how foolish is is to accept the output of models as valid predictors of future climate variability.

Modelers continue to tune their software playthings to match the last century's ups and downs, all the while ignoring the fact that their models are wrong. It was recently reported that all the aerosol models have been significantly wrong for decades (see Warming Caused by Soot, Not CO2). If this new result proves to be global, another important climate regulating factor has been wrongly implemented in most every model in use. Still we are told that that model results are valid, not to worry that the model's fundamental assumptions are incorrect. As I have been trying to communicate through this blog, the new discoveries being made day by day are not, in and of themselves, a repudiation of global warming. Instead, they are indications that climate change theory is fundamentally incomplete and so flawed that its predictions cannot be trusted.

Be safe, enjoy the interglacial and stay skeptical.


World low cloud cover in January 2008. NASA