Gross Errors In The IPCC Report On Global Tropical Cyclone Activity

by William M. Gray
October 31, 2011

“Intense TC activity has increased since about 1970.”  (NOT TRUE)

…“Globally, estimates of the potential destructiveness of hurricanes show a significant upward trend since the mid-1970s, with greater storm intensity. Such trends are strongly correlated with tropical SST.”  (NOT TRUE)

“These relationships have been reinforced by findings of a large increase in numbers and proportion of hurricanes reaching categories 4 and 5 globally since 1970  (NOT TRUE)

…. The largest increase was in the North Pacific, Indian and southwest Pacific Oceans.”  (NOT TRUE)

The Four IPCC reports have emboldened our politicians to come forth with the following erroneous statements –
Al Gore states in his book and movie – An Inconvenient Truth – “major storms (hurricanes) spinning in both the Atlantic and Pacific Oceans since the 1970s have increased in duration and intensity by about 50 percent.”  (NOT TRUE)

In November 2008 President-Elect Barack Obama said, “storms (i.e. hurricanes) are growing stronger with each passing hurricane season.”


The US government has expended billions of dollars in recent years to promote the questionable idea that human-induced increases in atmospheric CO2 will cause dangerous changes to the global climate system. Massive government and media campaigns have been launched to promote the dangers of CO2-induced anthropogenic global warming (AGW) and related influences such as the anticipated increases in global tropical cyclone (TC) frequency and intensity as well as other severe weather events. Pro-AGW advocates have pushed to have this warming gospel accepted across the world and taught to our children in their regular school programs. AGW advocates want to worry the public as much as possible in order to be better able to increase their influence and funding support.
There has yet to be an open and honest scientific debate on the future consequences of CO2 increases and of the potential social and negative economic consequences of efforts to slow down CO2 increases. A number of pro-AGW advocates have expended considerable efforts in recent years to develop theories and in arranging TC data in order to show that global TCs are increasing in frequency and intensity in response to rising CO2 levels. Global warming advocates have had a strong desire to find and to exploit increases in TC activity as further evidence of the human-induced warming scenarios.

The IPCC hierarchy had its mind made up years ago that they would make every attempt possible to link rising levels of CO2 with increases in global hurricane intensity and frequency. They knew that if such an association could be established in the public’s mind that this could be used to help scare and induce the public (and Congress) into funding the political, economic, and environmental agendas of a large number of special interest groups. Input from skeptics or any hypothesis or data that did not link rises in CO2 to increases in TC activity was to be avoided, suppressed, or rejected. The IPCC deliberately ignored the most experienced and knowledgeable TC experts in order to preserve their desired goal of propagandizing the public to believe that rising CO2 levels were creating a growing hurricane threat. Most of the IPCC statements on TCs, as will be shown, are not supported by observations.

After the very severe US hurricane landfalling seasons of 2004 and 2005, the public was more open and vulnerable to such arguments of CO2 induced increases in hurricane activity. A group of papers were rapidly published to exploit and to justify this assumption so that the authors might be able to jump onto the warming bandwagon and increase their potential for more federal grant support, publicity, and other envisioned gains.

These papers strived to arrange their observations and physical explanations in ways to show or imply a direct association between increasing levels of TC activity with increasing sea surface temperatures (SSTs) and rising levels of CO2. The majority of these authors who rapidly published papers between 2005-2008 had little background experience in TC research or forecasting, or in TC climatology. Nearly all of these papers were biased in the direction of implying more TC activity with rising levels of SST. Most of these papers should not have been able to get through the peer-review process. The journal editors of these papers appear to have sent them for review to known like-minded AGW sympathizers. Many of our country’s most experienced TC researchers and forecasters appear to have been left out of this review process.

Following these two disastrous US landfalling hurricane years of 2004-2005, the mainstream media (without a background knowledge of TCs and preconditioned to accept the AGW arguments) generally accepted the reality of these paper’s faulty results. This created a near panic among coastal residents over the implied coming increase of hurricane destruction that these papers indicated was on the way. Disaster stories made good press and fit in very well with the government and environmentalists’ AGW scenarios. The media, in general, chose not to discuss the views of established TC researchers and forecasters from the National Hurricane Center and many of my experienced TC colleagues who did not subscribe to such disaster scenarios.

I have been closely following the AGW debate for the last 25 years. It has been politically dominated from the start. All four IPCC reports have been slanted to support the AGW hypothesis. There has been much valuable data and analysis contained in these four reports that have been issued, but the report’s summaries have always been biased toward the organizers desired goal of saying to government policy makers that CO2 was causing increases in both global temperature, TC activity, severe weather events, etc.

I believe that rising levels of CO2 will manifest itself through a small enhancement of the global hydrologic cycle (by a few percent) but that we will see very little increase of global temperature when CO2 amounts double towards the end of the 21st century. The General Circulation Models (GCMs) on which predictions of 2-5oC (4-9oF) global warming for a doubling of CO2 are based have basic flaws and they should not be accepted. The four IPCC reports which have been issued over the last 16 years have done much harm in needlessly alarming the world over the dangers of rising levels of CO2 that are not realistic. The IPCC process has made it impossible to separate the overwhelming political nature of this effort from the desired unbiased scientific analysis.

This paper documents many of the false statements on tropical cyclones which were contained in the IPCC-AR4 and gives scientific arguments why rising levels of CO2 should have little or no significant influence on TC activity and only marginally so on global warming.


This section briefly discusses:
a. Last 20-year downward trend in global TC activity.
b. CO2’s extremely small relative energy influence.
c. Lack of SST vs. TC activity correlation.
d. Atlantic Ocean thermohaline circulation (THC) influence on Atlantic SST variations.


Although global surface temperatures appear to have increased during the 20th century by about 0.65°C or 1°F, there is no reliable data to indicate that increases in TC frequency or intensity changes occurred in any of the globe’s TC basins. Global Accumulated Cyclone Energy (ACE)1 shows significant year-to-year and decadal variability over the past 40 years (when global TC data is deemed reasonably reliable) but no period-long increasing trend. In fact, global TC activity has shown (red line) a distinct decrease over the last 20 years when CO2 amounts were increasing (Figure 2.1). Similarly, Klotzbach (2006) found no significant change in global TC activity during the period from 1986-2005 when tropical SSTs and CO2 amounts were rising (Figure 2.2). See section 13 for more discussion.


The energy change that will be brought about by rising levels of CO2 have been and will be for many decades far too small to cause a detectable influence on TCs. Figure 2.3 shows a vertical cross-section of the annual energy budget for the tropics (30oN-30oS; 0-360o). Note how large the surface, troposphere, and top of the atmosphere energy flux components are in comparison with the reduced infrared (IR) flux to space of 3.7 Wm-2 for a doubling of CO2 that is expected to occur by the end of the 21st century. We are now about one-third of the way (~ 1.4 Wm-2) to a doubling of CO2 from the background state of the mid-19th century. Any potential CO2 influence on TCs will be too miniscule to be isolated, and we do not know if once an influence is ever able to be detected whether it will have a positive or a negative effect on TC intensity and/or frequency.


These two parameters are only slightly related in all global TC basins besides the Atlantic (Figure 2.4). Long-period SST increases should not be expected to bring about significant global lapse-rate buoyancy increases or enhanced deep cumulonimbus (Cb) convection. If global surface temperature and surface moisture changes on a climate time scale do occur, so too will upper-level temperature and moisture conditions change in a way so as to maintain global rainfall and energy budgets near their long-period average. With global warming or cooling of but a degree or so it is to be expected that average global lapse-rates and TC activity will not appreciably change.

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