Global warming affects tropical cyclone patterns

Global warming is shifting patterns in the distribution of tropical cyclones rather than their frequency, according to an analysis of four decades of data published in the journal Proceedings of the National Academy of Sciences. 

These extreme weather events are becoming more common and severe in the Arabian Sea, central Pacific – impacting on Hawaii – and the North Atlantic, which laps the coasts of Europe and the US.

Meanwhile, despite a series of devastating storms that have battered east Asia, Japan, Africa and India, the analysis suggests the storms are occurring less frequently in the western North Pacific and Indian Ocean.

Together, atmospheric instability, wind, moisture and warm ocean temperatures provide a perfect storm for tropical cyclones (also known as hurricanes or typhoons), the planet’s most destructive and costly natural weather disasters.

There has been much emphasis on determining whether and how climate change is increasing the frequency and/or severity of these extreme weather events – which are complex and difficult to accurately measure.

Yet, despite clear hikes in average global temperatures, attributed to increased greenhouse gas emissions, the global frequency of tropical cyclones has stayed at around 86 since 1980.

Inadequate long-term data and natural decadal variations have hindered efforts to establish trends in their spatial patterns, which might contribute to this but hasn’t received as much attention despite the grave importance for coastal populations.

Hiroyuki Murakami, from the University Cooperation for Atmospheric Research in Boulder, US, and colleagues used observations between 1980 and 2018 to quantify changes in tropical cyclone activity and high-resolution dynamical models to deduce the causes of change.

They found that greenhouse gas emissions, aerosols and volcanic eruptions have influenced the variability in occurrence of tropical cyclone trends across different regions rather than their total number. 

Consistent with other studies, they found that the overall number of the extreme weather events is likely to decrease towards the end of the century, due largely to the impact of greenhouse gases on reducing cyclones in most of the tropics.

But the study didn’t address the intensity of cyclones, compounded by rising sea levels, which have both been predicted to increase as the impacts of climate change unfold.