Hurricanes and global warming

July 19, 2007

There’s an article in Scientific American (July 2007) about the relation between global warming and hurricanes. I learned a few things from this:
A cyclone, typhoon and hurricane are the same thing; they only differ in the region where they are observed.

How do hurricanes form?

  • The sun raises the Sea Surface Temperature (SST)
  • Water is evaporated to release the excess heat
  • The moisture raises and condenses into rain
  • When raindrops are formed, latent energy is released
  • The heat goes up and creates ‘updrafts and thunderclouds’
  • Beneath this area, a low pressure zone is created which ‘sucks up’ moist air
  • Due to Coriolis forces due to the earth’s rotation a vortex is created
  • “The eye” is a low pressure area at the bottom of this vortex
  • Due to the circling hot air, the rising air dries and gains energy
  • Some of this air is absorbed again in the eye, and some of the air ‘spirals out’ over a large area (many kilometres)

How hurricanes form - Copyright Scientific American

The different seasons play a role as well:
The energy released when raindrops form heats the atmosphere

  • In winter, the heat goes up and radiates into space
  • In summer, the heat rises to higher altitudes in tropical areas

Further ingredients needed to start a hurricane:

  • high SST (>26 degrees Celsius); SST may rise due to the greenhouse effect
  • plentiful water vapour
  • low pressure at the ocean’s surface
  • weak wind shear between low and high altitudes (strong winds destroy emerging vortices)

The rising SST may (partly) originate from the greenhouse effect. However, in 2004 and 2005 we saw a lot of hurricanes, but 2006 was a quiet year.

Some scientists believe this is due to the “Atlantic Multidecadal Oscillation” (AMO), which is basically a cycle in which temperatures rise and fall. But simulation shows that this can’t be the whole story (the temperature difference is only 0.5 degrees Celsius). The models do show (as far as they are correct; which is difficult to assess) that human action is likely a cause of the rising SST. Approximately 0.6 degrees Celsius can be attributed to human action (probably without the AMO) since 1970. It is noted that this may sound small, but only one degree can change the storm’s intensity to a higher category. This may well explain the rise in the number of ‘high’ category hurricanes.

The fact that 2006 was a quiet year (in stark contrast to 2004 and 2005) is due to a different factor. In 2004/2005, El Nino warmed the ocean. La Nina cooled the ocean the subsequent year. This is explained in the remainder of the article.

The article concludes that the hurricane threats are likely to get more severe.



  1. interesting point is arising from all this… The simple remark “proves 0.6 to be caused by humans”.

    Other reports state the opposite, and growing support… So it would be interesting if the article showed why it is so certain by human behaviour…? Human CO2, in the grand scale, seems to be peanuts.

    More interest should, according to some others, be directed towards the direct influence of the sun on our climate. Coincidently, weather is getting more intense – weather meaning solair storms and proven temperature rises on earth…

    Final thought… Even when there was a drop op sucking hurricanes, global trend indeed shows that storms are more intense then “ever?” before. As is said by some about the levels of CO2 in the atmosfere – only the Jura or something like that equaled us. That would mean big musquito’s for the future :/

    Peace – the ice age in 2020 will save us all of CO2 (if we do not all get killed in 2012 ;-)

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    /||’ /|

  2. Yeah, that’s why I made the remark about the correctness of the models. There are contradicting reports about it, and it’s difficult/impossible to prove any claim. However, I don’t believe humans didn’t have any influence whatsoever on the temperature. But again, it’s difficult/impossible to quantify the influence.

  3. Haha, we’re in a warm period at the moment if we are speaking about archaeological weather/climate periods. This will prolly be around for a couple of thousand years. Studies (pollen analysis/isotopes)have already shown the repetitive warm and cold periods in the past.
    No worries, we will all be toast or living in special environments or in space by then.
    I think the human influence has helped a hand when it comes to global warming. So maybe just maybe, the rise to a scorching heat and cold icey plains will come a tad quicker (Say a few hundred years earlier? xD).

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