Oklahoma tornado and climate change

Tornado damage_cropped_300

The Courier Mail had quite a good piece. If you want pics the BBC has a gallery or enter Oklahoma tornado at Google images. There are some videos collected here. The Courier Mail has a large photo gallery.

Climate Progress revisits tornadoes, extreme weather and climate change. The bottom line is that the jury is out.

In the US tornado alley warm moist air flows north from the Gulf of Mexico in the lower atmosphere and becomes unstable. Dry, cold air comes from the west over the Rockies in the upper atmosphere, with a shear effect to create the top of the column. The warm air becomes unstable and lifts. The shear effect of the upper wind spins the rising column. More air is sucked in by the spinning, rising column. That’s simplistic but those are the basic elements as I understand them.

With climate change the lower atmosphere warm air flow and instability are likely to be enhanced, but there could actually be less wind shear. We don’t know what the result of those factors will be over time, but the suggestion is that if anything there have been fewer severe tornadoes over recent decades.

Kevin Trenberth says:

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 [warmer] and 4 percent moister than in the 1970s.

There are also problems in counting. Graphs like this one look impressive:


On closer inspection the increase is mainly in the weaker events, which could be due to counting, and even if accurate do not represent a huge concern.

Increased tornado numbers tend to be associated with La Niña years.

Jeff Masters summed up in 2012:

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 the tornado season was actually delayed and the previous 12 months had seen a ‘tornado drought’.

The scale now used in the US since 2007 is the Enhanced Fujita Scale (EF). The scale is based on damage rather than wind speed, since damage provides the evidence for the strength of the event and wind speeds are not almeasured. However, that does translate into bands of wind speed. Essentially EF with winds of 320 kph or more will reduce a house to the concrete slab, so this image is relevant:


The Oklahoma tornado has been classified as EF5.

Moore has been hit by severe tornadoes four times in the last 15 years. In 1999 the winds were recorded at 486 kmh, the highest ever recorded near the earth’s surface.

There’s a simple account of the climate change issue, together with a video explaining tornadoes at The Carbon Brief.

Wikipedia has a comprehensive article on tornadoes.

On the Oklahoma tornado there’s also Andrew Freedman at Climate Central, Brad Plumer at Washington Post and Andrew Revkin at NYT’s Dot Earth.

I didn’t look at the denialist blogs.

While the climate change issue needs to be monitored, the more urgent issues relate to building codes, warning systems (this time about 16 minutes), availability of shelters in public venues like schools (tornadoes typically come late in the day, mercifully), rescue, retrieval, insurance, rebuilding and how the poor get on.


Of the links in the comments thread Dr Jeff Masters’ Tornadoes and Climate Change: Huge Stakes, Huge Unknowns is a ‘must read’.

A point well made is that severe thunderstorms can be just as dangerous and deadly as tornadoes.

20 thoughts on “Oklahoma tornado and climate change”

  1. Reason one – life’s too short. The effort/reward ratio doesn’t add up.

    Reason two – experience shows that doing so would pollute my brain. I actively avoid harm.

    Reason three…

  2. Brian
    if you want to cover the climate change issue credibly then surely you should do more than just read those who are deeply committed to the AGW theory?

    Surely the essence of any scientific understanding is to constantly challenge what you believe about a topic rather than reaching for the blinkers every time something that contradicts your orthodoxy is put forward.

  3. arguing about whether climate change is happening or not is just so passé. -a.v.

  4. Brian, your research methods have been analysed by someone with a little blinking emoticon. Clearly you are out of your league here.

  5. Commentators in the future pointing to the increased cost of weather related events in recent years will need to be careful to screen this event out.

  6. Well, okay, maybe fiercer tornadoes aren’t related to climate change, or if they are, its harder to tell. Or they are a La Nina related phenomenon. So what – Iaian @ 1 – severer hurricanes, extended drought, longer Polar summers, melting of the permafrost and rising sea levels are all, so far as the science can tell, products of global warming. Isn’t that enough to make us worry? I would think so.

  7. Every form of disaster does more damage in poor areas and areas with corrupt or weak building rules. It seems obvious to me that much of the damage in the USA from tornadoes will be the same. It’s a development issue. The obvious example is trailer parks: these are a form of rural slum, and they obviously should not be built anywhere near tornado alley. That they continue to be in the path of these storms tells me that huge amounts of the damage done by tornados in the USA can be prevented or mitigated.

    I would also suspect that, unless warming eliminates wind shear altogether, it will lead to occasional monster tornadoes, like this one, because occasionally the extra heat and the wind shear will coincide. I’m guessing there’s a power law relationship between number and strength, and global warming will make that power law have a tighter kink – so more weaker tornadoes and less stronger ones, but more of the extremely strong ones.

  8. Why aren’t there more Storm Cellars in Oklahoma – Megan Garber, The Atlantic

    I found this issue interesting* – expansive clays and unfriendly bedrock make basement construction difficult and expensive, so a lot of places in OK don’t have underground shelters. The soils they’re talking about are a bit like those on the Darling Downs and parts of Central QLD – anyone who’s driven on those roads will know.

    * certainly more interesting than watching the same old single-issue sniping…

  9. Iain, I’ve got a list of 72 sites that post stuff that’s serious about climate change, plus some feeds. I don’t get around all of them all the time but if something important comes up that’s different it should show up, I reckon.

    fn, the reduction in the shear factor was stated as fact by a couple of sites that were a bit contrarian in orientation, but others I tend to trust say we don’t know. I think the shear factor is associated with the jet stream, which has slowed and is more curvy north to south because of global warming. So a slight reduction in severe tornadoes may be caused by AGW.

    And you could be right. When things do line up, watch out!

  10. Grumphy, I believe OK is a ‘red’ state with somewhat libertarian political values. So the state doesn’t interfere with people and make them build shelters if they don’t want to.

    There’s a good chance they may set aside their political predispositions if more of these monsters show up.

  11. There’s very little evidence on tornadoes (or severe thunderstorms generally) and climate change – either observed historical changes or future projections. Part of this is the difficulty of observing them in a consistent manner (although the US is better than most) – for example, comparing tornado frequency per unit area around Australian capital cities (where one might expect reasonably comprehensive reporting) with that in rural areas suggests that 80-90% of all Australian tornadoes go unreported. There have been attempts made to look at changes in other atmospheric parameters favourable to severe storms (such as wind shear), but with inconclusive results so far. The 2011 IPCC Special Report on Extremes has a good summary of the state of knowledge (or lack thereof) in this area.

    One thing which does have a clear trend – downwards – is the number of deaths from tornadoes. Of the 15 tornadoes which have caused 100 or more deaths in the US, only one (Joplin in 2011) has occurred in the last 60 years. Improved warnings, and improved technology to communicate warnings, have a lot to do with that, and building standards will have helped too.

  12. That’s interesting, thanks Blair. 80-90% unreported is higher than I would have guessed, but quite understandable if it includes all tornadoes.

    Howard Brooks has a graph of US tornado deaths per million people. It has steadily declined from about 1920 to about 1990.

    I’d forgotten about the IPPC report.

  13. if you want to cover the climate change issue credibly then surely you should do more than just read those who are deeply committed to the AGW theory?

    Of course, just as any coverage of astronomy must do more than read those who are deeply committed to the heliocentric theory and the absurd fiction that planet earth is an oblate spheroid.

  14. Adam Kucharski on forecasting tornadoes.

    In short, it’s incredibly difficult and currently the average warning time in the US is 13 minutes. I did hear of one woman in Oklahoma who, warned by her meteorologist husband, went screaming home to get the dog underground. Wife and dog only just made it.

    Following the links led to this neat NOAA site explaining tornadoes.

  15. Before we can judge any effect of human CO2 on extreme wearher we have to take a scientific approach as to what causes extreme weather. To do this we need to know where the energy is coming from. Energy does not tend to go from a less concentrated to a more concentrated source. So where does the energy come from to drive hurricanes and tornadoes? Or for that matter how is the concentrated burst of energy known as lighting get created?

    There appears to be this tepid water theory of how hurricanes are powered. Well this is just silly.

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