Saturday 8 November 2008

Jos Verhulst on Hurricanes and Climate Change

In this post (in Dutch) on Belgium's biggest forum about politics Jos Verhulst, who is co-author on the conservative blog The brussels journal mentions that the the past two years have been below average on hurricane-activity.Jos Verhulst klimaatverandering

Verhulst writes :
Het voorbije jaar 2007 was, in schril contrast met allerlei deskundige voorspellingen, behoorlijk slap op orkaangebied. Het ACE-totaal kwam voor het noordelijk halfrond uit op 73% van het gemiddelde voor de laatste 26 jaar. En 2008 is tot op heden evenzeer in mineur verlopen.

in English, his word would mean something like (my translation) :
In sharp contrast with what experts predict, the last two years have been minor ones on the field of hurricanes. The ACE-total for the Northern Hemisphere ended on 73% of the average level of hurricane activity of the past 26 years. Above, 2008 also has shown a small hurricane-activity.

In science, hurricane activity in isn't measured by simply adding the number of hurricanes because that number doesn't say anything about the strenght of the hurricanes. Instead, scientists use an index developed by the American National Oceanic & Atmospheric Association (NOAA) which is called the ACE-index (Accumulated Cyclone Energy). This index takes into account the number, strength and duration of all tropical storms in the season.

Verhulst shows a graphic from Florida State University to support his findings :

Is Verhulst's claim correct that climate science's predicted increased hurricane activity is falsified by this graphic which shows the last two years have shown lower activity?

Well, err, no of course not !

Hurricane activity is closely related to the sea-surface temperature (SST), and this SST is something that shows huge interannual variability, most notably because of the El Nino and La Nina events, or as scientists call it : The Southern Oscillation (often referred to as the El Nino Southern Oscillation ENSO)

The KMMI (Royal Dutch Meteorological Institute) gives a nice explanation in Dutch : click

The reason the Nino/Nina events are important enough to be taken into account is the fact they alter the SST in the areas where hurricanes are formed. And the change is this big, that it clearly has an impact on hurricane activity : when you look at the years there were Nino/Nina years, and compare this to the image below, there's no doubt at all : these events have a dramatic impact on SST temperatures in areas where Hurricanes are formed.

If you look at the graphic presented by Jos Verhulst there's a very straight correlation with the Southern Oscillation :

  • The low parts of the graphic are the years there's a La Nina
  • The top parts are the years there's a El Nino event.
This means there's a very close relation between SST and hurricane activity !

This implies:
  1. science's claim that increasing temperatures could result in a higher ACE-index isn't all that weird
  2. Verhulst's claim on the ACE-index of 2007/2008 is incomplete : he forgets to take into account in which phase ENSO is at the moment, for this matters.
2007 & 2008 were years there's a ... La Nina.

Or in other words: those two years have had lower SST's because of the ENSO, and therefore showed lower hurricane activity.

Therefore, Verhulst's claim that the last two years have known hurricane below the average off the last 26 years is ... exactly what one would expect.

One again, we can see that in climate science, you cannot draw conclusions out of very short time periods. Verhulst's base period simply is way too small to conclude anything.

Shamefully, Verhulst made this post exactly one day after i explained to him his baseperiod on another topic (sea level rise) was ... too short. And this by far hasn't been the only error Verhulst has made on on the field of climate change.

My conclusion is very clear :
Despites his high level of arrogance towards the scientific community, Jos Verhulst demonstrates time after time after time he fails to understand climate science. Verhulst instead is just another libertarian who gets blinded by his bias. Hereby helped by the known inreliable websites he frequently cites like e.g. co2-science

Verhulst concludes his post with :
Men kan nu een eenvoudige geestelijke oefening uitvoeren. Beeld u in, dat tijdens de laatste twee jaren de orkaanactiviteit sterk bovengemiddeld ware geweest. Denkt u, dat de media over deze bovengemiddelde activiteit dan dezelfde radiostilte in acht zouden nemen, die we nu vaststellen in verband met de sterk verlaagde activiteit? Denkt u, dat men dan zou zeggen dat twee jaar een te korte periode is om conclusies te trekken?

De vraag stellen is ze beantwoorden. Let maar op het propagandistisch wolvengehuil dat zal opstijgen, zodra er weer een jaar komt met meer orkanen dan gemiddeld.

or, in English (once again, my translation) :
Time to make a little mental exercise : picture that the last two years, hurricane activity would have been above average : do u think the media would have been as silent about the topic as they are now activity is below average ?
Asking the question means you have to answer it : be sure that the wolves' cries of propaganda will rise again as soon as there'll be a year activity is above average.

As Sarah Palin would say : it's all about the liberal media elite.

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