On the January 25 edition of CNN's American Morning, co-host Miles O'Brien transitioned from a report on global warming to a weather forecast by describing CNN meteorologist Chad Myers as “a little bit of a skeptic on global warming.” Although Myers denied the label, he proceeded to put forward the theory -- a favorite of global warming skeptics -- that the growth of urban areas worldwide has skewed global warming data. Wholly apart from the question of the appropriateness of CNN hiring a meteorologist apparently known among the staff as “a little bit of a skeptic on global warming,” the so-called “heat island” theory promoted by Myers has been debunked by several recent studies.

From the January 25 edition of CNN's American Morning:

O'BRIEN: Let's check the forecast now. Chad Myers, you're a little bit of a skeptic on global warming, I know.

MYERS: No, I absolutely believe that CO₂ is heating the atmosphere, but also, some of these thermometers that we've had out in the plains for years or in the cities for years are getting surrounded by more buildings. So you get more buildings, you get more asphalt, you get more heat, so the thermometers are different. The whole -- metro areas are getting warmer, where, in fact, maybe you just see -- if you put that same thermometer out in the middle of a cornfield in Nebraska, maybe it wouldn't be too much different. We'll have to see. You know, I know that this is happening; it's just a matter of how much it is, that's all.

O'BRIEN: So, there's a little bit of global paving, too, along with global warming?

MYERS: Well, there you go.

Global warming skeptics have regularly put forth the theory the comparative warmth of cities via the “urban heat island effect” -- whereby metropolitan areas register considerably higher temperatures than their surroundings -- has skewed the global temperature record. For instance, at JunkScience.com, a website founded by Steven Milloy, who has claimed that global warming represents “flawed science,” a September 12, 2004, article suggested that the urban heat island effect “create[s] the illusion of 'global warming.' ” While the existence of the urban heat island effect is not disputed within the scientific community, several authoritative studies published in recent years have found that the effect on the global temperature record is negligible.

A 2001 study by the Intergovernmental Panel on Climate Change (IPCC) determined that between 1900 and 1990, the effect of urban heat islands on the global temperature record was no more than 0.05 degrees Celsius. By contrast, the surface temperature record is estimated to have warmed by 0.6 degrees to 0.8 degrees Celsius over the past century.

In 2003, Thomas C. Peterson of the National Climactic Data Center published a study that examined “the impact of urban heat islands (UHIs) on ... temperature observations” and found that “no statistically significant impact of urbanization could be found in annual temperatures.”

More recently, a study conducted by David Parker, of Britain's Hadley Centre for Climate Prediction and Research, also proved that the urban heat island effect is minimal. Published in the November 18, 2004, edition of Nature, the study compared temperature measurements taken in urban areas on calm and windy nights:

Controversy has persisted over the influence of urban warming on reported large-scale surface-air temperature trends. Urban heat islands occur mainly at night and are reduced in windy conditions. Here we show that, globally, temperatures over land have risen as much on windy nights as on calm nights, indicating that the observed overall warming is not a consequence of urban development.