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Sizzle factor for a restless climate

Enjoying the heat wave? • The answer is probably no if you live in Abilene, Texas, where temperatures have been at or above 100 degrees for 40 days this summer. It's been a little cooler in Savannah, Ga., where the mercury hit 90 or more for 56 days in a row. Texas, New Mexico and Oklahoma are coping with their driest nine-month stretch since 1895. • Yes, it has been a very hot summer after one of the most extreme-weather springs on record. It's time to face the fact that the weather isn't what it used to be.

Every 10 years, the National Oceanic and Atmospheric Administration recalculates what it calls climate "normals," 30-year averages of temperature and precipitation for about 7,500 locations across the United States. The latest numbers, released earlier this month, show that the climate of the last 10 years was about 1.5 degrees warmer than the climate of the 1970s, and the warmest since the first decade of the last century. Temperatures were, on average, 0.5 degrees warmer from 1981 to 2010 than they were from 1971 to 2000, and the average annual temperatures for all of the lower 48 states have gone up.

For climate geeks like me, the new normals offer a fascinating and disturbing snapshot of a restless climate. The numbers don't take sides or point fingers. They acknowledge both powerful natural climate fluctuations as well as the steady drumbeat of warming caused by roughly 7 billion people trying to live and prosper on a small planet, emitting heat-trapping greenhouse gases in the process.

Even this seemingly modest shift in climate can mean a big change in weather. Shifting weather patterns influence energy demand, affect crop productivity and lead to weather-related disasters. In the United States, in any given year, routine weather events like a hot day or a heavy downpour can cost the economy as much as $485 billion in crop losses, construction delays and travel disruptions, a recent study by the National Center for Atmospheric Research found. In other words, that extra 1.5 degrees might be more than we can afford.

And while the new normals don't point to a cause, climate science does. Drawing from methods used in epidemiology, a field of climate research called "detection and attribution" tests how human actions like burning fossil fuels affect climate and increase the odds of extreme weather events.

Heat-trapping pollution at least doubled the likelihood of the infamous European heat wave that killed more than 30,000 people during the summer of 2003, according to a study in the journal Nature in 2004. And if we don't ease our grip on the climate, summers like that one will likely happen every other year by 2040, the study warned. Human actions have warmed the climate on all seven continents, and as a result all weather is now occurring in an environment that bears humanity's signature, with warmer air and seas and more moisture than there was just a few decades ago, resulting in more extreme weather.

The snapshots of climate history from the NOAA can also provide a glimpse of what's in store locally in the future. Using climate models, we can project what future Julys might look like. For example, by 2050, assuming we continue to pump heat-trapping pollution into our atmosphere at a rate similar to today's, New Yorkers can expect the number of July days exceeding 90 degrees to double, and those exceeding 95 degrees to roughly triple. Sweltering days in excess of 100 degrees, rare now, will become a regular feature of the Big Apple's climate in the 2050s.

The next time the NOAA calculates its new temperature normals will be in 2021 — when there will be about another billion people on the planet. Lady Gaga may no longer be hot. But the climate almost surely will be.

Heidi Cullen, a scientist at Climate Central, a journalism and research organization, is the author of "The Weather of the Future: Heat Waves, Extreme Storms, and Other Scenes From a Climate-Changed Planet."

© 2011 New York Times

Sizzle factor for a restless climate 07/24/11 [Last modified: Sunday, July 24, 2011 5:30am]
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