Scientific instrument used for carbon dating
The transient climate response (TCR) to greenhouse gas emissions, the warming when carbon dioxide (CO) doubles in about 125 years, was estimated by climatologist Nicholas Lewis at 1.2 °C using an energy balance approach and the new aerosol estimates but assuming that there was no natural long-term warming nor any urban heat contamination of the temperature record.
However, proxy records demonstrate that there are millennium scale natural climate cycles and numerous studies indicate that the major temperature indexes are contaminated by the urban heat island effect (UHIE) of urban development.
Summary High estimates of climate sensitivity to greenhouse gases assume aerosols caused a large cooling effect, which canceled some of the previous warming effect, and little or no natural climate change.
Recent research indicates that the aerosol effect is much less than previously thought.
is the change in global average temperature between two periods, is the change in forcing between the two periods, and is the top-of-atmosphere radiative imbalance, which is the rate of heat uptake of the climate system.
The oceans account for over 90% of the climate system heat uptake.
Energy balance estimates of ECS and TCR use these equations: , where F.Ocean heat content is from Box 3.1, Figure 1 of AR5.The likely 83% upper bound of ECS was reported by the IPCC in AR5 at 4.5 °C, but this drops to 2.45 °C when calculated with the AR5 reported forcings, and drops to only 1.8 °C when substituting the Stevens estimate of aerosol forcing.Using the equations for TCR and ECS, the total forcing change during the interval was 2.21 W/m.Adjustment for Millennium Cyclic Warming This analysis by Lewis does not account for the long-term natural warming from the Little Ice Age (LIA), likely driven by indirect solar activity.