Climate Sense

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bserving

, P

redicting

and

rojecting

limate

onditions

are associated with higher temperature. The 120ppm elevation of CO

corresponds approximately to 1ºC. This is clearly significant for global

warming projection where a typical range of temperature rise is 2-4ºC.

Namely, there is a feedback loop between climate and carbon cycle, in

which warming raises CO

concentration and vice versa, meaning that

the feedback is positive.

One of the difficulties in developing ESMs exists in the short-

ages of available data to verify them. Interactive processes between

climate and carbon cycles in ESMs need to be verified against obser-

vations as soon as possible. A recent preliminary experiment with

a new version of MIROC-ESM – where a spatially explicit and

individual based dynamical global vegetation model is included –

shows a possibility of considerably reduced feedback compared to

the previous C4MIP case (under the same anthropogenic CO

emis-

sion scenario A2) through growth of new types of vegetation under

changing climate. Uncertainty in the intensity of climate-carbon

cycle feedback will be one of the central themes for the next assess-

ment report of IPCC. Geographical distributions of monthly mean

and methane, which will be available from the satellite GOSAT,

are expected to contribute with respect to verifying short-term proc-

esses in the carbon cycle and reducing associated uncertainties.

The climate-carbon cycle feedback has implications for the design

of a long-term mitigation plan against global warming. IPCC AR4 for

Working Group 2 discusses CO

stabilization targets and emission

pathways to achieve them, often without considering the feedback. By

appropriately adopting ESMs, it is possible to evaluate its impact on

emission pathways. Such experiments have been indeed performed

by some of the existing GCM-based ESMs. Results from MIROC-ESM

show that the permissible emission to accomplish CO

stabilization

is reduced by around 20 per cent when climate and carbon cycle are

allowed to interact. In order to provide a scientific basis

for mitigation planning in the Fifth Assessment Report of

IPCC, due in 2013, international coordination is under-

way to organize experiments for evaluating permissible

emissions with GCM-based ESMs.

Outlook

The concept of ESS has existed for a relatively long time,

but realization of the urgent need for it has only been

appropriately recognized over the last decade. This is

perhaps why scientists are still hesitant to acknowledge

this new field as a discipline. Another reason may be that,

while other new scientific fields have often defined them-

selves by restricting subjects and methods, ESS has in its

nature an inclination toward widening of subjects and

integration of exiting paradigms.

ESS should be regarded as a framework of thought rather

than an established discipline. This interpretation is perhaps

more readily acceptable to most scientists, but raises

another question, as to whether ESS is really a ‘specialty’

worth dedicating a considerable portion of a scientific career

to. However, under the current situation where responding

to global change is a pressing mission for earth science as

a whole, the necessity of a ‘bridge’ is obvious for connect-

ing ever-deepening traditional disciplines. It would be an

invaluable work if earth-system scientists could create and

develop a common mindset that commands a bird’s-eye

view of relevant fields of earth science and possibly social

science. Modelling will continue to contribute to a coopera-

tive growth of diversifying disciplines and expanding ESS.

Theoretical performance of the new Earth Simulator, upgraded in April 2009, is three times as high as that of the former

Image: JAMSTEC