Friday, December 6, 2013

New paper predicts tropical cyclones will decrease 6%-40% over the 21st century

A paper published today in the Journal of Climate predicts finds climate models "project significant decreases in global total frequency of occurrence of tropical cyclones by approximately 6%–40%" over the 21st century.  The paper corroborates many other peer-reviewed papers projecting a decrease of the frequency and intensity of tropical cyclones and hurricanes in the future. Multiple observational studies also find that tropical cyclones decrease with warming

Influence of model biases on projected future changes in tropical cyclone frequency of occurrence

Hiroyuki Murakami,1,2 Pang-Chi Hsu,1 Osamu Arakawa,2,3 and Tim Li1
1 Department of Meteorology and International Pacific Research Center, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA
2 Meteorological Research Institute, Tsukuba, Ibaraki, Japan
3 Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan

The influence of model biases on projected future changes in the frequency of occurrence of tropical cyclones (FOCs) was investigated using a new empirical statistical method. Assessments were made of present-day (1979–2003) simulations and future (2075–2099) projections, using atmospheric general circulation models under the Intergovernmental Panel on Climate Change (IPCC) A1B scenario and the fifth Coupled Model Intercomparison Project (CMIP5) models under the representative concentration pathway (RCP) 4.5 and 8.5 scenarios. The models project significant decreases in global-total frequency of occurrence of tropical cyclones by approximately 6%–40%; however, model biases introduce an uncertainty of approximately 10% in the total future changes. The influence of biases depends on the model physics rather than model resolutions and emission scenarios. In general, the biases result in overestimates of projected future changes in basin-total FOCs in the North Indian Ocean (by +18%) and South Atlantic Ocean (+143%), and underestimates in the western North Pacific Ocean (−27%), eastern North Pacific Ocean (−29%), and North Atlantic Ocean (−53%). The calibration of model performance using the smaller bias influence appears crucial to deriving meaningful signals in future FOC projections. To obtain more reliable projections, ensemble averages were calculated using the models less influence by model biases. Results indicate marked decreases in projected FOCs in the basins of the Southern Hemisphere, the Bay of Bengal, western North Pacific Ocean, eastern North Pacific, and the Caribbean Sea, and increases in the Arabian Sea and the subtropical central Pacific Ocean.

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