Temperatures in the Southwest are rising faster compared to those of the U.S. as a whole, a new White House report ion climate shows.
The National Climate Assessment, released today, also shows the continuing threats to the region from drought, wildfires, reduced snowpack, risks to the region’s energy and farming systems, heat-related deaths and health problems.
For California coastal regions, the report also highlights the threats from rising sea levels. Tourism and recreation, from everything to the ski industry to river rafting, will also be impacted by reduced streamflows and snowpack and a shorter snow season overall, the report says.
Overall, the report lays out existing climate change impacts, predicts future impacts and lays out strategies for both fighting and adapting to them.
The assessment was directed by Kathy Jacobs, a longtime Tucsonan who spent four years in that job, working out of the White House’s old Executive Office Building in Washington, D.C.
Jacobs returned this past winter to her professor’s post at the University of Arizona. She currently directs UA’s Center for Climate Adaptation Science and Solutions. Seven other UA faculty members, including provost Andrew Comrie and longtime climate scientist Gregg Garfin, contributed to the new White House report.
Specifically with temperatures, the Southwest's warming made the period 2001-10 the warmest decade in the 110 years of instrumental records, the new report says. The period since 1950 has been hotter than any period in at least 600 years.
Just in the past decade, Southwest temperatures have averaged almost two degrees Fahrenheit more than historic norms, with more heat waves and fewer cold air outbreaks, the report says. By contrast, nationally, annual average temperatures have risen by a range of 1.3 to 1.9 degrees – but those ranges cover a much longer period, since 1895, with temperatures nationally having risen more rapidly since 1870.
Other highlights from the report on Southwestern climate issues:
• If global carbon dioxide emissions keep growing as they have been growing in recent decades, this region’s annual average temperatures are predicted to rise by 2.5 to 5.5 degrees by the period 2041-70 and by 5.5°F to 9.5°F by 2070-99. If the world’s governments can find a path to substantially cutting emissions, temperatures will still keep rising at a milder pace: by 2.5 to 4.5 degrees in 2041-70 and 3.5 to 5.5 degrees in 2070-99.
• Snowpack in this region taken a punch from climate change, reducing water supplies. Over the past 50 years across most of the Southwest, less late-winter precipitation has fallen as snow. What does fall has melted earlier, meaning that most of the year’s streamflow arrives earlier. The bottom line: streamflow totals in Colorado, Rio Grande, Sacramento-San Joaquin river basins and the Great Basin were 5 percent to 37 percent lower between 2001 and 2010 than the 20th century average flows. These trends are expected to continue, posing increased risks to the water supplies that our cities, farms and natural landscapes and ecology depend on.
• Dust and soot that piles up on the snowpack compounds these problems, by increasing the amount of energy that the snow absorbs. This brings earlier snowmelt and evaporation – both carrying negative implications for water supply, alpine vegetation, and forests.
• Climate change could strike faster and more widely than farmers can adapt to it. Pastures used by cattle are highly susceptible to projected future droughts, and more than 92 percent of the region’s cropland outside Colorado is irrigated. A warmer, drier climate is likely to speed an already ongoing trend of transferring irrigation water to urban areas.
• The trend of increasing wildfires has been a reality for several decades now in this region. But while a century of federal fire suppression has greatly contributed to this problem, increased warming due to climate change, drought, insect buildups and accumulation of woody fuels and non-native grasses have added to the problem. Climate outweighed other factors in determining how much of the West burned from 1916 to 2003, based on 3,000-year reconstructions of Southwestern fire history.
• More trees are dying across the region, due to drought and higher temperatures. In addition, winter warming due to climate change has exacerbated bark beetle outbreaks. It’s allowed more survival and reproduction for the beetles, which normally die in cold weather. Overall, wildfire and bark beetles killed trees across 20% of Arizona and New Mexico forests from 1984 to 2008.
• Heat stress has been the leading, weather-related cause of death in this country since record-keeping started in this country, and the highest rates of heat-related illness nationally are in Arizona. Due to climate change, heat waves are projected to be more common, last longer and intensify over the coming decades, increasing the death toll. Poorer neighborhoods are most likely to suffer, due to their lack of greenery and less use of air conditioning.