Natural factors alone
cannot explain the recent warming of the EarthÕs surface
Black: Observed surface temperature changes
Attribution of
climate change to causes involves READ
Climate models
are important tools for attributing and understanding climate change.
Understanding observed changes is based on our best understanding of climate
physics, as contained in simple to complex climate models. For the 4rth
assessment report, we had a new and very comprehensive archive of 20th
century simulations available. This has greatly helped.
This figure
gives an example.
You see
observed global and annual mean temperature in black over the 20th
century compared to that simulated by a wide range of these models. On the
top, in red, are individual model simulations and their overall mean shown
fat, that are driven by external influences including increases in
greenhouse gases, in aerosols, in changes in solar radiation and by volcanic
eruptions. The observations rarely leave the range of model simulations. The
trends and individual events like cooling in response to volcanic eruptions
(POINT) are well reproduced. The fuzzy range gives an idea of uncertainty
with variability in the climate system.