Mountain Town News: Why is climate change frying the Colorado Plateau?

Map of the greater Colorado River Basin which encompasses the Colorado Plateau. Credit: GotBooks.MiraCosta.edu

From ParkRecord.com (Allen Best):

Colorado Plateau stands out on global warming map

Graphic credit: The Washington Post (Note: NOAA does not provide data for Alaska or Hawaii for this time period.)

Climbers gather each January in the canyon shadows of the San Juan Mountains to test their skills on giant columns of ice. The towers in the Ouray Ice Park are created by feeding water to the canyon walls, but the cold is natural.

It’s not as cold in Ouray County as it used to be, though. A data set assembled by The Washington Post shows Ouray as one of the places with the most rapid rise in temperatures in the lower 48 states since the late 19th century. Average temperatures have increased 2.3 degrees Celsius, or 4.4 degrees Fahrenheit.

Other counties in western Colorado and eastern Utah have warmed significantly. Utah’s Grand County, where Moab is located, increased 2.5 degrees C. Colorado’s San Miguel County, home to Telluride — a short distance from Ouray — had a 2.2-degree C rise.

The Washington Post drew on statistics from the National Oceanic and Atmospheric Administration’s Climate Division Database between the years 1895 and 1918. It found uneven warming across the United States, with some areas of the South actually cooling a bit. Rhode Island and New Jersey stand out for their heating, as did Los Angeles.

The biggest blob of red and burgundy on the Washington Post’s map was in the mountains and deserts of the Colorado Plateau. The newspaper noted that the area altogether has exceeded the 2-degree C threshold that policymakers, based on the advice of scientists, have identified as critical threshold for global warming.

The newspaper’s work echoes that of a 2014 report, “Climate Change in Colorado,” which also called out spiking warming in western Colorado through 2012. Every year since then with the exception of 2013 has been much warmer than the 20th century average.

Russ Schumacher, Colorado’s state climatologist, says he’s not sure why that portion of Colorado has been warming disproportionately. “We could definitely quibble about some of the details on their maps, but the overall picture is nicely represented,” he says.

The cause of rising temperatures globally has long been understood: the sharp increase in greenhouse gases, which traps heat near the Earth’s surface. The regional variations sometimes remain puzzling…

Directly linking greenhouse gases and changes in a mountain valley remains complicated. “Certainly a substantial fraction is connected to global warming, but in complex terrain areas, and with changes in land use over the last century, those factors can also be important,” he told Mountain Town News.

Broadly speaking, the higher latitudes will warm (and are warming) more than the tropics. Alaska has had outsized warming streak, but Costa Rica, not so much.

“But elevation effects are still an area of active research, in part because we don’t have a lot of reliable data at high elevations (say, above 10,000 feet) nor do models represent the terrain of Colorado particularly well.”

Several teams of scientists in recent years have issued studies that identified rising temperatures as playing a large role in declining flows of the Colorado River. About 92% of the river’s flows originate upstream of the Grand Canyon, much of it in western Colorado. Flows since 2000 have declined 19% from the 20th-century average.

Brad Udall, a scientist with the Colorado Water Institute, told a U.S. House of Representatives subcommittee in February that 2018 was the hottest and driest year in the Four Corners region since records were first kept in 1895.

Udall said that a study that he and two other researchers published in 2018 found 50% of flow reductions in the first 14 years of the century were due to higher temperatures. The other half were due to shifting precipitation patterns.

“It is clear the Colorado River, and the entire Southwest, has shifted to a new hotter and drier climate, and, equally important, will continue to shift to a hotter and drier climate for several decades after we stop emitting greenhouse gases,” he said.

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