Climate Change in the Arctic - The Changing Arctic Environment: The Arctic Messenger - page 233

Figure 10.2
Global warming: The map (a) shows the surface temperature anomaly 2005-2007 relative to 1951-1980.
The graph (b) presents the same data as zonal means. Note that Northern Hemisphere high latitudes and
particularly the Arctic have experienced the greatest degree of warming.
To understand why the Arctic is warming, we must first take a look at global climate
change. One of the big steps forward in the IPCC assessment process has been the in-
creasing confidence with which it is judged that the observed increase in global surface
temperature is due to anthropogenic GHG emissions. Here the IPCC is addressing what is
known as the “attribution problem”: “It is extremely likely that more than half of the ob-
served increase in global average surface temperature from 1951to 2010was caused bythe
anthropogenic increase in GHG concentrations and other anthropogenic forcings together.
The best estimate of the human-induced contribution to warming is similar to the observed
warming over this period.” 3
Tounderstandthescientific“mechanics”thatunderlinethisstatement,weneedtotake
a look at GHGs and be familiar with their role in maintaining or changing the world's cli-
mate.
The sun is very hot and consequently emits energy (short wavelength radiation - vis-
ible light). This radiation is absorbed at Earth's surface, which is consequently warmed.
Thewarmedsurfacethenemitslongwavelengthinfraredradiationbackintospaceinaway
that is described by the Stefan-Boltzmann law. That is a relationship that most readers have
probably not thought about since their last school examination in physics. However, it is
easy to follow - even for a biologist such as me. In an imaginary case of a naked Earth
without an atmosphere, the Stefan-Boltzmann relation simply means that outgoing infrared
energy loss to space takes place at a rate that depends on temperature. This is very import-
ant because it means that the warmer a naked Earth is, the faster it loses heat until a balance
is achieved between the incoming and outgoing movement of energy. If Earth did not have
reflection (albedo) or an atmosphere, it would have a surface temperature of −18°C.
Of course, the average temperature of Earth's surface is much warmer than −18°C be-
cause Earth has an atmosphere. Some of these atmospheric gases capture much of the out-