A paper in press for the journal Tellus finds the "best estimate" of climate sensitivity to CO2 is about 33% less than estimated by the IPCC. According to the authors, the best estimate of transient climate sensitivity is 1.5C for a doubling of CO2 levels, and equilibrium climate sensitivity [after hundreds of years] about 2C. The paper finds a lower bound on equilibrium climate sensitivity of 1.16C per doubling of CO2. The paper adds to many recent peer-reviewed papers finding climate sensitivity to CO2 is significantly less than claimed by the IPCC.
Determination of a lower bound on Earth’s climate sensitivity
Lennart Bengtsson 1, Stephen E. Schwartz 2
1 Environmental Systems Science Centre, University of Reading, UK;
2 Atmospheric Sciences Division, Brookhaven National Laboratory, Upton NY 11973, USA
Submitted to Tellus, October 23, 2012
Accepted, August 14, 2013 Revised, May 20, 2013; July 27, 2013; August 15, 2013
ABSTRACT: Transient and equilibrium sensitivity or Earth's climate have been calculated using global temperature, forcing, and heating rate data for the period 1970-2010. We have assumed increased long wave radiative forcing in the period due to the increase of the long-lived greenhouse gases. By assuming that the change in aerosol forcing in the period to be zero we calculate what we consider to be lower bounds to these sensitivities, as the magnitude of the negative aerosol forcing is unlikely to have diminished in this period. The radiation imbalance necessary to calculate equilibrium sensitivity is estimated from the rate of ocean heat accumulation as 0.37 ± 0.03 W m-2 (all uncertainty estimates are 1-σ). With these data we obtain best estimates for transient climate sensitivity 0.39 ± 0.07 K (W m-2)-1 and equilibrium climate sensitivity 0.54 ± 0.14 K (W m-2)-1, equivalent to 1.5 ± 0.3 and 2.0 ± 0.5 K (3.7 W m-2)-1, respectively. The latter quantity is equal to the lower bound of the "likely" range for this quantity given by the 2007 IPCC Assessment report. The uncertainty attached to the lower-bound equilibrium sensitivity permits us to state, within the assumptions of this analysis, that the equilibrium sensitivity is greater than 0.31 K (W m-2)-1, equivalent to 1.16 K (3.7 W m-2)-1, at the 95% confidence level.
Related: Why climate sensitivity is even less than these new estimates
The warming trend peaked in about 2003.The earth has been in a cooling trend since then.Had the authors looked at the last 11 years they would have had to acknowledge the cooling trend .This would have been a step too far for Nature- no doubt.The current IPCC - MET Office models are useless for climate forecasting because they are structured wrongly - mainly because they are built on the premise of a high climate sensitivity to CO2.ReplyDelete
For a complete discussion of forecasting methods and an estimate of the timing and extent of the coming cooling see the latest blogpost at
Here is a summary of the conclusions
"To summarise Using the 60 and 1000 year quasi repetitive patterns in conjunction with the solar data leads straightforwardly to the following reasonable predictions for Global SSTs
1 Significant temperature drop at about 2016-17
2 Possible unusual cold snap 2021-22
3 Built in cooling trend until at least 2024
4 Temperature Hadsst3 moving average anomaly 2035 - 0.15
5Temperature Hadsst3 moving average anomaly 2100 - 0.5
6 General Conclusion - by 2100 all the 20th century temperature rise will have been reversed,
7 By 2650 earth could possibly be back to the depths of the little ice age.
8 The effect of increasing CO2 emissions will be minor but beneficial - they may slightly ameliorate the forecast cooling and help maintain crop yields .
9 Warning !! There are some signs in the Livingston and Penn Solar data that a sudden drop to the Maunder
Minimum Little Ice Age temperatures could be imminent - with a much more rapid and economically disruptive
cooling than that forecast above which may turn out to be a best case scenario"
The IPCC created a positive feedback to keep temperatures rising. It claims CO2 causes temperature increase that increases evaporation and water vapour amplifies the temperature trend. Lindzen and Choi, discredited this in their 2011 paper which concluded “The results imply that the models are exaggerating climate sensitivity.”
Climate sensitivity has declined since and gradually approaches zero. A recent paper by Spencer claims “…climate system is only about half as sensitive to increasing CO2 as previously believed.”
Indeed, empirical – n.b. not model-derived – determinations each indicate climate sensitivity is ~0.6°C for a doubling of atmospheric CO2 equivalent. This value is indicated by the studies of
Idso from surface measurements
and Lindzen & Choi from ERBE satellite data
and Gregory from balloon radiosonde data
Idso published his eight “natural experiments” in Climate Research in April 1998. The IPCC has not mentioned, not reported and not referenced his work. My above link goes to his paper which has this as its Abstract
Over the course of the past 2 decades, I have analyzed a number of natural phenomena that reveal how Earth’s near-surface air temperature responds to surface radiative perturbations. These studies all suggest that a 300 to 600 ppm doubling of the atmosphere’s CO2 concentration could raise the planet’s mean surface air temperature by only about 0.4°C. Even this modicum of warming may never be realized, however, for it could be negated by a number of planetary cooling forces that are intensified by warmer temperatures and by the strengthening of biological processes that are enhanced by the same rise in atmospheric CO2 concentration that drives the 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, which suggests to me that little net temperature change will ultimately result from the ongoing buildup of CO2 in Earth’s atmosphere. Consequently, I am skeptical of the predictions of significant CO2-induced global warming that are being made by state-of-the-art climate models and believe that much more work on a wide variety of research fronts will be required to properly resolve the issue.
The IPCC has studiously ignored empirical information which indicates climate sensitivity (CS) is less than 1.0°C for a doubling of atmospheric CO2 concentration and has only reported high values of CS produced from model studies (i.e. climate ‘understandings’ programmed into computers).
The empirical determinations of CS indicate that effects of increasing atmospheric CO2 concentration above present levels would not be possible to discern natural climate variability is much larger. Therefore, any effect on global temperature of increase to atmospheric CO2 concentration only has an abstract existence; it does not have a discernible existence that has observable effects (observation of its effects would be its detection).