A new report published this week by dozens of scientists confirms what Republican politicians dispute: that human-caused climate change is influencing weather patterns around the world.
Heat waves in Australia, Korea, Japan, China, and Europe, for example, "overwhelmingly showed that human-caused climate change is having an influence," wrote the authors of the study.
For the sweeping report, dozens of scientists analyzed 22 studies of 16 extreme weather events from around the world in 2013, and published their findings on Monday in the "Bulletin of the American Meteorological Society."
Strong evidence exists for increases in some extreme events worldwide since 1950, especially more frequent hot days and heavy precipitation events. The findings indicate that human-caused climate change "greatly increased" the risk for the extreme heat waves assessed in the report, the scientists wrote.
The findings suggest that the record-setting heat waves in Australia, as well as unusual weather in the far western Pacific, were "largely attributable to human forcing of the climate system," the scientists wrote. The event was the country's hottest 12 months in more than 100 years of records.
Researchers were less clear, however, about the extent of human influence on droughts, heavy rain events, and storms. Thus, natural variability likely played a much larger role in the extreme events, according to the scientists. Linking higher temperatures to heat extremes is relatively straightforward, while connecting a human influence in droughts or storms is much more complex, they wrote.
Several groups examined the California drought. The researchers didn't reach a unified conclusion on the effects climate change had on the California drought, which began in 2013 and lasted through early 2014. It was the driest 12-month period on record in the state. "Although global warming has very likely increased the probability of certain large-scale atmospheric conditions, implications for extremely low precipitation in California remain uncertain," the scientists wrote in the report, which includes more than 100 pages of explanations.
The researchers also examined other significant weather events, including the October 2013 blizzard in western South Dakota, the drought over North Island in New Zealand, and severe precipitation in India.
Researchers published the study a week after the People's Climate March, where hundreds of thousands of demonstrators filled the streets of New York City with demands for global leaders to take action to avert catastrophic climate change. Days later, during the United Nation's 2014 Climate Summit last week, President Barack Obama made public several government initiatives intended to combat the threat of climate change. The most significant policy is an executive order requiring that federal agencies acknowledge environmental sustainability when they design new international development programs.
Obama also recently signed a proclamation that forbids commercial fishing in the now-protected area of the Pacific Remote Islands National Marine Monument.
In the first major study from the UN since 2007, the Intergovernmental Panel on Climate Change earlier this year in March found that the increasing threat of climate change will continue to grow if residents don't bring greenhouse gas emissions under control. The global threat will continue to worsen, the report said, if leaders don't rein in the release of greenhouse gases into the atmosphere.