Climate Change in the Arctic - The Changing Arctic Environment: The Arctic Messenger - page 239

very obvious coincidence that GHG levels have been on the rise ever since the advent of
industrialization. However, IPCC's confidence is founded on basic physical principles and
the fact that climate scientists have a wide range of quite independent tools with which to
investigate attribution and they all lead to the same conclusion. Our global temperature is
going up because of the increasing accumulation of GHGs in the atmosphere.
Some of the main tools used to investigate attribution are climate computer models
thataredeveloped frommodels usedforweather forecasting. Theyarebuiltbydividingthe
world's atmosphere into a three-dimensional grid, within which data on such parameters as
radiation, relative humidity and heat transfer can be added. By using basic laws of physics
(such as thermodynamics and hydrodynamics), the interactions with adjacent cells can be
investigated mathematically. The most sophisticated such models are coupled atmosphere-
ocean global climate models (AOGCMs) that combine this approach with the atmosphere
and the ocean, allowing the two to interact with each other.
When the models are run for time periods before the industrial era with only the nat-
ural external forcings (changes in the solar luminosity and the effect of explosive volcanic
eruptions), they are perfectly able to replicate the global temperature record derived from
proxy data. If the models are run for the last 100 years, taking into account all natural and
anthropogenic external forcing, they replicate the observed warming shown in the global
climate record. However, this ability to replicate the 100-year temperature record vanishes
if the anthropogenic forcing is removed. The key element of this anthropogenic forcing
over the last 100 years has, of course, been the dramatic rise in radiative forcing concen-
trations in the atmosphere. When these modelling experiments are run, they show that the
internal climate-forcing factors, such as the El Niño Southern Oscillation (ENSO), are im-
portant only for short periods of time. It is the external influences that matter in terms of
climate trends. You will have probably already spotted one of the most valuable contribu-
tions of this type of study. They are not structured as such to explain any particular global
climate change. They simply use the laws of physics and of atmospheric and marine geo-
chemistry to see what will happen according to a particular scenario of increasing concen-
trations of GHG emissions.