In the hot summer of 1988, James Hansen, a climatologist who is now director
of the NASA Goddard Institute for Space Studies, presented the above graph of
temperature projections to the US Congress when giving testimony on the
then-expected effect of carbon dioxide emissions on temperatures worldwide.
The upper, solid black line was Hansen's worst-case scenario: the dashed line
was what he considered the most likely outturn; the dotted line was his
estimate of the outturn if emissions of carbon dioxide had been reduced from
1988 onward and stabilized from 2000 onward. The red line showed the NASA/GISS
record of observed global temperatures to 1988.
Hansen was widely criticized for having exaggerated his “scenario A”
projection. He later responded to the criticism by updating the graph of
observed temperatures to take it as far as the El Nino year of 1998. Hansen is
reported as having said that his likely-outturn graph (the blue dashed line on
the graph below) has proven broadly accurate. However, from 1988 to 2006 his
likely-outturn graph closely follows the stabilized-CO2 graph. In 2005, his
likely-outturn and stabilized-CO2 graphs are puzzlingly shown as
near-coincident. However, atmospheric CO2 has not been stabilized: instead, it
has continued to rise monotonically and exponentially.
Observed temperatures are now diverging very considerably below Hansen's
worst-case scenario. The 2006 observed temperature is appreciably below even
the CO2 stabilization graph. It is becoming steadily more evident that there
is little cause for the alarm generated by the original graph.
Above: The graph presented to the US Senate by Hansen in 1988, redrawn
for clarity, set against the NCDC global mean annual temperature anomalies to
2006. Michael Crichton, in his best-selling novel “State of Fear”, said that
Hansen had forecast a rise of 0.35% in temperature to 2000, but that observed
temperature had risen by only one-third of that amount.
Below: Annual global mean land and sea surface air temperature
anomalies between 1900 and 2006, issued by the US National Climate Data Center.
The two highlighted values are for 1988, when Hansen gave his testimony, and
2000. The difference between the two values, i.e. the actual increase in
temperature between 1988 and 2000, is less than 0.06C.
Hansen's three scenarios, presented to Congress during the very hot summer of
1988, projected global mean temperature increases of 0.3C, 0.22C and 0.45C
respectively in the 12 years to 2000: an average of
0.32C,or at least five times the actual outturn. Even his
central case is at least three times the outturn, justifying Michael
Crichton's conclusion.
