Climate of extremes - Antarctica: Global Science from a Frozen Continent - page 133

Figure 4.28 Map of observed twentieth-

century warming over Antarctica. (Credit:
Steig E. J., D. P. Schneider, S. D. Rutherford
et al . (2009). Warming of the Antarctic ice-

sheet surface since the 1957 International
Geophysical Year. Nature , 457 , 459 - 464.)

activities have had in any observed change and estimating what future changes in
the climate system may result from human activity. The most recent IPCC report,
the Fourth Assessment Report, was released in 2007. The authors of this report
were awarded the Nobel Prize in 2007 for their contribution to this globally
important effort to understand climate change. Conclusions from this report
indicate that from 1906 to 2005 the globally averaged surface temperature has
warmed 0.74 ± 0.18ºC, with the rate of warming larger during the latter 50 years
of this period. Further, they determined that it is very likely that the warming
over the past 50 years is a result of increasing greenhouse gas concentrations
in the atmosphere.
How do atmospheric scientists determine if observed changes in global
temperature are due to increasing concentrations of greenhouse gases in the
atmosphere and how do they make projections of future climate change, given
that the climate system is extremely complex? In part scientists have turned to
the use of global climate system models to address these questions. These models
are computer programs that represent processes such as the transfer of longwave
andshortwaveradiationthroughtheatmosphereandtheresponseofthese
radiative transfers to changes in greenhouse gases. These models also represent
the atmospheric circulation, and other atmospheric physical processes, similar
to numerical weather prediction models. Finally, these models include details
on other parts of the climate system such as the oceans, sea ice and land
surfaces. These models have been shown to reasonably reproduce the current
state of the climate system. Given this fact climate scientists have con dence in

the fidelity of these models, and can then use these models to explore ' what-if '

scenarios.