Climate Sense

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overnance

and

olicy

recurring ocean-based El Niño phenomenon in the eastern Pacific

that revealed the true nature of Australia’s highly variable climate.

Recent research on somewhat more subtle variations in atmos-

phere/ocean interactions of the tropical India Ocean suggests a

further layer of complexity.

The continuous flow of observations from the atmosphere

and the oceans together with adequate computing capacity now

enable climate to be treated synoptically, with analyses of rain-

fall, temperature and other variables routinely available within a

few hours of the end of an averaging period (typically a calendar

month). Using base climates, derived from the more than one

hundred years of historical data, it is now possible to determine

with a high degree of precision a wide range of anomaly and

extreme value statistics for a month or a season just completed. It

is estimated that users of the Australian Bureau of Meteorology’s

website have virtually instant access to several thousand differ-

ent forms of analyses on the nature of the climate for any given

month across the breadth of the country, or for specified regions.

Predicting climate – the future

As for weather, establishing the current state of the climate

system through synoptic analysis is only part of the challenge.

Since the mid 1980s, seasonal forecasts of expected

rainfall and temperature anomalies have been issued

by the Bureau of Meteorology for Australia using

the Pacific Ocean (El Niño-Southern Oscillation)

and Indian Ocean relationships. The modest skill

of these statistical forecasts, while real and useful,

is inconsistent throughout the year and varies

from region to region. Strong trends in rainfall

and temperature over the past few decades for

large areas of Australia have further brought into

question the reliability of the forecasts. A major

research effort is now underway in Australia and

elsewhere to develop dynamical, computer-based

models of the coupled earth system, that can be

used to predict the variability in climate from

weeks through seasons to periods of a decade or

more. While predictions from these experimental

models have yet to attain sufficient skill for them

to be used operationally for rainfall and tempera-

ture outlooks, they are coming tantalisingly close to

achieving this goal and will very likely do so within

the next five to ten years.

Depleted Corin Reservoir near Canberra. Australia has developed a number of very large reservoirs that are used to supply water for irrigation and its major cities

during periods of erratic rainfall or longer intervals of drought. The prolonged drought that occurred over the 10-15 year period across much of southeastern

Australia leading up to 2009 led to a massive depletion in these reserves, which will likely take many years of better than average rain to replenish

Image: James Milligan