Climate Sense

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bserving

, P

redicting

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onditions

climate models will incorporate the carbon cycle, specified/simple

chemistry and aerosols. These models will be forced by new mitiga-

tion scenarios referred to as ‘representative concentration pathways’.

Mitigation and adaptation scenarios with permissible emission levels

that allow the system to reach gradually targeted concentration are to

be used (in place of the previous IPCC Special Report on Emissions

Scenarios). The new scenarios will have implicit policy actions to

target future levels of climate change.

Since we can only mitigate part of the problem, the challenge is to

use climate models to quantify time-evolving regional climate changes

to which human societies will have to adapt. A new focus area for

CMIP5 is a set of near-term projections that encompass 10- and

30-year prediction studies and high-resolution time slice experi-

ments.

WCRP researchers believe there are reasonable prospects for

producing decadal forecasts of sufficient skill to be used by planners

and decision makers. There are two aspects to the decadal problem,

the externally forced signal, and the predictable part of the internally

generated signal. The latter signal comes from intrinsic oceanic mech-

anisms, coupled ocean atmosphere processes, modulation of climate

modes of variability (for example, the El Niño/Southern Oscillation)

and – potentially – land and cryospheric processes.

The WCRP will continue to support the quadrennial WMO/United

Nations Environment Programme Ozone Assessment. The SPARC

Chemistry Climate Model Validation Activity (CCMVal) is the main

model-based analysis for the connection between atmospheric chem-

istry and climate. CCMVal provides strategic modelling

support to the ozone assessment process, which is

mandated by the Montreal Protocol. Ozone is a major

constituent in radiative processes and is also affected

by dynamics and transport. Only CCMs can simulate

the feedback of chemical processes on the dynamics

and transport of trace gases. The CCM simulations

are designed to support the WMO/UNEP Scientific

Assessment of Ozone Depletion/Recovery: 2010. The

main focus will lie on model validation against observa-

tions, as well as on assessments of the future development

of stratospheric ozone.

At present, ozone recovery is expected to take place

until the middle of the century,

when column ozone

is expected to reach 1980 values in southern polar lati-

tudes. This development is determined, on the one hand,

by a decrease in ozone depleting substances (ODSs) and

on the other by a decrease in stratospheric tempera-

tures – due to enhanced greenhouse gas concentrations

in the atmosphere, which affects polar stratospheric

cloud formation and heterogeneous ozone destruction.

An important issue is how changes in the tropospheric

abundances of ODSs translate to changes in the ozone-

depleting active chemicals in the stratosphere. For

studies of the future development of stratospheric ozone

it is of great importance to take into account interactions

between radiation, dynamics and the chemical composi-

tion of the entire atmosphere.

To date, climate projections have generally treated

internal variability as a statistical component of uncer-

tainty. Though there is no marked decadal peak in the

spectrum of the climate system, long timescales exist

and are potentially predictable. The challenge of predic-

tion/predictability studies is to identify the mechanisms

associated with regions/modes of predictability, to better

understand the connection between oceanic modes and

terrestrial climate variability, and to investigate predic-

tive skill by means of prognostic (including multi-model)

decadal predictions. The results of predictability studies

and demonstrations of forecast skill provide the founda-

tions for initiating a coordinated WCRP study of decadal

climate variability, predictability and prediction.

In summary, the WCRP has made great strides in

advancing understanding of the coupled climate system

from seasonal to centennial timescales. WCRP research

efforts formed the foundation of today’s seasonal climate

forecasting products and services. The WCRP has played

a major role in converting the resultant scientific infor-

mation and knowledge about the Earth’s climate system

for use in policy decisions. This has been achieved via

the IPCC, the UNFCCC Conference of Parties and its

Subsidiary Body on Scientific and Technological Advice.

More than half of the scientific and technical contribu-

tions used in the IPCC assessments were provided by

WCRP-affiliated scientists.

The WCRP has made a concerted effort to provide

worldwide access to its model predictions/projections

and research results. With such access scientists from

developing and least developed countries are able to assess

CMIP5 Decadal Predictability/Prediction Experiments. Draft from

WGCM meeting, September 2008

WCRP and the International Geosphere-Biosphere Programme combined their

expertise to advance climate model development and, hence, prediction capabilities.

By incorporating the more complex Earth system processes, models are also being

tested for their response to different forcings. Within the WCRP, the Working Group on

Coupled Modeling leads the development of coupled ocean-atmosphere-land models

used for climate studies on decadal and longer timescales

Source: Taylor et al. (2008)