Slowing economy doesn't slow greenhouse emissions
PRESCOTT - When a University of Arizona climate scientist displayed a chart Saturday showing an exponential increase in greenhouse gas concentrations in the Earth's atmosphere over the past 150 years, his Prescott audience emitted a collective gasp.
Michael Crimmins, an assistant professor at UofA and Extension Office climate science specialist, first displayed a relatively flat line showing greenhouse gas emissions over a 10,000-year time period. Then he added the last 150 years to show a vertical spike.
"This is not within natural variability," he told the audience at the Citizens Water Advocacy Group meeting.
As the CO2 level in its atmosphere rises, the Earth tries to force it out with increasing temperatures, Crimmins said.
"There's an imbalance in the planet's energy balance," he explained.
Despite the economic downturn, worldwide carbon dioxide emissions from burning fossil fuels set a new record in 2010, Crimmins noted.
Greenhouse gasses have long residence times, he said. So even if humans stabilized emissions immediately, it would take thousands of years for the gasses to reduce substantially in the atmosphere.
For Arizona, climate change means warmer temperatures that bring less winter snow, less spring runoff and less water in streams for the summer. Northern Arizona ecosystems have evolved to depend on spring runoff from these winter storms. The snowpack across the region holds much more water than reservoirs, and it has decreased over the past two decades, he said.
Climate change in Arizona also means more evapotranspiration (moisture lost to the atmosphere and plants), loss of water in reservoirs, and drier soils.
Experts predict more extreme weather events such as more intense drought periods, more flooding and more extreme heat events for Arizona, Crimmins added.
Scientists now have a "very high confidence" that these events will occur without efforts to decrease greenhouse gasses, Crimmins said.
"This is strong language for scientists," he added, later explaining that "We're not really in cahoots - we're always trying to prove each other wrong."
Arizona warmed up more than the other lower 48 states in 1993-2008, he said.
He displayed a chart showing Yavapai County average temperatures rising over the past century.
"This is disconcerting for a lot of reasons," he said, noting evapotranspiration has a direct link to rising temperatures.
Rising temperatures exacerbate the impacts of drought, he said. For example, the 1950s drought in Arizona was much drier than the current drought, but since it's much warmer now, the current drought has killed off just as much vegetation.
Different vegetation is likely to replace what has died. South of Prescott, for example, brush is growing where the ponderosa pine forest burned in the Indian Fire of 2002.
Arizona now is experiencing one of its worst wildfire seasons in history, with ponderosa pine forests burning at unnatural intensities. One reason is because they are so overstocked from decades of wildfire suppression.
The La Niña weather pattern set off by a cooling tropical Pacific Ocean helped produce below-average precipitation across much of the Southwest this past winter, too. In Arizona, the southeast portion of the state has been hit hardest. Crimmins said Douglas has received only one-tenth of an inch of rain since October.
The Pacific Ocean has a strong influence on Arizona, Crimmins noted.
While precipitation is harder to predict in a warming climate, scientists say the high-pressure systems over Arizona that push out precipitation are likely to strengthen and push winter storm tracks to the north because of climate change.
Crimmins cited several online sources of scientific information about climate change in Arizona, including southwestclimatechange.org and extension.org, where people can ask experts questions online.