Part 2: Are Hurricanes Becoming More Frequent?

Is climate change causing an increase in the power and frequency of these brutal tropical storms? Harvey and Irma are causing untold damage in the Caribbean as we reach the halfway mark for hurricane season in the atlantic. Is this the new norm?

*Side Note* This is part two of the hurricane series. If you haven’t already, view Part 1 HERE

First and Foremost

If warm moist air is the source of a hurricane’s power (See Part 1), a warming climate is going to increase the likely hood of a tropical storm gaining the destructive power of a category five hurricane.

Are WE making hurricanes more dangerous?

Moisture in the Air

As the temperature of the air rises it is able to hold more moisture. This could be up to 7% more moisture per 1 degree Celsius increase. This may not sound like much but when you think about the scale of a hurricane and the destructive power already locked, in adding more moisture to the mix isn’t a good idea.

When we release greenhouse gasses into the atmosphere, we increase the temperature. As the temperature increases the air holds more moisture. With more moisture in the air, hurricanes become more powerful.

The effect of greenhouse gas warmed environment on the intensity of a hurricane was modelled by Knutson and Tuleya (2004). In their study which modelled over 1000 simulations found that the increased temperature created more intense storms.

Urban Jungles

This is the second man-made influence making hurricanes more dangerous to humans which I would like to talk about.

Concrete. We love it. Mile after mile of our urban areas have been smoothed over and covered with the stuff. I’m a big fan of plants so I am bias but concrete has one major flaw when large amounts are put over an area. Drainage.

Green fields, soil and forests soak up rainwater where it falls, adding it to the water table. It then flows at a controlled rate through to streams and rivers until it reaches the sea. When rain falls on concrete the easy path to the water table is blocked. Concrete does not drain like soil so the water gathers and flows through drainage systems built to cope with  normal rain levels. This works until rain that is way beyond the normal level begins to fall.

During hurricanes such as Harvey, HUGE amounts of rainfall happen in a very short space of time, overwhelming the drainage capacity of the city. As the water starts to back up, sewage systems are also overwhelmed. Now peoples homes are filling up with a mixture of rainwater, street grime, storm surge and sewage. Nasty.


Untreated sewage flowing through the streets breeds disease. People already helpless are now under threat of contracting a fatal disease, putting the overstretched emergency services under even more pressure. Contaminated drinking water is a big risk for spreading diseases, especially in developing countries where access is even more limited after a natural disaster than in developed countries.


Green house gasses and concrete are two man-made factors making hurricanes more dangerous.

Next, are hurricanes becoming more frequent?

Are hurricanes becoming more frequent?

This graph found on the National Hurricane Centre’s website shows the number of tropical storms, hurricanes and major hurricanes each year since 1850!

This graph is taken from the National Hurricane Centre website.

As can be seen from this graph, there is an upward trend in the frequency of named storms, hurricanes and major hurricanes. In the earlier years there may have been storms missed. This could be because recording and measuring equipment was not as developed as the ones we have today. However, adequate equipment has been available for many years now and we can see from the graph an upward trend from the 1970’s onwards. This period of increasing frequency is longer than the abnormal readings taken during periods of the El Niño phenomenon which occurs every 2 – 7 years with effects lasting up to a year in some places*.

Webster, Holland, Curry, Chang

I then read the paper by Webster, Holland, Curry and Chang who examined  the number of tropical cyclones and cyclone days as well as tropical cyclone intensity over the past 35 years… They came to this conclusion:

“We conclude that global data indicate a 30- year trend toward more frequent and intense hurricanes, corroborated by the results of the recent regional assessment (29). This trend is not inconsistent with recent climate model simulations that a doubling of CO2 may increase the frequency of the most intense cyclones…”

If you want to read the paper and make your own conclusions the link is is the sources section.

The other interesting part of this paper was the table named Table 1. I have included a screenshot of it here:

Data presented by P. J. Webster, G. J. Holland, J. A. Curry and H.-R. Chang. Original can be found here:

As you can see from the table, in EVERY SINGLE basin the number of hurricanes in categories 4 and 5 have increase.


There you have it. Not only are we making storms worse for ourselves with our liberal application of concrete but we are also seeing an INCREASE in the number and intensity of tropical storms as a result of greenhouse gas emissions and global warming. It makes me wonder, are storms like Harvey and Irma the new norm? Finally, since we are still pumping our emissions into the atmosphere another question must now be asked: How much worse is it going to get?

Leave me a comment and tell me what you think!

Liked it?

If you enjoyed this and want to know more about how hurricanes are formed, check out Part 1 HERE.

Or if you fancy something different, check out THIS piece on Vertical Farming.


Sources USed

Emanuel, K. A. The dependence of hurricane intensity on climate. Nature 326, 483–-485 (1987)

Knutson, T.R. and Tuleya, R.E., 2004. Impact of CO2-induced warming on simulated hurricane intensity and precipitation: Sensitivity to the choice of climate model and convective parameterization. Journal of climate17(18), pp.3477-3495.

National Hurricane Centre Website

Webster, P.J., Holland, G.J., Curry, J.A. and Chang, H.R., 2005. Changes in tropical cyclone number, duration, and intensity in a warming environment. Science309(5742), pp.1844-1846.

Part 1: Understanding Hurricanes

With Harvey and Irma battering anything in their path, a question has to be asked: are these brutal hurricanes becoming more frequent? Before we can answer this question however, we need to understand exactly what a hurricane is and what causes this destructive weather pattern.

This is Part 1 of the Hurricane series.

This article will explain:

  1. What is a hurricane?
  2. What are the causes?
  3. When does a tropical storm become a hurricane?
  4. What are the different sections of a hurricane?
  5. When is hurricane season?
  6. How is the scale of a hurricane measured?
  7. What causes the damage?
What is a hurricane?

Defined as a tropical storm with violent winds, a hurricane is the same weather system as a cyclone or a typhoon. The main difference between these three is their location. A typhoon occurs in the Northwest Pacific whereas a cyclone occurs in the South Pacific. A hurricane is a tropical storm in the Atlantic and North-East Pacific.

What are the causes?
Warm air from tropical waters causes thunderstorms by rising to high altitudes and creating an area of low pressure close the to the oceans surface. Air from the surrounding areas floods in to equalise the pressure difference. Due to the Earth’s rotation, cyclones south of the equator spin clockwise whereas cyclones north of the equator spin counter-clockwise! For an awesome explanation of why this happens, check out this answer on Quora.
When does a tropical storm become a hurricane?

According to the National Hurricane Centre, when the sustained windspeed reaches a certain threshold (above 73mph) a tropical storm becomes a hurricane. To then be classed as a major hurricane, the storm needs to have sustained windspeed of greater than 111mph.

What are the different elements of a hurricane?
A hurricane is made up of three sections: the eye, the eye wall and the spiral rain bands.
At the centre of the storm the eye is relatively calm. There is little to no rain and it is the warmest part of the storm.
The eye wall encircles the eye and has the strongest winds. It also contains the most rain. This is the strongest part of the storm and causes the most damage as it passes.
The spiral rain bands are on the edges of the storm, sometimes trailing inwards for hundreds of miles. These can still have strong, dangerous winds but are not as powerful as those in the eye wall.
When is hurricane season?

Hurricane season in the Atlantic stretches from June 1st until November the 30th, with the peak of the season being September 10th.

How is the scale of a hurricane measured?

To measure the intensity of a tropical storm, the  Saffir–Simpson hurricane wind scale (SSHWS) is used. This sorts storms into 5 categories depending on wind speeds. Created by Herb Saffir and Bob Simpson, this tool has been widely used to predict the damage done to property by the various levels of hurricanes. For more detailed explanation of what damage can be expected from each category, have a look at the table on the National Hurricane Centre’s website.

What causes the damage?

The power and energy release by this massive weather system is hard to imagine. A force 5 hurricane such has sustained wind speeds of over 155 MPH, which can rip houses to shreds. Couple this with billions of gallons of rain that falls in a short space of time and our concrete jungles can quickly become overwhelmed. Damage is caused by flooding from rainwater as well as huge torrents of water coming off the ocean in a storm surge.

Damage is caused by:

  • High Winds
  • Intense Rainwater
  • Storm Surge
Thank you for taking the time to read this article. If you enjoyed this and want to read more, have a look at the related posts!

Worried about food security? Have a look at this post on vertical farming for something slightly different: HERE

Or alternatively, learn something odd about the yields from urban/ rural bees: HERE