Human activity is directly linked to the hot and dry winter in California, according to a paper published in Proceedings of the National Academy of Scientists. Scientists affiliated with two departments at Stanford University (the Department of Environmental Earth System Science and the Stanford Woods Institute for Environment) blamed the historic drought squarely on anthropogenic climate change.
The study used historical statewide data for observed temperature, precipitation and drought in California. Researchers came to a stunning conclusion about the relationship between climate change and the California drought using a process called bootstrapping, which is a technique that lets statisticians use the same sample over and over again to improve their estimates of specific effects. The bootstrapping in this study was used to compare climate data with measures of populations from different time periods to allow for analysis of how changes in population are associated with different climate conditions.
The study found that the warming across California happens in climate models that include both natural and human factors, but not in simulations that include only natural factors, arstechnica notes. The difference between the two scenarios has a very high level of statistical significance.
In their conclusion, the scientists say their results strongly suggest that human-caused warming has increased the probability of co-occurring temperature and precipitation conditions that have historically led to California’s droughts. They add that continued warming is likely to lead to situations where every future dry period, whether seasonal, annual or multiannual, will come along with historically warm conditions.