Tropical Cyclones and Climate Change: An Updated Assessment (Invited Presentation)

The possible impact of anthropogenic climate change on tropical cyclone activity is a topic of considerable societal and scientific interest, and has received renewed attention with the active 2017 Atlantic hurricane season. In this talk, I will provide a status report on an updated assessment of tropical cyclones and climate change-- an assessment report which is currently under development. The assessment is focused on two main issues: the detection and attribution of possible human influence on tropical cyclone activity; and projections of tropical cyclone activity for the late 21^st century based on model-simulated global warming scenarios.

Anthropogenic influence on hurricane activity is far less confidently known than is the case for a number of other climate variables such as global mean temperature. Nonetheless, several examples of multidecadal trends in tropical cyclone metrics have been identified in recent years, including poleward migration of the latitude of maximum intensity, a slowing of tropical cyclone propagation speeds, and intensity changes in some basins. These are assessed to estimate how unusual they are compared to expected variability from natural causes alone and whether anthropogenic forcing appears to have contributed to them or not. In addition, we review and assess several published examples of event attribution, as applied to tropical cyclone cases or seasonal activity, including Hurricane Harvey’s (2017) precipitation.

Future tropical cyclone activity projections, as obtained from updated models, tend to support earlier projections of increases in tropical cyclone rainfall rates (for a given storm), increases in global average tropical cyclone intensity, and decreases in global tropical cyclone frequency, at least in most studies.

This assessment activity has been initiated by the WMO, through its Working Group on Tropical Meteorology Research, which formed a Task Team on Tropical Cyclones and Climate Change, charged with updating an earlier (2010) assessment.