Hurricanes and Climate Change
by Joe Morris
This past September saw three major hurricanes strike the US mainland and the islands in the Caribbean, causing hundreds of lost lives and estimated damages exceeding $300B. Irma reached a Level 5 with the highest velocity winds ever measured in the Atlantic. This comes in the wake of Typhoon Patricia with the highest winds ever measured in the Pacific. Naturally, the question has been raised as to whether climate change influenced these storms. While the NOAA (weather service) announced that the last four years were the hottest on record, along with correspondingly warmer Atlantic waters, there seems to have been a hiatus of major storms since 2005. Hurricanes require warmer waters. So how can we rectify these seeming contradictions?
Sometimes climate change effects may seem counterintuitive, like colder winters in some areas despite a warming planet. This occurs because the effects of climate change must be superimposed on Earth’s complex climate patterns. Hurricane activity and intensity may be one of those cases. For example, the bane of hurricane formation is wind shear, i.e., the difference in wind speeds at high and low altitudes. The jet stream influences wind shear, and many climate patterns impact jet stream direction and velocity. We’ve all heard of one Pacific Ocean climate pattern, El Nino, along with its sister, La Nina. El Nino occurs as a result of warmer waters and changing trade winds in the eastern Pacific. It impacts weather in the western hemisphere by altering the direction and velocity of the jet stream. Warmer water in the Pacific will probably also mean warmer water in the Atlantic, a prime condition for hurricanes. However, El Nino alters the jet stream to create wind shear that inhibits the growth of hurricanes. So even though there are warmer waters, the wind shear counters that condition.
The Atlantic has its own patterns that can affect hurricane formation. The Atlantic Multidecadal Oscillation (AMO) affects ocean surface temperature, salinity, and other factors in a multi-decade-long cycle that influences rainfall in the western hemisphere as well as hurricane formation. The relationship between the AMO and climate change is still under study. The aforementioned decade-long hiatus in major storm formation has been attributed to the natural AMO cycle. There’s another complicating factor influencing hurricanes. The area of ocean warming in the Atlantic is growing larger each year, which should lead to increased hurricane creation with increased intensity. However, because this increased area of warm water is extending further east, some of these hurricanes may never reach the US mainland and pass into the Atlantic.
So, while we can intuitively associate an increase in hurricane frequency and intensity due to warmer waters in the Atlantic, the actual impact of climate change may be masked, enhanced, or modified by these complicating climate factors. In my opinion, we’ll have to wait for more data and improved simulations to firm up the direct effects of climate change on hurricanes. However, rising sea levels attributed to climate change already implies that hurricanes will produce more coastal flooding. Therefore, it doesn’t make sense to rebuild in the same way and ignore the potential of future flooding. It’s a national discussion we need to have.Last updated: January 1, 2018 at 13:12 pm