Wednesday, April 06, 2011

Faster sailing across the Central Pacific: Wind speeds and El Nino

The new paper by Young et al. about increasing wind speeds and wave heights over the past twenty years created a bit of a buzz in the climate science world, not to mention the sailing world. Finally some good news, the windsurfer in me first upon seeing the paper.

The paper itself does not speculate about whether human-caused climate change is the driver of the global trend in wind speeds. That may have been a wise choise, as it would be difficult, statistically or dynamically, to attribute the rend in the reasonably short time series (~23 years) to any single forcing factor.

The spatial pattern, however, is quite striking:

If there were no labels on this figure, I'd have guessed it was the trend in sea surface temperatures over the same time period. The steepest trend is in the Central Pacific, including the waters around the Gilbert and Phoenix Islands of Kiribati.

In a map of temperature trends over the past two to three decades, the Central Pacific should jump out because of the increasing frequency of "Central Pacific" El Nino events, also known as El Nino Modoki. The more freuqent occurences of the "CP" El Nino is a subject of much research, and has been attributed by some authors to climate warming. The CP El Nino is responsible for a number of mass coral bleaching events, including 2002-3 in the Phoenix Islands, 2004-5 in the Gilbert Islands, and 2009-10 across the whole region.

It is not surprising to find a similar -- at least visually, take this with a grain of salt, I've not done the statistics -- spatial pattern in the surface wind speeds across the Pacific. More frequent Central Pacific warm events likely means larger pressure gradients, more convergence, and higher winds across the region (my paper in  the Atoll Research Bulletin describesa CP El Nino event in relatively lay terms). More analysis will need to be done, but at first glance, the wind speed trends over the Pacific appear to be driven by temperature trends and the status of climate oscillations, which themselves may be driven in part by climate change.

1 comment:

fishonareef said...

Hi Dr Donner,
Did you know that your blog has been blocked on Facebook? Someone has flagged it as abusive/spam. I did write to them to let them know that that is an error that needs to be reversed.
Thank you for all of your great posts. Cheers, Darla