The last three Atlantic hurricane seasons (2016–2018) were very active. In 2018 the season started early and ultimately produced more named storms and more hurricanes than an average year. The 2017 season was the costliest on record, causing more than $200 billion in storm damage from June to November (Hurricane Katrina’s season cost an estimated $159 billion). The 2016 hurricane season lasted almost 11 months and included a category 5 storm.
Active hurricane seasons are associated with warm sea surface temperatures, which fuel tropical cyclones. Scientists have observed stronger storms in the North Atlantic since the 1980s. But how much have human activities contributed to this trend, and how much is from natural variability?
Trenary et al. examined several climate models to evaluate how human-caused factors like greenhouse gases and aerosols might have affected a hurricane’s potential intensity, or the theoretical maximum intensity a storm could reach based on the surrounding environmental conditions.
The team first found that greenhouse gas warming and aerosol cooling produced changes in potential intensity that had very similar spatial patterns, making them difficult to separate in observations. They then evaluated the impacts of the combined responses and could not find a coherent response across the models—some models simulated an increase in potential intensity while others simulated a decrease. This discrepancy reveals that potential intensity is sensitive to how an individual model responds to human-caused factors. Given this sensitivity and the large natural swings in potential intensity in the Atlantic, it is not surprising that a human influence on potential intensity has not been detected yet. This result is consistent with mainstream science: Although models disagree about past changes in hurricane potential intensity, they all agree that Earth is warming because of human activities. Moreover, although human impacts on potential intensity are not currently detectable, observations could potentially reveal detectable changes in other hurricane-related characteristics.
In the future, aerosol emissions are expected to decrease as a result of more aggressive air pollution policies. Meanwhile, greenhouse gases will undoubtedly continue to accumulate in the atmosphere, leading to future increases in potential intensity. (Geophysical Research Letters, https://doi.org/10.1029/2018GL081725, 2019)
—Elizabeth Thompson, Freelance Writer