An update on the influence of natural climate variability and anthropogenic climate change on tropical cyclones

A substantial number of studies have been published since the Ninth International Workshop on Tropical Cyclones(IWTC-9)in 2018,improving our understanding of the effect of climate change on tropical cyclones(TCs)and associated hazards and risks.These studies have reinforced the robustness of increases in TC intensity and associated TC hazards and risks due to anthropogenic climate change.New modeling and observational studies suggested the potential influence of anthropogenic climate forcings,including greenhouse gases and aerosols,on global and regional TC activity at the decadal and century time scales.However,there are still substantial uncertainties owing to model uncertainty in simulating historical TC decadal variability in the Atlantic,and the limitations of observed TC records.The projected future change in the global number of TCs has become more uncertain since IWTC-9 due to projected increases in TC frequency by a few climate models.A new paradigm,TC seeds,has been proposed,and there is currently a debate on whether seeds can help explain the physical mechanism behind the projected changes in global TC frequency.New studies also highlighted the importance of large-scale environmental fields on TC activity,such as snow cover and air-sea interactions.Future projections on TC translation speed and medicanes are new additional focus topics in our report.Recommendations and future research are proposed relevant to the remaining scientific questions and assisting policymakers.

Third assessment on impacts of climate change on tropical cyclones in the Typhoon Committee Region——Part Ⅰ:Observed changes, detection and attribution

Published findings on climate change impacts on tropical cyclones(TCs)in the ESCAP/WMO Typhoon Committee Region are assessed.We focus on observed TC changes in the western North Pacific(WNP)basin,including frequency,intensity,precipitation,track pattern,and storm surge.Results from an updated survey of impacts of past TC activity on various Members of the Typhoon Committee are also reported.Existing TC datasets continue to show substantial interdecadal variations in basin-wide TC frequency and intensity in the WNP.There has been encouraging progress in improving the consensus between different datasets concerning intensity trends.A statistically significant northwestward shift in WNP TC tracks since the 1980s has been documented.There is low-to-medium confidence in a detectable poleward shift since the 1940s in the average latitude where TCs reach their peak intensity in the WNP.A worsening of storm inundation levels is believed to be occurring due to sea level rise-due in part to anthropogenic influence-assuming all other factors equal.However,we are not aware that any TC climate change signal has been convincingly detected in WNP sea level extremes data.We also consider detection and attribution of observed changes based on an alternative Type II error avoidance perspective.

Third assessment on impacts of climate change on tropical cyclones in the Typhoon Committee Region-Part Ⅱ:Future projections

This paper assesses published findings on projections of future tropical cyclone(TC)activity in the ESCAP/WMO Typhoon Committee Region under climate change scenarios.This assessment also estimates the projected changes of key TC metrics for a 2℃anthropogenic global warming scenario for the western North Pacific(WNP)following the approach of a WMO Task Team,together with other reported findings for this region.For projections of TC genesis/frequency,most models suggest a reduction of TC frequency,but an increase in the proportion of very intense TCs over the WNP in the future.However,some individual studies project an increase in WNP TC frequency.Most studies agree on a projected increase of WNP TC intensity over the 21 st century.All available projections for TC related precipitation in the WNP indicate an increase in TC related precipitation rate in a warmer climate.Anthropogenic warming may also lead to changes in TC prevailing tracks.A further increase in storm surge risk may result from increases in TC intensity.The most confident aspect of forced anthropogenic change in TC inundation risk derives from the highly confident expectation of further sea level rise,which we expect will exacerbate storm inundation risk in coastal regions,assuming all other factors equal.

IMPACTS OF CLIMATE CHANGE ON TROPICAL CYCLONES IN THE WESTERN NORTH PACIFIC BASIN. PART Ⅱ: LATE TWENTY-FIRST CENTURY PROJECTIONS

This paper reviews the latest studies on the relationship between projected late 21 st century climate changes and tropical cyclone(TC) activity in the western North Pacific(WNP) basin, which is the region of the United Nations Economic and Social Commission for Asia and the Pacific(ESCAP)/World Meteorological Organization(WMO) Typhoon Committee members. Existing studies of projected changes of TC activity in this basin, such as frequency, intensity, precipitation, genesis location and track pattern are summarized, based on an assumed A1 B future climate change scenario. A review of available studies on projected future changes in WNP landfalling TC activity is also included.While it remains uncertain whether there has been any detectable human influence on tropical cyclone frequency, intensity, precipitation, track, or related aggregated storm activity metrics in the basin, modeling studies suggest changes in future tropical cyclone activity for the WNP basin. More models project decreases than increases in tropical storm frequency(range-70% to +60%);most studies project an increase in the TC intensity(range-3% to +18%);and all six available studies that include the WNP basin project increases in TC precipitation rates(range +5 to +30%).

IMPACTS OF CLIMATE CHANGE ON TROPICAL CYCLONES IN THE WESTERN NORTH PACIFIC BASIN. PART Ⅰ: PAST OBSERVATIONS

This paper reviews the current state of the science on the relationship between climate change and historical tropical cyclone(TC) activity in the western North Pacific(WNP) basin, which is the region of the ESCAP/WMO Typhoon Committee members. Existing studies of observed changes of TC activity in this basin, such as frequency, intensity, precipitation, genesis location and track pattern are summarized. Results from a survey on impacts of past TC activity on various members of Typhoon Committee are reported, along with a review of studies of past WNP landfalling TCs.With considerable interannual and interdecadal variations in the TC activity in this basin, it remains uncertain whether there has been any detectable human influence on tropical cyclone frequency, intensity, precipitation, track, or related aggregated storm activity metrics. Also, the issues of homogeneity and consistency of best track data sets in the WNP further add uncertainty to relevant research studies. Observations indicate some regional shifts in TC activity in the basin, such as a decreasing trend in TC occurrence in part of the South China Sea and an increasing trend along the east coast of China during the past 40 years. This change is apparently related to local circulation changes in the eastern Asia and WNP, though the cause of the circulation changes remains unknown.