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1955-2011. 22 They first ran the simulation using only volcanic and anthropogenic
influences on the climate. They ran the simulation again adding natural variability
contributed by the El Niño/La Niña process. Then they ran the simulation a final time
adding in a more complex situation involving a feedback from El Niño/La Niña onto
natural cloud characteristics. They then compared their model results with the set of
real-world observations. They found that the complex situation involving El Niño/La Niña
feedbacks onto cloud properties produced the best match to the observations, and, notably,
produced the lowest estimate for the earth's climate sensitivity to CO 2 emissions—a
value of 1.3°C. Climate models which do not accurately recognise this feedback will
produce climate sensitivity values from the doubling of the atmospheric concentration of
greenhouse gases far in excess of this observationally-determined value.
Otto et al. is highly significant because fifteen of the seventeen co-authors were also
authors of the 2013 IPCC report. 23 They acknowledge both 'the pause' and recent heat
uptakeandnotethattheseyieldalowersensitivitythanhasbeenfoundinpreviousmodels.
They prefer using the most recent decade because it contains more reliable baseline energy
balance data, and they calculate a five to 95 per cent confidence range of 1.2-3.9°C, and a
mean sensitivity that is also more than 40 per cent less than the average in the 2013 IPCC
report. Why this was not also a conclusion of that report, given the position of so many of
its authors, seems mysterious.
Lewis, in a highly-cited paper, tuned a climate model to provide an 'optimal
fingerprint' to calculate the temperature sensitivity most consistent with the observed
diffusion of heat through the ocean and changes in atmospheric transparency. 24 Their 90
per cent confidence interval is 1.0-3.0°C, virtually the same range found by Aldrin et al,
noted earlier. 25 Lewis notes he used the same basic temperature statistics as did Aldrin.
Masters, using the observed changes in heat content of the upper 2 kilometers of
the ocean, along with temperature observations since 1950, argued that the model family
employed in the 2013 IPCC report is too sensitive to changes from both warming
greenhouse gases and cooling aerosol emissions. 26 Their results suggest that the mean
equilibrium climate sensitivity is around 2.2°C, while the average of the IPCC models is
3.2°C.
Most recently, Loehle recognized that calculations relating human-induced changes in
theenergybalancewithobservedtemperaturesalsoyieldsthenow-familiar2°Csensitivity,
but that the temperature trends are also modulated by long-term natural oscillations, such
as the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation. 27 Removing
these from the surface record, and comparing them in a very straightforward relationship
toanthropogenerated emissionsyieldsthesamesensitivity butalsoincreasesconfidencein
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