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Posted at 10:30 AM ET, 08/24/2009

Climate Study Projects Hotter Augusts for D.C.

By Andrew Freedman

* A Very Warm Week: Full Forecast | NatCast *

Washington, DC like Orlando from Climate Central on Vimeo.

August in the Mid-Atlantic is notorious for its heat and humidity, which has long driven an annual exodus of official and unofficial Washington to cooler destinations. It's no accident; after all, that Congress takes the month of August - and not say October - off. According to a new analysis by the nonprofit organization Climate Central, by the middle of this century climate change is likely to make August in Washington significantly hotter and more uncomfortable, making the congressional schedule even more enviable.

During the 1980s and 90s, the report found, there were an average of ten August days in D.C. that reached or exceeded 90 degrees (this year, we've had tem). Yet by the 2050s, that number may jump to an estimated average of 19 days - a 90 percent increase.

According to Climate Central, which is a nonpartisan and nonadvocacy group, August days with a high temperature above 95°F have been relatively rare occurrences, with an average of just three such days per year during the 1980s and 90s. But by the 2050s, such days could be much more commonplace, with a best guess average of about ten such days per year during that decade. And the average number of August days at or above 100°F - which was zero in the 1980s and 90s - is projected to increase to an average of three days during the 2050s.

Climate Central's study examined August extreme heat in 20 other major U.S. metropolitan areas as well, and found that extreme heat is likely to become more frequent and intense in nearly all of the cities studied.

For example, at present there are only two cities on the list where more than half the days in an average August exceed 95°F. These are Phoenix and Dallas, which are both well known for their brutally hot summers. But by the 2050's, Climate Central scientists found that Houston, Sacramento, Tampa Bay and Orlando could join them on that list.

Dr. Ben Strauss, Climate Central's Associate Director for Strategic Initiatives, cautioned that the numbers should be taken as best guesses within a range of uncertainty, and that they are estimates of averages. "No matter how close the projections turn out to be, some years will have more hot August days, and others will have fewer," Strauss stated.

The analysis reinforces a broader result from climate science that large changes in extreme weather events can result from a relatively small amount of global warming. The likelihood that a warming planet will lead to more frequent, severe and longer lasting heat waves in the United States (as well as other extreme weather events) was detailed in a federal climate science assessment published last year.

Climate Central's study is based on findings from a dozen computer models that were used to simulate future climate conditions under a scenario of greenhouse gas emissions that is lower than the current trend. So far this decade, global emissions of these gases, such as carbon dioxide, have actually been outpacing the emissions scenario used for the study. All twelve computer models projected increased hot days from the present by the middle of the century.

Climate Central discusses its methods in detail on its web site, where it has also posted animations for the other cities in the report.

Disclaimer: Andrew Freedman worked as a graduate student intern at Climate Central this summer, where he helped write the results of the extreme heat study. He did not conduct the technical research (i.e. the modeling) that went into the report.

By Andrew Freedman  | August 24, 2009; 10:30 AM ET
Categories:  Climate Change, Freedman, Science  
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I just ran the numbers for 2000-2009 (and assume no more >95 days this month) and our average is (drum roll) 2.5 days in August above 95F. So the mean for the 1980s and 1990s is unchanged in the 2000s. Four summers had no occurrence (2008, 2004, 2003, 2003). Andrew, do they discuss a tipping point when we should expect these increased 95+ days to occur in DC? Maybe the 2040s? Or will it accelerate in the very next decade? Thanks!

Posted by: MattRogers | August 24, 2009 11:18 AM | Report abuse

There are no crystal balls. The climate scientists themselves say their own computer models are significantly unreliable and incomplete. I've extracted their concerns from the climate model chapter of the IPCC's Climate Report 2007 and posted them at After reading the scientists own words do you think we should restructure our energy economy based upon computer models?

-- Robert Moen,

Posted by: Rmoen | August 24, 2009 11:20 AM | Report abuse

Correction, 2000 was the fourth non-occurrence.

Posted by: MattRogers | August 24, 2009 11:40 AM | Report abuse

Matt, stop confusing the issue with facts. You are hereby reprimanded by the forces of good at WaPo.

Posted by: mcoghlan | August 24, 2009 11:44 AM | Report abuse

Matt - I will direct your question to a Climate Central scientist to get an answer for ya.

Rmoen - while computer models cannot offer definitive predictions of the future climate, they do shed light on key trends. Without such models, scientists would have little way to study how the climate system may respond to different scenarios of increasing greenhouse gas emissions, since there is no other Earth to play around with. Climate Central used a dozen well-established models in order to limit some of the uncertainties in their results. While all computer model results (both for weather and climate) should be taken with a grain of salt, they cannot be dismissed simply because there are uncertainties involved.

Also, it's worth noting that climate science relies on much, much more than just climate models. For example, scientists are examining physical science evidence of a changing climate, from tree rings to glacial ice cores, to get a clearer picture of our changing planet. Computer models are just one tool in the scientists' toolbox.

Posted by: Andrew-CapitalWeatherGang | August 24, 2009 11:51 AM | Report abuse

Thanks Andrew. Another quick question- why did they choose the 2050s? Was there perceived better skill by that time point compared to say the 2040s? Thanks! -Matt

Posted by: MattRogers | August 24, 2009 11:59 AM | Report abuse

Computer models show what the computer modeller wants them to show. These guys project that an increase in CO2 produces a concomitant increase in water vapor, and they also project that an increase in water vapor produces higher temperatures. Neither of these are proven assumptions, and in fact it is more likely that an increase in atmospheric water vapor content would lead to cooling, as it produces increased cloud cover, which relflects sunlight. The worst part is, they never mention this, they never tell anyone how much they really don't know. We had the coolest summer on record here in Chicago, as did most of the Midwest.

Al Gore should give back his Nobel Prize. Global warming? Prove it!

Posted by: mikermoon | August 24, 2009 12:14 PM | Report abuse

There have been some unusual patterns in DC July/August temperatures in the current decade. No clear indication of a connection to global warming, however.

Posted by: CapitalClimate | August 24, 2009 12:29 PM | Report abuse

My experience here is that August can be HOT and NASTY!!!

I can remember several days over 95F and even over 100F during the past thirty-five or so years.

Greenhouse gases aren't the ONLY cause of our local warming effects. The Metro area's abundant coterie of overeager contractors & developers has to shoulder a MAJOR portion of the blame for paving over green space with yet more concrete and asphalt, making us a HEAT ISLAND par excellence! You're seeing it everywhere this summer: the HOT lanes projects on the Beltway, the Intercounty Connector, the various construction projects [in the heart of what's supposed to be a RECESSION for crying out loud!]. There's a shining example right near me on South Jefferson Street off Columbia Pike, the new addition to the Baileys Crossroads Goodwin House. Over the past three years, these contractors removed some 100+ ash trees and lots of other shrubbery and woods and replaced it with a concrete eyesore with added parking garages. The whole thing, added to Skyline and the rest of this neighborhood has created a gigantic HEAT ISLAND which will likely make our summers in Baileys Crossroads up to three degrees HOTTER on the Fahrenheit scale. One further note here is that since I live in Arlington County, I couldn't input anything into the zoning hearings which were held in FAIRFAX County. Nevertheless this concrete eyesore will impact my climate for years to come. In closing I have to note that a lot of the forest cover around Baileys Crossroads which wasn't in the park system has disappeared in my thirty years of living here, and I'm afraid the developers may be casting hungry eyes on the parkland. Boy it sure would be nice to replant some of that greenery.

Posted by: Bombo47jea | August 24, 2009 12:35 PM | Report abuse

Matt, to address your questions:

This analysis did not go into any details of decade-by-decade timing. The estimates for the 2050's are based on climate model outputs from the period 2046-2064, which is a standard interval over which daily outputs from the scientific community's leading models have been archived to allow further analyses, such as this one. (Data storage costs and logistics prevented the archiving of daily model outputs for every year of this century--and the analysis we did required daily outputs.)

Beyond this point, these projections--and any climate projections you ever see--should never be regarded as predictions for a particular year or even decade. Natural variability pushes temperatures up and down in unpredictable ways at both annual and decade-long time scales, and can throw any projection off. Instead, the projections reflect our best guess of the average trend and where it is headed. It would not be surprising at all if the decadal averages published are reached earlier, or later, than the 2050's.

Posted by: BenStrauss | August 24, 2009 12:37 PM | Report abuse

Thanks so much Ben for the study clarifications. From this study, we have an idea where temperatures may be in the middle of this century, but unsure of how it gets there (gentle slope or steep increase by a certain "tipping point" decade). And these were statistical, not dynamical models I gather?

Posted by: MattRogers | August 24, 2009 12:45 PM | Report abuse

"coolest summer on record here in Chicago":
If you're quoting irrelevant weather factoids, you might as well get them correct. Second-coolest July since 1942 isn't exactly the same thing as coolest summer of all time, especially when June was barely below average and August so far has been above. If you want to look at real extremes for this summer, try Texas, Arizona, and the Pacific Northwest.

Posted by: CapitalClimate | August 24, 2009 12:49 PM | Report abuse

One note: The party responsible for Goodwin House seems to be the Episcopal Diocese of Northern Virginia. Generally the Episcopal Church has a better track record on environmental issues than their recent work at Goodwin House-Baileys Crossroads has shown thus far.

In addition to the trees I mentioned, they also destroyed their lawn and landscaping shrubbery to build this high-rise heat island and its accompanying concrete platform. They really need to add more greenery when they finish this project.

Posted by: Bombo47jea | August 24, 2009 12:52 PM | Report abuse

Capital Climate: here are the state-by-state ranks by NCDC for July. Several Midwest states were the "coolest" of 115 years per their estimates.

Posted by: MattRogers | August 24, 2009 1:05 PM | Report abuse

Matt: Given the data you provided (10 years, average 2.5, 4 years with zero) it looks like any given year has a standard deviation of about 3 for 95+ days. Given that, in a 10 year period you expect the average to have a standard deviation of 3/sqrt(10) or about 1.

Climate Central projects an increase of 7 95+ days over 65 years, or about 1/decade, which would be 1.5 from 1990 to 2005 if we assume linearity. A priori one would actually expect acceleration over time - both due to statistical effects of shifting a normal distribution, and because global mean temperatures in BAU scenarios are not linear - so I'd actually expect it to be significantly less than 1.5. But if we assume 1.5, then the "climatic mean" decadal average for 95+ days would now be 4.5, with expected 95% bounds of 2.5 to 6.5.

This also assumes that you are using the same weather station that Climate Central was using (which neither you nor they specify), doesn't take uncertainty into account for the forecast increase, and probably underestimates weather noise in the system.

Posted by: marcusmarcus | August 24, 2009 1:06 PM | Report abuse

Thanks Marcus, good point. I was using DCA (National Airport), but not sure of their data point for the study. Since 2000-2009 is only 2.5 (and not 4.5) and the last five years is only 2.0, are we behind schedule already!?

Posted by: MattRogers | August 24, 2009 1:11 PM | Report abuse

Please read my entire comment.

Posted by: CapitalClimate | August 24, 2009 1:14 PM | Report abuse

I just finished the 1980s and 1990s for DCA (and someone please check my math), the August 95+ day mean for DCA is 2.9 (1980s) and 2.3 (1990s) compared to our current decade's 2.5 (2000-2009).

Posted by: MattRogers | August 24, 2009 1:15 PM | Report abuse

I was trying to note that the increase was less than the mean expected increase using some very simple extrapolation techniques, but well within the noise of the system. For the case of 95+ days in the DC the noise in a 10 year average is just too large to be able to say much, given the size of the expected signal.

Posted by: marcusmarcus | August 24, 2009 1:58 PM | Report abuse

Marcus, you're correct about the noise issue. It seems every decade has about one year that blows the numbers right the 2000s it was 2002. If it weren't for that one year, we'd be considerably below the 1990s and 1980s on that mean. The 1980s actually had 5 no-hit Augusts, but it also had two blow-out years like it evened out anyway! But when working with relatively small numbers, your point about a high standard deviation makes sense.

Posted by: MattRogers | August 24, 2009 2:20 PM | Report abuse

One of the important implications of the Climate Central analysis is that major cities in the U.S. really need to be thinking about how they will adapt to warming conditions, with more common, extreme, and longer lasting heat waves. (This is notwithstanding the back and forth taking place here regarding the report's numbers, since many other studies support the projection that extreme heat will become more prevalent).

Does anyone have any ideas for practical ways to minimize the impacts of extreme heat in the future, short of following Congress' lead and getting out of town?

Posted by: Andrew-CapitalWeatherGang | August 24, 2009 4:45 PM | Report abuse

FWIW, I expect that DioVA will do significant replanting when all is completed. The ash trees were probably taken down en masse as much due to the problems with Emerald Ash Beetle as because they were in the way, so I would expect another species to be chosen as replacement.

There is an active diocesan committee on "stewardship of creation" which will push for replanting if it isn't already in the works.

Posted by: fsd50 | August 24, 2009 6:18 PM | Report abuse

I view any results based on regional output from global "projection" models, let alone local projections from the regional ones, as being no more credible than attempting time travel.

I have not read through the details of Climate Central's study, but it's difficult for me to believe that any realistic estimates of uncertainty would be sufficiently narrow to enable uncovering a meaningful signal.

I am a firm believer that the globe overall is warming and likely to continue to do so for decades to come. However, as someone quite familiar with global models and procedures for "downscaling" output of those models to limited areas, I feel justified in stating that sweeping statements about local climate change based upon TODAY's climate models and "post-processing" the output is likely considerably more misleading than helpful. Moreover, it does a disservice to the credibility of climate science to presume otherwise

Posted by: SteveT-CapitalWeatherGang | August 24, 2009 9:09 PM | Report abuse

Steve - I think the key statement in your comment may be: "I have not read through the details of Climate Central's study..." I'm curious to see your comments after reading the methodology.

Posted by: Andrew-CapitalWeatherGang | August 24, 2009 10:17 PM | Report abuse

Thankfully, Climate Central will be lavishly nurtured financially, by folks like Wendy Schmidt and her Schmidt Family Foundation. Wendy is of course married to one of the wealthiest men in America. There will be no need for sustenance from the public trough. Wendy throws millions of dollars around at various ventures as if mere peanuts and is quite opinionated about many issues. One focus for her is transforming "public perceptions about the climate crisis". Which climate crisis?????

Also, when folks like Heidi Cullen have been involved with sheepherding the agenda of Climate Central, nothing more need be said.....or read.

Posted by: AugustaJim | August 25, 2009 9:45 AM | Report abuse

Oh man, more 90 degree days... guess I'll just have to go to the pool more often

Posted by: tengoalyrunr30 | August 25, 2009 11:43 AM | Report abuse

Bombojea47 makes some good points, but focuses a little too narrowly on developers and contractors.

To be sure, they deserve a major piece of the blame.

But let's not forget the politicians they help elect, who pose as climate champions then build the kinds of highway projects that Bombojea47 lists.

And let's not forget the Washington Post and its wholly owned subsidiary, The Gazette, who shamelessly shill for just about every highway in the region and fail to report the facts -- all while the Post hypocritically wags it figure at Congress or the White House.

Rajendra Pachauri, the head of the Intergovernmental Panel on Climate Change just endorsed the goal of reducing atmospheric concentrations of CO2 equivalents to 350 parts per million, the same goal set by Jim Hansen at NASA.

We're currently at about 390 ppm -- well above the pre-industrial level of about 270 ppm, and rising fast.

So what does Martin O'Malley do?

* Embraces a project that was fast-tracked by George Bush and Bob Ehrlich under false pretenses.

* Hides behind the Bush-Ehrlich Environmental Impact Statement, which contains no greenhouse gas impact analysis and devotes a total of 3.75 pages to "Climate". That's "Climate", not "Climate Change", and that's 3.75 pages out of more than 10,000 or so.

* Commits more than $3 billion to an 18-mile highway that studies show will do little to relieve congestion, is projected to increase driving by 700 million miles per year, will directly destroy about 800 acres of forest, and will trigger thousands of acres of sprawl, which will destroy more forests and trigger more driving.

* Omits from his Climate Change Plan a science-based recommendation to halt spending on the ICC until Maryland assesses its greenhouse gas impacts.

* Opposes General Assembly legislation that would have halted work on the ICC until the Maryland had assessed its greenhouse gas impacts. In fact, the O'Malley administration opposed this bill even if were amended to allow construction to continue during the analysis.

* Claims that our greenhouse gas emissions would be lower if Maryland had built the ICC. No credible study supports that assertion.

O'Malley's driving the bus blind-folded. It's clear we're headed for a cliff. So he keeps the blind-fold on and steps on the gas.

Posted by: gpsmith1 | August 25, 2009 2:51 PM | Report abuse

AugustaJim: By your logic it would seem that the work of an organization should be dismissed if that group receives any money from a foundation headed by a wealthy individual. That would essentially eliminate most nonprofits in this country from public debate, including many think tanks that agree with your viewpoint that climate change is not something to worry very much about.

Posted by: Andrew-CapitalWeatherGang | August 25, 2009 4:09 PM | Report abuse

Hey Andrew,

Interesting findings. Thanks for the info. I am really glad Dr. Strauss emphasized the word projection in the comment section. Because many people think that a climate projection is equivalent to a climate prediction, which it is not.

To answer your question, "Does anyone have any ideas for practical ways to minimize the impacts of extreme heat in the future, short of following Congress' lead and getting out of town?"

ANSWER: ---> Paint all the buildings and roads white. ;)



Posted by: meteoscott | August 25, 2009 6:04 PM | Report abuse

Scott - Energy Secretary Stephen Chu has proposed just that, actually. Sounds like a funny idea at first, but it makes a lot of sense, although I don't think Dr. Chu intended it as a formal policy proposal.

Posted by: Andrew-CapitalWeatherGang | August 25, 2009 8:35 PM | Report abuse

Hello my friend!

I am simply observing that some elitist's who have haunted this blog during the past several years have been quick to denounce information because of the source. Always consider the source, we have been counciled to believe.

Considering the source and that influence on Climate Central, the results are so very predictable, therefore tainted, and rather useless.

I don't give credibility to people or "think tanks" on either side of this issue that are predictably biased.

Regarding my viewpoint: I am still searching for the truth! I don't buy a mindset because of personal inclination.

That would be and is somewhat foolish.

Posted by: AugustaJim | August 25, 2009 9:08 PM | Report abuse


Dr. Chu was criticized for those comments when It is actually a valid hypothesis that should be tested. Dr. Chu should find a small/medium sized city willing to allow federal dollars to fund an experiment painting white buildings and building lighter colored roads. We can model these changes in reflectivity, but it would be interesting to observational measure how it would change the diurnal cycle, radiational cooling and temperature gradients with surrounding areas. You would think this it would have been done already... Has it?

Just a thought.



Posted by: meteoscott | August 26, 2009 7:50 AM | Report abuse

AugustaJim: You wrote "Considering the source and that influence on Climate Central, the results are so very predictable, therefore tainted, and rather useless." As I noted in the article, I have worked with Climate Central. I have seen absolutely zero evidence that they are pushing any agenda other than communicating accurate scientific information in a politically neutral fashion. If I had seen such evidence, I would've left the group, because I have dedicated my entire young career to communicating politically neutral science and policy information to the public.

BTW, Climate Central was not the brainchild of some liberal activist, but actually was conceived by a large group of top climate scientists who gathered several years ago under the auspices of Yale University.

Posted by: Andrew-CapitalWeatherGang | August 26, 2009 3:04 PM | Report abuse

MeteoScott, yes, Sec. Chu was in fact ridiculed for discussing the white buildings idea, despite it's merits. To the best of my knowledge, there have not been any projects to implement the proposal in the U.S. Perhaps other readers may know of something I don't in this area, though.

Posted by: Andrew-CapitalWeatherGang | August 26, 2009 3:06 PM | Report abuse

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