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Monday, November 4, 2013

The certainty of science deniers. And what are the facts about hurricanes, tornadoes and Antarctic sea ice?

Sou | 7:39 PM Go to the first of 3 comments. Add a comment

Straw men are built to be blown away.  They can be constructed from anything really.  It doesn't have to be straw.  It could be wind and rain, like tornadoes and hurricanes, or sea ice.

justthefactswuwt wrote on WUWT today (archived here):
It is amazing how easy alarmist scare forecasts/predictions can be falsified with readily available data...The data shows no increase in tornado counts or strength. Claims about increasing or more dangerous Tornadoes are unfounded.

Unfounded?  That's a strong claim! But first just what are the "claims" and who is making them?

In today's article (archived here) Justthefacts mentioned three things: tornadoes, hurricanes and Antarctic sea ice.

justthefacts is adamant that the projections of what will happen over the coming 90 years or so are completely wrong.  This complete and utter certainty is based on less than a year's data.  Not only that but justthefactswuwt appears to be very certain about what expectations are held by climate scientists.  So I thought it would be useful to see what are the forecasts/predictions for each item to see whether or not they have been falsified.

It turns out that, in contrast to the absolute certainty of justhefactswuwt, there is a lot of uncertainty and little agreement in the science itself:

  • Tornadoes - might decrease relative to severe thunderstorms, although a new paper suggests an increase in frequency of severe tornadic storms over the coming century
  • Hurricanes and tropical cyclones - if anything they are expected to decrease or stay the same, but with low confidence, although a new paper argues they may increase.
  • Antarctic sea ice - expected to decline over the coming century, but again with low confidence.
The uncertainty and lack of strong agreement within the research is not really surprising, given the sporadic and relatively infrequent nature of tornadoes and hurricanes, and the difficulty of collecting data in the southern oceans and across the whole of the Antarctic continent.

And I must add that a single year's weather is hardly sufficient to falsify projections of climate!

Tornadoes in the USA

AR5 WG1 suggested that in the USA at least, the expectation is for more severe thunderstorms relative to tornadoes over time.  Tornadoes are expected to decrease or at least decrease relative to the number of severe storms.  It's all to do with energy vs shear.  But it won't be till towards the end of this century that trends will be able to be measured.  In any case, a single year's data isn't sufficient for "falsification" .  From AR5:
Severe thunderstorms, associated with large hail, high winds, and tornadoes, are another example of extreme weather associated with the water cycle. The large-scale environments in which they occur are characterized by large Convective Available Potential Energy (CAPE) and deep tropospheric wind shear (Brooks et al., 2003; Brooks, 2009). Del Genio et al. (2007), Trapp et al. (2007; 2009), and Van Klooster and Roebber (2009) found a general increase in the energy and decrease in the shear terms from the late 20th century to the late 21st century over the United States using a variety of regional model simulations embedded in global-model SRES scenario simulations. The relative change between these two competing factors would tend to favour more environments that would support severe thunderstorms, providing storms are initiated. Trapp et al. (2009), for example, found an increase in favourable thunderstorm conditions for all regions of the United States east of the Rocky Mountains. Large variability in both the energy and shear terms means that statistical significance is not reached until late in the 21st century under high forcing scenarios. One way of assessing the possibility of a change in frequency of future thunderstorms is to look at historical records of observed tornado, hail, and wind occurrence with respect to the environmental conditions (Brooks, 2013). This indicates that an increase in the fraction of severe thunderstorms containing non-tornadic winds would be consistent with the model projections of increased energy and decreased shear, but there has not been enough research to make a firm conclusion regarding future changes in frequency or magnitude. (Page 12-53)

I searched the AR4 and the Second Assessment report but could not find any projections for tornadoes.  I searched the third assessment report and there was this statement:
Although some evidence is available regarding increases in the intensity and frequency of some extreme weather events, it is not yet clear how tornadoes will be affected
By contrast, a more recent study published as open access in PNAS (Diffenbaugh et al 2013), quoted by justthefactswuwt does suggest that tornadoes, or at least severe thunderstorms, will most likely increase this century.  The paper has lots of caveats but the final paragraph in the conclusion states:
Given the substantial damage from severe thunderstorms in the current climate, uncertainty about the response of such storms to global warming has created an important barrier to climate change impacts assessment (1). Our results indicate that continued global warming might cause substantial increases in the occurrence of the atmospheric environments associated with severe thunderstorms, because the implied reduction in vertical wind shear may not be as important as previously thought. These increases include regions where severe thunderstorms currently are most common, and regions where severe thunderstorms currently are less common but where substantial assets are exposed (3, 6, 15). Although important uncertainties about storm-scale processes still exist, the fact that the projected increases in severe environments are robust across a suite of climate models, emerge in response to relatively moderate global warming, and result from robust physical changes suggests that continued increases in greenhouse forcing are likely to increase severe thunderstorm occurrence, thereby increasing the risk of thunderstorm-related damage.
Note that the above relates to "atmospheric environments associated with severe thunderstorms" and not specifically to tornadoes.  However elsewhere in the paper there is reference to tornadoes.  For example in the abstract, Diffenbaugh13 writes:
We also find that days with high convective available potential energy (CAPE) and strong low-level wind shear increase in occurrence, suggesting an increasing likelihood of atmospheric conditions that contribute to the most severe events, including tornadoes.

It is also worth pointing out that Diffenbaugh13 notes the paucity of data, writing:
First, there is no reliable, independent, long-term record of severe thunderstorms—and particularly tornadoes—with which to systematically analyze variability and trends.

The science is much less certain about tornadoes than is justthefactswuwt.

Hurricanes (and tropical cyclones and typhoons)

It doesn't look as if the projections for hurricanes have been falsified, either.  From AR5 WG1 - there has been an increase in the frequency and intensity of the strongest tropical cyclones but not overall.
In summary, this assessment does not revise the SREX conclusion of low confidence that any reported longterm (centennial) increases in tropical cyclone activity are robust, after accounting for past changes in observing capabilities. More recent assessments indicate that it is unlikely that annual numbers of tropical storms, hurricanes and major hurricanes counts have increased over the past 100 years in the North Atlantic basin. Evidence however is for a virtually certain increase in the frequency and intensity of the strongest tropical cyclones since the 1970s in that region. (Page 2-60)
And tropical cyclones are projected to stay the same or decrease, according to AR5.  But the ones that emerge will be fiercer and wetter:
There is low confidence in the projections for the tropical Atlantic, both for the mean and interannual modes, because of systematic errors in model simulations of current climate. The implications for future changes in Atlantic hurricanes, tropical South American and West African precipitation are therefore uncertain. ...
...Based on process understanding and agreement in 21st century projections, it is likely that the global frequency of occurrence of tropical cyclones will either decrease or remain essentially unchanged, concurrent with a likely increase in both global mean tropical cyclone maximum wind speed and precipitation rates. The future influence of climate change on tropical cyclones is likely to vary by region, but the specific characteristics of the changes are not yet well quantified and there is low confidence in region-specific projections of frequency and intensity.(Page 14-4)

From AR4 - tropical cyclones will become more severe and intense:
Earlier studies assessed in the TAR showed that future tropical cyclones would likely become more severe with greater wind speeds and more intense precipitation. More recent modelling experiments have addressed possible changes in tropical cyclones in a warmer climate and generally confirmed those earlier results. 


From AR4 - tropical cyclones and hurricanes will become more intense but globally, less frequent (low confidence)
Based on a range of models, it is likely that future tropical cyclones (typhoons and hurricanes) will become more intense, with larger peak wind speeds and more heavy precipitation associated with ongoing increases of tropical sea surface temperatures. There is less confidence in projections of a global decrease in numbers of tropical cyclones. The apparent increase in the proportion of very intense storms since 1970 in some regions is much larger than simulated by current models for that period. {9.5, 10.3, 3.8}

From the Third Assessment Report:
Climate models currently are unable to project accurately how hurricanes will change in the future. 

However not all research points to a decrease in tropical cyclones.  A recent paper by Kerry Emanuel suggests that tropical cyclones may increase, but large uncertainties remain:
An increase in global mean frequency during roughly the first three quarters of the 21st century is indicated, with a total increase in the range of 10-40%. ... most of the increase in frequency is in the North Pacific, but with substantial increases in the North Atlantic and South Indian oceans as well. The only coastal region that experiences a substantial decline in track crossings is the southeast coast of Australia....
...The differences between our results, those arrived at by applying the same technique to CMIP3 models, and the conclusions of other groups using different models and/or using different methods suggest that projections of the response of tropical cyclones to projected climate change will remain uncertain for some time to come.

All I can say once again is that justthefactswuwt is a lot more certain than the science itself.

Antarctic sea ice


On the other hand, Antarctic sea ice is expected to decrease over time - presumably over winter because there's precious little sea ice in summer.  However, but there is only low confidence in the projection.  From AR5 WG1 (page 12-5)
It is very likely that the Arctic sea ice cover will continue shrinking and thinning year-round in the course of the 21st century as global mean surface temperature rises. At the same time, in the Antarctic, a decrease in sea ice extent and volume is expected, but with low confidence....There is however low confidence in those values as projections because of the wide inter-model spread and the inability of almost all of the available models to reproduce the mean annual cycle, interannual variability and overall increase of the Antarctic sea ice areal coverage observed during the satellite era.

Again, justthefactswuwt is much more certain than the science.


From the WUWT comments

There aren't too many people jumping on justthefactswuwt bandwagon.  Maybe they've been bitten too many times in the past, jumping in too soon. Or maybe they are remembering the massive tornado that tore through Oklahoma in May this year. There are a few more Gore-bashing comments than usual, probably because justthefactswuwt let fly in the article.  (Comments archived here.)


sophocles says "it's cooling":
November 3, 2013 at 12:14 pm
The National Academy of Sciences said:
“…are forecast to see a “robust” increase across parts of the U.S. in upcoming decades because of climate change …”
===========================================================
Unfortunately, they may be correct but not for the reasons they are thinking.
If past records are any hint, the onset of cooling can bring bad storms, (from
Brian Fagan’s book “The Little Ice Age”), not warming.
The AMO and PDO have turned over, the Sun is sliding into another minimum
and cooling is already apparent (only slight, so far but…) so the next ten years
are going to be interesting …


Paul Homewood predicts the lull in tornadoes won't last and says:
November 3, 2013 at 12:17 pm
It’s extremely unextreme.
And next year, no doubt, NOAA will be bragging off about “a big jump in tornado numbers from last year”. 

3 comments:

  1. There's a vicious asymmetry at play when it comes to attribution. Impressionists such as Tony Abbott don't hesitate to make definite statements about attribution, while people more concerned with facts are required to be more cautious.

    It stands to reason that second-order effects such as storm intensity are more difficult to tease out. That said, bold people such as myself observe that a boiling pot turned up from "simmer" to "medium" becomes more kinetic. I'm not sure how intuition is going to fail here; is it reasonable to suppose that all of our "extra" energy is going to be sweetly and peacefully homogeneous? The way the atmosphere works on its own suggests otherwise. Polar amplification and all the rest...

    ReplyDelete
    Replies
    1. Whether or not tropical cyclones and tornadoes decrease in frequency, there is general agreement that the tropical cyclones, hurricanes and severe thunderstorms we do have will be fiercer and wetter!

      (I've now highlighted that bit in the article.)

      Delete
    2. Yeah, energy doesn't vanish. Too bad, in this case. :-)

      Delete

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