Please stop claiming humans are causing more hurricanes

Soldiers with the Texas Army National Guard move through flooded Houston streets as floodwaters from Hurricane Harvey continue to rise. US Army photo by 1st Lt. Zachary West. (Taken from Wikimedia)

After 12 years during which no “major hurricane” made landfall in the US (a major hurricane is defined as Category 3 or higher), 2017 tragically saw an end to this “hurricane drought” when Hurricane Harvey hit Texas as a Category 4 hurricane on 25th August, quickly followed by Hurricane Irma hitting Florida as a Category 4 hurricane on 10th September. This Monday, the remnants of Hurricane Ophelia hit us here in Ireland (on the other side of the Atlantic!), although by the time it had reached us, it had been downgraded to a “storm”.

All of this hurricane activity has prompted several campaign groups, such as Greenpeace and Friends of the Earth, as well as many other commentators (including the Pope!) to put the blame on “human-caused climate change” from carbon dioxide (CO2) emissions, i.e., our so-called “carbon footprint”.

For instance, just this morning, the director of Friends of the Earth (Ireland) wrote an essay for the popular Irish website,, specifically claiming that Hurricane Ophelia would not have occurred if it hadn’t been for our carbon dioxide emissions:

“Make no mistake, Ophelia is what climate change looks like. Every storm now bears the fingerprint of global warming.” — Oisín Coghlan (Director, Friends of the Earth Ireland),, 18th October 2017

Their claim is that by increasing the concentration of carbon dioxide (CO2) in the atmosphere through our fossil fuel usage, we are supposedly causing unusual “anthropogenic (i.e., human-caused) global warming” and that this is leading to a dramatic and unusual increase in hurricane activity.

In other words, in addition to dealing with the tragic aftermath of these devastating hurricanes, we should also feel guilty for causing them to occur in the first place! Not only that, but we are being led to believe that “the solution” to dealing with hurricanes is to urgently work on “reducing our carbon footprint”.

We should be actively encouraging more investment into improving our ability to better prepare for and respond to hurricanes (“climate adaptation”). However, it is not helpful to promote the claim that these tragedies are the result of carbon dioxide (CO2), and that the “solution” is to reduce our carbon footprint (“climate mitigation”). Aside from being wrong (as I will discuss below), it shifts the focus away from badly-needed climate adaptation policies.

For instance, the destruction that places like Puerto Rico have had to deal with in the aftermath of Hurricane Irma are truly heart-aching. We should be encouraging the development of better hurricane response infrastructure in such at-risk countries. But, if you have ever seen the 1961 musical, West Side Story, you will know that this has always been a well-known problem for Puerto Rico, as can be seen from the opening to the song, “America”:

“Puerto Rico,
My heart’s devotion —
Let it sink back in the ocean!
Always the hurricanes blowing,
Always the population growing,
And the money owing…”

America”, West Side Story (1957, music by Leonard Bernstein, lyrics by Stephen Sondheim)

In the mid-2000s, several studies were published which seemed (at the time!) to suggest that humans were causing more hurricanes through our CO2 emissions, e.g., Webster and colleagues (2005) (pdf here)and Trenberth & Shea (2006). Coincidentally, this happened around the same time as the disastrous 2004 and 2005 hurricane seasons, including Hurricane Katrina (2005) which devastated New Orleans and much of the surrounding area. Moreover, in his highly influential 2006 film, An Inconvenient Truth, Al Gore implied that the devastation of Hurricane Katrina was a direct result of our CO2 emissions.

All of this seems to have embedded into the popular psyche the notion that CO2 is causing more (and bigger) hurricanes. However, in the following years, the scientific community studying hurricane trends began to realise there were serious problems with the data those early studies had been based on.

There were two main types of data which had initially seemed to imply a link to CO2. But, it turned out that neither of these links held up to close scrutiny.

  1. The damage caused by hurricanes has increased dramatically since the early 20th century. This led many people to mistakenly conclude that the hurricanes were getting bigger and stronger.

However, it turned out that the main reasons for the increases in damages are that: a) the population has increased, b) more people are living in hurricane zones and, c) the value of the properties, infrastructure and businesses in these areas has also increased.

This is illustrated by the two photos below showing the same stretch of Miami Beach (Florida, USA) in 1926 (left) and 2006 (right). Shortly after the photograph on the left was taken, Miami Beach was struck by a Category 4 major hurricane (the 1926 “Great Miami Hurricane”. The hurricane did a lot of damage, but because there were less people living there at the time, and there wasn’t as many buildings and property, it has been estimated that, even after correcting for inflation, the total damage was only about 1% of what it would be today — see Pielke Jr. and colleagues, 2008.

Comparison of the same stretch of Miami Beach, Florida in 1926 vs. 2006. From an online presentation by Dr. Christopher Landsea, NOAA Hurricane Research Division

2. Since the early 20th century there has been a fairly continuous increase in the number of hurricanes that are identified each year.

Initially, this seemed to suggest that we are getting more and more hurricanes — and this seemed to fit into the narrative that CO2 was responsible.

But, it turns out that there was a subtle, but important, point — the increase was in the number of hurricanes that are identified, not necessarily in the actual number of hurricanes. Since the start of the 20th century, and particularly in recent decades, our ability to monitor and detect hurricanes has increased dramatically due to much better technology.

Today, we have powerful satellites, computers and rapid telecommunication systems which allow us to detect and monitor even quite small storm systems out in the middle of the ocean, even if they dissipate without ever making landfall.

But, in the early 20th century, we didn’t have that technology. If a hurricane formed and then dissipated out in the middle of the ocean, but nobody was around to detect it, it wasn’t reported!

We can’t definitively know how many undocumented hurricanes occurred but went unreported in the early pre-satellite days. However, several groups have used different statistical analyses to try and estimate the approximate numbers, e.g., Landsea and colleagues (2010).

Most of these studies suggest that there were probably just as many hurricanes in the early 20th century as today — it’s just that we weren’t able to detect them because they never made landfall. In the video below, Dr. Chris Landsea from NOAA’s Hurricane Research Division describes the results of one such study:

So, if we can’t use the damage data or the “identified hurricanes” data to study long-term hurricane trends, can we say anything about hurricane trends?

Fortunately, there is one remaining dataset which we can use to test if there has been any increase in a) the number or b) the intensity of hurricanes. It’s the hurricane landfall data. When a hurricane actually makes landfall, it is pretty hard to miss, and the maximum intensity it has when it makes landfall can also be recorded.

Here’s what the landfall data (for the US) shows:

Top graph: Total numbers (and types) of hurricanes that have made landfall in the US from 1850 up to today (17th October, 2017). Bottom graph: The concentration of carbon dioxide (CO2) in the atmosphere over the same period.

The top graph shows the number (and type) of hurricanes which made landfall in the US from 1850 up to today. I’ve shown the US record, partially because Hurricanes Harvey & Irma struck here, but mainly because the US record is the longest and most complete record (most countries only began systematically recording this type of information in the 1970s or later). The data up to 2016 was downloaded from the NOAA Hurricane Research Division (the group in charge of US hurricane data), and I manually added the data for 2017 so far (two Cat 4 and one Cat 1 at US landfall).

The bottom graph shows the concentration of CO2 in the atmosphere since 1850. This data was downloaded from the Scripps Institution (the main group in charge of monitoring CO2 since 1959). The data from 1959 onwards comes from direct atmospheric measurements at the Mauna Loa Observatory. The data for before 1959 is derived from analysis of Antarctic ice cores.

So, what does the data say?

We can see that, yes, CO2 has increased from 0.03% to 0.04%.

…But, despite what many climate campaigners are claiming, the data show NO link between CO2 concentrations and the number (or intensity) of hurricanes making landfall.

Yes, hurricanes are dreadful. As I mentioned above, the remnants of Hurricane Ophelia hit us here in Ireland on Monday, and even though it had been downgraded to a “storm”, it still caused a lot of damage! But, CO2 is not to blame.

So, can we please stop repeating this non-scientific claim?

And, could campaign groups, e.g., Greenpeace, Friends of the Earth, and the Sierra Club stop exploiting the heart-achingly tragic devastation caused by hurricanes for their “climate action” fundraising campaigns?

Dr. Ronan Connolly is an independent scientist and environmentalist based in Dublin, Ireland. He did not receive any funding for the above research. But, he is passionate about science, and wants to do his bit to ensure the discussion about climate change is based on actual science.



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