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Strange Scholarship in the Wegman Report V1.0 09/26/10
1.2 Trends – natural and human factors
From [IPC2007, p.13] at right are NH temperatures relative to average
temperature in 1980-1999, not immediately comparable to the previous
chart (global relative to 1961-1990), but representative. Black is historical,
with gray uncertainty range. The others show projections with their
uncertainty ranges for different levels of future GHG emissions chosen by
humans. None of these predict exact tracks, due to natural variability
(noise). Early drafts [IPC2006] were available to the WP.
Basic physics by paper-and-pencil
Sunlight is absorbed by the Earth. Some is re-emitted as heat radiation.
GHGs (CO2, CH4, N2O, water vapor) absorb such radiation and transfer
energy to nearby molecules. Some energy is re-emitted Earthward, a good
thing as temperatures would be uncomfortably lower otherwise. In 1896,
Svante Arrhenius roughly calculated the warming expected from doubling
pre-industrial atmospheric CO2. He was a little high, near the edge of
current uncertainty ranges, but not far off, not bad for 1896. See Spencer
Weart‘s excellent history, Theme-B❹, Theme-C❹
www.aip.org/history/climate/co2.htm,
Computer models help reduce uncertainty limits and improve
regional projections, but the basics are fairly straightforward.
Energy is neither created nor destroyed . GHGs slow emission in the
regions of the spectrum where GHGs absorb thermal radiation. As GHG
concentrations rise, the surface warms to maintain balance between
incoming solar radiation and thermal radiation to space. Most incoming
solar energy is first absorbed in the oceans, measured as Ocean Heat
Content, which is increasing. Ocean oscillations cause more or less heat to
be returned to the atmosphere, so El Nino years cause warmer
atmospheres. Still, energy is always conserved. Unlike some areas of
statistics or economics, physics has strong conservation laws, which are not
mere correlations. Earth‘s energy balance does not change quickly
without reasons, called forcings, such as changes in solar irradiance,
GHGs, aerosols. Earth‘s orbital changes matter, but occur slowly.
Past and future
The Earth‘s future temperature track will be determined by:
� The current state of the Earth, especially total energy content, glacier
masses, vegetation coverage and other factors that affect Earth‘s
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overall albedo, i.e., fraction of energy reflected into space without
creating heat. Ice and snow reflect more than oceans.
� Biological, chemical and physical processes.
� Human choices, with ―public policy implications, as in [SAI2007, p.5].
Difference fromNH
Average 1980-1999
Human emissions choices,
fossil fuels, land use, etc
Not at all likely.
From:
AR4 WG I
SPM.6, p.13
Future natural temperatures simply do not depend on the temperature in
1000AD or on our knowing anything about it. Wegman even said this in
testimony, A.3. However, better understanding of the past‘s natural
variability helps researchers calibrate climate models, which is why
researchers argue fiercely over the shape and jiggles of the shaft. If people
somehow got a full set modern-grade temperature measurements from
1000AD onward, nothing would change for the future except our ability to
forecast it better.
The uncertainty limits on each emissions scenario represent huge
differences of impacts and costs , so narrowing those limits helps inform
human choices.