Decadal Warning Systems - Reducing Disaster: Early Warning Systems for Climate Change - page 308

Although predictions over land are not yet improved in general by initialization,
models do capture the observed warming trend driven by increases in greenhouse
gases, and this is suffi ciently strong even on multi-year timescales to enable skilful
predictions of the likelihood of extreme temperatures (Eade et al. 2012 ; Hanlon
et al. 2013 ).

16.5 Future Directions

Decadal climate prediction is an immature, though rapidly expanding, area of cli-
mate science. The level of skill already achieved is, by defi nition, a lower limit. An
upper limit cannot be determined. However, there are potential sources of skill that
are currently untapped. These include the land surface, sea ice and stratosphere, and
experiments are currently underway to address these. There are also other missing
processes, including coupled vegetation, chemistry and land ice, which could
improve skill. Key requirements and possibilities for improving the skill are sum-
marized in Box 16.2.

Box 16.2 Key Requirements for Improved Decadal Predictions

• Sustained and improved observations . A major goal of decadal prediction

is to predict the evolution of the oceans and subsequent impacts on the
atmosphere. This requires observations especially of sub-surface ocean
temperature and salinity, both of which affect the density and hence dynam-
ical balance of sea water. A step change in ocean observations was achieved
in the last decade through the deployment of around 3,000 Argo fl oats
which sample the upper 2,000 m. Sustaining, and preferably extending
below 2,000 m, this coverage, alongside other observations of the climate
system, is therefore a high priority for improved decadal predictions.

• Improved climate models . In present generation decadal predictions, ini-

tialization improves predictions in key regions of the oceans, but improve-
ments over land are limited. Future improvements over land might be
possible with climate models that better simulate the teleconnections
between ocean and land.

• Improved representation of external forcing . Anthropogenic aerosol effects

are highly uncertain in current climate models. Given their potential
impacts on AMV and related climate, improved representation of aerosol
processes is a high priority. Volcanic eruptions likely affect climate on
decadal timescales, but further work is needed to improve model simula-
tions and understand how the response depends on the background state.
Recent satellite observations of solar irradiation suggest that changes in

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