Is U.S. climate getting more extreme?

By: Dr. Jeff Masters , 1:54 PM GMT on March 13, 2009

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Is the climate in the U.S. getting more extreme? The answer to this question depends upon how one defines "extreme". For example, the number of extreme tornadoes (violent EF-4 and EF-5 twisters) has not increased in recent years. We lack the data to judge whether there has been an increase in severe thunderstorms and hail. There has been a marked increase in Atlantic hurricane activity since 1995 (though the possible contribution of human-caused global warming to this increase is not something hurricane scientists agree upon). Since it is difficult to quantify how severe storms like tornadoes and hurricanes are changing, a better measure of how climate extremes are changing is to look at temperature and precipitation, which are well-measured. NOAA's National Climatic Data Center (NCDC) has developed a Climate Extremes Index to attempt to quantify whether or not the U.S. climate is getting more extreme. The Climate Extremes Index (CEI) is based upon three parameters:

1) Monthly maximum and minimum temperature
2) Daily precipitation
3) Monthly Palmer Drought Severity Index (PDSI)

The temperature data is taken from 1100 stations in the U.S. Historical Climatology Network (USHCN), a network of stations that have a long period of record, with little missing data. The temperature data is corrected for the Urban Heat Island effect, as well as for station and instrument changes. The precipitation data is taken from 1300 National Weather Service Cooperative stations. The Climate Extremes Index defines "much above normal" as the highest 10% of data, "much below normal" as the lowest 10%, and is the average of these five quantities:

1) The sum of (a) percentage of the United States with maximum temperatures much below normal and (b) percentage of the United States with maximum temperatures much above normal.

2) The sum of (a) percentage of the United States with minimum temperatures much below normal and (b) percentage of the United States with minimum temperatures much above normal.

3) The sum of (a) percentage of the United States in severe drought (equivalent to the lowest tenth percentile) based on the Palmer Drought Severity Index (PDSI) and (b) percentage of the United States with severe moisture surplus (equivalent to the highest tenth percentile) based on the PDSI.

4) Twice the value of the percentage of the United States with a much greater than normal proportion of precipitation derived from extreme (equivalent to the highest tenth percentile) 1-day precipitation events.

5) The sum of (a) percentage of the United States with a much greater than normal number of days with precipitation and (b) percentage of the United States with a much greater than normal number of days without precipitation.


Figure 1. The Annual Climate Extremes Index (CEI), updated through 2008, shows that U.S. climate has been getting more extreme since the early 1970s. Image credit: National Climatic Data Center. On average since 1910, 20% of the U.S. has seen extreme conditions in a given year (thick black line).

As summarized by Gleason et al. (2008), the National Climatic Data Center concludes that based on the Climate Extremes Index, the percentage of the U.S. seeing extreme temperatures and precipitation generally increased since the early 1970s. These increases were most pronounced in the summer. No trend in extremes were noted for winter. The annual CEI index plot averaged for all five temperature and precipitation indices (Figure 1) showed that five of the fifteen most extreme years on record occurred since 1997. Shorter-lived periods with high CEI values occurred in the 1930s and 1950s, in association with widespread extreme drought and above-average temperatures. The most extreme year in U.S. history was 1998, with 1934 a close second. The year 1998 was the hottest year in U.S. history, with a record 78% of the U.S. experiencing minimum temperatures much above normal. That year also had a record 23% of the U.S. with much greater than normal precipitation from extreme 1-day precipitation events. The 1934 extreme in CEI was due in large part because of the most widespread drought of the century--a full 52% of the U.S. was affected by severe or extreme drought conditions. That year also saw a record 64% of the U.S. with much above normal maximum temperatures.

The impact of maximum and minimum temperatures on the Climate Extreme Index
It is very interesting to look at the five separate indices that go into the Climate Extremes Index. Today I'll look at temperature, and next week, I'll focus on drought and precipitation. The portion of the U.S. experiencing month-long maximum temperatures either much above normal or much below normal has been about 10% over the past century (black lines in Figure 2). However, over the past decade, about 20-25% of the U.S. has been experiencing monthly maximum temperatures much above normal, and the portion of the U.S. experiencing much colder than normal high temperatures has been near zero. Minimum temperatures show a similar behavior, but have increased more than the maximums (Figure 3). Over the past decade, minimum temperatures much above normal have affected 25-35% of the U.S. This means that the daily range of temperature (difference between minimum and maximum) has decreased over the past decade, which is what global warming says should be happening if greenhouse gases are primarily to blame for the rise in temperatures.

While there have been a few years (1921, 1934) when the portion of the U.S. experiencing much above normal maximum temperatures was greater than anything observed in the past decade, the sustained lack of maximum temperatures much below normal over the past decade is unique. The behavior of minimum temperatures over the past decade is clearly unprecedented--both in the lack of minimum temperatures much below normal, and in the abnormal portion of the U.S. with much above normal minimum temperatures. Remember that these data ARE corrected for the Urban Heat Island effect, so we cannot blame increased urbanization on the increase in temperatures. Recall that the all-time record maximum and minimum temperature data, which I presented in a post in February, are not corrected for the Urban Heat Island Effect, but look very similar to the CEI maximum and minimum temperature trends presented here.

A lot of people have told me that they believe we are experiencing more wild swings of temperature from hot to cold from day to day in recent years, but the CEI data does not answer this question. To my knowledge, a study of this kind has not been done.


Figure 2. The Annual Climate Extremes Index (CEI) for maximum temperature, updated through 2008, shows that 20-25% of U.S. has had maximum temperatures much above normal over the past decade. Image credit: National Climatic Data Center.


Figure 3. The Annual Climate Extremes Index (CEI) for minimum temperature, updated through 2008, shows that 25-35% of U.S. has had minimum temperatures much above normal over the past decade. Image credit: National Climatic Data Center.

References
Gleason, K.L., J.H. Lawrimore, D.H. Levinson, T.R. Karl, and D.J. Karoly, 2008: "A Revised U.S. Climate Extremes Index", J. Climate, 21, 2124-2137.

Annual WeatherDance contest ready for registration!
Armchair forecasters, now's your chance to shine! WeatherDance, based on teams in the men's and women's NCAA basketball tournaments, allows players to predict which team's city will be hotter or colder on game day in each round of the Big Dance. Beginning today, players can make their forecasts at the Weather Dance Web site at: www.weatherdance.org. The site will be updated with cities promptly after NCAA seeding announcements. First round Weather Dance selections must be entered by 11:59 p.m. EDT Wednesday, March 18.

"Officially, Weather Dance began as a class project to get students involved in weather forecasting, but we kept it around because it got popular. People think they can do better forecasting than the meteorologists. Well, here's their shot!" said Perry Samson, WeatherDance creator, co-founder of the The Weather Underground, Inc., and Professor in the Department of Atmospheric, Oceanic and Space Sciences at the University of Michigan.

This is the fifth year for the game. Last year more than 2,000 people played. Most play merely for the thrill, but many K-12 science teachers involve their classes as part of meteorology units. The winning teacher will receive an expense-paid trip to join the Texas Tech/University of Michigan Storm Chasing team this spring for a day of tornado chasing in Tornado Alley. Other winners will receive a Weather Underground umbrella, "Extreme Weather" mugs, or a copy of the book "Extreme Weather," by Christopher C. Burt.

I'll talk about drought and precipitation trends in my next post, Monday or Tuesday.

Jeff Masters

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It's a date KEH...and Tampa...thanks for the Portlight effort....
Member Since: Posts: Comments:
Member Since: September 10, 2007 Posts: 0 Comments: 11538
Press
See ya at 11:00
Member Since: August 19, 2008 Posts: 6 Comments: 2490
Quoting StormW:


Hey Tampa...just dropped in to post some info.


Have you seen my new Web Site
Member Since: September 2, 2007 Posts: 179 Comments: 20448
haha...I'll pass it on....muchos gracias...
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Hope your wife feels better press
Member Since: August 12, 2007 Posts: 2 Comments: 2838
her pride is seriously wounded...and, at the moment, she's pretty stoned on Percocet...but she's otherwise fine....Date tomorrow KEH...
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310. presslord
Yikes! That must have hurt.
How's she doing now?
Member Since: August 19, 2008 Posts: 6 Comments: 2490
Drak ya, i think when we get our next storm he will do a very good job.
Member Since: August 12, 2007 Posts: 2 Comments: 2838
Quoting hahaguy:


At least Glazer brings personality unlike WPBF mets.


Yea. When he came on he was noticeably perkier than the other mets. Took a while to get used to such an effervescent personality.
Member Since: Posts: Comments:
Quoting Drakoen:


I didn't mind Dean. I can't stand the other meteorologists on the other stations. They need jumper cables or something, especially John. Very stale.


At least Glazer brings personality unlike WPBF mets.
Member Since: August 12, 2007 Posts: 2 Comments: 2838
all is well....my wife fell at my birthday party today and cut her lip...had to get 3 stitches...she does not, by the way, drink a drop...
Member Since: Posts: Comments:
Quoting hahaguy:


I was just joking . But i like Weagle but i'm glad that dean tendrich left he was a camera hog


I didn't mind Dean. I can't stand the other meteorologists on the other stations. They need jumper cables or something, especially John. Very stale.
Member Since: Posts: Comments:
Hey StormW
Member Since: September 2, 2007 Posts: 179 Comments: 20448
Press, how goes it?

Member Since: August 19, 2008 Posts: 6 Comments: 2490
I Prefer a short walk for him on a short Pier with a big push......LOL
Member Since: September 2, 2007 Posts: 179 Comments: 20448
Long walk off a short pier?!?!?!?!?!

I LOVE that!!!!!!!!!!

Plan to steal it and use it liberally.....
Member Since: Posts: Comments:
Quoting Drakoen:


Weagle is the best for Palm Beach County.


I was just joking . But i like Weagle but i'm glad that dean tendrich left he was a camera hog
Member Since: August 12, 2007 Posts: 2 Comments: 2838
Quoting hahaguy:
He's better than weagle and his crap team lol j/k


Weagle is the best for Palm Beach County.
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Portlight is supported by many WU members, DDR.

So is Surfmom.

You? long walk, short pier, please.

'nuff said.
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300. GBlet
1:39 AM GMT on March 16, 2009
DDR, sorry but surfmom is one of our most respected... SEE YA!
Member Since: September 13, 2007 Posts: 0 Comments: 435
299. beell
1:37 AM GMT on March 16, 2009
Quoting DDR:

LOL--> nonsense,welcome to my ignore list


Welcome to ignorance-a short trip for you, I'm sure...
Member Since: September 11, 2007 Posts: 145 Comments: 16920
298. DDR
1:29 AM GMT on March 16, 2009
Quoting surfmom:
speaking of hurricanes..... Hurricane Ike was good for three things, my Portlight.Org Hurricane T-shirt, a certificate of participation - with my name in Calligraphy by a most special pyrate queen, and my PORTLIGHT.ORG BUMPER STICKER!!!
New to WU? check out Portlight's Blog.
Surf hurricane generated waves? Your pleasure is someone's misery.
Got a blog buddy walking - Donate
No Buddy? Pick a city you love - Donate


LOL--> nonsense,welcome to my ignore list
Member Since: April 27, 2007 Posts: 14 Comments: 1729
297. TampaSpin
1:26 AM GMT on March 16, 2009
I just finished my Picks!
Member Since: September 2, 2007 Posts: 179 Comments: 20448
296. hahaguy
1:20 AM GMT on March 16, 2009
Quoting GeoffreyWPB:
last season i watched channel 10 more than our local stations..


i really only watch them and wpec
Member Since: August 12, 2007 Posts: 2 Comments: 2838
295. GeoffreyWPB
1:18 AM GMT on March 16, 2009
last season i watched channel 10 more than our local stations..
Member Since: September 10, 2007 Posts: 0 Comments: 11538
294. hahaguy
1:15 AM GMT on March 16, 2009
He's better than weagle and his crap team lol j/k
Member Since: August 12, 2007 Posts: 2 Comments: 2838
293. GeoffreyWPB
1:15 AM GMT on March 16, 2009
hi haha...I just can't take John Matthews seriously...watch other stations when serious weather approaches...
Member Since: September 10, 2007 Posts: 0 Comments: 11538
292. GeoffreyWPB
1:13 AM GMT on March 16, 2009
I think I have heard thunder one time in the last five months...That is good though now..parched land, no thunder, no lightning, less threat of fires.
Member Since: September 10, 2007 Posts: 0 Comments: 11538
291. hahaguy
1:09 AM GMT on March 16, 2009
Quoting GeoffreyWPB:
bummer indeed...our local mets still forecasting it...see what they say tomorrow

'Ya john Matthews keeps on say it lol
Member Since: August 12, 2007 Posts: 2 Comments: 2838
290. surfmom
1:08 AM GMT on March 16, 2009
I have a raindance video on my blog -- feel free to activate.
Member Since: July 18, 2007 Posts: 30 Comments: 26536
289. surfmom
1:07 AM GMT on March 16, 2009
speaking of hurricanes..... Hurricane Ike was good for three things, my Portlight.Org Hurricane T-shirt, a certificate of participation - with my name in Calligraphy by a most special pyrate queen, and my PORTLIGHT.ORG BUMPER STICKER!!!
New to WU? check out Portlight's Blog.
Surf hurricane generated waves? Your pleasure is someone's misery.
Got a blog buddy walking - Donate
No Buddy? Pick a city you love - Donate

Member Since: July 18, 2007 Posts: 30 Comments: 26536
288. GeoffreyWPB
1:05 AM GMT on March 16, 2009
bummer indeed...our local mets still forecasting it...see what they say tomorrow
Member Since: September 10, 2007 Posts: 0 Comments: 11538
287. GeoffreyWPB
1:02 AM GMT on March 16, 2009
Redoubt has supposed to have blown months ago...just from reading posts on here...plenty of time to get out of the way...a hurricane coming your way...really not comparable to Redoubt..
Member Since: September 10, 2007 Posts: 0 Comments: 11538
286. TampaSpin
1:01 AM GMT on March 16, 2009
You all better play in the Portlight Charity March Maddness Event.....Heck SurfMom could flip coins on every pick and do better than me probably......LOL
Member Since: September 2, 2007 Posts: 179 Comments: 20448
285. TampaSpin
12:58 AM GMT on March 16, 2009
My friend CCHS is a bet over anxious as i am but, it looks like the Front dries up before it gets to South Florida.....Bummer...:(

Member Since: September 2, 2007 Posts: 179 Comments: 20448
284. GeoffreyWPB
12:57 AM GMT on March 16, 2009
Forecast for West Palm next Weds. thru Friday...about 75% of showers or thunderstorms...Please Rain!!!!!!
Member Since: September 10, 2007 Posts: 0 Comments: 11538
283. surfmom
12:54 AM GMT on March 16, 2009
Quoting TampaSpin:


SurfMom you are so right...hate to live in that condition.....about as bad as earthquakes.


True I'll still take a 'cane -- least I have enough time to get out of the way
Member Since: July 18, 2007 Posts: 30 Comments: 26536
282. surfmom
12:53 AM GMT on March 16, 2009
Quoting KEEPEROFTHEGATE:
only problem being so dry most of what ever falls will run off with ground being compacted so hard unless a 3 or 4 day event with light steady rains occur it may not make much of a difference


Yes, this is true -- it's going to be major runoff -- we need a three day slow soak
Member Since: July 18, 2007 Posts: 30 Comments: 26536
281. TampaSpin
12:52 AM GMT on March 16, 2009
Quoting surfmom:
Not thrilled to see Mama Redoubt waking up again..... every time I think she's old news -- she starts rumbling -- must be soo stressful on the locals


SurfMom you are so right...hate to live in that condition.....about as bad as earthquakes.
Member Since: September 2, 2007 Posts: 179 Comments: 20448
280. surfmom
12:52 AM GMT on March 16, 2009
257 - Moisture heading to FLORIDA???? Please say it is so -- we are sooo parched.... when it rains I am going out and sitting in it, running in it... dancing in it
Member Since: July 18, 2007 Posts: 30 Comments: 26536
279. surfmom
12:49 AM GMT on March 16, 2009
Not thrilled to see Mama Redoubt waking up again..... every time I think she's old news -- she starts rumbling -- must be soo stressful on the locals
Member Since: July 18, 2007 Posts: 30 Comments: 26536
278. surfmom
12:48 AM GMT on March 16, 2009
Wow Orca -- you certainly do have wind..(LOL - sorry) better hope you critter cam stays attached to the house.

Member Since: July 18, 2007 Posts: 30 Comments: 26536
277. hahaguy
12:46 AM GMT on March 16, 2009
I hear ya surfmom an amazing site.
Member Since: August 12, 2007 Posts: 2 Comments: 2838
276. surfmom
12:45 AM GMT on March 16, 2009
saw my first shuttle launch - I whooped so loud the neighbor's came out -- really wonderful to see!
Member Since: July 18, 2007 Posts: 30 Comments: 26536
275. BahaHurican
12:35 AM GMT on March 16, 2009
Quoting zoomiami:
Hi Baha - finally on at the same time. How are you?
I'm fine, even though my internet seems to be freaking out for some reason . . . how's tricks?
Member Since: October 25, 2005 Posts: 19 Comments: 22725
274. TampaSpin
12:15 AM GMT on March 16, 2009
Redoubt Activity - Color Code ORANGE : Alert Level WATCH

Its now back to Orange.....
Member Since: September 2, 2007 Posts: 179 Comments: 20448
273. TampaSpin
12:12 AM GMT on March 16, 2009
Holy smoke look at Redoubt.......



Member Since: September 2, 2007 Posts: 179 Comments: 20448
272. TampaSpin
12:00 AM GMT on March 16, 2009
The Teams are picked and the Tourney is set.....join the Charity Event for the first annual Portlight Charity March Maddness drive! Details are on my Web site if anyone would like to Play for a small Donation and alot of smack talk....LOL

http://tampaspinsweather.webs.com/index.htm

If anyone has any questions email!

Thanks for the Support as someone will be in need this Summer. You can bet on it!

Tim
Member Since: September 2, 2007 Posts: 179 Comments: 20448

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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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