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 study came up on the press call.  The key point is that you can’t draw conclusions about the climate from any single weather event, but instead need to do statistical analyses across large regions to understand what is happening.


I blogged on this study 3 months ago, but when I mentioned it on the call, the journalist hadn’t heard about it.  It is timely to repost especially since I’ll be doing a lot of media in the next few days and sending people to this website.  Apologies to regular readers for the repetition, but you’re going to see more in the coming days as it’s increasingly we need to start over on explaining the science to the media and public.

And yes it is worth noting, as one reader did, that the study left out Alaska, the state where temperatures are rising the fastest.  Including it would likely have increased the trend.

Here is an explanation of the figure, followed by a video by the lead author discussing it:

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).  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 — and we’re seeing more record high temperatures — as the science predicted.

Oh, and for the anti-science crowd out there who bought the myth pushed by former TV weatherman Anthony Watts that “bad” U.S. temperature stations overestimate recent warming — see Watts not to love: New study finds the poor weather stations tend to have a slight COOL bias, not a warm one.

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

  1. John McCormick says:

    Very interesting chart.

    I know something about US electric power generation expansion using cheap and dirty coal (unscrubbed without precipitators)following the end of WWII and tracking the rapid expansion of US industrial output and home ownership.

    The heavily polluted air prior to enactment and enforcement of the Clean Air Act followed by acid rain control in the early 1990s can be an explanation for the dip in temperatures during the 1960s and 1970s.

    It is said the Asian Brown Cloud is masking about a half degree Centigrade temperature increase and as China and India improve their air quality, temperatures in Central and South Asia will increase.

    And, yes, Mt. Pinatubo had a year-long impact on temperatures in the Northern Hemisphere.

    In my view, polluted air in post-war US explains the dip in the chart.

    John McCormick

  2. Michael T. says:

    This is a great study about the long-term U.S. temperature changes. It should make clear to people that cold weather will continue to happen even in a warming climate. I want to let everyone know that I’m new to this blog, and that my interest is mostly in the science. Everyone is welcome to check out my YouTube channel, which is about climate change science and the environment. I think climate progress is the best.

  3. La Quiro says:

    This is an extremely short term study. Of course we have many less readings over 50 years ago.

  4. Leif says:

    La Quiro, #3: Short term study but with lots of data points condensed into an obvious trend.

  5. MapleLeaf says:

    La Quiro,

    Approx. how old is the earth?

  6. PurpleOzone says:

    Air pollution in the U.S. has noticeably increased in the last few years; I suspect due to Asia.

    Cerulean blue, cloudless skies occur infrequently now and only after a lot of heavy precipitation. Most the sky is full of dingy white clouds and jet contrail streaks, in the absence of any rain clouds.

    Whether the chronic cloudiness adds heat or reflects it, I don’t know.

  7. Harold Brooks says:

    #3. No, this study used stations that existed for the whole time period, so that the number is same every year (~1800). The recent change in the ratio is a result of the decreasing number of minimum temperature records (the number of records in the post-2000 period is approximately what would be expected by chance.)

  8. slanted tom says:

    Can our civilization really collapse from ever increasing ‘bad weather’? Probably. Bad weather is usually just ‘unseasonable’ weather, but has now become a manifestation of climate change. This is just the sort of thing you are studying. Excellent, and thanks.

  9. True Science says:

    How does one answer the charge that this report may be flawed ab initio, because the temperature data that it relies on has built-in warming biases. For example, the 0.5 degree celsius warming bias that was introduced with the HO-83 thermometers in the mid to late 1990’s, which undoubtedly contributed to the number of record highs in the 2000’s, the migration away from the old instrumentation to automated sensors that do not meet the WMO siting requirements, which further enhanced the urban heat-island effect, and the arbitrary selection of end dates, to name a few?

    [JR: I’ll be patient here and assume that you aren’t a concern troll. Try reading the WHOLE post and go to the link to the actual scientific study that answers your questions! The temperature data does not have built-in warming biases — in fact, the “bad” temperature stations appear to have a built-in cooling bias!]

  10. MarkA says:

    “study left out Alaska, the state where temperatures are rising the fastest”

    Don’t think so…temperatures in Alaska have been stable for at least 30 years:

    In fact temperatures from 2006-2009 were among the coldest in the past 30 years!

  11. EricG says:

    It would be interesting to see the same analysis for the converse records: the lowest high temperatures and the highest low temperatures. This would show whether warm nights are getting warmer and cool days no longer as cool as they once were.

  12. Peter Bellin says:

    Looking at the figure, I think it is reasonable to conclude that it is likely that new record low temperatures will continue to be set in the coming decades.

    The researchers can probably conduct some trend analysis, and predict a future decade when the number of record low temperatures will fall to a statistically insignficant number. In other words, although sometime in the future, if temperatures continue to increase, the number of record low temperatures reported will be a small value

    I don’t know if such a situation will arise, even with several degrees increase in temperatures, since the weather variation is so large.

    The figure is a good demonstration of the fact that individual temperature extremes will not invalidate (or validate) climate change, but the trend demonstrated above is clearly supportive of climate change.

  13. Peter Bellin says:

    Mark A says temperatures in Alaska have not changed, but see the link here, obtained in a google search:

    A table included there shows that the larger temperature increases were in the polar (northern) regions.

  14. Lore says:

    #14 macia

    This gets to be a rather tiresome drumbeat from the denial crowd. If you can’t refute the science with facts, then suggest conspiracy, dishonesty and poor record keeping.

    Rather then make spurious accusations how about refuting the science with some peer-reviewed science of your own?

  15. Harold Brooks says:

    #13: The site you show says basically the same thing that MarkA’s figure shows: little change since ~1980. The text on your site does say that Barrow has seen an increase since then, but the table gives data from 1949-2008, while MarkA’s figure starts in 1980. Looking at MarkA’s figure and the time series figure in U of Alaska web site, they’re close to the same. There’s a different number of stations and perhaps a different way of getting a state-wide average, but the two figures are within the uncertainty of each other.

  16. MapleLeaf says:

    Re Alaska,

    I hope this link works,

    If not go to NASA GISS and select based period 1971-2000, and then plot trend (wrt that base) for 1971-2009.

    The data show that since 1971, the mean annual temperatures over Alaska have warmed by 1-2 C relative to the 1971-2000 based period.

    There sure is a lot of positive anomalies on that map, especially the high latitudes of the N. Hemisphere!

  17. MarkA says:

    #16 Sorry, the data speaks for itself. The mean statewide temperature across Alaska shows no warming trend over the past 1/3 century extending back to 1977. There was a rather abrupt climate shift in 1977 related to changes in the Pacific Ocean circulation called the PDO. Download the DS3220 dataset from NCDC and do the analysis yourself, if you don’t believe me.

  18. George says:

    MarkA you are quiet confused as it seems. Visit the link from 16#.

  19. MapleLeaf says:

    MarkA, those data represent the temperature trends between 1971 and 2009. I really should not need to spell this out for you. Annual temperatures in Alaska have warmed between 1971 and 2009. This is corroborated by lower tropospheric satellite data (channel TLT). I’m not convinced that you completely understand what an anomaly is or how is is calculated.

    Additionally, internal climate modes (e.g., PDO, ENSO and NAO) do not explain all the warming that we have experienced globally. For example, read Swanson et al. (2009, PNAS), they conclude:

    “Here we present a technique that objectively identifies the component
    of inter-decadal global mean surface temperature attributable
    to natural long-term climate variability. Removal of that
    hidden variability from the actual observed global mean surface
    temperature record delineates the externally forced climate signal,
    which is monotonic, accelerating warming during the 20th century.”

    Also, look at their Fig. 3.

  20. Michael T. says:

    It should also be pointed out that the PDO, AO, ENSO etc. are oscillations. Meaning they redistribute heat within the climate. They don’t add heat to the atmosphere over time like GHGs do. Therefore the PDO, for example, has no effect on the background warming of GHGs of the global mean temperature. These natural variability are still happening, except now on a long-term warming trend. That is the way that I come to understand it.

  21. MarkA says:

    #19 Read the quote again, “study left out Alaska, the state where temperatures are rising the fastest”. Rising is present tense. But I have just shown there has been no warming in Alaska for the past 1/3 century. His statement is simply incorrect.

  22. MapleLeaf says:

    MarkA, we seem to be getting our wires crossed. The GISS data do show cooling over N. America, including AK between 2006 and 2009. However, when climatologists talk about temperature trends they are referring to long-term trends (typically 30 yrs), so it is appropriate to use the *present tense* to refer to the current period for which the long term trend has been calculated. It is absolutely pointless calculating trends for periods of time less than 15 years if you wish to extract a stat. sig. long-term change in SATs. There are some very valid scientific and statistical reasons for using 30 years in order to calculate trends in SAT data which are stat. sig.

    These data are for 1977-2009, the period during which you allege AK has not warmed, show warming over AK, and that the warming over AK was greater then over the lower 48:

    This warming is corroborated by independent satellite data for the lower troposphere for the period 1979-2009 (not these data are not surface temp data):

    MichaelT @ 20, as far as my knowledge goes your understanding summarized bove is correct. Lord Monckton would disagree with you though– in Australia today, in a debate with Dr. Lambert, Monckton attributed EL Nino events to undersea volcanoes in the western equatorial Pacific which just happen to erupt every 4 years. He seems oblivious to the role of the so-called delayed oscillator effect following westerly wind bursts and to the impact of eastward propagating Kelvin wave on ocean temperatures. that and the fact that the TAO/TRITON buoys show the positive anomalies to *develop* in the top 100-200 metres below the ocean surface.

  23. Dano says:

    Apparently the melting permafrost in AK and the collapsing infrastructure on top of it are not listening to Mark A! Sacre Bleu! Mark A, quick, fly to Alaska and tell the permafrost it needs to re-freeze as it isn’t any warmer there! Hurry! The Public Works people’s budgets will thank you too!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! *heart!*



  24. Derecho64 says:

    I know that further research on this topic will include a weighted scheme to measure record temps. For example, a record high temp that is also a new all-time high, breaking a (say) 100-year-old record, will be given greater weight.

  25. Mark says:

    If it’s true that record highs have outpaced record lows, then show us the data and the facts. It’s one thing to make up a graph showing whatever one wants but another thing entirely to give us the beef. Show me all the info, I don’t care how many pages of data and stuff it takes up. Where’s the beef? Any idiot can make claims and draw up a graph in a spreadsheet, but please back it up. At they list all the record lows from many sources including weather sites, radio and TV stations and the like. All very reliable sources and difficult to dispute. Why can’t this site do that with their so-called record highs? Well, I think I know why!! Because they can’t show very many examples, that’s why. had hundreds of examples of record lows that they show and back up with facts.

  26. Oxford Kevin says:


    Why don’t you e-mail the authors and ask for the data. The e-mail addresses and contact phone numbers for the scientists who published the work are available from the link at the top of this piece. Let us know how you got on. If you do e-mail the scientists let them know you might be publicizing their response here, it is only polite to let people know when what they write might be made available for public consumption.

    Not quite the same but the UK metoffice for the central england temperature (The longest temperature instrument record in the world, 351 years) have nicely organized their data so that one version of it is sorted by ranking of coldest to hottest months and years.

    You can see the various forms the data can be downloaded here:

    The ranked average temperature series can be downloaded here:

    The lowest ranked month for any in the noughties is December 2009 at a ranking of 98. But what is disturbing is just how many of the months of the noughties have some of the highest rankings.