Climate Sensitivity Considering Urban and Natural Warming

Guest Post 

By Ken Gregory, P.Eng.


This blog post summarizes the paper Climate Sensitivity by Energy Balance with Urban and Natural Warming.

Climatologists Nicholas Lewis and Dr. Judith Curry published a paper in the Journal of Climate in (LC2018) that used the observationally-based energy balance method to estimate the Equilibrium Climate Sensitivity (ECS) and the Transient Climate Response (TCR). The ECS is the global average surface temperature change due to a doubling of CO2 after allowing the oceans to reach temperature equilibrium, which takes about 1500 years for the upper 3 km of the ocean. The TCR is more relevant to climate policy as it is the global surface temperature change at the time of the CO2 doubling.

Solar forcing may be several times larger than just that caused by the change in the total solar irradiance (TSI) as interpreted by the IPCC. A paper Scafetta et al 2019 shows that the TSI forcing was greater than that used in LC2018. The large variations of solar ultraviolet radiation affect ozone in the upper atmosphere which causes a significant solar forcing. High solar activity reduces cosmic rays entering the atmosphere, reducing lower cloud cover and causing warming by increased incoming solar radiation.

As it is difficult to quantify each of these forcings, temperature proxies are used to estimate the natural warming since the start of the base period by extrapolating the millennium scale temperature cycle. The surface temperature change should be revised downward to remove the natural warming from the Little Ice Age so that the temperature change used in the energy balance calculations includes only the portion that was caused by the change in anthropogenic forcing.

Fredrik Ljungqvist prepared a temperature reconstruction of the Extra-Tropical Northern Hemisphere (ETNH) during the last two millennia as shown in figure 1. Human-caused GHG emissions did not cause significant temperature change to the year 1900 because cumulative CO2 emissions to 1900 were insignificant. Extrapolations of the millennium cycle from 1900 to 2010 provide an estimate of the natural component of the temperature change.

The global temperatures changed by 75% of the ETNH temperatures from 1900-1919 to 2002-2015. The global natural temperature change between the base and final periods of the LC2018 analysis is estimated at 0.084 °C/century. The temperature changes used in the climate sensitivity calculations must be reduce by 0.114 °C to account for natural climate change.



Numerous papers have shown that the UHIE contaminates the instrument temperature record. Most long-term temperature records are recorded in or near cities which have gotten warmer as they grow. A study by McKitrick and Michaels 2007 showed that about half of the warming over land since 1980 in instrument data sets is due to the UHIE. The global UHIE is about 0.041 °C/decade. A paper by De Latt and Maurellis shows the global UHIE is 0.040 °C/decade. These studies are supported by numerous other studies. The temperature change used in the LC2018 climate sensitivity calculations must be reduce by 0.133 °C to account for the UHIE from 1979.

The millennium cycle natural warming and UHIE corrections reduce the temperature change between the two periods of the LC2018 analysis due to GHG by 0.247 °C. The best estimates of ECS and TCR are 1.04 °C and 0.83 °C, respectively.



The probability density functions (PDF) of the LC2018 ECS and TCR were replicated for this study. Standard deviations and CIs were assigned to factors used to calculate the millennium cycle and UHIE adjustments to determine a PDF for the corrected ECS estimates. Figures 2 and 3 show the LC2018 PDF and the corrected PDF of ECS and TCR, respectively.

The forecast of global temperature rise from 2019 due to anthropogenic GHG emissions assumes that atmospheric CO2 concentrations continue to increase at the current rate of 0.60%/year and that non-CO2 GHG continue to contribute 18% of the CO2 forcing.

This estimate includes the effects of increasing GHG concentration prior to 2019. Actual temperatures may rise or fall depending on natural climate change. Figure 4 shows the projected temperature response to continued exponential growth in GHG concentrations. The 2019-2100 temperature rise is 0.63 °C with a likely 17-83% range of 0.51 to 0.79 °C.

A paper published in Energies by Peter Lang and me shows that the impact of a 3 °C temperature rise from 2000 on USA energy expenditures would have a positive impact on USA economic wealth of +0.07% of gross domestic product (GDP). A paper by me (Gregory 2020) extends the analysis to global impacts. A paper by Dayaratna, McKtrick & Michaels recommends that the CO2 fertilization effect in the FUND economic model be increased by 30% due to recent studies of the effect. Incorporating these two changes in FUND and using an ECS of 1.0 °C shows that a 2 °C global mean surface temperature rise from 2000 would increase global wealth by 1.45% in 2147, equivalent to 2019US$1.26 trillion.

CO2 emissions have a large social benefit, so policies to restrict CO2 emissions are harmful and misguided. The paper contains more information, details of the calculations and a link to an Excel file.


This the Abstract of Ken’s paper:



November 12, 2020 at 06:03AM

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