The atmospheric conditions observed during California's drought have been linked to human
generated climate change. This all according to
new study published today:
In a new study, a team led by Stanford climate scientist Noah Diffenbaugh used a novel combination of computer simulations and statistical techniques to show that a persistent region of high atmospheric pressure hovering over the Pacific Ocean that diverted storms away from California was much more likely to form in the presence of modern greenhouse gas concentrations.
The research, published on Sept. 29 as a supplement to this month's issue of the Bulletin of the American Meteorological Society, is one of the most comprehensive studies to investigate the link between climate change and California's ongoing drought.
Just to bring you up to speed on how bad this drought is:
The exceptional drought currently crippling California is by some metrics the worst in state history. Combined with unusually warm temperatures and stagnant air conditions, the lack of precipitation has triggered a dangerous increase in wildfires and incidents of air pollution across the state. A recent report estimated that the water shortage would result in direct and indirect agricultural losses of at least $2.2 billion, and lead to the loss of more than 17,000 seasonal and part-time jobs in 2014 alone. Such impacts prompted California Governor Jerry Brown to declare a drought emergency, and the federal government to designate all 58 California counties as "natural disaster areas."
The study was the result of of using the most modern statistical analysis in tandem with scientific observation and modeling simulations. Scientists are in agreement that the immediate cause of the California drought is a "blocking ridge" in the Pacific (Known as "Triple R" for Ridiculously Resilient Ridge). The Triple R has prevented winter storms from making their way to California over the last 2 rain seasons.
An important question for scientists and decision-makers has been whether human-caused climate change has influenced the conditions responsible for California's drought. Given the important role of the Triple R, Diffenbaugh's team set out to measure the probability of such extreme ridging events. The team first assessed the rarity of the Triple R in the context of the 20th century historical record. They found that the combined persistence and intensity of the Triple R in 2013 was unrivaled by any event since 1948, which is when comprehensive information about the circulation of the atmosphere is first available.
To more directly address the question of whether climate change played a role in the probability of the 2013 event, the team collaborated with Bala Rajaratnam, assistant professor of Statistics and of Environmental Earth System Science, and an affiliated faculty of the Woods Institute for the Environment. Rajaratnam and his graduate students Michael Tsiang and Matz Haugen applied advanced statistical techniques to a large suite of climate model simulations. Using the Triple R as a benchmark, the group compared geopotential heights–an atmospheric property related to pressure– between two sets of climate model experiments. One set mirrored the present climate, in which the atmosphere is growing increasingly warm due to human emissions of carbon dioxide and other greenhouse gases. In the other set of experiments, greenhouse gases were kept at a level similar to those that existed just prior to the Industrial Revolution.
Read more from one of the researchers, Daniel Swain,
here.
