Geoscience Reference
In-Depth Information
ently the tuning had not been a fatal cheat. Models without flux adjustments soon
became standard.”
11
No matter how powerful their latest supercomputer, modelers managed to push
it to the limit. NASA's Goddard Institute of Space Studies, under James Hansen (b.
1941), built its model to forecast weather, hoping that the results might also shed
light on the atmospheres of planets, including the suffocating clouds of Venus that
Hansen had studied for his Ph.D. thesis.
Hansen earned his degrees at the University of Iowa and in 1967 began work
at the Goddard Institute, where he remained until he retired in 2013. Hansen has
not only been one of the most productive climate scientists but also one of the
most courageous and outspoken, warning in every possible forum of the dangers
of global warming. He has been arrested for protesting mountaintop removal min-
ing and for urging President Obama to reject the Keystone oil pipeline. In 2013,
Hansen won the Ridenhour Courage Prize.
Manabe's figure for climate sensitivity (the global temperature rise resulting
from doubled atmospheric CO
2
) settled in at about 2°C, whereas Hansen's model
initially gave about 4°C. In 1979 the National Academy of Sciences convened a
panel to study the issue, headed by Jules Charney (1917-1981). The panel recom-
mended splitting the difference: “We estimate the most probable global warming
The Charney panel had “tried but been unable to find any overlooked or underes-
statement remains as true as when it was written. No one, whether climate scient-
ist or global warming denier, has ever found a negative feedback large enough to
offset the effects of the several positive feedbacks. This is sad but true.
The Charney panel did hold out one faint hope: that the oceans would absorb
enough heat to delay the onset of warming by several decades. In 1985, Hansen's
group saw this as a trap that would lull humanity into a dangerous complacency:
If equilibrium climate sensitivity is 3°C or greater for a doubling of the carbon dioxide concen-
tration, then most of the expected warming attributable to trace gases added to the atmosphere
by man probably has not yet occurred. This yet to be realized warming calls into question a
policy of “wait and see” regarding the issue of how to deal with increasing atmospheric carbon
dioxide and other trace gases.
14
As the global climate models grew larger and more powerful, some questions
could still be addressed using a “simple model” with fewer complexities and lines
of code. In 1981, Hansen's group used a one-dimensional climate model to invest-
igate a wide set of climate influences: solar intensity, aerosols, clouds, soot, ice
