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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 nois

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/full http://onlinelibrary.wiley.com/wol1/doi/10.1029/2007GC001844...

marcus_holmes 9y ago
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"?
- jacquesm 9y ago
  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.
  - Brakenshire 9y ago
    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).
    - jacquesm 9y ago
      > 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.
      - vitus 9y ago
        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."
        jacquesm 9y ago
        Right you are, but the main point stands.
      - Brakenshire 9y ago
        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.
- martingoodson 9y ago
  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.
dfsegoat 9y ago
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).
- martingoodson 9y ago
  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 http://www.stat.ualberta.ca/~hooper/teaching/misc/Pvalue.pdf
mirimir 9y ago
If the trend in Fig 2 continues, it'll be obvious in a decade or so.

marcus_holmes 9y ago

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"?

jacquesm 9y ago
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.
- Brakenshire 9y ago
  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).
  - jacquesm 9y ago
    > 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.
    - vitus 9y ago
      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."
      - jacquesm 9y ago
        Right you are, but the main point stands.
    - Brakenshire 9y ago
      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.
martingoodson 9y ago
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.

dfsegoat 9y ago

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).

martingoodson 9y ago
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 http://www.stat.ualberta.ca/~hooper/teaching/misc/Pvalue.pdf

mirimir 9y ago

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