Full colour version of the BP magazine

The Big Issue
CLIMATE MODELS: FORECASTING THE FUTURE
Climate models increasingly help us understand
the reasons behind climate change and what might
happen in the future. Scientists
from the Met Office discuss the
benefit of having this knowledge.
Climate is something different from
weather. The difference is often
described as climate being the kind
of weather patterns you might expect, while
weather is the conditions you get on any
given day. However, both need complex
computer models to make predictions.
There is considerable scientific evidence
that the world’s climate is changing and
that we are responsible for most of the recent
acceleration in warming. Climate models help us
understand the causes of climate change and provide
the means to assess a range of likely future changes. For
example, we know some change is inevitable; but we
need to know how sensitive the climate is to greenhouse
gases so we can adapt to those variations. Climate
projections will also help identify changes which are
avoidable if we act to reduce our greenhouse gas emissions.
Because the Earth’s climate is highly complex, huge
supercomputers are needed to make these kinds of
projections. Our climate models represent the physical,
chemical and biological processes of the atmosphere, ocean, and
biosphere, and how each system reacts with the others.
Mathematical equations are solved by a computer programme on
a 3D lattice of grid points which cover the globe. Such a ‘virtual
Earth’ is used for experiments to examine the effects of different
influences – both human-induced and naturally occurring – to
explain the causes of past climate changes, and make future
projections under different scenarios of greenhouse gas emissions.
Limited projections
As in every field of science, there are uncertainties in climate
projections. Much is still not known about how the climate system
works: for instance, we have an incomplete understanding of icesheet
dynamics and so, therefore, we are uncertain about the rates
at which glaciers will melt and slide into the sea. Projections are
also limited by available computing resources, which restricts the
number and detail of the processes that can be represented.
In spite of the limitations of computer power, we are steadily
improving our understanding of the atmosphere and its
interactions with the ocean and biosphere. In the 1970s, carbon
dioxide concentrations, their warming impact and rain were
included in climate models, but not the effect of clouds. Nor did
those models capture the interactions of the atmosphere with the
ocean and biosphere. Today’s state-of-the-art models include a far
more complete and interactive treatment of clouds and aerosols,
as well the coupling of the atmosphere to oceans and ecosystems.
Further research will see this improvement continue.
More sophisticated models are starting to include more of the
detailed chemistry of the carbon cycle, enabling the modeller to
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consider whether plants, soils and oceans will absorb less carbon
as warming continues. Future computer models will include
refined atmospheric processes and a wider range of feedback
mechanisms that may contribute to climate change.
These models enable projections of future climate and the
investigation of reasons for changes in the geological past
(paleoclimate). As information from geological observations fills
in the picture, models of the atmosphere are constrained and
improved. If the aim is to assess vulnerabilities to climate change
and prepare for changes in general, climate models can only go so
far. The spatial or temporal resolution required for certain
assessments may be finer than the models can currently resolve,
and interpreting the results in the context of the application still
presents a significant scientific challenge.
Added benefits
However, climate modelling is not exclusively reserved for policy
guidance. The Met Office Hadley Centre climate model
(HadGEM3) is unique in using the same basic model for weather
forecasting and projections of climate change. The Met Office has
extended its forecasting to seasonal, decadal and centennial
timescales. In seasonal forecasting, recent developments in
tropical storm and wave-height modelling have brought added
benefits to the oil and gas industry; and on longer scales, climate
models are being used to explore new threats and opportunities
to the industry, such as changes in permafrost regimes.
For more information on the development of climate
modelling and how Princeton University is using it to better
understand the nature of climate change, see pages 48-51. ■
Illustration: David Lyttleton