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14.1 Introduction
There has been encouraging progress over this first decade of the IPCC process.
We understand better the coupling of the atmosphere and ocean. Significant steps
have been taken in linking the atmosphere and the terrestrial systems although
the focus tends to be on water-energy and the biosphere with fixed vegetation
patterns. Even so, revealing and unexpected teleconnections are being discovered;
moreover, progress is being made towards model structures and data sets that
will allow implementation of coupled atmosphere-ocean-terrestrial models that
include key biological-biogeochemical feedbacks. There is also encouraging progress
in developing integrated assessment models that couple economic activity, with
associated emissions and impacts, with models of the biogeochemical and climate
systems. This work has yielded preliminary insights into system behaviour and
key policy-relevant uncertainties.
The challenges are significant, but the record of progress suggests that within
the next decade the scientific community will develop fully coupled dynamical
(prognostic) models of the full Earth system (e.g., the coupled physical climate,
biogeochemical, human sub-systems) that can be employed on multi-decadal time-scales
and at spatial scales relevant to strategic impact assessment. Future models
should certainly advance in completeness and sophistication; however, the key
will be to demonstrate some degree of prognostic skill. The strategy will be
to couple the biogeochemical-physical climate system to representations of key
aspects of the human system, and then to develop more coherent scenarios of
human actions in the context of feedbacks from the biogeochemical-physical climate
system.
Developing these coupled models is an important step. From the perspective
of understanding the Earth system, determining the nature of the link between
the biogeochemical system and the physical climate system represents a fundamental
scientific goal. Present understanding is incomplete, and a successful attack
will require extensive interdisciplinary collaboration. It will also require
global data that clearly document the state of the system and how that state
is changing as well as observations to illuminate important processes more clearly.
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