Highly unusual upward trends in rapidly intensifying Atlantic hurricanes are caused by global warming

Desdemona Despair

By Dr. Jeff Masters
13 February 2019

(Weather Underground) – Atlantic hurricanes showed “highly unusual” upward trends in rapid intensification during the period 1982 – 2009 that can only be explained by including human-caused climate change as a contributing cause, according to research published last week in Nature Communications. The study, led by NOAA/GFDL hurricane scientist Kieran Bhatia, is titled, Recent increases in tropical cyclone intensification rates.

The paper used two different data sets to study historical tropical cyclone intensification rates: a relatively coarse-resolution satellite data set (HURSAT), and a higher-resolution “best track” data set (IBTrACS) that included all available data, including satellite and hurricane hunter data. Both data sets found that for the Atlantic, there was a significant increase in the proportion of 24-hour intensification rates greater than 30 knots (35 mph) between 1982 and 2009. The greatest change was seen for the strongest 5% of storms, whose intensification rates increased by 3 – 4 knots per decade.

For tropical cyclones across the entire globe, the two data sets disagreed. The “best track” data set showed a significant increase in 24-hour intensification rates, while the satellite-only data set did not. The authors theorized that the satellite-only data set was faulty, likely because of well-documented problems judging tropical cyclone intensities during formation of the eye. Due to this discrepancy in the two data sets, the authors were unable to make conclusions on how tropical cyclone intensification rates might be changing globally.

By itself, a 28-year upward trend in one measure of hurricane intensification does not necessarily mean that human-caused climate change is to blame. Natural variability of the climate system, like the decades-long natural cycle in Atlantic hurricane activity called the Atlantic Multidecadal Oscillation (AMO), could be to blame. To see if this was the case, the authors used one of the best global climate models available for studying long-term trends in Atlantic hurricanes, the HiFLOR model. [more]

Recent increases in tropical cyclone intensification rates

ABSTRACT: Tropical cyclones that rapidly intensify are typically associated with the highest forecast errors and cause a disproportionate amount of human and financial losses. Therefore, it is crucial to understand if, and why, there are observed upward trends in tropical cyclone intensification rates. Here, we utilize two observational datasets to calculate 24-hour wind speed changes over the period 1982–2009. We compare the observed trends to natural variability in bias-corrected, high-resolution, global coupled model experiments that accurately simulate the climatological distribution of tropical cyclone intensification. Both observed datasets show significant increases in tropical cyclone intensification rates in the Atlantic basin that are highly unusual compared to model-based estimates of internal climate variations. Our results suggest a detectable increase of Atlantic intensification rates with a positive contribution from anthropogenic forcing and reveal a need for more reliable data before detecting a robust trend at the global scale.

Recent increases in tropical cyclone intensification rates