The Effect of Forced and Unforced Variability on Heat Waves, Temperature
Extremes, and Associated Population Risk in a CO2-Warmed World
Abstract
This study investigates the impact of global warming heat and humidity
extremes by analyzing 6-hourly output from 28 members of the Max Planck
Institute Grand Ensemble driven by forcing from a 1%/year
CO2 increase. We find that unforced variability drives
large changes in regional exposure to extremes in different ensemble
members, and these variations are mostly associated with ENSO
variability. However, while the unforced variability of the climate can
alter the occurrence of extremes regionally, variability within the
ensemble decreases significantly as one looks at larger regions or at a
global population perspective. This means that, for metrics of extreme
heat and humidity analyzed here, forced variability of the climate is
more important than the unforced variability at global scales. Lastly,
we found that most heat wave metrics will increase significantly between
1.5°C and 2.0°C, and that low GDP regions shows significant higher risks
of facing extreme heat events compared to high GDP regions. Considering
the limited economic adaptability of population on heat extremes, this
reinforces the idea that the most severe impacts of climate change may
fall mostly on those least capable to adapt.