Climate change a factor in U.S. east coast hurricane threat: Researchers

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Climate change is a factor in the intensity of hurricanes that threaten to strike the east coast of the United States, according to researchers who say that CO2 and greenhouse gases are helping to diminish the wind shear that can act as a barrier to storms.

hurricane-irma-2017Wind shear along the U.S. east coast has long been attributed to being a factor that can help to diminish the power of hurricanes as they approach the seaboard, known to disrupt the structure of tropical storms and as a result lower the chances of them making an intense landfall.

The presence or otherwise of wind shear can dictate the direction hurricanes travel in, their ability to organise and intensify, the intensity they can reach, their size and other factors of relevance to insurance, reinsurance and ILS market interests.

The presence of vertical wind shear (VWS) exhibits a strong control over Atlantic hurricanes, the researchers explain in a recently published Scientific Reports paper.

In particular, when wind shear is lessened in the main development region (MDR) of the Atlantic, a “protective barrier” of high vertical wind shear can often be seen to inhibit hurricane intensification along the U.S. East Coast.

The paper explains that this pattern is largely driven by natural variability, but also that greenhouse gases, in particular those most often linked to climate change, are seen to degrade this natural wind shear barrier along the U.S. east coast.

Using modern climate models, the researchers work shows that the vertical wind shear barrier during decadal periods of enhanced hurricane activity is substantially reduced under greenhouse gas forcing.

The researchers go on to explain that climate change related increases in CO2 and greenhouse gases are expected to result in raised sea surface temperatures (SST’s), another important factor in hurricane season activity and the intensity of storms, but that the impact on vertical wind shear was less certain.

They found that vertical wind shear has not been particularly influenced by the anthropogenic radiative forcing of greenhouse gases in recent decades, but their modelling shows that as greenhouse gas forcing increases the vertical wind shear will be affected.

Vertical wind shear could be influenced in different ways for different regions, with the U.S. east coast the most likely to see a weakened state, while other areas such as the Gulf of Mexico may see vertical wind shear actually increase under a climate change induced greenhouse gas increase.

“The implication of the anthropogenically forced future VWS suppression along the U.S. East Coast is that future hurricanes may go through stronger intensification and cause more powerful destructions when moving into the coastal region,” the researchers state.

They go on to discuss hurricane potential intensity (PI) and relate that to sea surface temperature increases and greenhouse gas forcing, resulting in a more concerning forecast for insurance and reinsurance interests, as well as those living along the U.S. eastern seaboard, that the hurricanes of the future could be more intense than the hurricanes of the past

“The fast increase in PI along the U.S. East Coast, coupled with the more favorable wind shear environment for hurricane intensification there, suggests that hurricanes tracking toward the U.S. East Coast will have a better chance of achieving its PI in the future, which may be much stronger than what we’ve experienced in the past,” the researchers warn.

Model runs suggest that the natural protection that Atlantic multidecadal variability and its influence on wide shear provides the U.S. may be substantially eroded by anthropogenic (climate change related) forcing by the year 2050, with effects perhaps being seen as early as 2020 according to some climate models.

The researchers summarise, “Our results emphasize the potential threat that hurricanes may become more intense in the future as they move toward the East Coast of the United States. This is mainly caused by a reduction of future vertical wind shear (VWS) along the U.S. East Coast, which favors the intensification of hurricanes by less dispersion of latent heat energy, compared to the case of strong VWS. The weak vertical wind shear environment would help hurricanes reach their potential intensity, the maximum possible intensity given the environmental conditions, which has already increased in magnitude due to warmer sea surface temperatures.”

So the U.S. east coast may not be able to rely on wind shear providing a barrier to hurricanes in years where multidecadal conditions are set up in the right manner, reducing the overall effect that the multidecadal variability in the Atlantic has on east coast hurricane potential intensity and perhaps also landfalls, if the barrier is less effective.

The results provide an intriguing look into how anthropogenic climate change and related greenhouse gas plus CO2 forcing could influence hurricane season activity and perhaps even impacts, as a reduced wind shear barrier could mean more landfalls and potentially stronger storms reaching the coastline, as well as the potential for hurricanes to sustain their intensity for longer when they near the coast.

Climate change related models are notoriously difficult to interpret, but this piece of research looks like one the insurance, reinsurance, insurance-linked securities (ILS) and catastrophe bond community would be wise to delve deeper into, especially with the 2019 Atlantic hurricane season set to officially begin on June 1st.

You can find more on the research here.

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