Not Your Average Weather Map

Published: June 29th, 2011

These days, extreme weather and climate is on everyone’s mind, thanks to the Southwestern wildfires, the Missouri and Mississippi River floods and the most active month on record for tornadoes, which occurred in April. There are so many headline-grabbing weather events taking place at the same time, in fact, that a lot of people are asking scientists, what's the connection to long-term climate change?

A new map from the Pew Center on Global Climate Change shows some of the most notable climate extremes of the past 15 years. Credit: Pew Center on Global Climate Change.

That’s exactly the question the Pew Center on Global Climate Change has just weighed in on. The Center released a new map earlier this week that illustrates some of the most extreme incidents that have happened in the U.S. since 1995, including major floods, droughts, heat waves, and wildfires. The map doesn’t go beyond the U.S., so it doesn’t point out events like last year’s Russian heat wave or Pakistan floods.

Surprisingly, the map also doesn’t capture some of the costliest U.S. storms from the past 15 years, including Hurricanes Katrina and Ike, and this year’s wild tornado season — but that’s because the scientific case for a climate change connection with these events is not yet ironclad.

What is becoming more scientifically sound is how much the warmer global atmosphere has increased the likelihood of floods, droughts, heat waves and wildfires happening in the U.S. (and around the world).

Droughts, floods, and wildfires obviously aren’t new. They’ve been happening for far longer than humans have been around to notice them. Generally speaking, though, evidence is mounting for a link between increasing global temperatures — brought on by increasing amounts of greenhouse gases in the air — and wild weather like the kind on the new Pew Center map. Accompanying the map is a white paper that explains why droughts, floods, heat waves, and wildfires could be affected by global warming.

It’s not that climate change is causing these more unusual events. Scientists say that it’s more appropriate to ask, how is the warmer atmosphere changing their frequency and intensity — or to ask, more simply: has global warming changed the odds in favor of extreme weather? Would these events have occurred if the atmosphere were not juiced up with more greenhouse gases and water vapor?

And many scientists are confidently saying, yes, the odds are changing, for some types of weather.

If you’re confused about the difference, here’s an analogy that I’ve used before: Not everyone who smokes develops lung cancer. Not everyone who has lung cancer was a smoker. But we know that smokers are far more likely to get lung cancer. In other words, smoking greatly increases your risk of developing the disease.

It’s a similar situation with climate change and extreme weather events.

Is it possible that the extreme weather events from the past year could have happened if greenhouse gas emissions hadn’t caused global temperatures and atmospheric water vapor to increase? Yes. But research shows that the warmer atmosphere we have now is more likely to foster this unusual weather, compared to what things would have been like without the extra greenhouse gases, such as carbon dioxide (CO2). Which means that there’s a good chance the new extremes map will have to be updated several more times in the coming years.

The Pew Center also sponsored a three-part series on climate change and extreme weather events in Scientific American that ran this week, but it did not have editorial control over the stories. The series is worth reading. You can also check out a piece I wrote for YaleE360, which details how scientists are trying to resolve difficult questions concerning the attribution of extreme weather events.

Posted in Impacts, Trends, Climate, Extremes, Drought, Flooding, Heat, Wildfires, Weather, Extreme Weather, Extreme Planet

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Andrew Freedman

Andrew Freedman is a senior science writer for Climate Central, focusing on coverage of extreme weather and climate change. Prior to working with Climate Central, Freedman was a reporter for C...