The temperature history shows an obvious millennium scale temperature oscillation, indicating that natural climate change accounts for a significant portion of the temperature recovery since the LIA. Richard Lindzen writes, “Lewis does not take account of natural variability, and, I suspect, his estimates are high.” Fredrik Ljungqvist prepared a temperature reconstruction of the Extra-Tropical Northern Hemisphere (ETNH) during the last two millennia with decadal resolution [Ljungqvist 2010] here emissions to 1900 were insignificant.The approximate temperature trends during each of the periods identified in figure 1 were estimated.In terms of TCR, using the Stevens aerosol forcing causes the upper 95% limit to be reduced from 2.5 °C to 1.65 °C.
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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.
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.
Adjusting the energy balance calculations to account for the natural recovery from the Little Ice Age and the UHIE reduces the TCR to 0.85 °C.
Equilibrium climate sensitivity is estimated at 1.02 °C.
This allows climate models to have high sensitivity to greenhouse gases while still roughly matching the historic temperature record.
Aerosol forcing depends strongly on very uncertain estimates of the level of preindustrial aerosols.
The two periods used for the analysis were 1859-18-2011.
They were chosen to give the longest early and late periods free of significant volcanic activity, which provide the largest change in forcing and hence the narrowest uncertainty ranges.
The average of the absolute natural temperature change over the four periods was 0.095 °C/century, as shown in Table 1 and Figure 2. Extra-tropical Northern Hemisphere temperatures utilizing many palaeo-temperature proxy records, adapted from Ljungqvist 2010.