Steve Scolnik at Capital Climate analyzed the data from NOAA’s National Climatic Data Center (NCDC) and created the chart above.
So if you live on the East Coast and thought it was unusually warm the last few weeks, you were right. Although “unusual” isn’t what it used to be. As the figure makes clear, this was a very hot summer (see “Third Hottest Summer Globally, Second Warmest for U.S. With Stunning Weather Extremes, Texas Drought Worst in Centuries”).
I like the statistical aggregation across the country, since it gets us beyond the oft-repeated point that you can’t pin any one record temperature on global warming.
If you want to know how to judge whether the 2.8-to-1 ratio for the entire year is a big deal, here’s what a 2009 National Center for Atmospheric Research study found over the past six decades (see “Record high temperatures far outpace record lows across U.S.“):
This graphic shows the ratio of record daily highs to record daily lows observed at about 1,800 weather stations in the 48 contiguous United States from January 1950 through September 2009. Each bar shows the proportion of record highs (red) to record lows (blue) for each decade. The 1960s and 1970s saw slightly more record daily lows than highs, but in the last 30 years record highs have increasingly predominated, with the ratio now about two-to-one for the 48 states as a whole.
So, yes, 2.8-to-1 (along with 2.3-to-1 for 2010) continues the warming trend of the past few decades.
NCAR explained their 2009 findings in a news release:
Spurred by a warming climate, daily record high temperatures occurred twice as often as record lows over the last decade across the continental United States, new research shows. The ratio of record highs to lows is likely to increase dramatically in coming decades if emissions of greenhouse gases continue to climb.
“Climate change is making itself felt in terms of day-to-day weather in the United States,” says Gerald Meehl, the lead author and a senior scientist at the National Center for Atmospheric Research (NCAR). “The ways these records are being broken show how our climate is already shifting.”
The scientific paper itself is here (subs. req’d). And NCAR posted a video of lead author Meehl discussing his findings here. The study looked into the future and found that “if nations continue to increase their emissions of greenhouse gases in a ‘business as usual’ scenario, the U.S. ratio of daily record high to record low temperatures would increase to about 20-to-1 by mid-century and 50-to-1 by 2100.”
Stanford climate scientists forecast permanently hotter summers
The tropics and much of the Northern Hemisphere are likely to experience an irreversible rise in summer temperatures within the next 20 to 60 years if atmospheric greenhouse gas concentrations continue to increase, according to a new climate study by Stanford University scientists….
“According to our projections, large areas of the globe are likely to warm up so quickly that, by the middle of this century, even the coolest summers will be hotter than the hottest summers of the past 50 years,” said the study’s lead author, Noah Diffenbaugh, The study, based on observations and models, finds that most major countries, including the United States, are “likely to face unprecedented climate stresses even with the relatively moderate warming expected over the next half-century.”
I interviewed Diffenbaugh for my book, Hell and High Water, and in 2008 wrote about his earlier work in a post titled, “When can we expect very high surface temperatures?”
Bottom line: By century’s end, extreme temperatures of up to 122°F would threaten most of the central, southern, and western U.S. Even worse, Houston and Washington, DC could experience temperatures exceeding 98°F for some 60 days a year.
The peak temperature analysis comes from a Geophysical Research Letters paper that focused on the annual-maximum “once-in-a-century” temperature. The key scientific point is that “the extremes rise faster than the means in a warming climate.”
The results, depicted above (in °C), are quite remarkable, especially when you consider that this is just the A1B scenario. In 2100, A1B hits about 700 ppm with average global temperatures “only” about 3°C (5 F) warmer than today.
In fact, on our current emissions path, a 3C temperature rise will happen much sooner (see Hadley Center: “Catastrophic” 5–7°C warming by 2100 on current emissions path and M.I.T. doubles its 2095 warming projection to 10°F — with 866 ppm and Arctic warming of 20°F). And remember, the worst-case scenario is that this happens by mid-century [see Royal Society special issue details ‘hellish vision’ of 7°F (4°C) world — which we may face in the 2060s!]
On our current emissions path, these record temperatures could be seen closer to 2060 than 2100:
… values in excess of 50°C [122°F] in Australia, India, the Middle East, North Africa, the Sahel and equatorial and subtropical South America.
As you can see from the map, extreme temperature peaks are only slightly lower over large parts of this country. The study notes:
Such temperatures, if lasting for some days, are life threatening and receive relatively little attention in the climate change debate.
So now the question is, has anybody done an analysis of what global warming could do to intense heat waves that last very long times, weeks or months? The answer is yes, and the results of that study are more worrisome — and it also received relatively little attention.
The November 2005 study in the Proceedings of the National Academy of Sciences, “Fine-scale processes regulate the response of extreme events to global climate change,” found that “peak increases in extreme hot events are amplified by surface moisture feedbacks.” The study looked at the A2 scenario (about 850 ppm in 2100) in the second half of this century (from 2071 to 2095). It examined temperature rise projections, plus “fine-scale processes,” such as how local warming is affected by loss of snow cover and loss of soil moisture. I interviewed the lead author, Noah Diffenbaugh, of Purdue University, for my book.
Houston and Washington, DC would experience temperatures exceeding 98°F for some 60 days a year. Oklahoma would see temperatures above 110°F some 60 to 80 days a year. Much of Arizona would be subjected to temperatures of 105°F or more for 98 days out of the year–14 full weeks. We won’t call these heat waves anymore. As Diffenbaugh told me, “We will call them normal summers.”
And again, that’s not even the worst case, since it’s “only” based on 850 ppm.
The definitive NOAA-led U.S. climate impact report from 2010 warns of scorching 9 to 11°F warming over most of inland U.S. by 2090 with Kansas above 90°F some 120 days a year with 850 ppm. By 2090, it’ll be above 90°F some 120 days a year in Kansas — more than the entire summer. Much of Florida and Texas will exceed 90°F half the days of the year. These won’t be called heat waves anymore. Again, it’ll just be the “normal” climate.
And remember, high heat means dry areas become drier and humid areas become intolerable.
On our current emissions path, we may well exceed the A2 scenario and hit A1FI, 1000 ppm (see here). In a terrific March 2010 presentation, Climate scientist Katherine Hayhoe has a figure of what the A1FI would mean:
Mother Nature is just warming up.
The time to act is yesterday.
- Science stunner — On our current emissions path, CO2 levels in 2100 will hit levels last seen when the Earth was 29°F (16°C) hotter: Paleoclimate data suggests CO2 “may have at least twice the effect on global temperatures than currently projected by computer models”