Record high temperatures far outpace record lows across U.S.

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.


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.  (©UCAR, graphic by Mike Shibao.)

This is from the news release of the National Center for Atmospheric Research (NCAR).  The scientific paper itself is here (subs. req’d).  A blog post on this by the NYT‘s Andy Revkin is here.  And NCAR posted a video of lead author Gerald Meehl discussing his findings:

Here are more excerpts from the news release:

“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.”

… If temperatures were not warming, the number of record daily highs and lows being set each year would be approximately even. Instead, for the period from January 1, 2000, to September 30, 2009, the continental United States set 291,237 record highs and 142,420 record lows, as the country experienced unusually mild winter weather and intense summer heat waves.

A record daily high means that temperatures were warmer on a given day than on that same date throughout a weather station’s history. The authors used a quality control process to ensure the reliability of data from thousands of weather stations across the country, while looking at data over the past six decades to capture longer-term trends.

This decade’s warming was more pronounced in the western United States, where the ratio was more than two to one, than in the eastern United States, where the ratio was about one-and-a-half to one.

The study also found that the two-to-one ratio across the country as a whole could be attributed more to a comparatively small number of record lows than to a large number of record highs. This indicates that much of the nation’s warming is occurring at night, when temperatures are dipping less often to record lows. This finding is consistent with years of climate model research showing that higher overnight lows should be expected with climate change.

And that is in keeping with what the scientific models had predicted.  Given that the past projections were right, we should have more confidence in the future ones:

The modeling results indicate 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. The mid-century ratio could be much higher if emissions rose at an even greater pace, or it could be about 8-to-1 if emissions were reduced significantly, the model showed.

The authors caution that such predictions are, by their nature, inexact. Climate models are not designed to capture record daily highs and lows with precision, and it remains impossible to know future human actions that will determine the level of future greenhouse gas emissions. The model used for the study, the NCAR-based Community Climate System Model, correctly captured the trend toward warmer average temperatures and the greater warming in the West, but overstated the ratio of record highs to record lows in recent years.

The scientists made use of an extensive dataset in this analysis:

The study team analyzed several million daily high and low temperature readings taken over the span of six decades at about 1,800 weather stations across the country, thereby ensuring ample data for statistically significant results. The readings, collected at the National Oceanic and Atmospheric Administration’s National Climatic Data Center, undergo a quality control process at the data center that looks for such potential problems as missing data as well as inconsistent readings caused by changes in thermometers, station locations, or other factors.

Bottom line:  We’re still warming, as the science predicted.

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13 Responses to Record high temperatures far outpace record lows across U.S.

  1. K Nockels says:

    I saw figures close to these on the Weather Chanel not that long ago. They said that these figures coupled with extreme weather events occuring with more frequencey are emerging signs of Climate Change. I was so surprised to hear it said on a Cable Station.

  2. MarkB says:

    Interesting study, although if the main conclusion is that the climate is warming, examining records isn’t as useful as examining trends in mean temperature, and at the global scale of course.

    The study does help expose the various individuals selectively highlighting cold weather events and record lows to deny global warming as propagandists. Readers duped by those individuals should demand an apology.

  3. Shannon says:

    Good information. I hope we can get this under control. I think we are impacting the world to a negative and we need to turn it around soon for our grand children.

  4. Jeff Huggins says:

    Joe, although I’ve certainly missed many earlier posts (I only joined in recently), I think it might help, periodically, to try to run posts (from yourself, or guests) that strive to do a better-and-better job of providing the basic explanation of the central causal chain. There is so much focus on temperature itself that many, many, many people (especially non-scientists, but even perhaps many scientists) seem to think that our only way of thinking about climate change, or understanding it as it progresses, is via temperature data. Or, put another way, many people seem to have the impression that temperature data represent our only way of assessing “what’s up” and what we are getting ourselves into.

    Too few people (in the public) understand, with any clarity or weight, the basic chain of causality and the fact that, even if we had no thermometers, we should most likely EXPECT the climate to heat up when we pour CO2 into it, all else equal. I’m not suggesting that every person should become a scientist. But, people don’t see (it’s not well covered in the media) the basic argument put in simple and understandable terms, illustrated with accurate metaphors, and explained clearly. Hydrocarbons (oil/gasoline, gas, coal, etc.) generate CO2 when burned, and a lot of it. That increases the CO2 concentration in the atmosphere (as well as in the oceans). CO2 absorbs energy and converts that energy to heat in the atmosphere (and here, in simple terms, is how, why, and how we know). And etc.

    There is SO much focus on temperatures and statistical analyses of those, in public (media) communications and miscommunications, that one can get the impression that we know nothing, or little, about the causal factors. Very few communications seem to convey the idea that we would be unwise NOT to EXPECT warming, given what we are doing. I’m not suggesting that the temperature analyses shouldn’t be covered. They should, of course. But, in ADDITION to the focus on temperature, I think that science and the media have to keep trying, hard, to convey a simple and clear understanding of the causal chain, i.e., what’s really going on.



    [JR: I do a great deal of posts on warming. I can’t explain everything in all of them. Here I excerpt it at length the NCAR release, linked to Revkin’s piece, and provided 3 follow up links. Many people have asked me for shorter posts! So I’m doing a mix.]

  5. ecostew says:

    The readings, collected at the National Oceanic and Atmospheric Administration’s National Climatic Data Center, undergo a quality control process at the data center that looks for such potential problems as missing data as well as inconsistent readings caused by changes in thermometers, station locations, or other factors.

  6. Steve Bloom says:

    How about some observations, Michael:

    — The Greenland and West Antarctic ise sheets steadily losing mass with an increasing trend.

    — The small glaciers going fast.

    — The atmospheric circulation shifting poleward. (Joe, have you posted on this?)

    None of these could be happening without a substantial increase in global temperatures. But by all means, stay focused on those thermometers.

  7. Paul K says:

    I am interested in the next steps in this research. I would like to see this sequence of analyses and results.

    1. Since more high temperatures are being set, can the data can be mined to look for successive high temperatures in the same region? Would this give some statistical data to support the hypothesis that there are more heat waves?

    2. Is there a link between mortality statistics and heat waves? If so, can a link be established between increased heat waves and increased fatalities?

    3. Research resulting in an analysis linking heat waves to water demands would be helpful.

    4. Is there a link between heat waves and agricultural crop failures? I imagine this is much more complicated, but if rainfall data and heat wave data could be combed, and compared with estimates of crop yields, then perhaps a this link can be established.

    Hopefully the EPA is doing the analysis in points 1 and 2 as part of the work resulting from the lawsuit settlement that required they look at the health impacts of GHG emissions.

  8. Phil Camill says:

    There’s another important issue of the social impacts that extreme heat will bring, which I described in the context of the Meehl article two weeks ago:

    (1)Say so long to your furnace and hello to a new air conditioner
    (2) Chicago 1995: How social disparities lead to environmental disasters

  9. paulm says:

    The combination of hot nights, heatwaves, carbon pricing and peak oil is going to change the way we sleep.

    A peek at whats to come…

    Brazil Power Cut Chaos
    For residents the street was a more comfortable place to spend the evening than sweltering at home

  10. Dan B says:

    Jeff at 4.

    I agree that we should focus more on causality than data sets. Most communications and cognitive science experts agree, particularly based upon cognitive science and communications in the past decade. The emerging consensus is that there is an emotional base for all thought and we are primarily metaphorical in our organization of input. Scientists and mathematicians have a strong metaphorical connection between numbers and data sets and their own personal experience. The general public, the one that seems to increasingly believe that global warming is just a normal weather cycle, does not connect numbers with everyday life experiences. Most can’t even tell which way is north or south, let alone what’s the difference between 50% and 1/4.

    Cause and effect is easier to grasp.

    At the same time research has shown that when you communicate to people the facts about global warming they tune out and turn you off as often as they believe. The most effective method to get skeptics on board is to lead with solutions. This has been focus group tested extensively. Once they’re engaged in the discussion it’s time to talk about ‘Opportunities’: cleaner energy, cool new technologies, reduced dependence upon imported oil, smart direct current transmissions grids (which we should be doing even if we continue burning fossil fuels), etc. The key piece in communication is to finish the discussion with the moral / principled reasons. There are many – security, obligation to generations unborn, caring about people’s well being – are but a few.

    Liberals tend to leave out their moral basis. Cognitive science has demonstrated that it is essential to continually reassert our moral basis if we are to transform both the debate and reverse our path towards chaos.

    Cause and effect, yes, and… Solutions, Opportunities, and Moral Values.

  11. DrD says:

    Dr. Romm,
    Another good and useful post.
    Two things occured to me, though, as I was reading it.
    1. By looking at the contiguous 48 states, the study left out Alaska ,the state where temperatures seem to be rising the fastest. I wonder what the chart would have looked like if that had been included as well. (I realize the study’s parameters; just wondering about how those limits affected the chart.)
    2. If high temperature records continue to be set at a rising pace, that should make us especially nervous, since each record that’s established should be harder to break than the one just broken. Consider this in terms of track and field records, which last longer and longer as the limits of human record setting are (mistakenly) thought to be reached. Each record becomes harder to break and the record holds for a longer period. But in the case of temperature records, the pace of record breaking appears to be going up rather than leveling off.
    Thanks for all you do.

    [JR: Good points. I have also wondered how the statistics would change if they would include Alaska.]

  12. mike roddy says:

    Paul M, #9:

    In India, many people already sleep on rooftops or in the street, since AC is too expensive and concrete block houses are ovens at night. The R value of block housing is low, so AC is not practical even for the middle class.

    India is the hottest place I’ve ever visited, hotter than Texas or Palm Springs in the summer. Try living in 115 degrees and high humidity for a while. In about 50 years, a 4C increase could be 7C in India, since the 4 degree average includes temperatures over the oceans. That means 127F in India, with high humidity. Never mind if crops will grow- by then we will probably have high tech GM greenhouses. The country will be basically uninhabitable, since people drop dead when it’s 127 and humid, especially babies and the elderly.

    This is the world we will be leaving our grandchildren, unless we convert to renewable power, now.

    David Lewis, we need to talk- I’ve moved to Seattle, and can be reached at

  13. Richard Brenne says:

    Since I was told about this study months ago by the scientists involved I’ve been using it with the public in op-eds and talks with considerable success. Today I gave a talk at Lewis and Clark National Park about the climate they encountered relative to the one today, based on Lewis and Clark’s own conscientious records. They regularly calibrated their three thermometers by putting them in boiling water, then in slushy water.

    I concluded my talk with this study, and even many of the creationists and deniers in the audience told me they found this evidence compelling. To me it is one of the best single tools to use, as Bruce Sussman of KOIN-TV just did in one of his recent weather broadcasts.

    Conversely, everyone at every FOX affiliate is evidently told never to mention climate change in any way that makes it appear credible. Evidently the chip Rupert Murdoch has implanted in the brains of each of his employees is doing it’s designed evil task.