Warming Wallops Southwest

Floods, fires, plant loss already escalating as a result of “unequivocal” global warming trend


Los Angeles reports its hottest day ever. Lake Powell and Lake Mead dwindle toward water rationing.

Rim Country suffers a bewildering sequence of flood and drought.

Arizona aspens and pinyon pines die off, ponderosa pines shift elevation and forest fires grow in size and intensity.

Well, get used to it. The Southwest will warm up dramatically in coming decades, according to an assessment published recently in the journal Science.

The study on the impact of rising temperatures on the Southwest augments two other recently released studies — one documenting the temperature rise, both globally and nationally, and the second suggesting that one in five of the world’s plants are now in danger of extinction. Some 32 percent of those endangered plants grow in habitats represented in Rim Country.

The study of the heat rise in the Southwest suggests such losses could escalate.

“Temperatures across the west are rising: the region is significantly warmer than the average during the 20th Century,” said co-author Brad Udall, with the University of Colorado.

“The warming is having substantial impacts already — including late-season snowpack in the Colorado River headwaters and it is contributing to the worst and hottest drought since the start of the 20th Century.”

The higher average temperatures have shifted the winter storm tracks further north, which has resulted in a significant decline in the snowfall in the Rocky Mountains. That decreased snowpack has resulted in the steady decline of water levels in Lake Powell and Lake Mead, which sustain water users in seven states, the author said.

“The two biggest reservoirs on the Colorado River are now the emptiest they’ve been since Lake Powell was first filling back in the 1970s,” he said, “and there hasn’t been a substantial refilling since they began their precipitous decline in volume around 10 years ago.”

Udall says the “unequivocal and unprecedented warming and drying in the west is also contributing to dramatic increases in vegetation death and large wildfires.”

For instance, University of Arizona climate researcher Dave Breshears heads a team that has documented the deaths of pinyon pines on 2.5 million acres.

A report by the National Oceanic and Atmospheric Administration put the regional warming trend in a global perspective. The planet has just completed the warmest decade on record, according to the consensus report by 300 scientists based in 48 countries. Previously, the 1990s ranked as the warmest decade on record.

The report compiled measurements of 10 “indicators” — seven of which are rising rapidly. The rising indicators include: air temperature over land, ocean surface temperatures, sea level, ocean heat, humidity and tropospheric temperature.

Three other indicators declined during the decade, including Arctic sea ice, glaciers and spring snow cover in the Northern Hemisphere. The researchers concluded that the measurements point to significant global warming.

“For the first time the analysis brings together a single compelling comparison from the top of the atmosphere to the depths of the ocean, concluded NOA Administrator Jane Lubchenco.

Recorded average global temperatures have set a new record in each of the past three decades. The planet has clearly undergone periods with a much higher average temperature when it had no ice caps at all, but not since humans began keeping reliable temperature records.

The report says average global temperatures have risen by 1 degree F in the past 50 years. That increase has resulted in a sea level rise, declines in glaciers and ice caps, longer growing seasons, changes in river flows, earlier snow melt and increases in heavy downpours.

The study on plant extinctions suggests another possible impact, although much of the decline probably relates to massive clear cutting of tropical rain forests, which harbor the great majority of the planet’s plant species.

The extinction rate among the world’s 380,000 plant species is exceeded only by the even greater rate of extinction among the planet’s 5,490 species of mammals, according to the researchers from the Royal Botanic Gardens, the Natural History Museum and the International Union for the Conservation of Nature.

The researchers concluded that botanists don’t know enough about one-third of the world’s plant species to even decide whether they’re in danger. However, they focused on 7,000 well-documented species from the five major groups of plants to conclude that 22 percent stand in danger of extinction.

About 63 percent of the endangered plant species live in tropical rain forests. Another 13 percent live in “rocky areas,” 13 percent in temperate forests and 8 percent in temperate shrub land — all habitats represented in Rim Country. The researchers say the extinction rate among plants is higher than the rate among the 10,000 species of birds or the 6,285 species of amphibians.


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