Research & Commentary: Extreme Weather

Published November 4, 2013

For more than two decades the United Nations’ Intergovernmental Panel on Climate Change (IPCC) has supported the model-based narrative that carbon dioxide (CO2)-induced global warming will cause (or is already causing) more extreme weather, including more frequent and more severe heat waves, precipitation extremes (droughts and floods), storms, tropical cyclones, and other extreme weather-related events.

A report from the Nongovernmental International Panel on Climate Change (NIPCC), an independent group of some 50 scientists from 15 countries, titled Climate Change Reconsidered II: Physical Science, summarizes the large body of research reviewing historical trends in extreme weather events and examines how they interrelate with other weather and climate variables. It is clear in almost every instance of each extreme weather event examined, there is little support for predictions that CO2-induced global warming will increase either the frequency or intensity of those events. The real-world data overwhelmingly support the opposite conclusion: Weather will more likely be less extreme in a warmer world.

The main reason for this is that air temperature variability decreases as mean air temperature rises, on all time scales. The claim that global warming will lead to more extremes of climate and weather, including of temperature itself, is theoretically unsound in addition to contradicting the empirical evidence. Although specific regions experienced significant changes in the intensity or number of extreme events in the twentieth century, for the globe as a whole there was no relationship between such events and global warming over the past 100 years.

After Hurricane Sandy, scores of environmental groups and media outlets claimed global warming will lead to more frequent and more intense hurricanes, also called tropical cyclones (TCs). In his 2009 paper published in Proceedings of the Royal Society, Dr. Johnny C.L. Chan studied records for three ocean basins in 1960–2007 and two in 1981–2007. For all but one of the five, maximum potential intensity (MPI, an index of thermodynamic forcing) over each basin had no correlation or a statistically insignificant correlation with the number of intense TCs. In the Atlantic basin, this relationship explained about 40 percent of the observed variance.

Chan writes, “the results from this study suggest that such an increase [in thermodynamic energy] does not necessarily imply a concomitant increase in the number of intense TCs, because how the dynamic factors will vary are still not clear. Until we can demonstrate that the dynamic factors will also become more favorable for TC intensification, it remains uncertain whether the frequency of occurrence of intense TCs will increase under a global warming scenario.”

In the face of such facts, the most prudent climate policy is to prepare for and adapt to extreme climate events and changes regardless of their origin. Adaptive planning for future hazardous climate events and change should be tailored to provide responses to the known rates, magnitudes, and risks of natural change. Once in place, these plans will provide an adequate response to any human-caused change that may or may not emerge.

The above introduction is based on text from Climate Change Reconsidered II: Physical Science and its Summary for Policymakers, published by The Heartland Institute for the Nongovernmental International Panel on Climate Change (NIPCC).

The following documents provide additional information about extreme weather.


Chapter 7 of Climate Change Reconsidered II
In Chapter Seven of Climate Change Reconsidered II: Physical Science, Craig Idso and Madhav Khandekar review important extreme weather events in the climate system. They find the IPCC models fail to match the observed record of extreme weather events.

Summary for Policymakers of Climate Change Reconsidered II
The IPCC claims to know, apparently with rising certainty over time, that “most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations” (IPCC AR4 SPM, p. 10). This Summary for Policymakers summarizes and interprets Climate Change Reconsidered II, a major scientific report that refutes this claim.

Climate Change Reconsidered: Temperature Variability
This excerpt from the first edition of Climate Change Reconsidered, published in 2009, reviews the climate change measure of temperature variability and examines whether Earth has experienced more record highs or record lows during the Current Warm Period. After evaluating a large body of research, NIPCC finds air temperature variability almost always decreases when mean air temperature rises.

Trends in Twentieth-Century Temperature Extremes across the United States
In this paper published in 2001 in Journal of Climate, Arthur DeGaeton and Robert Allen review long-term temperature data to analyze extreme temperature trends across the United States. They find “trends in the occurrence of maximum and minimum temperatures greater than the 90th, 95th, and 99th percentile across the United States are strongly influenced by urbanization.”

Thermodynamic Control on the Climate of Intense Tropical Cyclones
In his 2009 paper published in Proceedings of the Royal Society, Johnny C.L. Chan studied five ocean basins—the Atlantic (1960–2007), the Western North Pacific (1960–2007), the Eastern North Pacific (1960–2007), the South Indian Ocean (1981–2007), and the South Pacific (1981–2007)—examining the relationship between the seasonally averaged maximum potential intensity (MPI, an index of thermodynamic forcing) over each basin and the frequency of occurrence of intense tropical cyclones (TCs) within that basin. This work revealed, in Chan’s words, “only in the Atlantic does the MPI have a statistically significant relationship with the number of intense TCs, explaining about 40% of the [observed] variance,” whereas “in other ocean basins, there is either no correlation or the correlation is not significant.”

Drought on the Northern Great Plains of America
On September 9, 2010, the Nongovernmental International Panel on Climate Change referenced a 2000 paper published in Quaternary Research that concluded “solar variability may influence the duration of dry periods …” This implies any new period of intensified drought on America’s Northern Great Plains is not necessarily a vindication of climate-alarmist predications.

Compilation and Discussion of Trends in Severe Storms in the United States: Popular Perception v. Climate Reality
In their 2003 paper published in Natural Hazards, Robert C. Balling and Randall S. Cerveny found little empirical evidence to confirm the theory that increasing levels of greenhouse gases in the atmosphere will lead to mid-latitude land areas becoming more unstable resulting in more severe weather events.

Has the Magnitude of Floods Across the USA Changed with Global CO2 Levels?
In their 2012 paper published in Hydrological Sciences Journal, Robert M. Hirsch and Karen R. Ryberg divided the conterminous United States into four regions and explored the relationship between global mean carbon dioxide concentration and flood magnitudes. They found no statistically significant relationship in three of the regions. The southwest region showed a statistically significant negative relationship between atmospheric CO2 and floods.

Nothing in this Research & Commentary is intended to influence the passage of legislation, and it does not necessarily represent the views of The Heartland Institute. For further information on this and other topics, visit the Environment & Climate News Web site at, The Heartland Institute’s Web site at, and PolicyBot, Heartland’s free online research database, at

If you have any questions about this issue or The Heartland Institute, or would like a scientist to testify in your state, contact Heartland Institute Policy Analyst Taylor Smith at [email protected] or 312/377-4000.