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Round up of hurricane – climate change claims and rebuttals

What you need to know & are not told about hurricanes

Summary: Millions of words were expended reporting about Hurricanes Harvey and Irma, but too little about the science connecting them to climate change. Here are the details, contrasted with the propaganda barrage of those seeking to exploit these disasters for political gain. Let’s listen to these scientists so we can better prepare for what is coming. Failure to do so risks eventual disaster.

NASA photo of Hurricane Katrina on 28 August 2005
NASA photo of Hurricane Katrina on 28 August 2005.

A politically useful catastrophe: the Left speaks


The record-setting twelve-year long hurricane “drought” (no major hurricane landfalls on the US) was just weather. But the Left immediately boldly and confidently declared Harvey and Irma to be caused (or worsened) by anthropogenic climate change. Some of these screeds are mostly rational, just exaggerated or imbalanced. Such as “Harvey Is What Climate Change Looks Like” by Eric Holthaus at Politico — “It’s time to open our eyes and prepare for the world that’s coming.” And “Stop talking right now about the threat of climate change. It’s here; it’s happening” by Bill McKibben at The Guardian — “Hurricane Harvey, Hurricane Irma, flash fires, droughts: all of them tell us one thing – we need to stand up to the fossil fuel industry and fast.”

Many are simple political propaganda. “Irma Won’t ‘Wake Up’ Climate Change-Denying Republicans. Their Whole Ideology Is on the Line.” by Naomi Klein (activist) at The Intercept. Note this story is not labeled as an “op-ed”. “As Planet Rages With Fires and Storms, Ire Aimed at Murderous Climate Denialism” by Jessica Corbett (staff writer) at Common Dreams. “Climate Denialism Is Literally Killing Us” by Mark Hertsgaard (editor) at The Nation — “The victims of Hurricane Harvey have a murderer — and it’s not the storm. …It is past time to call out Trump and all climate deniers for this crime against humanity. No more treating climate denial like an honest difference of opinion.”

Many just assume the science says what they want it to say, without recourse to the IPCC, NOAA, or a similar authority. For example, Paul Krugman (professor of economics at Columbia, Nobel Prize 2008) says this at his NYT blog.

“The disaster in Houston is partly Mother Nature — natural disasters will happen sometimes whatever we did — but with a powerful assist from human action. Climate change definitely made such an event more likely …”

Similarly, Joseph E. Stiglitz (Professor of economics at Columbia, Nobel Prize 2001) in “Learning from Harvey” says this at Project Syndicate.

“It is ironic, of course, that an event so related to climate change would occur in a state that is home to so many climate-change deniers – and where the economy depends so heavily on the fossil fuels that drive global warming.”

Model of a hurricane.
Vapor visualization of a hurricane in the Weather Research & Forecasting Model. NCAR/UCAR.

Scientists tell us about hurricanes and global warming


Although many on the Left ignore, misrepresent, or exaggerate the science, there is well-established data about these matters. Here is a look at recent research (i.e., since the IPCC’s AR5 report), the foundation for the statement at NOAA’s website that concludes this section. Red emphasis added.

Look at the trends in the number and intensity of Atlantic hurricanes.

A good place to start is “Extremely Intense Hurricanes: Revisiting Webster et al. (2005) after 10 Years” by Philip J. Klotzbach and Christopher W. Landsea in Journal of Climate, October 2015. Abstract…

“Ten years ago, Webster et al. documented a large and significant increase in both the number as well as the percentage of category 4 and 5 hurricanes for all global basins from 1970 to 2004, and this manuscript examines whether those trends have continued when including 10 additional years of data.

“In contrast to that study, as shown here, the global frequency of category 4 and 5 hurricanes has shown a small, insignificant downward trend while the percentage of category 4 and 5 hurricanes has shown a small, insignificant upward trend between 1990 and 2014. Accumulated cyclone energy globally has experienced a large and significant downward trend during the same period.

“The primary reason for the increase in category 4 and 5 hurricanes noted in observational datasets from 1970 to 2004 by Webster et al. is concluded to be due to observational improvements at the various global tropical cyclone warning centers, primarily in the first two decades of that study.”

Articles about hurricanes often say there is a strong and direct link to sea surface temperatures (SST). Reality is more complex. Philip Klotzbach explained his findings to me in more detail.

“Our paper found that the large increasing trends in Category 4-5 hurricanes observed in Webster et al. (2005) were primarily due to changes in observational technology at the various warning centers.  Most model projections predict a slight increase (on the order of 5-10%) in storm intensity, with perhaps fewer storms, over the next century.

“SSTs correlate tightly with Atlantic hurricane activity, due to other large-scale climate features such as sea level pressure and vertical wind shear. In the tropical Atlantic, warm sea surface temperature anomalies result in lower tropical and subtropical Atlantic pressure.  The associated weaker pressure gradient results in weaker trade winds, reducing vertical wind shear (since upper level winds blow out of the west in the tropical Atlantic).  The weaker trade winds cause less mixing, evaporation and upwelling of the sea surface, which then feed back into reinforcing the warm SST anomalies in the tropical Atlantic.

This wind-evaporation-SST feedback process in the Atlantic has been shown to be critical for the Atlantic Meridional Mode.  Generally, positive values of the Atlantic Meridional Mode are associated with warm SSTs, low sea level pressure, and reduced vertical wind shear.  The actual impact of the SST anomalies themselves is shown to be relatively small in partial correlation analysis.  This was first demonstrated two decades ago in “Atlantic Sea Surface Temperatures and Tropical Cyclone Formation” by Lloyd J. Shapiro and Stanley B. Goldenberg in Journal of Climate, April 1998.

These types of relationships do not necessarily occur in other basins.  For example, the NW Pacific has just had its 2nd Cat. 3+ typhoon this year, while the average to date is 4.5.  All of this despite record warm SST anomalies in their Main Development Region.  Circulation features are a far more critical driver of typhoon activity than SSTs, since they are always plenty warm to support intense activity.”

Dr. Klotzbach is a research scientist at the Tropical Research Project at Colorado State U.

Cliff Mass describes the relationship of global warming to hurricanes.

See “Global Warming and Hurricane Harvey” by Cliff Mass at his website. He gives a rebuttal to those articles asserting a clear link between Global Warming and Hurricane Harvey. Opening…

“Before the rains had ended, dozens of media outlets had published stories suggesting that global warming forced by humans (mainly by emissions of CO2 into the atmosphere) played a significant role in producing the heavy rainfall and resulting flooding associated with Hurricane Harvey.

“Most of the stories were not based on data or any kind of quantitative analysis, but a hand-waving argument that a warming earth will put more water vapor into the atmosphere and thus precipitation will increase.  A few suggesting that a warming atmosphere will cause hurricanes to move more slowly.

“This blog will provide a careful analysis of the possible impacts of global warming on Hurricane Harvey.  And the results are clear:  human-induced global warming played an inconsequential role in this disaster. …”

Dr. Mass is a professor of atmospheric sciences at U Washington. See his bio, presentations and papers.

Roger Pielke Sr. tells me about an important but often ignored point.

“Model projections of hurricane frequency and intensity are based on climate models. However, none have shown skill at predicting past (as hindcasts) variations in hurricane activity (or long term change in their behavior) over years, decades, and longer periods. Thus, their claim of how they will change in the future remains, at most, a hypothesis (i.e. speculation). When NOAA, IPCC and others communicate to the media and public, to be scientifically honest, they should mention this.”

Dr. Pielke Sr. is a Senior Research Scientist in CIRES and Emeritus Professor of Atmospheric Science at Colorado State U. See his bio.

Judith Curry discusses the link between global warming and Hurricane Harvey.

From her post about Hurricane Irma at Climate Etc.

“Ever since Hurricane Harvey, the global warming – hurricane hysteria has ratcheted up to levels I haven’t seen since 2006. NOAA GFDL has written a good article on Global Warming and Hurricanes. {See below.} …I much prefer {NOAA’s} model-based quantitative estimates (but they need some serious uncertainty estimates, including structural uncertainty), relative to hysterical arm waving by Mann and Trenberth using undergraduate basic thermodynamics reasoning.  There is nothing basic or simple about hurricanes. …

“{See} my 2010 post Hurricane Katrina – 5 years later, particularly relevant given the cool SST values that Irma formed and intensified.”

Dr. Curry is a professor emeritus at the Georgia Institute of Technology and President of Climate Forecast Applications Network (CFAN). See her bio.

NOAA logo

NOAA gives their verdict.

The bottom line comes from NOAA’s Geophysical Fluid Dynamics Laboratory: “Global Warming and Hurricanes – An Overview of Current Research Results.” Journalists should consider this definitive. But few of them mention it.


“It is premature to conclude that human activities–and particularly greenhouse gas emissions that cause global warming – have already had a detectable impact on Atlantic hurricane or global tropical cyclone activity. …”

A. Statistical relationships between SSTs and hurricanes.

… The Power Dissipation Index (PDI) …is an aggregate measure of Atlantic hurricane activity, combining frequency, intensity, and duration of hurricanes in a single index. …

This is in fact a crucial distinction, because the statistical relationship between Atlantic hurricanes and local Atlantic SST shown in the upper panel of Figure 1 would imply a very large increases in Atlantic hurricane activity (PDI) due to 21st century greenhouse warming, while the statistical relationship between the PDI and the alternative relative SST measure shown in the lower panel of Figure 1 would imply only modest changes of Atlantic hurricane activity (PDI) with greenhouse warming. In the latter case, the alternative relative SST measure in the lower panel does not change very much over the 21st century in global warming projections from climate models, because the warming projected for the tropical Atlantic in the models is not very different from that projected for the tropics as a whole. …

B. Analysis of century-scale Atlantic tropical storm and hurricane records.

To gain more insight on this problem, we have attempted to analyze much longer (> 100 yr) records of Atlantic hurricane activity. If greenhouse warming causes a substantial increase in Atlantic hurricane activity, then the century scale increase in tropical Atlantic SSTs since the late 1800s should have produced a long-term rise in measures of Atlantic hurricanes activity.

Existing records of past Atlantic tropical storm or hurricane numbers (1878 to present) in fact do show a pronounced upward trend, which is also correlated with rising SSTs (e.g., see blue curve in Fig. 4 or Vecchi and Knutson 2008). However, the density of reporting ship traffic over the Atlantic was relatively sparse during the early decades of this record, such that if storms from the modern era (post 1965) had hypothetically occurred during those earlier decades, a substantial number would likely not have been directly observed by the ship-based “observing network of opportunity.”

We find that, after adjusting for such an estimated number of missing storms, there is a small nominally positive upward trend in tropical storm occurrence from 1878-2006. But statistical tests reveal that this trend is so small, relative to the variability in the series, that it is not significantly distinguishable from zero (Figure 2).

In addition, Landsea et al. (2010) note that the rising trend in Atlantic tropical storm counts 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. …

“While major hurricanes show more evidence of a rising trend from the late 1800s, the major hurricane data are considered even less reliable than the other two records in the early parts of the record. Category 4-5 hurricanes show a pronounced increase since the mid-1940s (Bender et al., 2010) but again, we consider that these data need to be carefully assessed for data inhomogeneity problems before such trends can be accepted as reliable.”

E. Summary for Atlantic Hurricanes and Global Warming.

In summary, neither our model projections for the 21st century nor our analyses of trends in Atlantic hurricane and tropical storm counts over the past 120+ yr support the notion that greenhouse gas-induced warming leads to large increases in either tropical storm or overall hurricane numbers in the Atlantic. …

Wildfire Earth

About those wildfires!


The National Interagency Fire Center shows year-to-date statistics for wildfires in the US. This year ranks third in the past eleven years. The total acres burned per year have been in a flat range since 1999 (details here).

In the 20th century forests were managed by Smokey the Bear — “only you can prevent forest fires” — in the mistaken belief that forest fires must be prevented. This made the western US forests into tinderboxes. The Left blames the resulting massive fires on climate change.

Results from the propaganda campaign


Much of the propaganda about Harvey and Irma has been directed at Trump. How has his job approval levels changed — an instant measure of their success? Harvey made landfall in Texas on August 26. Trump’s approval numbers began to improve on September 1 and have remained flattish since September 3. Lots of firepower expended on Trump to no visible effect.