Hurricane Matthew- Is this Climate change?

Hurricane Matthew- October 2016 

Figure 1: Definition of a hurricane

Source: http://oceanservice.noaa.gov/facts/hurricane.html

I am sure most of you reading this have read or seen in the news about Hurricane Matthew. The first I heard about Matthew was from my Nan, who rang from Jamaica, to tell us that a Category 5 hurricane was about to hit Jamaica. From the fear in her voice we knew it was more than just a bit of thunder, wind and rain that they were preparing themselves for. Luckily they escaped the worse of the impacts as it weakened, however it headed aggressively towards Haiti and the South- East coast (figure 2).

                                                                                  

Hurricane Matthew was a very powerful tropical cyclone, which set several records:

• The first Category 5 Atlantic Hurricane since Hurricane Felix in 2007. 
• The longest-lived category 4 (or higher) Atlantic hurricane in October
• The strongest storm to hit Haiti in 50 years, with the death toll being reported as over 1000.
• It joined the list of the top 10 deadliest hurricances
• And many more......

Figure 2: Path of Hurricane Matthew 

Source:http://www.nj.com/weather/index.ssf/2016/10/hurricane_matthew_questions_and_answers.html

Hurricanes and Climate Change

Hurricanes extract heat energy from the ocean and convert it to the power of the wind (figure 3), therefore the warmer the ocean, the stronger the hurricane will be, if all the other conditions it needs are met. Hurricanes generally occur over oceans when sea- surface temperatures (SSTs) exceed 26 ℃. Climate Change scientists are therefore confident that if we continue to heat up the oceans, we will see more Hurricanes like Matthew (Kossin, 2013).

Figure 3: The formation of hurricanes

Source:http://www.windows2universe.org/earth/Atmosphere/hurricane/formation.html

Studies have shown that while the amount of Hurricanes may slightly dip in the future, the most destructive ones will actually increase (Kang, 2015). Holland (2013) found that the proportion of Category 4 and 5 hurricanes has increased at a rate of ~25-30% per ℃ of global warming (figure 4). The message being put forward is that hurricanes that do occur in the future will be stronger and will intensify a lot quicker. But is this due to anthropogenic climate change?

Matthew remained a category 4-5 hurricane for 102 hours. This is the longest amount of time on record that a hurricane of this strength has persisted in the Atlantic Ocean during October. This is an indicator of climate change increasing powerful hurricanes, not only the frequency, but they are occurring in months that do not usually support tropical storms of this strength, due to warmer waters. Furthermore a prolonged length of the hurricane season has been observed- this has been increasing since 1995, which is one of the big signals of the impacts of climate change (Huffington post, 2016).

figure 4: Hurricane 1-2 category events decreasing and hurricane 4-5 events increasing - with temperature

Source: http://link.springer.com/article/10.1007/s00382-013-1713-0

What we do know for sure, is that Global warming is causing sea level rise which makes storm surges more destructive- meaning that Hurricanes such as Matthew are creating more damage, than they may have otherwise. Higher sea levels, give coastal storm surges a higher starting point when major storms approach the shore. The storm surge which is created therefore, reaches higher and penetrates further inland. This increases the risk of flooding and landslides.

What does the future hold?

As global temperatures increase, the frequency of intense category 4-5 hurricanes in the North Atlantic is projected to increase. However, the overall number of hurricanes globally is expected to either decline or remain unchanged (Bender, 2010).

Models by Emanuel (2013) suggest that under the RCP8.5 emissions pathway, the power dissipation will increase by 45% by 2100, with a 40% global increase in category 3-5 hurricanes. Bender (2010) produced very similar model projections, which projects that the frequency of category 4-5 storms increasing by 50% in the Atlantic by 2100. There are however disputes over whether the total frequency of tropical storms will increase in the future. Emanuel (2013) suggests that by the end of 2100 there will be substantial increases in tropical cyclones. However, in agreement with Bender (2010), Knutson (2010) concluded that the mean global frequency in tropical cyclones will decrease from 6- 34% by 2100.

There is however only limited evidence to suggest that these past and projected changes are due to anthropogenic warming.

Next week's blog will look at the main findings from the IPCC report on extreme events and climate change.