UPDATE: Tornadoes, Extreme Weather And Climate Change, Revisited

“Likely …. the most prolific five-day period of tornado activity on record for so early in the year

NBC: “It’s as if a huge chunk of the country has suffered a deep, deep scar.”

National Weather Service Warnings for Past Week

The unexpectedly fierce and fast tornado outbreak so early in the season has folks asking again about a possible link to climate change. Climatologist Dr. Kevin Trenberth emailed me that, because of climate change, “there is every expectation that the [tornado] season will move up in time.  The warm winter in the US is perhaps an indicator of the nature of the changes to be expected.”

The former head of the Climate Analysis Section of the National Center for Atmospheric Research stands by his 2011 statement, “It is irresponsible not to mention climate change in stories that presume to say something about why all these storms and tornadoes are happening.” Below is some clarification of the context of that quote that he added. Trenberth also said:

Joe, what we can say with confidence is that heavy and extreme precipitation events often associated with thunderstorms and convection are increasing and have been linked to human-induced changes in atmospheric composition.

Insured losses due to thunderstorms and tornadoes in the U.S. in 2011 dollars. Data and image from Property Claims Service, Munich Re.

After April 2011 saw records set for most tornadoes in a month and in 24 hours, I examined the link in great detail here, looking at the data, the literature, and expert analysis.  That piece concluded:

  1. When discussing extreme weather and climate, tornadoes should not be conflated with the other extreme weather events for which the connection is considerably more straightforward and better documented, including deluges, droughts, and heat waves.
  2. Just because the tornado-warming link is more tenuous doesn’t mean that the subject of global warming should be avoided entirely when talking about tornadoes.

This post will run through the scientific literature along with some analyses from this year and last by leading experts.

First, though, some of the details on this week’s tornado outbreak.

MONDAY UPDATE: USA Today has a good piece, “Warm winter helped fuel tornado outbreak,” which cites today’s post by Weather Underground meteorologist Dr. Jeff Masters

This year’s unusually mild winter has led to ocean temperatures across the Gulf of Mexico that are approximately 1°C above average–among the top ten warmest values on record for this time of year, going back to the 1800s. (Averaged over the month of February, the highest sea surface temperatures on record in the Gulf between 20 – 30°N, 85 – 95°W occurred in 2002, when the waters were 1.34°C above average). Friday’s tornado outbreak was fueled, in part, by high instability created by unusually warm, moist air flowing north from the Gulf of Mexico due to the high water temperatures there. This exceptionally warm air set record high temperatures at 28 airports in Louisiana, Arkansas, Mississippi, Alabama, Tennessee, Kentucky, and Georgia the afternoon of the tornado outbreak (March 2.) Cold, dry air from Canada moved over the outbreak region at high altitudes. This created a highly unstable atmosphere–warm, low-density air rising in thunderstorm updrafts was able to accelerate rapidly upwards to the top of the lower atmosphere, since the surrounding air was cooler and denser at high altitudes. These vigorous updrafts needed some twisting motion to get them spinning and create tornadoes. Very strong twisting forces were present Friday over the tornado outbreak area, thanks to upper-level jet stream winds that blew in excess of 115 mph. These winds changed speed and direction sharply with height,imparting a shearing motion on the atmosphere (wind shear), causing the air to spin. High instability and a high wind shear are the two key ingredients for tornado formation.

Here’s more from Masters on the record-setting storms:

A key ingredient for tornado formation is the presence of warm, moist air near the surface, which helps make the atmosphere unstable. On the day of the March 2, 2012 outbreak, record warm air surged northwards into the tornado formation region, setting or tying daily high temperature records at 28 airports in Louisiana, Arkansas, Mississippi, Alabama, Tennessee, Kentucky, and Georgia.

The March 2 – 3 tornado outbreak: one EF-4, 39 deaths

The violent tornado rampage killed 39 and injured hundreds more, wreaking property damage that will likely exceed $1 billion. Hardest hit were Kentucky and Southern Indiana, which suffered 21 and 13 dead, respectively. Three were killed in Ohio, and one each in Alabama and Georgia. The scale of the outbreak was enormous, with a preliminary total of 117 tornadoes touching down in eleven states, from southern Ohio to Northern Florida. The National Weather Service issued 297 tornado warnings and 388 severe thunderstorm warnings. At one point, 31 separate tornado warnings were in effect during the outbreak, and an area larger than Nebraska–81,000 square miles–received tornado warnings. Tornado watches were posted for 300,000 square miles–an area larger than Texas….

Incredibly fast-moving storms
The speed with which some of the storms moved was truly exceptional, thanks to jet stream winds of up to 115 mph that pushed the thunderstorms forward at amazing speeds. A number of the tornadoes ripped through Kentucky with forward speeds of 70 mph, and two tornado warnings in Central Kentucky were issued for parent thunderstorms that moved at 85 mph. NWS damage surveys have not yet determined if one of the tornadoes from the outbreak has beaten the record for the fastest moving tornado, the 73 mph forward speed of the great 1925 Tri-State Tornado, the deadliest U.S. tornado of all-time.

Largest 5-day and 2nd largest 2-day tornado outbreak for so early in the year?

The March 2 tornado outbreak spawned 107 tornadoes, according to preliminary reports as of 8 am EST March 5 from NOAA’s Storm Prediction Center. An additional 10 tornadoes (preliminary) touched down on March 3, in Florida and Georgia; 3 additional tornadoes touched down on March 1 (Wikipedia does a great job tallying the stats for this tornado outbreak.) These preliminary reports are typically over-counted by 15%, but a few delayed reports will likely come in, bringing the total number of tornadoes from the March 2 – 3 outbreak to 90 – 100, propelling it into second place for the largest two-day tornado outbreak so early in the year. The top five two-day tornado outbreaks for so early in the year, since record keeping began in 1950:

January 21 – 22, 1999: 129 tornadoes, 4 deaths
March 2 – 3, 2012: 117 tornadoes (preliminary), 39 deaths
February 5 – 6, 2008: 87 tornadoes, 57 deaths
February 28 – March 1, 1997: 60 tornadoes, 10 deaths
January 7 – 8, 2008: 56 tornadoes, 4 deaths

Though the 36 tornadoes that occurred during the February 28 – 29 Leap Day outbreak were part of a separate storm system, the five-day tornado total from February 28 – March 3, 2012 is likely to eclipse the late January 18 – 22, 1999 five-day tornado outbreak (131 tornadoes) as the most prolific five-day period of tornado activity on record for so early in the year.

And yes we need to improve housing for those in tornado alley.  That’s a great thing for blogs that don’t focus on climate to write about.  Just as obviously we need an aggressive strategy for reducing GHGs that also supports real adaptation.

You can donate to the American Red Cross disaster relief here.


For decades, scientists have predicted that if we kept pouring increasing amounts of heat-trapping greenhouse gases into the atmosphere, we would change the climate.   They specifically predicted that that many key aspects of the weather would become more extreme — more extreme heat waves, more intense droughts, and stronger deluges.

As far back as 1995, analysis by NOAA’s National Climatic Data Center (led by Tom Karl) showed that over the course of the 20th century, the United States had suffered a statistically significant increase in a variety of extreme weather events, the very ones you would expect from global warming, such as more “” and more intense “” precipitation. That analysis concluded the chances were only “5 to 10 percent” this increase was due to factors other than global warming, such as “natural climate variability.” And since 1995, the climate has gotten measurably more extreme.

Multiple scientific studies find that indeed the weather has become more extreme, as expected, and that it is extremely likely that humans are a contributing cause (see “Two seminal Nature papers join growing body of evidence that human emissions fuel extreme weather, flooding that harm humans and the environment” and links therein).

Beyond that, as Dr. Kevin Trenberth, former head of the Climate Analysis Section of the National Center for Atmospheric Research, explained here in 2010: “There is a systematic influence on all of these weather events now-a-days because of the fact that there is this extra water vapor lurking around in the atmosphere than there used to be say 30 years ago. It’s about a 4% extra amount, it invigorates the storms, it provides plenty of moisture for these storms.”  He told the NY Times, “It’s not the right question to ask if this storm or that storm is due to global warming, or is it natural variability. Nowadays, there’s always an element of both.”

Munich Re, one of the world’s leading reinsurers, issued a news release in 2010, “large number of weather extremes as strong indication of climate change,” which noted:

Munich Re’s natural catastrophe database, the most comprehensive of its kind in the world, shows a marked increase in the number of weather-related events. For instance, globally there has been a more than threefold increase in loss-related floods since 1980 and more than double the number of windstorm natural catastrophes, with particularly heavy losses as a result of Atlantic hurricanes.

The rise in natural catastrophe losses is primarily due to socio-economic factors. In many countries, populations are rising, and more and more people moving into exposed areas. At the same time, greater prosperity is leading to higher property values. Nevertheless, it would seem that the only plausible explanation for the rise in weather-related catastrophes is climate change. The view that weather extremes are more frequent and intense due to global warming coincides with the current state of scientific knowledge as set out in the Fourth IPCC Assessment Report.

Here is their data:


I have tended to focus on the extreme weather events for which the causal chain is clearest and which will do the most damage to the most people in the foreseeable future.  Dust-Bowlification is probably at the top of that list (see NCAR analysis warns we risk multiple, devastating global droughts even on moderate emissions path).

But tornadoes are among the most visibly and viscerally destructive events — though I do find it interesting how much media coverage these tornadoes have gotten compared to, say, Tennessee’s 1000-year deluge aka Nashville’s ‘Katrina’.   So it was inevitable that scientists would be asked the obvious question of whether recent remarkable outbreaks are connected to human-caused climate change — and they were indeed remarkable.

Many scientists have weighed in on the climate-tornado link.  Two of the people who have done more research and publication on extreme weather and climate change than most are Trenberth and Karl, now director of NCDC.  I emailed Karl for his thoughts and here is what he wrote me last year:

Best info we have on the relationship between a warmer world and severe convective storms that can produce tornadoes is in the 2008 Synthesis and Assessment Report of the US Global Change Research Program. Chapter three of that Weather and Climate Extremes Assessment indicates that several studies do show that environmental conditions favorable for convection are more likely with more greenhouse gases, but results are not conclusive.

We now have improved resolution models running at our Oak Ridge Supercomputer thanks to the Stimulus funding.  We may be  able to make more definitive statements (one way or the other) after these get analyzed over the next few years. Meanwhile, we know that La Nina years tend to have a greater chance of severe outbreaks.  So as usual, there are natural factors that have to be considered, and any human made factors would be confounded within these naturally occurring events making our attribution much more difficult.

Joe, what we can say with confidence is that heavy and extreme precipitation events often associated with thunderstorms and convection are increasing and have been linked to human induced changes in atmospheric composition.

You can find that 2008 Report here.  I wrote about it here (see Sorry, deniers & delayers, Even Bush Administration says human emissions are changing the climate).

Trenberth made clear to me a year ago in an extended interview that he was dismayed by the media coverage of extreme weather, especially extreme deluges, that made no mention whatsoever of global warming:

I find it systematically tends to get underplayed and it often gets underplayed by my fellow scientists. Because one of the opening statements, which I’m sure you’ve probably heard is “Well you can’t attribute a single event to climate change.” But there is a systematic influence on all of these weather events now-a-days because of the fact that there is this extra water vapor lurking around in the atmosphere than there used to be say 30 years ago. It’s about a 4% extra amount, it invigorates the storms, it provides plenty of moisture for these storms and it’s unfortunate that the public is not associating these with the fact that this is one manifestation of climate change. And the prospects are that these kinds of things will only get bigger and worse in the future.

I emailed Trenberth last year to check his quote in ThinkProgress. And I again checked with him yesterday. He stands by the quote with the clarification he had added of the context:

It is irresponsible not to mention climate change in stories that presume to say something about why all these storms and tornadoes are happening.

The environment in which all of these storms and the tornadoes are occurring has changed from human influences (global warming). Tornadoes come from thunderstorms in a wind shear environment. This occurs east of the Rockies more than anywhere else in the world. The wind shear is from southerly (SE, S or SW) flow from the Gulf overlaid by westerlies aloft that have come over the Rockies. That wind shear can be converted to rotation. The basic driver of thunderstorms is the instability in the atmosphere: warm moist air at low levels with drier air aloft. With global warming the low level air is warm and moister and there is more energy available to fuel all of these storms and increase the buoyancy of the air so that thunderstorms are strong. There is no clear research on changes in shear related to global warming. On average the low level air is 1 deg F and 4 percent moister than in the 1970s.

Just because attribution is difficult doesn’t mean that the subject of global warming should be avoided entirely when talking about tornadoes.  Equally important, when discussing extreme weather and climate, tornadoes should not be conflated with the other extreme weather events for which the connection is considerably more straightforward and better documented:

TP quotes climate scientist Gavin Schmidt, climate modeller at the NASA Goddard Institute for Space Studies, who said:

It is a truism to say that everything has been affected by climate change so far and therefore this latest outbreak must in some sense have been affected, but attribution is hard and the further down the chain the causality is supposed to go, the harder this is. For heat waves it is easier, for statistics on precipitation intensity it easier – there are multiple levels of good modelling, theory and observations to back it up. But we have much less to go on with tornadoes.

There are lots of posts from last year on this.  Stu Ostro, Weather Channel Senior Meteorologist, wrote in his May 2011 post, “The Katrina of tornado outbreaks“:

The atmosphere was explosively unstable with summerlike heat and humidity, interacting with a classic wind shear setup as a strong jet stream and upper-level trough crashed overhead”….

The atmosphere is extraordinarily complex, and ultimately what’s happened the past month is probably a combination of influences, including La Nina, other natural variability, and anthropogenic global warming.

Here is how meteorologist and former hurricane hunter Dr. Jeff Masters put it May 31, 2011:

In summary, this year’s incredibly violent tornado season is not part of a trend. It is either a fluke, the start of a new trend, or an early warning symptom that the climate is growing unstable and is transitioning to a new, higher energy state with the potential to create unprecedented weather and climate events. All are reasonable explanations, but we don’t have a long enough history of good tornado data to judge which is most likely to be correct.

Here is how Masters puts it today:

Last year’s tornado season was incredibly severe, and we are off to one of the worst early-season starts to tornado season on record now in 2012. However, it is too soon to ring the alarm bells on climate change being responsible for this. The tornado data base going back to 1950 doesn’t show an increasing trend in strong tornadoes in recent decades. While climate change could potentially lead to an increase in tornadoes, by increasing instability, it could also decrease them, by decreasing wind shear. I’d need to see a lot more bad tornado years before blaming climate change for the severe tornado seasons of the past two years. One thing that climate change may be doing, though, is shifting the season earlier in the year. The 5-day total of tornadoes from February 28 – March 3 will probably break the record of 131 set in 1999 for the largest tornado outbreak so early in the year. Warmer winters, and an earlier arrival of spring due to a warming climate, will allow tornado season to start earlier–and end earlier. This year’s early start to tornado season is consistent with what we would expect from a warming climate. I have a more extensive article on this subject that has just been published by Weatherwise magazine….

Michael Tobis pointed out Judith Curry’s post, which I wouldn’t normally link to given her general abandonment of science, but she pointed out the study I cited at the top, The Effect of Climate Change on Tornado Frequency and Magnitude:

research project by Michael Pateman and Drew Vankat found that the frequency of tornadoes had increased between 1950 and 1999″”though better detection likely played a significant role in those statistics. But if there’s strong evidence that climate change and tornadoes are connected, researchers have yet to uncover it….

The researchers themselves found:

There is an obvious increase in tornado frequency between 1950-1999. This could be due to increased detection. Also this could be due to changing climatic conditions. Looking at the raw data we have seen that there are generally less tornadoes in El Nino years compared to La Nina Years. But, since we were unable to get climate data, we were unable to see if the change in the frequency was due to climate factors.

Our data has failed to show a strong correlation in increase in tornado frequency and magnitude during El Nino and La Nina events.

The jury is out.

For more data on the increase in frequency, which is certainly due in large part to better detection, here is NCDC’s State of the Climate:  Tornadoes Annual 2010:

NYT blogger directed us to this chart:

tornado trends

There is no apparent trend in the strongest tornadoes (F5 is the most destructive).  The NYT blogger quotes Harold Brooks of the National Severe Storms Laboratory:

The primary changes appear to occur ~1975, most likely as a result of the retrospective rating process that assigned ratings to tornadoes prior to the near-real-time ratings that began when the [National Weather Service] adopted the F-scale operationally in the mid-1970s, and ~2000, for reasons that aren’t completely clear, but are likely due to an increased emphasis on examining construction details and policies that changed the nature in how the ratings are created for the strongest tornadoes. Both have lead to a decrease in probability of a tornado being very strong, given that it’s strong. It’s possible that there’s a meteorological component, but the reporting practice changes are large enough that I don’t think we can pull a physical signal out, even if it’s fairly large.

So it may simply be that the data is simply is too confused by the reporting practices for analysis to draw any strong conclusions.  That doesn’t mean the question shouldn’t be asked or that scientists shouldn’t give their best answer.

In general I do think it’s best to avoid statements like “global warming is to blame for” or “global warming caused” or “this is evidence of global warming,” especially in regards tornadoes.

Finally, while tornadoes will continue to grab the headlines wherever they flatten cities and take lives, it is virtually certain that other extreme events — and ultimately the permanently changed climate — will cause the greatest harm attributable to human emissions of greeenhouse gases.

The population hasn’t even acclimatized to the climate change we’ve had already — in part because the GOP and the fossil-fuel-funded disinformation campaign have obfuscated efforts to inform the public.

We’ve only warmed about a degree Fahrenheit in the past half-century.  If we keep listening to the disinformers, we are on track to warm nearly 10 times that this century (see M.I.T. doubles its 2095 warming projection to 10°F — with 866 ppm and Arctic warming of 20°F).  We ain’t seen nothing yet. Or, as one commenter put it:

“Mother nature is only warming up.”

Note: The NBC quote is by Tom Costello from the March 3, 2012 Evening News. Also, h/t Gail at Wit’s End

Related Posts:

  • NOAA: Climate change “largely irreversible for 1000 years,” with permanent Dust Bowls in Southwest and around the globe.  This January 2009 PNAS paper finds “¦the climate change that is taking place because of increases in carbon dioxide concentration is largely irreversible for 1,000 years after emissions stop”….   Among illustrative irreversible impacts that should be expected if atmospheric carbon dioxide concentrations increase from current levels near 385 parts per million by volume (ppmv) to a peak of 450-600 ppmv over the coming century are irreversible dry-season rainfall reductions in several regions comparable to those of the “dust bowl” era


38 Responses to UPDATE: Tornadoes, Extreme Weather And Climate Change, Revisited

  1. BBHY says:

    It is not “early in the season”. February and early March is not tornado season. Illinois, Indiana, Ohio and West Virginia should be having snowstorms, not tornadoes. This climate change slapping us in the face, demanding that we pay attention.

  2. Leif says:

    Another clean up for “We the People” complements of the Ecocidal Fossil Industry and its ongoing tax funded efforts to prevent any meaningful mitigation efforts by rational thinking folks that might disrupt their “profits” by a percent or two. Capitalism considers any increase in GDP good , hence a BIG mess is good for them as well. “We the People”??? Systems change, not climate change… Remove profits from the pollution of the commons.

  3. David F. says:

    This is one area where I do feel further research is needed. It does seem like the number of tornadoes is increasing in recent years — and it seems like the twisters are increasingly happening in places or times where they used to be rare. I agree that a lot of the increase since 1950 is probably attributable to better detection, but even since the late 1980s/early 1990s, when widespread deployment of doppler radar occurred, there seems to be an upward trend. So I think it’s probably safe to say there has been some increase, at least in recent years.

    Also, I wanted to point out (as you alluded to in your post), the slight decrease in the strongest tornadoes (F4/F5) is likely artificial. Deniers have used that as a proxy to claim that tornadoes are actually down — this is a silly and fallacious argument. The classification system has been refined over time — I think a substantial change occurred around 1975. Some of the past tornadoes classified as very strong may have actually produced F2-F4 (now EF2-EF4) winds. Also, another common denier meme is to use casualties as a proxy for tornado occurrence. Obviously, this is just completely disingenuous as we didn’t have tornado warning systems like we do today in the past.

  4. fj says:

    Another 1-in-100-year storm (or worse) in NYC could easily knock out the subway system for one month minimum greatly impacting daily $4 billion economic activity; and the electrical system is also highly vulnerable; and could be the “climate pearl harbor” moving this country to action at wartime speed against climate change.

    Of course, a net zero transit system could be built quite rapidly to be highly resilient to such extreme climate events at the same time producing minimum emissions building it and ongoing emissions thereafter.

    Rapid retrofits bringing the city’s buildings to near net zero would also have the same effect except that the initial emissions doing the retrofits would likely be higher.

    Rapid implementation of solar, currently which is in the works, would add considerable resilience to the electrical system but would also require higher emissions during the transition.

  5. The overall conclusion seems to be that it’s too soon to say that the increase in tornados is due to global warming. (Or, as you phrase it, “the jury is still out.”)
    That seems fair. It’s clear that climate changes will have effects on severe weather, but there’s a little too little evidence so far to be able to confidently say that these effects are definitely caused by global climate change.

  6. Gail Zawacki says:

    I note with horror that you can’t even find the state borders of Kentucky on that first map, they are obliterated by the warnings…and that just happens to be where middle daughter is headed after graduation from UPenn Vet school in May, for a one-year internship at a horse clinic in Lexington.

    Sigh. Something else to panic about.

  7. SteveR says:

    Seems like it would be reasonably straightforward to test whether the increase in counts has to do with reporting practices: gather historical data about changes in reporting practices year by year, and compare that to year by year changes in tornado counts. If there’s an increase in a year in which there were significant changes in reporting, then that’s probably attributable to reporting. If there’s a change in a year where there was no change in reporting, then that’s an objective change. Right? I mean, I’m making the analysis sound easier than it would be, but if there are decent records about reporting changes, it can be done.

  8. Jim Pettit says:

    After every outbreak of severe weather over the past several years, I’ve found myself involved in numerous discussions, often heated, on this very subject. And over time, I’ve learned this truism, which I’m always more than happy to pass along (much to the consternation of denialists): while it may be wrong at this point in time for anyone to claim with absolute certainty that there exists a direct correlation between warming and the increase in tornadoes, it’s every bit as wrong for anyone to claim with absolute certainty that there’s not.

  9. An excellent post, Joe. Another good summary to look at:

    A Brief Assessment of the Impact of Large-Scale Climate Change on Severe Thunderstorms and Tornadoes – A summary of the current scientific understanding of: 1) observed changes in severe thunderstorms and tornadoes, and 2) the possible role of human influences in modulating past and future changes in these events.

    Eight members of the Climate Science Rapid Response Team contributed to this response to an informational request from the White House Office of Science and Technology Policy.

  10. John Tucker says:

    That was a really good post and one of the best discussions ive seen on the matter, I agree, it is horribly irresponsible not to mention climate change when discussing these outbreaks.

  11. Paul Magnus says:

    Slow Extreme climate devastation….

    Climate Chaos shared a link.

    Farmers say snails wrecking crops
    Yorke Peninsula farmers say they are losing a battle against four snail species which are threatening their crops.

  12. Raul M. says:

    Hi, if Grace is passing by does it show an uplift? Do the satellites that stucy particle density of the air show a great point of activity during a tornado? Though satellites for weather and climate may have different positions in space, it does seem that something could be said of the satellite imagery.

  13. Doug Bostrom says:

    It would be genuinely odd and inexplicable if more heat and more moisture in the atmosphere had no discernible effect. Short of the atmosphere somehow simultaneously becoming more homogeneous with increasing heat and moisture content, how could it not behave more energetically?

  14. yogi-one says:

    It’s too bad that the change in reporting practices obscures whether AGW is a large component of the increase in their ferocity and frequency. Intuitively, I think it is, but unless the data clearly show it, you can’t make a public statement about it.

    The tragedy will be that by the time we have such crystalline clear, overwhelming data, we will already be in the middle of the mess we would have been seeking to avoid by collecting the data in the first place.

    I picture a poor CNN correspondent circa 2050 reporting from some disaster zone “yes, it’s abundantly clear by now that we are getting fried-out and blown away due to global warming.”

    Not exactly an “I told you so” victory.

  15. SteveR wrote:

    Seems like it would be reasonably straightforward to test whether the increase in counts has to do with reporting practices: gather historical data about changes in reporting practices year by year, and compare that to year by year changes in tornado counts.

    If you are talking about a jump one year to the next, that could easily be due to natural variability. A bit like one year being warmer or colder than the next. If you are talking about enough years to really determine whether or not there has been a jump, that could be due to a change in technology or a change in the climate.

    What we have had up until last year? The data is very noisy. What we are seeing now? May be step-like behavior in moving from one climate regime to another, a bit like when you watch the pattern of dripping from a faucet as you gradually increase the flow of water. Or it could be that last year was a once in a century year.

    Time will tell. But the trend in droughts is much clearer, and will have a far greater effect on the availability of water and food, and even on political stability.

  16. Mulga Mumblebrain says:

    Well observed, Leif. Capitalism does not care where it gets its loot from. Climate disasters will be good for business, in just the same way that the obesity epidemic is good for junk food peddlers, advertisins psychological molesters and the medical-industrial complex (not to forget the makers of bariatric coffins). No morality but greedy self-interest, the modus operandi of the cancer cell, right up until the time that it kills its host.

  17. Mulga Mumblebrain says:

    There will be no ‘climate Pearl Harbor’ because, in Roosevelt’s day, the US President was the head of state and commanded respect and obedience, if grudging and contested. Today Obama is the employee of the true ruling force, the capitalist elite, and he, or any other President, follows their orders. You can date that change from November 22, 1963, and we require an awakening from the Bosses before anything will happen.

  18. Mulga Mumblebrain says:

    Yeah-let’s wait another twenty years, to be certain. I mean we’ve got nothing to lose, and those fossil fuel profits are beguiling. Let the next few generations deal with it.

  19. Doug wrote:

    It would be genuinely odd and inexplicable if more heat and more moisture in the atmosphere had no discernible effect.

    If storm tracks move poleward due to expanding Hadley cells, this could actually result in a decrease in tornadoes. If on the other hand the jet stream slows, this could could cause it to bunch up, bringing cooler air farther south and simultaneously warmer, more humid air farther north. Like last year. Resulting in an increase in the number of tornadoes or more powerful tornadoes, at least during some la Nina years.

    Likewise, greater windshear over the Atlantic would tear the tops off while potential hurricanes are in the process of forming, resulting in a decrease in hurricanes, at least for the Southeast United States. Even though there is more moisture and energy being put into the atmosphere.

    Droughts are going to by far have the greatest effect upon humanity by reducing and playing havoc with the food supply. The trend is clear. But they generally take a fair amount of time to really make their effects felt and consequently aren’t as dramatic. The trend is still fairly clear with flooding. That’s much more dramatic than drought, particularly when you have a thousand year flood (Tennessee), a couple of hundred year floods separated by only a few years (Iowa), flooding over an area larger than France and Germany combined (Australia), one fifth of a country under water (Pakistan) and one third of another (Thailand), or sufficient flooding to cause sea levels to drop 6 mm for over a year, and the trend may actually capture the attention of those who are otherwise in denial.

  20. Mulga Mumblebrain says:

    The tremendous rains (often records) and floods continue apace in Australia, but none dare mention ‘climate change’. During last year’s inundations, there was an active campaign to deny that anthropogenic climate destabilisation could possibly have any role, and the MSM, with that ‘spooky synchronicity’ of opinion for which it is infamous, histrionically insisted that it was all caused by ‘La Nina’ and there was nothing untoward. This year climate change has totally disappeared from public discourse, and even La Nina has been dismissed. You wouldn’t want to wake the peasants from their stupour, now would you? A career-ending mistake, that would be.

  21. It’s clear that climate changes will have effects on severe weather, but there’s a little too little evidence so far to be able to confidently say that these effects are definitely caused by global climate change.

    Tornadoes? At the moment, yes. Although we may be on the cusp.


    The global very dry areas, defined as PDSI +3.0) declined slightly during the 1980s. Together, the global land areas in either very dry or very wet conditions have increased from ~20% to 38% since 1972, with surface warming as the primary cause after the mid-1980s. These results provide observational evidence for the increasing risk of droughts as anthropogenic global warming progresses and produces both increased temperatures and increased drying….

    Our PDSI results, which are based on atmospheric moisture supply and demand near the surface, are con- sistent with increased evaporation under greenhouse gas–induced warming, as predicted by comprehensive coupled climate models (Cubasch et al. 2001; Dai et al. 2001). Global temperature increases have become pro- nounced after the 1970s (Folland et al. 2001) and have been attributed to human-induced climate changes arising primarily from increased greenhosue gases (Mitchell et al. 2001; Dai et al. 2001; Karl and Trenberth 2003). Higher temperatures increase the water-holding capacity of the atmosphere and thus increase potential evapo- transpiration. Hence global warming not only raises temperatures, but also enhances drying near the surface, as is captured by the PDSI. The increased risk of drought duration, severity, and extent is a direct consequence (Trenberth et al. 2003), and the theoretical expectations are being realized, as shown here and discussed by Nicholls (2004).

    Dai, Aiguo et al.: A Global Dataset of Palmer Drought Severity Index for 1870-2002: Relationship with Soil Moisture and Effects of Surface Warming, Journal of Hydrometeorology, Vol. 5, No. 6, pp. 1117–1130, December 2004

  22. It should be noted that these tornadoes were not only very strong for so early in the season, but they were also the strongest ever observed in some areas:
    Confirmed EF3 Tornadoes in Eastern Kentucky Strongest Ever Observed in At Least 3 Counties

  23. Joe Romm says:

    Dai has a more recent piece. I should blog on it.

  24. caerbannog says:

    Just thinking out loud here….

    If we take AGW-driven warming of the Gulf of Mexico, and combine it with a warming Arctic that creates “kinks” in the jet stream that send cold fronts far south, in future decades might we see “whopper” tornado events that far exceed anything we’ve seen to date?

    Not every year, of course, but perhaps every few years we could see extreme cold air masses meeting extreme warm air masses (with temperature/humidity differentials far exceeding what we’ve seen in the past few years) along with the jet-stream in between to “spin things up”.

  25. Paul Magnus says:

    This could be the start of the unstable trend of climate. The threshold appears to be around the global temp seen in 1998,2005,2010.

    We are moving through this threshold and so will probably see this level of extreme weather, globally, from now on. Basically the insurance industry is toast.

    Societies, including western ones, are not going to be able to cope with the current level of extreme events much less the escalation we will be seeing year on year.

  26. Doug Bostrom says:

    We’ll really benefit from better modeling when it comes to figuring out where all this extra content in the atmosphere is going to work itself out. It’s not at all obvious, as you imply.

    More generalized energetic seething, or hammer blows in particular places? There’s lots of circumstance to allow for both.

  27. John Mason says:

    Joe, being a storm-chaser here in the UK this was of especial interest – thanks.

    I’d go along with Trenberth where he notes: “With global warming the low level air is warm and moister and there is more energy available to fuel all of these storms and increase the buoyancy of the air so that thunderstorms are strong.” What he is suggesting – and carefully examining temperature/humidity of these low-level moist airmasses that originate from the Gulf would provide the required detail to asses – is that the more low-level heat the more powerful any thunderstorm updraught in an environment conducive to supercell development. Shear and mid/upper-level cold air can remain unchanged: if that buoyancy jumps up a notch due to extra low-level heat then it positively encourages tornadogenesis.

    Cheers – John

  28. Rabid Doomsayer says:

    I don’t know if the data supports this yet, but it seems we are getting less tornado’s most years and many more in bad years. So conditions will not favor tornados most of the time but when conditions are right; wham.

    Should give us just enough time to think tornados are no longer a problem and get far too complacent.

  29. SecularAnimist says:

    Unfortunately, I think Jeff Masters is likely correct when he writes that this may be “an early warning symptom that the climate is growing unstable and is transitioning to a new, higher energy state with the potential to create unprecedented weather and climate events“.

  30. Harold Brooks says:

    I strongly disagree with Dr. Trenberth’s statement “there is every expectation that the [tornado] season will move up in time.” That is certainly not an expectation of the severe thunderstorm-climate change research community. It is not in the literature anywhere and there is no observational evidence to support it. The season has not begun earlier in recent years. If you look at first date of at least 10 F1 or stronger tornadoes over the years (F1+ has been relatively consistently reported since 1954), the trend is insignificant (the correlation coefficient from the linear regression is <0.01 for 1975-2011). The long-term mean of the date is 1 March and several recent years (2002, 2003, 2005, 2010) haven’t had it occur until April.
    He also is in error when he says “There is no clear research on changes in shear related to global warming.” There are multiple papers in the peer-reviewed literature indicating that shear is likely to decrease in the future. The community’s confidence in expected changes in shear is similar to the confidence in expected changes in potential energy. Simply increasing the moisture in the boundary layer does not necessarily mean that energy will increase, depending upon temperature changes aloft. The same studies that have projected increases in energy have also projected decreases in shear.

  31. Doug Bostrom says:

    Always worth remembering when it comes time for voting that the GOP response to all of this that of killing funding for climate research, which of course means ending a lot of climate related investigations.

    Ignorance isn’t bliss, really.

  32. Joan Savage says:

    I have yet to find trend graphs for incidence of supercell storms, common source of tornado swarms, though it seems possible that NOAA has already done stats. Also, I’m looking for stats on incidence of the non-supercell tornadic storms.

    Cheers back at ya!

  33. M Tucker says:

    No, it’s all good. The international negotiators and policy makers have drawn a line in the sand at 2 degrees Celsius warming. It will all be just peachy with more GHG, including more water vapor, in the atmosphere and more energy in the weather system. It will all be wonderful with more CO2 dissolved in the oceans. You just have to trust the policy makers. They say we will all be safe and happy. They all agree we will hardly notice any change to precipitation and storms. They are confident the risks of catastrophic droughts are exaggerated. They are saying nothing about preparing for sea level rise due to 2 degrees of warming. It’s all good…

  34. RH factor says:

    Anytime we get high precipitable water or PW’s in the atmosphere in the Northeast, bad things tend to happen, and this not just a summer time deal as witness to Lake Champlain lake levels last spring setting new records. It takes a high volume of snow melt and rain to do that. The concentration of higher water vapor in a warming world via Gulf of Mexico is pretty easy to see especially considering SST’s 3 degrees F. above normal in the Gulf. Should not take a lot of imagination to move this further north to see climate change effecting day to day meteorology. You’d have to be blind not to visualize this and I’m wonderment just how slow others are to recognize this. A daily practitioner of operational Meteorology here.

  35. anonymous says:

    Tornados until drought?

  36. TehachapiCA says:

    I truly appreciate that the scientists have finally become vocal. However, from President Obama down to the average citizen there is a rush to use industrial wind and solar. What the hell are they thinking. The forests and desert are our life support systems. Instead of protecting the integrity of what is left of them, the profiteers have run over the people to put up that horrible technology world wide. I truly feel that it will take a full out war against the companies and governments to stop this insanity. This comes from a person that doesn’t even kill bugs.

  37. John Mason says:

    Harold, if pressure-patterns are maintained you will still have phenomenal shear due to the upper-level westerlies.

    Changing BL moisture is a consequence of increasing the energy i.e. adding heat to it.

    All the work I have seen on shear WRT global warming concerns the field of hurricane development/persistence. I’d be interested in any references to work on shear over the Great Plains.

    Cheers – John

  38. Harold Brooks says:

    The primary references are:

    Del Genio, A. D., M.-S. Yao, and J. Jonas, 2007: Will moist convection be stronger in a warmer climate? Geophys. Res. Lett., 34, L16703, doi:10.1029/2007GL030525
    Trapp, R. J., N. S. Diffenbaugh, H. E. Brooks, M. E. Baldwin, E. D. Robinson, and J. S. Pal, 2007: Changes in severe thunderstorm frequency during the 21st century due to anthropogenically enhanced global radiative forcing. Proc. National Acad. Sci., 104, doi: 10.1073/pnas.0705494104.
    _____, _____, and A. Gluhovsky, 2009: Transient response of severe thunderstorm forcing to elevated greenhouse gas concentrations. Geophys. Res. Lett, 36, L01703, doi:10.1029/2008GL036203
    Vecchi, G. A. and B. J. Soden, 2007: Increased tropical Atlantic wind shear in model projections of global warming. Geophys. Res. Lett., 34, L08702. doi:10.1029/2006GL028905

    There’s also a MS thesis from a University of Oklahoma student.

    The Vecchi and Soden paper is the primary work on Atlantic tropical cyclone regional shear, but the figures contain the mainland US.

    The decrease in shear is what would be expected from first principles. Decrease the equator-to-pole temperature gradient and the mean shear should decrease by the thermal wind relationship.