Hurricanes, Rainfall, and Climate Change
By James D. Agresti
September 12, 2017
In the midst of a severe hurricane season and the destruction wrought by hurricanes Harvey and Irma, many people are claiming that man-made global warming has intensified rainfall and hurricanes. However, comprehensive facts show that rainfall and hurricane activity are well within the bounds of natural variation, and there is no cogent evidence that they have increased over the past century.
Moreover, the United States contains only 1.9% of the world’s surface area, and the earth’s climate oscillates widely over time and place. Hence, focusing on U.S.-area hurricanes in a single year can easily misinform the issue of climate change.
While Hurricane Irma was razing the Caribbean and barreling toward Florida, climate scientist David Hastings told the Washington Post, “Hurricane Harvey and Irma should resolve any doubt that climate change is real.” Likewise:
- CNN’s Ron Brownstein reported during Hurricane Harvey, “There is no doubt that climate change, particularly because of warming the ocean waters and the gulf waters, makes storms like this more common.”
- Meteorologist Eric Holthaus wrote in Politico that “climate change is making rainstorms everywhere worse, but particularly on the Gulf Coast.”
- The BBC’s Laura Trevelyan stated, “Of course we do have a changing climate we do have warming waters. With more warming waters, you get more moisture coming into the atmosphere, and what hurricanes absolutely love is moisture because that gives them rainfall. And that’s what’s happened in this situation with Hurricane Harvey.”
In the same vein, FactCheck.org science writer Vanessa Schipani asserted that global warming “makes intense storms like Harvey more likely to occur.” In support of this statement, she declared that:
- “a warmer world leads to greater moisture in the atmosphere, which leads to greater precipitation, which leads to more intense storms.”
- a 2013 Intergovernmental Panel on Climate Change (IPCC) report “found that scientists are “virtually certain” (99 percent to 100 percent confident) that there has been an ‘increase in the frequency and intensity of the strongest tropical cyclones since the 1970s’ in the North Atlantic Ocean.”
- one of the “key findings” of a draft report by the U.S. Global Change Research Program is that “human activities have ‘contributed to the observed increase in hurricane activity’ in the North Atlantic Ocean since the 1970s.”
- the same report says that “studies that have looked at this question have come up with a ‘fairly broad’ range of contributions for humans, but ‘virtually all studies identify a measurable, and generally substantial, [human] influence,’ it adds.”
The claims above paint a distorted picture of reality by ignoring the most relevant and comprehensive facts about this issue.
Global Rainfall Trends
Contrary to the notion that global warming has caused more rain, the authors of a 2015 paper in the Journal of Hydrology studied rainfall measurements “made at nearly 1,000 stations located in 114 countries” and found “no significant global precipitation change from 1850 to present.” The paper noted that previous studies had analyzed shorter timeframes and found rainfall changes that some people had attributed to global warming, but those results were generally not statistically significant and “not entirely surprising given that precipitation varies considerably over time scales of decades.”
Beyond total rainfall, many climate models predict that global warming will cause the rain to fall in shorter periods, and thus, with more intensity. Yet, even according to the IPCC—which has engaged in deceitful actions to exaggerate global warming—evidence for such an outcome is highly questionable:
Since 1951 there have been statistically significant increases in the number of heavy precipitation events (e.g., above the 95th percentile) in more regions than there have been statistically significant decreases, but there are strong regional and sub-regional variations in the trends. In particular, many regions present statistically non-significant or negative trends, and, where seasonal changes have been assessed, there are also variations between seasons (e.g., more consistent trends in winter than in summer in Europe).
This issue becomes even murkier when looking at the bigger picture, because apparent changes in rainfall intensity sometimes vanish when examining longer timeframes that better account for natural variations. For example, the International Journal of Climatology published a paper in 2015 about extreme rainfall in England and Wales that revealed, “Contrary to previous results based on shorter periods, no significant trends of the most intense categories are found between 1931 and 2014.”
Global Storms and Hurricanes
A “tropical cyclone” is a circular wind and low-pressure system that develops over warm oceans in the tropics. Cyclones with winds ranging from 39 to 73 miles per hour are called “tropical storms,” and those with winds exceeding 73 miles per hour are called “hurricanes.” Technically, there are different names for cyclones with hurricane-force winds in different areas of the world, but for the sake of simplicity, this article refers to them as hurricanes.
The datasets below, which were originally published in the journal Geophysical Research Letters in 2011, show that the global number and intensity of tropical storms and hurricanes have not increased over the past four decades:
Corroborating this data, the IPCC reported in 2012, “There is low confidence in any observed long-term (i.e., 40 years or more) increases in tropical cyclone activity (i.e., intensity, frequency, duration), after accounting for past changes in observing capabilities.”
In spite of these facts, a national scientific poll commissioned by Just Facts shortly before the 2016 presidential election found that 44% of Trump voters and 77% of Clinton voters believed that the global number and intensity of hurricanes and tropical storms have generally increased over the past 30 years. This sharp disconnect between reality and perception accords with a flood of global warming-related misinformation spread by the media and environmental groups.
North Atlantic Storms and Hurricanes
In the North Atlantic region, where hurricanes Harvey and Irma formed, tropical storm and hurricane activity have increased significantly over the past four decades. However, this trend fades in the wider context of variation over the past century. As explained by the National Oceanic and Atmospheric Administration (NOAA):
No robust trends in annual numbers of tropical storms, hurricanes and major hurricanes counts have been identified over the past 100 years in the North Atlantic basin.
NOAA states that North Atlantic tropical storms show a “pronounced upward trend” since 1878, but this is because these records are “relatively sparse” in their early decades. After NOAA adjusts for the “estimated number of missing storms,” the trend in storm activity is “not significantly distinguishable from zero.” Furthermore, NOAA notes that the upward trend in the unadjusted data:
is almost entirely due to increases in short-duration (<2 day) storms alone. Such short-lived storms were particularly likely to have been overlooked in the earlier parts of the record, as they would have had less opportunity for chance encounters with ship traffic.
With regard to the most intense storms, NOAA reports that “the reported numbers of hurricanes were sufficiently high during the 1860s-1880s that again there is no significant positive trend in numbers beginning from that era…. This is without any adjustment for ‘missing hurricanes’.”
Even more relevant to the implications of Harvey and Irma, NOAA notes that the record of North Atlantic hurricanes that reach land are “more reliable” than for the entire North Atlantic, and they “show a slight negative trend beginning from 1900 or from the late 1800s.” In other words, the most reliable data shows the opposite of what many media outlets are reporting.
NOAA emphasizes that one cannot logically assess hurricane trends based only on those that reach land, because they are “much less common” than the full number of hurricanes that form at sea. This highlights the absurdity of drawing conclusions based on hurricanes that make landfall, much less hurricanes that make landfall in one region in a single year.
After reviewing the data above, NOAA states, “In short, the historical Atlantic hurricane record does not provide compelling evidence for a substantial greenhouse warming-induced long-term increase.”
Similarly, the very same 2013 IPCC report cherry-picked by FactCheck.org states, “No robust trends in annual numbers of tropical storms, hurricanes and major hurricanes counts have been identified over the past 100 years in the North Atlantic basin.” This is word-for-word the same as stated by NOAA.
Three times in her FactCheck.org article, Schipani used the phrase “scientists say” as if she were citing the universal opinion of scientists. Given the contents of her article, a longer but honest rewording of this phrase would be that “some scientists who have previously misled the public about global warming say so, but some scientists disagree.”
For example, Schipani quoted climate scientist Michael Mann—creator of the notorious hockey stick chart and inventor of a “trick” to “hide the decline“ in temperatures—as though he were an unquestionable authority. Mann claimed that global warming may have caused Hurricane Harvey to stall over Houston and drop a devastating amount of rain in this location. However, Schipani failed to inform her readers that some other climate scientists, like Roy Spencer, disagree with Mann and wrote:
I don’t know of any portion of global warming theory that would explain why Harvey stalled over southeast Texas. Michael Mann’s claim in The Guardian that it’s due to the jet stream being pushed farther north from global warming makes me think he doesn’t actually follow weather like those of us who have actual schooling in meteorology (my degree is a Ph.D. in Meteorology). We didn’t have a warm August in the U.S. pushing the jet stream farther north.
Similarly, Schipani uncritically cited:
- the IPCC, whose scientists wrote an array of incriminating emails in which they said things like, “I tried hard to balance the needs of the science and the IPCC, which were not always the same.”
- Kevin Trenberth, an IPCC lead author who participated in a press conference where he misrepresented the facts about global warming and hurricanes. As a result, Chris Landsea, a scientist who Trenberth had tasked to draft a chapter on Atlantic hurricanes for the IPCC, quit the IPCC and stated, “I personally cannot in good faith continue to contribute to a process that I view as both being motivated by pre-conceived agendas and being scientifically unsound.”
- the U.S. Global Change Research Program, which cited a certain paper as evidence that climate change is causing more floods, while in reality the paper states, “In none of the four regions defined in this study is there strong statistical evidence for flood magnitudes increasing with increasing” greenhouse gas levels.
Certain media outlets have linked hurricanes Harvey and Irma to global warming by ignoring wide-ranging facts and cherry-picking timeframes, geographical locations, report contents, and the opinions of scientists. As explained in an academic book about analyzing data, “One of the worst abuses of analytics is to cherry pick results. Cherry pickers tout analysis findings when the results serve the purpose at hand. But, they ignore the findings when the results conflict with the original plan.”
Webster’s College Dictionary defines science as the “systematic knowledge of the physical or material world gained through observation and experimentation.” By this standard, there are no grounds to claim that global warming has increased rainfall or hurricane activity.
Thank you, excellent piece
I doubt my comment will ever be published here. This article bases a lot of its comment and position on whether global warming/climate change has affect on cyclone frequency and intensity by referencing “scientific” papers found in Elsevier Reed’s database. Unfortunately Elsevier Reed has been exposed multiple times recently “tilting the field” in favor of preferred clients. You can google “Elsevier controversities” and find these claims for yourself. While there are many legitimate in their database I am taking the ones cited here as fictional or misreprented until the data claims pass a peer review.
As always in an era of fake news we all have to vet what’s published
Okay, so I took you up on your invitation to google Elsevier, earlier known as Reed Elsevier by the way, and it appears to me that most of the controversy surrounding the company (which is essentially a very large publisher, based in The Netherlands, of scientific journals and articles) is about its pricing and lobbying against “open” publishing. I did not get the sense, from a quick perusal of what I found, that Elsevier was often being accused of deliberately distorting the data or analyses enclosed in the articles or journals that it publishes. I think that is what you meant by “tilting the field.” Are you claiming that because a paper is found on Elsevier’s database that it is necessarily scientifically suspect?
This article cites a wide array of credible sources, and only one of them is a paper published by an Elsevier journal.
Furthermore, Elsevier is a highly respected publisher of scientific literature.
Hard to take your point seriously. First of all, it was “Reed Elsevier”, you didn’t even get the name right. So there is that. Even worse, that doesn’t even exist anymore, the organization is now officially named the “RELX Group”.
Read this for some corroboration on your conclusions, especially the end where there is mention of a horrific storm pre- 20th century.
This kind of thing is what is very difficult to talk about with climate change pushers. We’re not talking about CO2 levels or anything else, we’re talking about extreme storms. We’re talking about a very real dishonesty coming out of groups like the IPCC. This kind of thing is what causes confusion around what human caused climate change is, its effects, and its dangers. Yet, bring this kind of thing up and you just get ander and shouted slogans like “99% of scientists agree!” I’m glad sites like this can take it one issue at time and find the facts rather than dogmatically taking a “side” as if there were a political issue.
Unfortunately, the climate change ‘consensus’ IS a political issue; that is how the great majority of scientific organizations have to tow the line- if they hope to receive their next government-financed research grant.
Toe the line: adhere strictly to an imposed rule or standard.
Good to see someone address that we have a great deal more information on weather than was available 40 years ago. Just because we now see a great deal of activity is not in itself indicative of global change, one has to account that there are many more measurements taken. Likewise, dollar value of damage cannot be taken at face value, one needs to account for increased property values and increased population densities in desirable costal regions which are vulnerable to hurricanes. We are also being fed an ever increasing volume of information, and weather has been deemed to have entertainment value, so we are presented with a torrent of weather related content. Does this mean the weather is enormously worse – no, the media has bandwidth to fill.
Speaking of cherry picking …
The NOAA paper cited does indeed conclude that it is *premature* to conclude that global warming has caused a detectable change in Atlantic hurricane activity.
But, it also concludes that “it is likely that climate warming will cause hurricanes in the coming century to be more intense globally and to have higher rainfall rates than present-day hurricanes”
It further concludes that *global* frequency will be reduced in a warmer climate, but “also an increase in average cyclone intensity, the number and occurrence days of very intense category 4 and 5 storms in most basins (Figure 9) and in tropical cyclone precipitation rates (Figure 10).”
Further, your inclusion of Spencer as an authority is laughable. Spencer’s research has been shown time and again to be guilty of cherry picking datasets and ignoring contrary evidence in the models. (http://www.realclimate.org/index.php/archives/2011/07/misdiagnosis-of-surface-temperature-feedback/)
Surely you understand the difference between what someone projects will occur and what has actually occurred, which is the subject of this article.
Dr. Spencer’s credentials are extraordinary, and the critique of him that you linked to is from a well-known climate alarmist site.
Dr. Spencer believes God is in control of the climate.
Ok, everyone pack it all up, Spencer figured it all out, God did it! No, seriously, it was that simple all along. We’ve wasted our whole lives looking at this. Let’s go home.
Great job once again by Agresti for making the very clear point that we should ignore the talking heads on TV, in the White House, in Congress, and ideological shills like himself on the internet and go straight to the scientific literature for our information.
Nothing like fighting cherry-picking with even more egregious cherry-picking. Also, how many times can we see these laughable “smoking gun” emails referenced completely out of context.
Keep finding the “just facts” that your bias wants you to find!
Since you provide no evidence to support your claims, they can be dismissed without evidence.
Well, after people realize the global warming alarmists are mostly people that don’t even have the common sense to understand that we have at best, 150 years ( and probably more like 90 years ) of accurate data to base all the claims made on, and that every few years we hear of scandles in the community of so called scientists playing with the numbers and models, maybe they will get over it. To make the claims that are made with such an incredibly small data set, tells me people need to go back to school and learn about statistics. Compaired to the millions of years the earth has been around, and the fact that we only have 40 or 50 years since weather sattilites have been going into space, I say ba humbug to the whole topic of Global warming.
The weather changes, that’s about the only fact that can be proven beyond the shadow of a doubt.
1960 was the year the U.S. launched the first Weather Satellite and before that we relied on Land Based and Ships at Sea for Weather Information. Columbus encountered a Tropical Storm in 1495 well before the Industrial Age and I’d bet there have been Hurricanes for as long as their have been a Tropics and the Ocean. I also did not read anything about the Cycle of the Sun and the effect it has on Earth’s Weather! Earth was once a frozen Snowball and has gone through many Ice Ages as well as Global Warming Cycles long before Man! Who is to blame for those? I’d bet that long after Man is gone if the Sun hasn’t burnt away the Atmosphere yet, Earth will still have Cycles of Weather Change!
“Who is to blame for those?”
Here’s a hint, read some science and you will find out what, not who, was to blame for those. Good luck out there.
Please dispense with your elementary logic and read some science.
Besides the fact that we actually have hundreds of thousands of years of direct climate data, and hundreds of millions more of indirect data, scientists make accurate predictions and build robust models on very limited data sets every single day. I will let you do your own homework and find some examples. Now, go study.
Why did i not get my email from JustFacts when I made my contribution like you said I would??? If you don’t acknowledge no more contribution!