For a Lack of Better Words.... W.T.F?

[skierinvermont]

One of the reasons that Trenberth's comments leaned a little towards the side of AGW increasing tornadic activity (while still specifically stating that WE DONT KNOW) is that that is what most of the studies suggest, although the results are not conclusive. It seems the increased CAPE due to AGW may outweigh the decreased shear related to AGW and tornado season will shift earlier in the year.

This paper shows that although shear is expected to decrease, the severe thunderstorm season shifts earlier, and the number of days with BOTH the critical shear and cape values increases:

http://www.pnas.org/...4/50/19719.full

This paper shows that the number of days with weather patterns favorable for tornadoes increases with AGW (using principle component analysis):

http://etd.ohiolink....=kent1274371690

Due to the shortcomings of contemporary global climate models (GCMs), the impacts of climate change on the frequency and seasonality of tornadoes has not been well studied. Prevailing research on the topic favors an ingredients-based methodology which uses instability, moisture and wind shear estimations derived from GCM output data in order to project the change in the number of favorable environments for severe weather. However, by utilizing synoptic climatological methods, this thesis takes an entirely different approach to directly projecting future tornado occurrence.

Using a six-step process, that includes principal components analysis, cluster analysis, and discriminant function analysis, this thesis first creates a continental-scale map pattern classification at three levels of the atmosphere, from geopotential height (at 500mb and 700mb) and temperature (850mb) data fields. These patterns are then associated to F2 and stronger United States (US) tornado days from 1957-2002 using binary logistic regression. Then, using output data from two GCMs, spanning five different model emissions scenarios, this synoptic climatology of tornadoes is utilized in order to project the changes in the frequency and seasonality of US tornadoes due to a changing climate. Results indicate that US tornado days will increase anywhere from 3.8% to 12.7% by the 2090s. The majority of this increase is likely to be manifested in the earlier part of the tornado season – from February through April, while a slight decrease is expected over the US as a whole from May through August. In addition to the shift in seasonality, a broadening of the peak tornado season is also noticed under some scenarios – from a one month peak in May in the 20th Century, to a two or three month peak by the end of the 21st Century. Geographically, portions of the Northern and Central Plains, the High Plains, the Lower Great Lakes, the Mid-Atlantic states, and the Southeast are projected to experience an increase in tornado days under some future scenarios. The Upper Great Lakes states and the Southern Plains are projected to experience a decrease in tornado days.

Another paper:

http://www.stanford....augh_Eos_08.pdf

[tacoman25]

I call BS.

Now that you have done a little digging and found some papers supporting more tornadoes (possibly) because of AGW, you are admitting his comments "lean" more on the side of AGW...now more comfortable doing so because you have found some "evidence".

It's completely transparent, skiier. You arrived at your conclusion first, went on and one about how Trenberth was not advocating AGW as a cause - but now come up with this.

And I guess I should remind you again: just because you find some research supporting one thing doesn't make it true. At different points in time, you can find scientific papers representing all sorts of views/conclusions on the same issue. One reason I put minimal faith in the peer-reviewed process, and citing scientific papers in general as "proof".

[skierinvermont]

I call BS.

Now that you have done a little digging and found some papers supporting more tornadoes (possibly) because of AGW, you are admitting his comments "lean" more on the side of AGW...now more comfortable doing so because you have found some "evidence".

I already said specifically that his comments leaned a little towards AGW possibly increasing tornadic activity but that he also is quite clear that we DO NOT KNOW.

Now that I have done a little digging, it is clear that this was probably because that is what most studies suggest.

[tacoman25]

One problem with the position that AGW causes more/stronger tornadoes is that so far it hasn't. Rising temperatures? Check. Rising tornado rates? Nope.

As others have pointed out, the trend we have since reliable records began is downwards. This is likely mostly due to starting in a -PDO/-ENSO phase, and then having +PDO/+ENSO dominate until recent years. -PDO/-ENSO favors colder, stronger airmasses pushing south in the spring, clashing with warm spring temperatures in the SE. Exactly what we saw last week.

[Isotherm]

I call BS.

Now that you have done a little digging and found some papers supporting more tornadoes (possibly) because of AGW, you are admitting his comments "lean" more on the side of AGW...now more comfortable doing so because you have found some "evidence".

It's completely transparent, skiier. You arrived at your conclusion first, went on and one about how Trenberth was not advocating AGW as a cause - but now come up with this.

And I guess I should remind you again: just because you find some research supporting one thing doesn't make it true. At different points in time, you can find scientific papers representing all sorts of views/conclusions on the same issue. One reason I put minimal faith in the peer-reviewed process, and citing scientific papers in general as "proof".

Bingo. To even call the peer-reviewed process objective is laughable in my opinion. Manipulation and biases are at play on both sides of the fence, which is why it's often so difficult to extract the truths from these papers.

[tacoman25]

I already said specifically that his comments leaned a little towards AGW possibly increasing tornadic activity but that he also is quite clear that we DO NOT KNOW.

Now that I have done a little digging, it is clear that this was probably because that is what most studies suggest.

When did you say that before the post at the top of this page? Everything I read from you was emphasizing that the only reason he talked about AGW was because that was his "pet peeve", everything in weather being related to it.

[skierinvermont]

One problem with the position that AGW causes more/stronger tornadoes is that so far it hasn't. Rising temperatures? Check. Rising tornado rates? Nope.

As others have pointed out, the trend we have since reliable records began is downwards. This is likely mostly due to starting in a -PDO/-ENSO phase, and then having +PDO/+ENSO dominate until recent years. -PDO/-ENSO favors colder, stronger airmasses pushing south in the spring, clashing with warm spring temperatures in the SE. Exactly what we saw last week.

The decreasing trend in strong tornadoes may be as poor as the dramatic increasing trend in the overall number. Neither of them are "climate quality" data suitable for long-term analysis. Estimates of strength back in the 50s and 60s is not very good.

I should have pointed this out sooner but like others I assumed that the F2+ data was of better quality. Several studies I just read said it is not high quality data. Just goes to show why you MUST check the quality of your data source.

[skierinvermont]

When did you say that before the post at the top of this page? Everything I read from you was emphasizing that the only reason he talked about AGW was because that was his "pet peeve", everything in weather being related to it.

I guess you missed it:

I can agree that ideally he would have been more balanced in his comments, as long as we agree that what he said was correct. And as long as we understand that he is making an academic point that all weather is affected by climate. There really isn't anything earth-shattering or biased about saying that. What I objected to early in this thread is those interpreting him as saying "tornadic activity will increase" or "AGW caused the tornadoes." That clearly was not what he said.. in fact he says the exact opposite. "We don't know."

We also don't know how completely he was quoted. We can see that the article quoted one aspect of his statement but only paraphrased the part where he says that we don't know how AGW will affect tornadic activity.

I said he wasn't totally balanced because he mentioned the mechanism that would increase tornadic activity (increased CAPE) but not the possible mechanisms that would decrease it. As it turns out, that is probably because most stuides suggest the increased CAPE will outweigh the other factors and the number of days with critical cape and shear will increase.

[tacoman25]

The decreasing trend in strong tornadoes may be as poor as the dramatic increasing trend in the overall number. Neither of them are "climate quality" data suitable for long-term analysis. Estimates of strength back in the 50s and 60s is not very good.

Well, that is obviously due to much better reporting these days.

However, strong tornadoes are much easier to spot than smaller, briefer ones, so I don't think that effects their trend as much.

[skierinvermont]

Well, that is obviously due to much better reporting these days.

However, strong tornadoes are much easier to spot than smaller, briefer ones, so I don't think that effects their trend as much.

That's what I assumed as well initially, the problem is they weren't as good at estimating the strength back 40-60 years ago.

[tacoman25]

I guess you missed it:

I said he wasn't totally balanced because he mentioned the mechanism that would increase tornadic activity (increased CAPE) but not the possible mechanisms that would decrease it. As it turns out, that is probably because most stuides suggest the increased CAPE will outweigh the other factors and the number of days with critical cape and shear will increase.

Saying he "could have been more balanced" is not the same thing as saying he was "leaning more on the AGW side of things". That response was to Will pointing out that ENSO was a much more obvious and proven factor, so why didn't Trenberth mention that? It sure wasn't obvious what you were referring to.

[tacoman25]

That's what I assumed as well initially, the problem is they weren't as good at estimating the strength back 40-60 years ago.

Eh, a strong tornado is a strong tornado. Yeah, some F-2s back then might be reported as EF-1s today due to somewhat better construction materials and standards for damage. But an EF-4 or EF-5 is going to cause cautostraphic damage now just as it did then.

[skierinvermont]

Eh, a strong tornado is a strong tornado. Yeah, some F-2s back then might be reported as EF-1s today due to somewhat better construction materials and standards for damage. But an EF-4 or EF-5 is going to cause cautostraphic damage now just as it did then.

But the large majority fall in this borderline F1-F2 category. A slight change in classification could lead to a large change in the number of F2+s.

[tacoman25]

But the large majority fall in this borderline F1-F2 category. A slight change in classification could lead to a large change in the number of F2+s.

Neither EF1 or EF2's are strong/violent tornados. That's my point.

[skierinvermont]

Neither EF1 or EF2's are strong/violent tornados. That's my point.

Well we have two datasets that I am aware of... the number of F0+ and the number of F2+... the F0+ is biased by better reporting, the F2+ is biased by poor classification in the 50s and 60s. Now maybe if someone posted data for F3 or F4+s?

But then we might have problems with too small a sample size..

[tacoman25]

Regardless of possible classification/reporting issues...there is no compelling evidence that AGW has or will lead to more or stronger outbreaks. There IS compelling evidence that -PDO/-ENSO does just that. That's what really should be emphasized in any discussion of what climactic factors likely contributed to this latest outbreak.

[skierinvermont]

Regardless of possible classification/reporting issues...there is no compelling evidence that AGW has or will lead to more or stronger outbreaks. There IS compelling evidence that -PDO/-ENSO does just that. That's what really should be emphasized in any discussion of what climactic factors likely contributed to this latest outbreak.

I agree.

However, in a discussion of how AGW will affect tornadoes, I don't expect people to spend too much time discussing all the other proximate causes.

Given this is the CC forum, I would prefer to have the latter discussion rather than the former. If you want to discuss the weather patterns that lead to the outbreak, there is a forum for that. The same goes for an interview or a lecture about AGW. If you want to hear about how ENSO affects tornadoes, go to a lecture on that. If you want to hear about how AGW will affect tornadoes, go to a lecture or read an interview on that.

[tacoman25]

I agree.

However, in a discussion of how AGW will affect tornadoes, I don't expect people to spend too much time discussing all the other proximate causes.

Given this is the CC forum, I would prefer to have the latter discussion rather than the former. If you want to discuss the weather patterns that lead to the outbreak, there is a forum for that. The same goes for an interview or a lecture about AGW. If you want to hear about how ENSO affects tornadoes, go to a lecture on that. If you want to hear about how AGW will affect tornadoes, go to a lecture or read an interview on that.

I'm sorry, but this thread has been about a lot more than just "climate change and tornados". Everything we have discussed on here has been relevant; it was completely on topic for several of us to point out that Trenberth (ENSO expert that he is) mentioned nothing about ENSO in his comments on the tornado outbreak. He either knowingly fed the AGW hype machine or got played by some journalist, and either way he should know better.

[skierinvermont]

Everything we have discussed on here has been relevant; it was completely on topic for several of us to point out that Trenberth (ENSO expert that he is) mentioned nothing about ENSO in his comments on the tornado outbreak.

Because the interview was about AGW.

Do you expect him to explain the 43,000 other proximate variables that contributed to the outbreak?

This is just silly.

[skierinvermont]

He either knowingly fed the AGW hype machine or got played by some journalist, and either way he should know better.

Hmm.. let's look at the source here.. ThinkProgress.com ... they sound like a reputable source of objective reporting and thorough investigative journalism.

Trenberth's comments were a straightforward representation of the science. I do not see the issue here.

[Isotherm]

The idea that -ENSO/-PDO is more favorable for severe wx outbreaks, and more violent tornadoes, is a very accurate one. It's simple physics -- colder relative to norms across the nern tier and warmer over the sern US yields a much more intense thermal gradient, and as we all know, this means big storms.

Note the following maps.

1980-1999 April temp departures:

1980-1999 May temp departures:

A rather Nino-ish appearance with colder anomalies in the southern tier; not that conducive for strong severe weather outbreaks.

Contrast those maps with April 1960-1979:

And May 1960-1979:

Don't need a brain surgeon to tell that the meteorological pattern was more favorable for violent tornadoes in the 1960s and 70s, with the -PDO/ENSO regime, a decrease in the 80s/90s with +PDO/ENSO (aan inverse temp anomaly orientation in the US). Now in the late 2000s and this year we're beginning to see a ramp up in tornadic activity, which again, isn't much of a surprise based upon Earth's natural oscillating cycles. The higher frequency and greater intensity of tornadoes is yet another indication that we've definitely made the switch into a -PDO regime, which is also influencing the recent global temperature decrease.

[skierinvermont]

Yep you can definitely see the effect that the PDO had on the temperature contrasts and therefore probably tornadoes.

[tacoman25]

Because the interview was about AGW.

Do you expect him to explain the 43,000 other proximate variables that contributed to the outbreak?

This is just silly.

43,000 other variables? Please.

A reasonable and honest response would have been: "There is no conclusive evidence that AGW will lead to more or stronger tornadoes. What we do know is that the current -ENSO/-PDO regime favors more outbreaks, and that's the most likely cause of this outbreak from a climate standpoint."

Would that have been so hard?

[Snow_Miser]

Because the interview was about AGW.

Do you expect him to explain the 43,000 other proximate variables that contributed to the outbreak?

This is just silly.

Okay Skier... where on Earth did you get the number 43,000 other variables...?

[WeatherRusty]

Here is what I think was the basis for Trenberth's statements:

1) The Gulf water's are currently 1.0F to 1.5F warmer than average. The flow of warm, moist air off the Gulf fed the thunderstorms. That the atmosphere contains 4% more moisture than 30 years ago is a global average and does not apply here. However, because the Gulf is so warm, the moisture content of the warm air feeding the convection in this case was very high.

2) A strong jet stream was producing a great amount of shear. Almost every thunderstorm became a supercell as a result. Regardless of thinking that we might expect GW to reduce shear, in this case there was tremendous shear. This April produced over 800 tornadoes, by far a new all time record, and April is not even the peak month for tornadoes. Possibly many spin ups would have been missed in the past, so how valid is the record? In any case over 800 is very unusual.

I read many comments here claiming AGW does this or doesn't do that. Even if the warming were 100% natural, the same attributes would apply. For whatever the reason the world is warmer than several decades ago. This warming should be expected to alter what, when, where and how severe or tranquil the weather will average out in any given locale.

It is reasonable to think that since averaged conditions will change, the component weather making up the averaged condition will change. All climate change can tell us is, how likely certain types of weather are for particular areas of the Earth. The overall conditions feeding this tornado outbreak were extremely favorable for their production. How likely in a warming world will this total set of conditions be to reoccur? Obviously it can occur in a warmer world, because it just did.

[VAwxman]

The Gulf water's are currently 1.0F to 1.5F warmer than average. The flow of warm, moist air off the Gulf fed the thunderstorms. That the atmosphere contains 4% more moisture than 30 years ago is a global average and does not apply here. However, because the Gulf is so warm, the moisture content of the warm air feeding the convection in this case was very high.

The Gulf should be warmer in a classic Niña pattern like we have had for the last 3 months.

Conversely, it was cool coming out of last year's El Niño event. It is clear the vast majority of the warmth this year is due to ENSO. Could a fraction be due to AGW? Sure, but the vast majority of the anomalous warmth isn't.

[WeatherRusty]

The Gulf should be warmer in a classic Niña pattern like we have had for the last 3 months.

Conversely, it was cool coming out of last year's El Niño event. It is clear the vast majority of the warmth this year is due to ENSO. Could a fraction be due to AGW? Sure, but the vast majority of the anomalous warmth isn't.

Why then might the average +ENSO and -ENSO have warmed over the course of the past century? La Nina is cooler than El Nino, but they are both warmer than decades ago equal to the time smoothed anomaly.

[VAwxman]

Why then might the average +ENSO and -ENSO have warmed over the course of the past century? La Nina is cooler than El Nino, but they are both warmer than decades ago equal to the time smoothed anomaly.

Yes, both ENSO phases are warmer now versus decades ago. I didn't say there was no GW occurring. But the Gulf itself does not show that warming when correlated with trend. ENSO itself has much more impact than GW here, when looking at the last 50 years.

[WeatherRusty]

Yes, both ENSO phases are warmer now versus decades ago. I didn't say there was no GW occurring. But the Gulf itself does not show that warming when correlated with trend. ENSO itself has much more impact than GW here, when looking at the last 50 years.

Isolating on the Gulf, I agree. The Gulf shows no discernible long term trend.

There appears not to be a direct causative connection between the tornado outbreak and Global Warming, although the current warmth and moisture certainly aided in their production.

[VAwxman]

Isolating on the Gulf, I agree. The Gulf shows no discernible long term trend.

There appears not to be a direct causative connection between the tornado outbreak and Global Warming, although the current warmth and moisture certainly aided in their production.

But for tornado outbreaks, the instability and shear are the big keys. We have warmth and moisture all summer long but those are not tornado months typically. How GW impacts the shear and instability is what the focus should be on, and that isn't really discernable based on what we know right now. We can't just say GW is enhancing the risk for tornadoes because we don't know if it should have a mitigating impact on the other important parameters. It may or may not.