Did global warming contribute to the punishing heat wave much of the country endured during the summer of 2012? How about Superstorm Sandy?
A group of 78 scientists led by experts from the National Oceanic and Atmospheric Administration last week gave their preliminary answers, releasing a series of peer-reviewed analyses on those and other major weather events from last year. The picture they offer is of a planet in which warming has boosted the chances, in some cases significantly, that certain unwelcome weather or weather-related disasters will occur.
Not every instance of bad weather is related to global warming. Of the 12 extreme weather events scientists studied, experts saw evidence of a climate-change component in only half.
One of them, though, was that 2012 heat wave: Global warming probably factored into the magnitude of the highs. One of the papers reckons that climate change was responsible for about 35 percent of last year's heat.
"High temperatures, such as those experienced in the U.S. in 2012, are now likely to occur four times as frequently due to human-induced climate change," NOAA notes, citing findings from a different paper in its report on the same event. Another phenomenon last year, very low Arctic sea ice, "cannot be explained by natural variability alone."
Sandy, meanwhile, was an unlucky break, a big storm that slammed into New York during high tide, inundating population-dense areas of the city. But, regardless of where the storm came from, rising sea levels related to climate change make catastrophic flooding more likely; the probability of a Sandy-like storm surge is already double what it was in 1950.
NOAA warns: "Ongoing natural and human-induced forcing of sea level ensures that Sandy-level inundation events will occur more frequently in the future from storms with less intensity and lower storm surge than Sandy."
These findings, often expressed in percentages and probabilities, aren't as satisfying as sure proof linking one effect to one clear cause. Get used to it; experts are still sorting out the best ways to attribute weather events, and they should be cautious. They also don't offer a total picture of the effects of climate change on weather phenomena, let alone everything else.
One thing NOAA is clear about, though, is that continued warming will increase the frequency and severity of certain events, which will require humans to adapt. Then there are the long-term consequences that are harder to predict.
These knowns and unknowns are why humans shouldn't just adapt but head off excessive future warming by reducing greenhouse-gas emissions now.