Research & Commentary: Global Climate Models and Their Limitations

Published October 9, 2013

Many scientists, policymakers, and engaged citizens have become concerned over the possibility that manmade greenhouse gas emissions, in particular carbon dioxide (CO2), may be causing dangerous climate change. A primary reason for this public alarm is a series of reports issued by the United Nations’ Intergovernmental Panel on Climate Change (IPCC).

The IPCC places great confidence in the ability of global climate models (GCMs) to simulate future climate and attributes observed climate change to anthropogenic emissions of greenhouse gases. In a Summary for Policymakers describing its latest assessment report, the IPCC claims the “development of climate models has resulted in more realism in the representation of many quantities and aspects of the climate system,” adding, “it is extremely likely that human activities have caused more than half of the observed increase in global average surface temperature since the 1950s.”

Climate models are important tools that can be used to advance our understanding of current and past climate. They also provide qualitative and quantitative information about potential future climate conditions. But in spite of their sophistication, they remain merely models. They represent simulations of the real world, constrained by their ability to correctly capture and portray each of the important processes that affect climate. Notwithstanding their complexities, the models remain deficient in many aspects of their portrayal of the climate, which reduces their ability to provide reliable simulations of future climate.

In general, GCMs perform poorly when their projections are assessed against empirical data. Several IPCC forecasts made by GCMs have been falsified by real-world data, as documented in Climate Change Reconsidered II: Physical Science, by the Nongovernmental International Panel on Climate Change.

To have any validity for future projections, GCMs must incorporate not only the many physical processes involved in determining climate, but also all important chemical and biological processes that influence climate over long time periods. Several of these important processes are missing or inadequately represented in today’s state-of-the-art climate models.

The current generation of GCMs cannot make accurate projections of climate even 10 years ahead, let alone the 100-year period that has been adopted by policy planners. The output of such models should therefore not be used to guide public policy formulation until they have been validated and shown to have predictive value.

The above introduction is based on text from Climate Change Reconsidered II: Physical Science and its Summary for Policymakers, published by The Heartland Institute in September 2013 for the Nongovernmental International Panel on Climate Change (NIPCC). 

The following documents provide additional information about global climate models.


Chapter 1 of Climate Change Reconsidered II: Physical Science
In Chapter One of the latest report from the Nongovernmental International Panel on Climate Change, atmospheric scientist Anthony Lupo and meteorologist William Kininmonth evaluate climate models against real-world climate and biospheric data. They found the IPCC overestimates the ability of current state-of-the-art GCMs to accurately simulate past and future climate. 

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 the findings of Climate Change Reconsidered II, a major scientific report that refutes the IPCC’s claim.

Validity of Climate Change Forecasting for Public Policy Decision Making
In a 2009 paper published in International Journal of Forecasting, Kesten Green, J. Scott Armstrong, and Willie Soon examine procedures used to evaluate forecasts of global mean temperatures over the policy-relevant long term. They find the forecasts contained in IPCC reports have been far off target, and they recommend instead a forecast of no more than 0.5 degrees Celsius warming or cooling relative to 2008 temperatures by the end of the twenty-first century. 

CO2-Induced Global Warming: A Skeptic’s View of Potential Climate Change
In this groundbreaking 1998 paper published in Climate Research, scientist Sherwood Idso professes skepticism toward the predictions of significant CO2-induced global warming then being made by state-of-the-art climate models. He cites the number of planetary cooling forces that are intensified by warmer temperatures and the strengthening of biological processes that are enhanced by the same rise in atmospheric CO2 concentration that drives warming. Several of these cooling forces have individually been estimated to be of equivalent magnitude, but of opposite sign, to the typically predicted greenhouse effect of a doubling of the air’s CO2 content, all of which suggests little net temperature change will result from the ongoing buildup of CO2 in Earth’s atmosphere. 

Biases in the Output of Global and Regional Circulation Models
In a 2012 Hydrology and Earth System Sciences “Opinion” article, Ehret et al. write, “despite considerable progress in recent years, output of both global and regional circulation models is still afflicted with biases to a degree that precludes its direct use, especially in climate change impact studies.” They also note, “this is well known, and to overcome this problem, bias correction (BC, i.e., the correction of model output towards observations in a post-processing step) has now become a standard procedure in climate change impact studies.” Ehret et al. argue this bias correction “hides rather than reduces uncertainty,” which they suggest may lead to avoidable mistakes by end users and decision makers. They thus conclude bias correction is often “not a valid procedure.”


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, contact Heartland Institute Policy Analyst Taylor Smith at [email protected] or 312/377-4000.