UK Meteorological Office/Science Photo Library
Wrong but useful
Many policymakers have traditionally seen climate models as irrelevant, but Gavin Schmidt argues that
recent advances are making such models an essential tool in informing policy choices
A quick tour of the Internet reveals some very strong
feelings on the subject of climate models. Unsurprisingly, on climate contrarian sites, such models are
described in all sorts of unflattering terms and dismissed out of hand as fundamentally useless. However, in more rational forums, and sometimes even
among scientists themselves, one occasionally comes
across a basic ignorance of whether climate models are
any good, and, even more importantly, what they are
good for. By the time one gets to policymakers, climate
models are seen at best as black boxes, and at worst as
simply irrelevant to their detailed concerns. However,
climate models – appropriately used – might have a
vitally important part to play in breaking through some
of the log jams now hampering policymakers.
The complexity of climate
Models of any stripe are simply quantitative or numerical expressions of the theories we have for how the real
world works. Climate models encapsulate what we
know about how the Sun’s rays travel through the
atmosphere and how heat from the surface of the
Earth gets absorbed by clouds, water vapour and, of
course, carbon dioxide. They contain sophisticated
(though imperfect) representations of cloud formation and rainfall, floating sea ice and ocean turbulence,
rivers and lakes, and soil and vegetation. Each representation is based on direct observations of the processes in question and is tested against many different
constraints. The models (and there are many) have
numerous common behaviours – they all cool following a big volcanic eruption, like that at Mount Pinatubo
in 1991; they all warm as levels of greenhouse gases are
increased; they show the same relationships connecting water vapour and temperature that we see in observations; and they can quantify how the giant lakes
left over from the Ice Age may have caused a rapid
cooling across the North Atlantic as they drained and
changed ocean circulation patterns.
This gives us a hint: models are useful for tying together causes and effects in complex systems where
answers are often only obvious in hindsight. We can
apply them for climate changes in the past – global
changes in temperature or rainfall patterns inferred
from the paleoclimate data for instance – and help
attribute events to causes. Indeed, the attribution of any
particular climate trend or set of events is inherently a
model-based exercise. Without a way of telling the dif-
Gavin Schmidt is a
climate scientist at
NASA’s Goddard
Institute for Space
Studies in New York
and co-author with
Joshua Wolfe of
Climate Change:
Picturing the Science
(2009, Norton),
e-mail gavin.a.
schmidt@nasa.gov
