From the ABC 7 Weather team

Extreme weather: The new normal?

March 27, 2013 - 03:33 PM
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Is the weather getting more extreme in general? Bob Ryan takes a look at the recent fluctuations in weather and explains it all.

Is the weather really going to extremes, or are we just more aware about “extreme weather” thanks to the news and blogs?  Well, March 2013 has sure been an extreme change from March 2012. 


March 2012 was the warmest one on record here in Washington and across the United States. But at the same time across the globe, March 2012 was the coolest since 1999. 


In fact, while March 2012 set more than 6,000 record highs across the U.S., March 2013 so far has seen only a bit over 500 with most in the west. The National Climatic Data Center (NCDC) plot of the climate extremes index (extremes of temperature and precipitation across the U.S.) shows extremes of weather increasing, or at least becoming more probable. 



Why is this happening? Are weather patterns changing? Many climate scientists think the answer is yes. Like any good detective, let’s look at the scientific - not political - footprints.

Earth is warming, the chemistry of Earth’s air and water/oceans is changing and we are sure a large part of the reason why. 

ZZZZZThe famous Keeling Curve shows not only about a 40 percent increase in carbon dioxide in the air over the last 150 years, but an increasing rate of change.
Changes in the global temperature are most dramatic in high latitudes in the Arctic.


 Courtesy Dr. Jennifer Francis-Rutgers University

This greatest warming in the Arctic, by the way, was predicted about 50 years ago, in some of the earliest simulations of a world with increasing concentrations of greenhouse gases.
So what if the Arctic warms? Not everyone in Greenland and marginal agricultural areas think longer growing seasons are terrible. But look at the changes in Arctic sea ice in this warming world.  

Courtesy Cryosphere Today
It shows dramatic decreases not only in summer, but in winter.  
A warmer arctic with less and thinner ice means more Arctic Ocean surface water. 
Of course, more water means more evaporation.

Courtesy Dr. Jennifer Francis
Some recent studies suggest a weakening in the mid-latitude jet stream
You can see that there's not as strong a temperature contrast from the equator to the poles.
Weaker westerly winds (also called Rossby waves in the general circulation) and a higher probability of blocking patterns or patterns with slower moving waves and persistent north to south, or south to north winds at high latitudes. 

 CourtesyDr. Jennifer Francis-Rutgers University

The result is a higher probability of extremes in the weather. That means  possibly longer droughts and heat waves, but also persistent cold waves or stormy patterns.

Depending on the persistence of these blocking patterns (Stu Ostro of The Weather Channel has a wonderful extensive presentation that he has developed over the years), some weather may be just unusual or a once-in-a-lifetime extreme event over days or weeks.

The long term outlook? More extremes. A simulation of a world with three times the carbon dioxide we’ve already added to the air shows dramatic decreases in the normal west-to-east jet and dramatic increases in the flow (meridional) from north to south and south to north.  


Courtesy Dr. Jennifer Francis Rutgers University

Does all this mean no more snow in Washington?  No, but maybe the super snowy winter 2009-2010 followed by our recent two almost snowless winters will become the new normal.

Summers may be hotter, contain more persistent droughts and longer heat waves, but they also could feature increasing probabilities of heavier rains storms.

Not every extreme weather event is due to us, but as many researchers have said, “We are stacking the deck."

Stay tuned. We’ll all find out over the next 20-50 years. More interesting resources and recent blogs on this and related topics can be found here:

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