Monday, February 22, 2010

Tropical cyclones and climate change

An abstract from Nature Geoscience by Thomas R. Knutson, John L. McBbride, Johnny Chan, Kerry Emanuel, Greg Holland, Chris Landsea, Isaac Held, James P. Kossin, A. K. Srivastava & Masato Sugi: Whether the characteristics of tropical cyclones have changed or will change in a warming climate — and if so, how — has been the subject of considerable investigation, often with conflicting results. Large amplitude fluctuations in the frequency and intensity of tropical cyclones greatly complicate both the detection of long-term trends and their attribution to rising levels of atmospheric greenhouse gases.

Trend detection is further impeded by substantial limitations in the availability and quality of global historical records of tropical cyclones. Therefore, it remains uncertain whether past changes in tropical cyclone activity have exceeded the variability expected from natural causes.

However, future projections based on theory and high-resolution dynamical models consistently indicate that greenhouse warming will cause the globally averaged intensity of tropical cyclones to shift towards stronger storms, with intensity increases of 2–11% by 2100. Existing modelling studies also consistently project decreases in the globally averaged frequency of tropical cyclones, by 6–34%. Balanced against this, higher resolution modelling studies typically project substantial increases in the frequency of the most intense cyclones, and increases of the order of 20% in the precipitation rate within 100 km of the storm centre. For all cyclone parameters, projected changes for individual basins show large variations between different modelling studies….

Before the year 2004, only two tropical cyclones had ever been noted in the South Atlantic Basin, and no hurricane. The crew of the International Space Station was notified of the cyclone and acquired excellent photographs of the storm just as it made landfall on the southern Brazilian state of Santa Catarina (the storm has been unofficially dubbed “Cyclone Catarina”). Note the clockwise circulation of Southern Hemisphere cyclones, the well-defined banding features, and the eyewall of at least a Category 1 system. The coastline is visible under the clouds in the upper left corner of the image.

No comments: