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Scientific Critique of IPCC's 2013 'Summary for Policymakers'

Craig Idso, Robert M. Carter , S. Fred Singer, Willie Soon

Heartland Institute


Antarctic Temperature Trend 1981-2007The United Nations’ Intergovernmental Panel on Climate Change (IPCC) released a final version of the Summary for Policymakers (SPM) of its Fifth Assessment Report on September 27, 2013. It differs in important ways from a draft SPM dated June 2013 that circulated widely in the preceding months.

As discussed below, the new SPM reveals the IPCC has retreated from at least 11 alarmist claims promulgated in its previous reports or by scientists prominently associated with the IPCC. The SPM also contains at least 13 misleading or untrue statements, and 11 further statements that are phrased in such a way that they mislead readers or misrepresent important aspects of the science.

Two weeks before the IPCC released its report, an alternative perspective was presented by a different group of scientists, the Nongovernmental International Panel on Climate Change (NIPCC) (Idso et al., 2013). Unlike the IPCC, NIPCC’s charter is to investigate the causes and consequences of climate change “in the round,” or from all perspectives, rather than to search only for evidence of a human impact on climate. The NIPCC report, titled Climate Change Reconsidered II: Physical Science contradicts many of the IPCC’s findings. 

In the discussion that follows, IPCC quotations are identified by their page number in the SPM using the same numbering method (e.g., SPM-3) used in the SPM itself. Chapters in the NIPCC  eport providing evidence contrary to the IPCC’s claims are referenced as “NIPCC, Chapter X.” The NIPCC report and its Summary for Policymakers are available online at

Eleven statements made in the 2013 SPM apparently retreat from more alarmist positions struck in earlier Assessment Reports or in related research literature. These repositionings are to be welcomed when they move the IPCC's commentary closer to scientific reality. 

1. "The rate of warming over the past 15 years (1998-2012; 0.05 deg. C/decade) is smaller than the trend since 1951 (1951-2012; 0.12 deg. C/decade)" (SPM-3).

The IPCC concedes for the first time that a 15 year-long period of no significant warming occurred since 1998 despite a 7% rise in carbon dioxide (CO2). It also acknowledges that on a longer (more climatic) time scale the rate of global warming has decelerated since 1951, despite an accompanying 80 ppm or 26% increase in carbon dioxide (312 to 392 ppm).

The statement represents a significant revision in IPCC thinking, because their concern about  dangerous warming rests upon the assumption that temperature increases will proceed in parallel fashion with CO2 increases, and not just sometimes or in a stepped fashion. NIPCC, in contrast,  has documented that temperatures in the geologic time scale, the twentieth century, and the early twenty-first centuries have not changed in parallel with CO2 levels (NIPCC, Chapter 4).

2. "Continental-scale surface temperature reconstructions show, with high confidence, multi-decadal intervals during the Medieval Climate Anomaly (950-1250) that were in some regions as warm as in the late 20th century" (SPM-4).

IPCC-related scientists have previously argued that the magnitude of the late twentieth century global warming exceeded that of the Medieval Warm Period (MWP). The notorious "hockey stick" featured in the IPCC's Third Assessment Report, and still visible in the Fourth Assessment Report, appeared to erase the MWP from the historical temperature record by showing little temperature change for thousands of years followed by a sharp rise in the twentieth century.

From an independent survey of paleoclimatic data records, NIPCC found the MWP to have been of near-global extent, and that the magnitude of warming was often similar to or exceeded that observed for the twentieth century from thermometer data (NIPCC, Chapter 4).

3. "It is very likely that the annual mean Antarctic sea ice extent increased ... (by) 1.2-1.8% per decade between 1979 and 2012"




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