Human Contribution to Warming is 10% or Less

SCIENCE EDITORIAL (April 17, 2010) by S. Fred Singer, PhD

Due Diligence on the IPCC Assessment Report #4 [2007]

I know it’s a tough job – but let’s just check the Intergovernmental Panel on Climate Changes (IPCC 2007) iconic, widely-quoted conclusion and parse its meaning:

“Most of the observed increase in globally-averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GH gas concentrations.”

How should one interpret this ex cathedra declaration to the faithful?

IPCC helpfully defines ‘very likely’ as ‘90-99% certain’, but they don’t tell us how they reached such well-defined certainty.

What remarkable unanimity! Just how many and whom did they poll? No word.

IPCC doesn’t define the word ‘most.’ We may assume it means anything between 51 and 99%. That’s quite a spread.But a footnote informs us that solar forcing is less than 10% of anthropogenic [0.12/ 1.6 W/m2]; so ‘most’ must be closer to 99% than to 51%.

OK; let’s check out the data since 1958. But we don’t want to rely on contaminated surface data – which IPCC likely used (although they omitted to say so).

However, atmospheric data were readily available to the IPCC in the CCSP-SAP-1.1 report (Fig 3a, p.54; convening lead author John Lanzante, NOAA), with independent analyses by the Hadley Centre and NOAA that agree well. And further, according to GH models, atmospheric trends should be larger than surface temperature trends.

1958 – 2005: Shows a total warming of +0.5 C . But how much of that is anthropogenic? (The IPCC ascribes pre-1958 warming to natural forcings) So let’s break it down:

1958 – 1976: Cooling
1976 – 1977: Sudden jump of +0.5 C (Cannot be due to GH gases)
1979 – 1997: The satellite data show only a slightly positive trend
1998 – 1999: El Nino spike
2000 – 2001: No detectable warming trend
2001 – 2003: Sudden jump of +0.3 C (Cannot be due to GH gases)
2003 – present: No trend, maybe even slight cooling

In conclusion: The IPCC’s ‘most’ is not sustained by the best observations; the surface data (1979 to 1997) are suspect – until the raw data and algorithms of CRU are examined.

Therefore, the human contribution is very likely only 10% of observed warming --or even less.


Dr. S. Fred Singer is distinguished Professor Emeritus of Environmental Science at the University of Virginia. His previous government and academic positions include Chief Scientist, U.S. Department of Transportation (1987- 89); Deputy Assistant Administrator for Policy, U.S. Environmental Protection Agency (1970-71); Deputy Assistant Secretary for Water Quality and Research, U.S. Department of the Interior (1967- 70); founding Dean of the School of Environmental and Planetary Sciences, University of Miami (1964-67); first Director of the National Weather Satellite Service (1962-64); and Director of the Center for Atmospheric and Space Physics, University of Maryland (1953-62). He has a PhD in physics from Princeton University.