Over the past few years, a large patch of unusually warm water has appeared off the coast of Alaska, popularly known as “the blob.” These warm waters have allowed toxic algae blooms to spread across the region, killing seabirds by the thousands and forcing local fisheries to close.
A new study, led by John E. Walsh of the University of Alaska, called the blob “unprecedented” and argued that it “cannot be explained without anthropogenic climate warming,” although natural factors such as El Niño and atmospheric variability also played an important role. The study also concluded that more such blobs were likely to occur with further warming, which “will result in a profound shift for people, systems, and species.”
But climate attribution remains complex
Climate attribution remains easier for some weather events than others. Temperature records are the simplest to link to climate change. But droughts — which are influenced by a complex interplay of temperature, precipitation and soil moisture — can be trickier to connect to warming trends. And hurricanes are more difficult still, because they occur so rarely.
Overall, however, attribution science has improved significantly since the Bulletin of the American Meteorological Society began publishing its annual investigations into weather extremes six years ago, said Heidi Cullen, chief scientist at Climate Central, a news organization that focuses on climate science.
“In 2011, people were still of the mind-set that you couldn’t attribute any individual event to climate change,” Dr. Cullen said. “But with each subsequent issue, people are able to say that climate change really is increasing the risk” of certain extremes occurring.
Crucially, however, the journal does not explicitly set out to prove links between specific weather extremes and global warming. Instead, the editors accept proposals to investigate certain weather events before the results are known, in order to minimize publication bias.
In some cases, scientists either ruled out or could not find a significant role for climate change, effectively arguing that a given weather extreme could just as likely have occurred in a world without global warming. That was true of Brazil’s brutal drought, which was largely influenced by El Niño, as well as a major snowstorm in the Mid-Atlantic United States.
“A few events from this past year were judged to have been of such a magnitude that they would not have been possible in the climate of a few hundred years ago,” said Martin P. Hoerling, a meteorologist at NOAA who edited the collection. But, he added, “not everything is being made demonstrably more severe because of climate change.”
In the future, scientists are hoping to refine and standardize their attribution methods, so that a community hit by a storm, wildfire or other extreme event can learn much more quickly how that event might have been swayed by global warming — and take steps to adapt.