Is climate change to blame for recent weather disasters?
Summer isn’t even half over, and we’ve seen heat waves in the Pacific Northwest and Canada with temperatures that would make news in Death Valley, enormous fires that have sent smoke across North America, and lethal floods of biblical proportions in Germany and China. Scientists have warned for over 50 years about increases in extreme events arising from subtle changes in average climate, but many people have been shocked by the ferocity of recent weather disasters.
A couple of things are important to understand about climate change’s role in extreme weather like this.
First, humans have pumped so much carbon dioxide, methane and other greenhouse gases into the atmosphere that what’s “normal” has shifted. Extreme heat waves that were once ridiculously improbable are on their way to becoming more commonplace, and unimaginable events are becoming possible.
Second, not every extreme weather event is connected to global warming.
Like so many things, temperature statistics follow a bell curve — mathematicians call these “normal distributions.” The most frequent and likely temperatures are near the average, and values farther from the average quickly become much less likely.
All else being equal, a little bit of warming shifts the bell to the right — toward higher temperatures. Even a shift of just a few degrees makes the really unlikely temperatures in the extreme “tail” of the bell happen dramatically more often.
The stream of broken temperature records in the North American West lately is a great example. Portland hit 116 degrees — 9 degrees above its record before the heat wave. That would be a once-unimaginable extreme at the end of the tail, but it’s now inching closer.
The width of a bell curve is measured by its standard deviation. About two-thirds of all values fall within one standard deviation of the average. Based on historical temperature records, the heat wave in 2003 that killed more than 70,000 people in Europe was five standard deviations above the mean, so it was a 1 in 1 million event.
Without eliminating emissions from fossil fuels, heat like that is likely to happen a few times a decade by the time today’s toddlers are retirees.