Simulating our climate using computer models has been an important tool in understanding how rising levels of carbon dioxide in the atmosphere affect global processes. Now, world-leading modellers are building a high-resolution vision of our own island’s future climate. [10 November 2009 | Peter Boyer]
TOP: The grid resolution of the global model (left) compared to that of the new Climate Futures models. BOTTOM: How preliminary Climate Futures modelling envisages changes in seasonal mean rainfall from now until the end of the century. Dark brown indicates a severe drying trend; dark green the opposite. White means no change.
When we want to know what the weather’s doing now we look up to the sky and check the wind direction and the clouds, usually in the western half of the sky. When we want to look ahead, to tomorrow or next week, we need a forecaster.
But for the weather over years and decades ahead, we have remained at the mercy of nature and usually-unreliable soothsayers. Now we have a new kind of future-gazer whose crystal ball is a supercomputer and whose tools are high-quality data on the many factors that affect Tasmanian climate. These people are climate modellers, and Tasmania has some of the world’s leaders.
Not so long ago, the most successful weather forecasters were older folk who’d lived in the one place a long time and had got to know the signs: the lie of the land, the behaviour of local winds, the approach of storms or fire weather, changes in soils and plants and animal behaviour.
They were strictly local people. You couldn’t turn up one day and expect to know everything the next, especially in Tasmania, where weather is as hard to predict as anywhere on the planet. You needed to stay around a while to make sense of things here, because just over those hills could well be an entirely different climate.
For climate modellers at the Antarctic Climate and Ecosystems (ACE) cooperative research centre at the University of Tasmania, the thing most lacking in the global climate models coming out of the Intergovernmental Panel on Climate Change was local knowledge.
For anyone seeking information on Tasmania’s future climate, the IPCC’s global maps are a disappointment. Where the brightly-coloured grid gives you a handle on the broad sweep of climate in the big land masses, including Australia, Tasmania appears as a couple of lonely squares, lumped in with the big island to our north.
In 2007, vexed by the apparent inability of scientific modelling to come up with sensible pictures of possible future climate directions for Tasmania, scientists and administrators created a new entity in Tasmania’s already-rich array of climate research bodies. They called it Climate Futures Tasmania, based at ACE CRC, and charged it with working out the impact of global warming on our island.
This task is anything but simple. Over 20-odd years, using ever-more powerful computers, scientists have been able to develop with increasing confidence models of future global climates by calculating the impact of energy sources, mainly solar radiation, on the rotating sphere we call Earth and its dynamic, inter-related complex of lands, oceans, ice and atmosphere.
Difficult though that has been, calculating likely climate directions for a small slice of that sphere — especially this mountainous island jutting into the Southern Ocean, battered by weather systems coming from all points of the compass — has proven a much tougher assignment.
A few years ago Hydro Tasmania, ever-sensitive to rainfall prospects, contracted CSIRO to model likely climate trends to 2040. The model projected a drying in most populated areas and more rainfall in the West (reported in this column in October 2007), but there were caveats because of uncertainty over some weather systems and scarcity of data from more remote parts.
With access to greater computing power, using CSIRO software to scale output from six global climate models down to Tasmanian proportions, Climate Futures Tasmania’s modelling takes into account our convoluted topography and ocean influences to simulate local-scale weather and climate all the way out to 2100.
Where the global grid is 200 km across and that of the 2005 Tasmanian study about 70 km, the Climate Futures model is down to a mere 14 km — a world-leading level of climate model resolution.
For each of those 14 km grid cells, the model applies more than 140 climate variables including rainfall, minimum and maximum temperature, topography, evaporation, radiation and wind. For the technically-minded, its output took up more than 70 terabytes of disk space and took more than 1200 days of supercomputer processing time to produce.
Preliminary results suggest that Climate Futures Tasmania projections will be something of real, practical value to Tasmanian authorities and others planning for agriculture or other land use, for environmental management, for infrastructure planning or anything else requiring the longer view.
We won’t be around in 2100 to know how accurate these projections are. But we can at least admire the limitless ingenuity of human intelligence, and acknowledge that this future vision is as good as we’ve ever had, in all our history. This looks a pretty good place to put climate research dollars.
• Climate Futures Tasmania operates with funding support from the Australian Government’s Commonwealth Environment Research Facilities Program; the Tasmanian Government, through the Department of Primary Industries and Water and the State Emergency Service; the Australian Government’s Natural Disaster Mitigation Program (through the Attorney-General’s Department); Hydro Tasmania; and the Antarctic Climate & Ecosystems Cooperative Research Centre (ACE CRC). Its research partners are ACE CRC; CSIRO Division of Marine and Atmospheric Research; Hydro Tasmania; the Tasmanian Government through the Department of Primary Industries and Water; the University of Tasmania, through the Tasmanian Partnership for Advanced Computing and the Tasmanian Institute of Agricultural Research; Geoscience Australia; and the Bureau of Meteorology.
Modelling and climate change
Among all the animals, only humans bother to think further ahead than the next meal or preparing the winter den — a unique facility that has given us the burden of knowing about man-made climate change.
Computer modelling has taken crystal ball gazing into a whole new place. Climate models are seen as an output of science because they are produced by scientists. That has caused some people, including some scientists, to express concern that they could be given a status they don’t deserve.
Models like the 2100 rainfall projections illustrated here are not evidence. No-one can say with any certainty that what is suggested in the maps is actually what is going to happen. In a sense they are no more than the result of a computer applying mathematical formulas to a lot of data about intricately-connected climate events and developments to determine how these might change over time. But they do represent our best guess, using the best data and the most advanced tools so far available to us, at what the future may hold. If we want a handle on the future, this is as good as it gets.
For Climate Futures researcher Stuart Corney, whose group produced these projections, modelling is above all a tool to help us understand the ramifications of a colossal global experiment that humans are conducting by altering the composition of the atmosphere, over a relatively short time span, through burning fossil fuels.
Dr Corney asserts that testing the output from computer models against evidence from actual observations has demonstrated current models’ high and improving ability to simulate reality.
Virtual test-flying by means of computer models is our only means of testing possibilities, says Dr Corney: “We don’t have a second Earth to find out what would happen in a carbon dioxide-free atmosphere, and we can’t shift back and forth in time to check if our predictions are true. In about 100 years we will know if we were right or not.”