Mitigation of hurricane potential intensity by the Montreal Protocol

Abstract:

In the last decade, it has become apparent that the regulation of
ozone depleting substances (ODS) by the Montreal Protocol has had
profound impacts on the climate system, affecting not only surface
temperatures but also the atmospheric circulation and the entire
hydrological cycle. In this study we demonstrate that he Montreal
Protocol will also be very effective in mitigating the potential
intensity (PI) of hurricanes in the coming half century.

We accomplish this by comparing the projections of a standard CMIP5
RCP4.5 scenario to those of the so-called "World Avoided" scenario, in
which ODS grow unabated in the absence of regulations. For this
comparison, we use ouput from two 3-member ensembles of Whole
Atmosphere Community Climate Model (WACCM), integrated between 2005
and 2065. WACCM is the most comprehensive member of the Community
Earth System Models (CESM), and includes interactive stratospheric
chemistry, in addition to coupled land, ocean, and sea-ice components,

In the World Avoided projections we find that the hurricane PI is
substantially larger that in the standard RCP4.5 case. Specifically,
over the decade 2056-2065, the increase in PI is comparable to the one
between RCP4.5 and RCP8.5 for the entire multi-model mean of the CMIP5
models. Similar to what is projected by the CMIP5 models for
increasing CO2, in the World Avoided scenario the increase in hurrican
PI is due to a combined increase in sea surface temperature and CAPE,
and a decrease in the temperature in upper levels, near 70hPa.

Our WACCM simulations indicate that the mitigating effect of the
Montreal Protocol is highly significant: without ODSs regulations the
PI would be twice as large as currently projected by the middle of
this century.