Image courtesy of Dave Pierce/SIO
Scientists have long shied away from attributing any one small-scale event - irrespective of its magnitude - to global warming, reasoning that the complexity and number of factors at play makes it extremely difficult, if not inadvisable, to do so. Yet, at least in the case of the American West's recent bout with several severe water shortages, some researchers have stepped forward and confidently asserted that there does indeed exist a link between anthropogenic global warming and the scarcity - the shrinking snowpacks.
At the fall meeting of the AGU, Tim P. Barnett, a climatologist at the Scripps Institution of Oceanography, explained that the West typically depends on a large, late-melting snowpack to replenish its reservoirs in late spring. However, due to global warming-induced effects, the snowpack has been shrinking earlier and at a faster pace, a trend that will worsen in coming years - depriving the West of a significant source of freshwater. This, he said, would result in a large-scale "water crisis in the West."While many of these changes - diminishing snowpacks, earlier melting - had already been noticed several decades ago, nobody quite knew whether they were part of a larger natural cycle, one that would eventually switch back to a cooler climate, or a general trend. Barnett and his colleagues, who ran several climate models, concluded that, as he put it: "There's no way we can make a natural-variability explanation for what we've seen. I'd put the odds at between one in 100 and one in 1000 that we were fooled. Quite frankly, it's us."
Indeed, the models could only reproduce the observed trends seen over the past few years if greenhouse gas emissions and pollutant hazes were included. The concern for water users in the West, Barnett explained, is that while there is still the same level of precipitation as in years past, more is falling as rain instead of as snow. Dammed reservoirs already overflowing with water in the winter risk producing floods downstream; in the late spring, when the level of stored water is decreased to allow for meltwater from the snowpacks to come in, it will already have been much depleted by the warming and additional rain.
Barnett is worried that these water problems will only become more common - in more areas - as time goes by. There are very few well-studied areas, he says, and many in Asia, South America and India that "don't even know they have a problem."
"I've gotten a look at the future," he said, "and I don't like it."
Via ::ScienceNOW: Global Warming Coming Home to Roost in the American West (news website)