In its last Summary for Policymakers, on page 16 [1], the Intergovernmental Panel on Climate change (IPCC) writes : “Equilibrium climate sensitivity is likely in the range 1.5°C to 4.5°C (high confidence), extremely unlikely less than 1°C (high confidence), and very unlikely greater than 6°C (medium confidence).”

In its jargon the term equilibrium climate sensitivity (ECS) means the average temperature rise at the surface of the globe that the climate system would show for any doubling of the atmospheric concentration of carbon dioxide (CO₂).

Since the beginning of the industrial era the CO₂ concentration rose from 280 to 400 ppm, a 43% increase.

What would then be the calculated temperature if we use the IPCC values?

It needs to be remembered that the radiative forcing implied in the warming by so-called greenhouse gases varies in proportion to the logarithm of the concentration. Thus a 43% concentration increase will result in approximately half of the ECS (51.5%).

Calculated temperature increases implied by IPCC’s statement:

IPCC parameter	ECS °C	Calculated ΔT °C
Low	1.5	0.77
Medium (table 9.5 of the full report)	3.22	1.66
High	4.5	2.32
Actually observed temperature increase		approx. 1.0 °C

Thus we can interpret that, in its lowest estimate, IPCC attributes 77% of the observed warming to CO₂, leaving the rest to other anthropogenic sources such as methane, and other emissions of so-called greenhouse gases, and soot. Almost nothing is left to natural causes, because none was sought and therefore none was identified.

Worse, in its medium scenario, CO₂ would have contributed to 166% of the observed warming which would imply that other causes would have contributed to a 0.62 °C cooling, still without discussion and quantification. The same observation applies for the high ECS estimate where a cooling of not less than 1.32 °C should have taken place if we would not have burnt fossil fuels and produced cement.  We would find ourselves in a regime even colder than the minimum of the little ice age, from which we began to get out well before any human consequence of the industrial era could have played any warming role. IPCC does not tell this to decision makers, why?

Reader: use your own mind to assess if the above IPCC statement has anything to do with reality.
See also more details on my site MR-climate.

 

[1] IPCC, 2013: Summary for Policymakers. In:Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

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