Global Warming and Hurricanes, an Overview of Current Research Results | Hacker News Reader

Global Warming and Hurricanes, an Overview of Current Research Results

gfdl.noaa.gov

90 pointspron36 comments

Scientific consensus, as published by IPCC AR5, is that there was no clear change in floods, droughts, storms in the last century. People are often surprised to find this because of sensational media reports, but that's what we have.

https://scienceofdoom.com/2017/02/12/impacts-v-climate-chang... has detailed discussion.

But you're leaving out the more important part (per the NOAA summary):

Anthropogenic warming by the end of the 21st century will likely cause tropical cyclones globally to be more intense on average (by 2 to 11% according to model projections for an IPCC A1B scenario). This change would imply an even larger percentage increase in the destructive potential per storm, assuming no reduction in storm size.

There are better than even odds that anthropogenic warming over the next century will lead to an increase in the occurrence of very intense tropical cyclone in some basins–an increase that would be substantially larger in percentage terms than the 2-11% increase in the average storm intensity. This increase in intense storm occurrence is projected despite a likely decrease (or little change) in the global numbers of all tropical cyclones.

Anthropogenic warming by the end of the 21st century will likely cause tropical cyclones to have substantially higher rainfall rates than present-day ones, with a model-projected increase of about 10-15% for rainfall rates averaged within about 100 km of the storm center.

Here's a table of the number of category 4 or 5 Atlantic hurricanes broken down by year range. Note that the first two rows are 50 year ranges, the next two are 25 year ranges, and the last is 18 years, so the import columns are the rate columns, which give the average number of storms per year of each category during the corresponding year range:

   Years     Cat 4     Cat 5     4 or 5
            Num Rate  Num Rate  Num Rate
 1851-1900   13 0.26    0 0.00   13 0.26
 1901-1950   29 0.58    8 0.16   37 0.74
 1951-1975   22 0.88    7 0.28   29 1.16
 1976-2000   24 0.96    7 0.27   31 1.24
 2001-2017   21 1.2    10 0.59   31 1.82

Data taken from Wikipedia lists of category 4 and category 5 Atlantic hurricanes:

https://en.wikipedia.org/wiki/List_of_Category_4_Atlantic_hu...

https://en.wikipedia.org/wiki/List_of_Category_5_Atlantic_hu...

How accurate and complete are measurements across these time periods?

Are more recent periods inherently going to have more hurricanes because we now have the capability to detect more hurricanes? How has measurement changed over the past 175 years?

Doesn't seem out of line with casual observations. The last really disastrous hurricane was Katrina and that was over a decade ago.

How disastrous a hurricane is depends both on how strong it is and where it goes.

Since Katrina there have been 4 Atlantic hurricanes (not counting Irma) that were as strong or stronger, and one that was just slightly weaker.

They all devastated places that they hit, but they managed to not hit any major large population areas so they did not cause as much damage as Katrina.

While maintaining human induced climate influence, I think it's important to remember coastal areas were not as populated 50, 100 years ago. So what might have affected 100,000 people 70 years ago might affect 500,000 today, given pip increases and urbanization and paving over (as opposed to historical gravel).

So I read that as there's no measurable impact on hurricane activity yet. The modelling indicates that they won't get more frequent, but will become more intense in the future (stronger winds, more rainfall).

Look at figure 2. There is a 'measurable' increase in hurricane activity that gets very severe in recent years. The problem is that the time series is very noisy because records were patchy going back to 1880. Therefore statistical tests cannot robustly distinguish signal from noise (if any).

The authors do cite a paper that analysed more recent records (from 1950 onwards) [1]. This paper (see figure 1a) demonstrates a very strong statistical correlation between sea surface temperature and hurricane activity. This supports a causal link between climate change and hurricane activity.

[1] http://onlinelibrary.wiley.com/wol1/doi/10.1029/2007GC001844...

I summarised their conclusion (section E) in which they specifically state there's no connection between warming and numbers of hurricanes.

what do you mean when you say "activity"?

That's a summary that leaves out some pretty crucial information. Here is the total of section 'E' and it reads - to me at least - as if there is an effect, but not that particular effect:

In summary, neither our model projections for the 21st century nor our analyses of trends in Atlantic hurricane and tropical storm counts over the past 120+ yr support the notion that greenhouse gas-induced warming leads to large increases in either tropical storm or overall hurricane numbers in the Atlantic. One modeling study projects a large (~100%) increase in Atlantic category 4-5 hurricanes over the 21st century, but we estimate that this increase may not be detectable until the latter half of the century.

Therefore, we conclude that despite statistical correlations between SST and Atlantic hurricane activity in recent decades, it is premature to conclude that human activity–and particularly greenhouse warming–has already caused a detectable change in Atlantic hurricane activity. (“Detectable” here means the change is large enough to be distinguishable from the variability due to natural causes.) However, human activity may have already caused some some changes that are not yet detectable due to the small magnitude of the changes or observation limitations, or are not yet confidently modeled (e.g., aerosol effects on regional climate).

We also conclude that it is likely that climate warming will cause hurricanes in the coming century to be more intense globally and to have higher rainfall rates than present-day hurricanes. In our view, there are better than even odds that the numbers of very intense (category 4 and 5) hurricanes will increase by a substantial fraction in some basins, while it is likely that the annual number of tropical storms globally will either decrease or remain essentially unchanged. These assessment statements are intended to apply to climate warming of the type projected for the 21st century by IPCC AR4 scenarios, such as A1B.

The relatively conservative confidence levels attached to these projections, and the lack of a claim of detectable anthropogenic influence at this time contrasts with the situation for other climate metrics, such as global mean temperature. In the case of global mean surface temperature, the IPCC 5th Assessment Report (2013) presents a strong body of scientific evidence that most of the global warming observed over the past half century is very likely due to human-caused greenhouse gas emissions."

Intensity and amount of rainfall would definitely qualify as elements in determining activity. So of the two factors that make up activity only one of those factors is now supported by the data and the jury is out on the other.

I think his initial comment is a fair summary of that section:

> So I read that as there's no measurable impact on hurricane activity yet. The modelling indicates that they won't get more frequent, but will become more intense in the future (stronger winds, more rainfall).

> The modelling indicates that they won't get more frequent

Is simply incorrect.

"One modeling study projects a large (~100%) increase in Atlantic category 4-5 hurricanes over the 21st century, but we estimate that this increase may not be detectable until the latter half of the century."

Isn't saying they will not get more frequent, it is saying they may get much more frequent but that it will take a long time before we will be able to detect this reliably.

Which is logical given the limited number of data points.

That's not quite an accurate rebuttal. That modeling study projects a large increase in severe hurricanes, not in hurricanes overall.

My understanding is that the models suggest that hurricanes will get more severe, in a fashion that outpaces any downward trend in quantity.

"In the Bender et al. 2010 study, we estimate that the effect of increasing category 4-5 storms outweighs the reduction in overall hurricane numbers such that we project (very roughly) a 30% increase in potential damage in the Atlantic basin by 2100."

Right you are, but the main point stands.

That's a difference in phrasing. All hurricanes won't increase in frequency, but they will get stronger. That isn't contradicted by saying that high strength hurricanes will become more frequent.

"One study projects" but how many other studies are there on the same subject that do not project that? Or, is there only one study found that covers this range of years?

It's in the cited paper. The Power Dissipation Index is a measure of hurricane intensity, not number (defined here ftp://texmex.mit.edu/pub/emanuel/PAPERS/Factors.pdf).

There is a strong link between the hurricane intensity and surface sea temperature.

Curious to know how you are looking at an R2 value (correlation coefficient) of 0.53 to 0.63 in Figure 1a, and interpreting that as 'strong statistical correlation' -- that is pretty terrible actually (most highschool AP chemistry students can produce values of 0.8 - 0.9 for titration curves, for instance).

The correlation between sea surface temperature and hurricane intensity was significant with a p-value < 0.0001. Anything less than 0.001 is defined as 'very strong evidence' [1].

High school chemistry experiments are not like measuring natural phenomena (like weather) which show much more variation.

[1] http://www.stat.ualberta.ca/~hooper/teaching/misc/Pvalue.pdf

If the trend in Fig 2 continues, it'll be obvious in a decade or so.

That's how I read it too. They failed to answer the first question:

>> Have humans already caused a detectable increase in Atlantic hurricane activity or global tropical cyclone activity?

>> It is premature to conclude that human activities–and particularly greenhouse gas emissions that cause global warming–have already had a detectable impact on Atlantic hurricane or global tropical cyclone activity. That said, human activities may have already caused changes that are not yet detectable due to the small magnitude of the changes or observational limitations, or are not yet confidently modeled (e.g., aerosol effects on regional climate).

The answer is NO, they have not already caused a detectable increase in Atlantic hurricane activity or global tropical cyclone activity. That is not to say there is no effect or that it won't be detected in the future, but right now the text reads as NO, couched in a bunch of leave-the-door-open language.

That's not saying it was undetectable that's saying we are not sure it's been detected. In other words looking at the same data in the future with better models of what's going on it may be clearly detectable with our data. However, we don't feel confident enough to say it's been detected.

Also, it should be noted that the current administration is very hesitant about damage from global warming so this could just be weasel words for any significance can always fail the 0.0000...1 significance test.

This is unrelated to the current administration. "No detectable change in storm" has been the finding for at least a decade. (I just checked AR4 published in 2007.) Your allegation of using more stringent test is also groundless.

Sure, but the same was said in 1980 and before. Still, climate change continues and we are collecting more data.

So, there will be a transition point. In the end there are two forces, one is the random nature of weather which adds variability with any change. Another is the increase in storm strength from increasing temperature.

So, we are already at the point where strong storms are statistically more likely. However, at what point can rule out randomly getting lucky such that existing storms have not gotten worse due to random luck?

That question of what is considered enough has become a political question, so you can't expect the transition point to be chosen on a purely empirical basis.

>> So, we are already at the point where strong storms are statistically more likely.

You make statements like that but we are debating the conclusions of an article that says the data does not support that.

What they are saying is the magnitude of change falls below the noise floor. That does not mean there was no change.

It further links future changes with warming.

Both of which agree with what I am saying, but you seem to be missing the difference.

> there's no measurable impact on hurricane activity yet

They've walked that back from their most recent publication [0], linked in section 4, though. Likely this was done for political reasons, given that a Trump appointee has been leading NOAA ad interim since January [1], and an assistant administrator was just formally appointed [2]. BTW, the temporary head just shut down NOAA's climate change advisory panel [3].

> While these changes are apparent in the globally averaged tropical cyclone statistics, they are not necessarily present in each individual basin.

[0] http://journals.ametsoc.org/doi/full/10.1175/JCLI-D-15-0129....

[1] https://en.wikipedia.org/wiki/Under_Secretary_of_Commerce_fo...

[2] http://www.the-scientist.com/?articles.view/articleNo/50248/...

[3] http://www.cnn.com/2017/08/21/politics/white-house-climate-c...

My understanding is there are likely to be fewer hurricanes, but more powerful (and with more rain).

Irma may be a preview of what to expect more of.

Am I misreading this or is it saying something like: Our models suggest we should be seeing an increase in qty or severity of storms. However, to this point the historical evidence does not agree with the models. That said, since effect should increase over time, we'll probably see it down the road. Either that, or we will need new models. :)

Close. The problem is not so much that the historical evidence disagrees with the models, but rather that it is consistent with both the models, and the null hypothesis. A major reason for this cited by the article is the low quality of historical records makes it difficult to use historical evidence. A related problem is that the trends observed in the historical record could be noise.

Similarly, the historical record does not provide enough evidence to conclude that are models are wrong.

As an extreme example, suppose our entire historical record was "September 10, 1900: sunny skys in Florida. September 10, 2017: Category 5 hurricane in Florida".

This is simply not enough information to draw any conclusion.

I find myself wondering whether the information published in this article is reliable or not, given the current Administration's bias and hostility against science (http://thehill.com/policy/energy-environment/349877-climate-...). I cannot just take the data, arguments, and conclusions and assume they have been reviewed and vetted by a panel of experts prior to publication. It is a sad day....

Its disingenuous to imply that there is not an incredible amount of money pushing for "Climate Change" scenarios. The entire construct is to create carbon credit exchange (ie. Chicago Climate Exchange) which JP Morgan estimated to be potential $1.5T a year market.

Pretending that its honorable scientist on one side and medieval science-haters on the other is a childlike simplification.

Either scientific studies are infallible or politically influenced. If you believe the later, why would you trust those done under other administrations or governments more?

I'm assuming the "% change in PDI" means "% change relative to some fixed point in time" and not "% change relative to previous data point" in that diagram.

But then what does the sharp downturn if annual PDI at the "present" point in time mean? Does that mean that this year's season is actually weaker than last year's?

More on Bayesian approaches to detection and attribution

http://julesandjames.blogspot.fi/2017/09/more-on-bayesian-ap...

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