Projections of Changing Cyclone Fre-quency in Relation to Climate Change Demonstrating Uncertainty

While a steadily increasing global temperature is not much in dispute, the effect of such a warming on climate is subject to much debate.  Knutson et al. (2010) compared older modeling studies, which tended to project a decrease in overall cyclone<!–[if supportFields]> XE “cyclone” <![endif]–><!–[if supportFields]><![endif]–> frequency with newer, higher resolution studies, which are more likely to predict an increase in the most intense cyclones<!–[if supportFields]> XE “cyclones” <![endif]–><!–[if supportFields]><![endif]–>.  The newest methods of projection, satellite analysis, and downscaling techniques are examined, as well as the newer, high-resolution projection models of tropical storm activity. The results suggest that while climate model<!–[if supportFields]> XE “climate model” <![endif]–><!–[if supportFields]><![endif]–>s are progressively more reliable, we cannot identify anthropogenic signals in past cyclone data, and therefore are severely limited in our ability to make projections with current data. Further research is highly recommended by Knutson et al. in order to enhance the reliability of climate-relevant observations in the future, since there is a high level of societal impact of tropical storms.—Brian Nadler
Knutson, T.R., McBride, J.L., Chan, J., Emanuel, K., Holland, G., Landsea, C., Held, I., Kossin, J.P., Srivastava, A.K., and Sugi, M. 2010. Tropical Cyclones and Climate Change. Nature Geoscience, 3, 157–163.

          The primary challenge for tropical cyclone<!–[if supportFields]> XE “cyclone” <![endif]–><!–[if supportFields]><![endif]–> detection and attribution research is determining whether or not an observed change in tropical cyclone activity exceeds the natural variability of the event, and if so, attributing the change to a specific climate forcing<!–[if supportFields]> XE “climate forcing” <![endif]–><!–[if supportFields]><![endif]–>.  For projections in the future, the ultimate goal is to develop a reliable projection of these changes in factors that influence cyclone activity, as the resulting effect on storm frequency, track, and distribution.
          T.R. Knutson and colleagues conducted their research with the World Meteorological Organization, along with support by the West Australian Government Indian Ocean Climate Initiative.  In all models, there was a strong tendency to project an increase in stronger tropical cyclones<!–[if supportFields]> XE “cyclones” <![endif]–><!–[if supportFields]><![endif]–><!–[if supportFields]> XE “cyclone” <![endif]–><!–[if supportFields]><![endif]–> over the 21st century.  Detection and attribution was observed for characteristics such as tropical cyclone rainfall, genesis, tracks, duration and surge flooding, as well as activity versus sea surface temperature.  It was also observed that tropical cyclone frequency would likely remain the same overall, but that there would be a shift to more radical tropical storm activity, of a range of category 4 or higher.
          Throughout the study there were numerous variables that were identified as having a potential effect on tropical storm activity.  Knutson and colleagues were able to improve several aspects of cyclone<!–[if supportFields]> XE “cyclone” <![endif]–><!–[if supportFields]><![endif]–> activity projections, resulting in their predictions that tropical cyclone frequency will remain essentially the same, along with a global increase in the average frequency of strongest tropical cyclones<!–[if supportFields]> XE “cyclones” <![endif]–><!–[if supportFields]><![endif]–>.  It was recommended that newer models be created that have an increasingly more detailed spatial resolution and new approaches for observing past tropical cyclone records that would reduce uncertainty of causes of past changes, and be able to better predict future tropical cyclone activity.  Future projections of variables such as sea-level rise<!–[if supportFields]> XE “sea-level rise (SLR)” <![endif]–><!–[if supportFields]><![endif]–>, regional storm structure, and storm characteristics, need to be taken into account, as well as examining the assumption that there will be no future changes that have a markedly different effect on tropical cyclone behavior than is seen today. 

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