Is Global Warming Responsible for the Increased Number and Strength of Hurricanes?

The hurricane season for 2017 is just past its half way point and already this year has proven to be abnormally deadly and destructive. Hurricane Harvey inundated southeast Texas with over a meter of rain while Hurricane Irma wrecked several Caribbean Islands before causing a trail of destruction the length of the Florida peninsula. By some measurements Irma was the strongest Atlantic storm ever seen, remaining a category five storm longer than any on record with the second highest wind speed ever measured. For a short time both Irma and Jose were cat 5, the first time ever two such powerful storms have existed at once. Plus, I just heard on the news that Jose has now been officially a hurricane longer than any storm on record.

Even now there are three powerful storms in the Atlantic. Jose has been downgraded to a cat 1 but is still a possible threat to the US east coast. Maria has strengthened to a cat 5 and is expected to strike Puerto Rico today and then perhaps hit the Carolina coast. Finally there is tropical storm Lee, so far out in the Atlantic we don’t yet know what it’s going to do. And hurricane season still has two months to go! The picture below is Irma taken from space and while beautiful you can still feel something of its power in the image. By the way, the small brown object to the left of the storm is Puerto Rico giving an idea of just how big this storm was.

Hurricane Irma from the Space Station (Credit: NASA)

The number and destructive power of these storms force us to ask the question, could global warming be responsible? Has all the carbon dioxide and methane we’ve been pouring into the atmosphere increased storm activity in the Atlantic?

First of all there is simply no doubt that carbon dioxide and methane are greenhouse gasses. Any college freshman chemistry lab is capable of making the necessary measurements. I know that because I did it way back in the 1970s!

Secondly, we know with great accuracy the amount of those gasses that are produced by our burning fossil fuels in our vehicles and power plants. Yes, I know the Earth’s atmosphere is huge but over 30 trillion kilograms of pollution every year is also an enormous amount, many cities throughout the world have smog problems and air pollution is a major health concern.

Thirdly, we can measure the rise in temperature over the last 50 years of the atmosphere, 0.6 degrees Celsius, and the oceans, 0.32 degrees. While these may seem like at small changes when you consider the world’s oceans it is simply an enormous amount of energy. The graph below from the National Oceanographic and Atmospheric Administration (NOAA) shows the increase in the amount of energy in the Oceans due to global warming. The total amount is about 15×1022 joules but to give you an idea just how much energy that is it’s more than the energy in 35 million one megaton nuclear bombs. That’s right, the increase in energy is more than 35 million nuclear bombs!!!

Increase in Oceanic Heat Content (Credit: NOAA)

So even if only a small fraction of that energy increase gets into the storms that form over the oceans it would certainly be enough to significantly amplify the number and power of those storms. So, what are the numbers? Has there been an increase in the number of tropical storms and hurricanes in the Atlantic?

The table below shows the average number of both tropical storms and hurricanes as a function of decade for the 1970s, 80s, 90s, 2000s along with 2010 to 2016. The obvious increase is between the 1990s and 2000s, a more than 40% increase but the increase from the 80s to the 90s is not insignificant. Now, climatologists like to look at long term trends, to them even a decade is a short period of time. Nevertheless over the last 16-17 years there has been an undeniable increase in both the number and strength of Atlantic storms.

Yearly Average of Tropical Storms in decades (Credit: R. A. Lawler)

Now I’ve only been talking about tropical storms in the Atlantic. The Pacific Ocean has also seen an uptick in activity along with an increase in tornadoes across North America and just an increase in rainfall in general throughout the world. All this is a strong indication that global warming is causing more powerful, more violent weather everywhere.

The time is past for debates, the effects of climate change are already upon us. There’s much worse to come unless we seriously reduce the amount of polluting gasses we generate. Sea level rise combined with increased hurricane activity could soon lead to much greater destruction than we’ve seen so far. Quick and decisive action is required before it’s too late.

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