Understanding Uncertainties in Projections of Western North Pacific Tropical Cyclogenesis

Reliable projections of tropical cyclone (TC) activities in the western North Pacific (WNP) are crucial for climate policy-making in densely-populated coastal Asia. Existing projections, however, exhibit considerable uncertainties with unclear sources. Here, based on future projections by the latest Coupled Model Intercomparison Project Phase 6 climate models, we identify a new and prevailing source of uncertainty arising from different TC identification schemes. Notable differences in projections of detected TCs and empirical genesis potential indices (GPIs) are found to be caused by inconsistent changes in dynamic and thermodynamic environmental factors affecting TC formations. While model uncertainty holds the secondary importance, we show large potential in reducing it through improved model simulations of present-day TC characteristics. Internal variability noticeably impacts near-term projections of the WNP tropical cyclogenesis, while the relative contribution of scenario uncertainty remains small. Our findings provide new insights to TC projections that understanding relative contributions of different uncertainty sources helps devote future efforts to addressing the key uncertainties. With coordinated efforts in high-quality observations, improved process understanding and high-resolution multi-model ensemble covering a long future period with same forcings, we may expect a further increased confidence in projections of TC activities.