16 February 2018

Changes in Tropical Cyclones Under Stabilized 1.5oC and 2.0oC Global Warming Scenarios as Simulated by the Community Atmospheric Model under the HAPPI Protocols


We present a projection of future tropical cyclone statistics for both 1.5oC and 2.0oC stabilized warming scenarios by direct numerical simulation using a high-resolution global climate model. As in similar projections at higher warming levels, we find that even at these low warming levels the most intense tropical cyclones become more frequent and more intense, while simultaneously the frequency of weaker tropical storms is decreased. We also conclude that in the 1.5oC stabilization, the effect of aerosol forcing changes complicates the interpretation of greenhouse gas forcing changes.


The United Nations Framework Convention on Climate Change (UNFCCC) invited the scientific community to explore the impacts of a world where anthropogenic global warming is stabilized at only 1.5oC above pre-industrial average temperatures. This work is cited in the special report of the Intergovernmental Panel on Climate Change.


The Half a degree additional warming, Prognosis and Projected Impacts (HAPPI) experimental protocol was designed to rapidly inform the Intergovernmental Panel on Climate Change about the differences between stabilized climate at 1.5oC and 2.0oC above pre-industrial global temperatures. However, it does not isolate all of the effects of forcing changes required to stabilize the climate from the present day conditions. It is fair to say that the simulated differences tropical cyclone statistics between the 1.5oC and 2.0oC stabilization scenarios as defined by the HAPPI protocols are small. Indeed, both warmer climates produce fewer tropical storms over all intensities in the global sense and the reduction increases as the sea surface temperature (SST) becomes warmer. Also, the most intense storms become more intense in both warmer SST configurations with the highest peak wind speeds and lowest central pressure minima simulated in the warmer of two stabilizations. Given the similarities between the two HAPPI scenarios and the importance of aerosol forcings, a more complete understanding of tropical storm frequency in aggressively stabilized climates requires detailed descriptions of the changes in those forcings.

William D. Collins
Lawrence Berkeley National Laboratory (LBNL)