Whether it’s the result of global warming or growth and the accompanying “heat island effect,” Nevada’s largest cities are heating up faster than most others in the nation based on a study of weather data released Wednesday by an environmental group.
Last year, especially, in Las Vegas and Reno and at 84 percent of the 255 weather stations the temperature was at least a half-degree warmer than the 30-year average, according to the report by Environment America Research and Policy Center.
The average temperature in Reno last year was 4 degrees above normal, hotter than the next hot spot where six Tennessee weather stations registered 3 degrees or more above normal.
From 2000 through 2007 Reno soared more above normal than any site, 5.3 degrees.
The Denver-based, non-profit center advocates clean air and defeating special interest to “win real results for the environment.” The researchers claim carbon dioxide and greenhouse gas emissions are to blame for the warming conditions, an indication that global climate change is taking hold.
Reno also topped the list for average minimum temperature on given days, 5.5 degrees above normal in 2007. Las Vegas was third at 3.9 degrees above normal. Helena, Mont., was second at 4.8 degrees above normal for the average minimum.
Could that mean so-called urban heat islands are having a more profound effect on Nevada’s cities? That’s when pavement absorbs heat from the sun and causes nighttime temperatures to rise more than surrounding rural areas.
At first glance, State Climatologist Jeffrey Underwood thought that could be the case. But when he looked at the report’s data from 2007 of the past eight years “it made me bite my tongue that it was all heat island effect.”
“The Las Vegas urban heat island contributes but in Reno we get wind that mixes the (warm) air. We don’t have a strong urban heat island effect to begin with.”
Though he wasn’t involved with compiling the report, Underwood said his review of last year’s data indicates outside forces are probably at work that caused domes of heated air — ridges — to hang over Reno and Las Vegas at mid- to high-latitudes.
“There is something else to this,” he said. “In Las Vegas there may have been some contributions from urban heat island, but heat islands there have been potent for several decades. … We had an anomaly pumping those temperatures up.
“What I think it means is the last three summers especially have been killers as far as heat,” he said. “Last year there were more than 10 days above 100 in Reno which is a record.”
Underwood said he can’t say positively that the large scale pattern that drove temperatures up for eight months last year was related to global warming as the center alludes to in its report.
“Whether this is the result of humans adding more greenhouse gases to the atmosphere, whether that’s the primary cause or half the cause is almost a moot point,” he said.
“No matter how we got here, whether it’s part natural or man-made, going forward nothing good could become of carbon dioxide or methane dumping in the atmosphere,” said Underwood and a University of Nevada, Reno professor who holds a doctorate in climatology.
Researchers for the center cited at least two studies that found urban heat-island effects on average temperatures worldwide were negligible and that overall warming is not a consequence of urban development.
Average daily high temperatures were 2.1 degrees above normal in Reno and 1.9 degrees above normal in Las Vegas last year. Reno had 81 days of temperature of at least 90 degrees, 28 more than the historical average. Las Vegas hit 90 degrees 138 times in 2007.
Last year was the 10th warmest year on record in the United States and the second warmest globally.
The 40-page report by the center’s Emily Figdor calls for mandatory, science based caps on pollution that contributes to global warming and development of renewable energy sources to relieve dependence on fossil fuels.
Kyle Davis, policy director for the Nevada Conservation League, said the report’s title, “Feeling the Heat,” is fitting.
“The big message is this is something that is actually happening and we need to do something about it,” he said.
Contact reporter Keith Rogers at firstname.lastname@example.org or 702-383-0308.