Variability of the Earth’s climate - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 47

not refer to these prior papers, which essentially carried out the same calculation
but with different parameters, and in the case of Kohler et al. with much greater
detail.
Hansen and Sato (2011) then proceeded to estimate the forcings over the past
800,000 years including about eight ice ages and interglacials using the measured
CO 2 and CH 4 concentrations in ice cores, and estimates of sea level during that
period. These fit the oxygen isotope data from the ice cores quite well. But this
should not be a surprise. The variation of CO 2 and CH 4 over the past 800,000
years is known to have very nearly the same shape as the isotope curve. Hansen
and Sato assigned temperatures to the isotope ratios both from the ice cores and
from ocean sediments and claimed good agreement. According to Hansen and
Sato, variation of global average temperature from glacial maxima to interglacials
was estimated to be typically about 3 C about 800,000 years ago, and this slowly
increased to roughly 6.8 C in the most recent ice age-interglacial transition.
By comparing ice core isotope records with deep-sea isotope records, Hansen
and Sato (2011) estimated that temperature changes derived from Antarctic ice
cores were roughly double the global average temperature changes in the past.
This, of course, must be a very rough approximation, although Hansen and Sato
(2011) seem to have adopted it as fact.
Hansen and Sato (2011) then embarked on a discussion of the temperatures
reached in the past several interglacial periods as compared with our own inter-
glacial of the past 10,000 years. In particular, ice core data indicate that the
interglacials that peaked about 125,000 and 400,000 years ago were warmer than
today. Hansen and Sato (2011) concluded that the peak warm periods were ''less
than 1 C warmer than peak Holocene global temperature'' and therefore ''were
also less than 1 C warmer than global temperature in year 2000.'' It is not clear
how they reached this conclusion. It was necessary for Hansen and Sato (2011), as
global-warming activists, to insist that previous interglacials were not much
warmer than our own interglacial, since that would suggest that even a moderate
warming compared with today's climate would result in potentially catastrophic
climate changes. However, others have interpreted the data as inferring that pre-
vious interglacials were several degrees warmer than our own. Section 4.4 provides
a number of references and data that show that previous interglacials were con-
siderably warmer than the current one (e.g., Kopp et al., 2009; Sime et al., 2009).
Another aspect of Hansen and Sato (2011)'s rhetoric regarding climate alarmism is
their need to claim that today, after a global temperature rise of 0.7 C in the
past 120 years, ''global temperature in year 2000 had returned, at least, to
approximately the Holocene maximum.'' The data are not accurate enough to be
certain whether this is true. Nevertheless, Hansen and Sato (2011) would like to
conclude that a temperature rise of another 1 C from today's climate might raise
the ocean level by 7 to 9m. A related argument has to do with the global average
temperature some 5 million years ago and the associated sea level. Hansen and
Sato (2011) asserted that the global average temperature 5 million years ago was a
mere 1 Cto2 C warmer than that prevailing in the 19th century prior to the
industrial era, or only 1 C warmer than today. They also asserted that sea level