20 September 2006

Predicting the future: it’s becoming a science

Science Alert
No longer the domain of gypsies with crystal balls, predicting the future is a complicated science. It's all about crossing the threshold, say researchers.
Predicting the future: it's becoming a science

Threshold and pattern dynamics may allow everything from earthquakes, drougths and even epidemics to be predicted Credit: AFP

Since the first augur peered into a sheep’s entrails or the alchemist his crystal ball, humans have been searching for a reliable way to divine the future. In the 21st century the quest has been taken up by science.

In the case of major natural events like earthquakes, volcanic eruptions, violent floods, disease epidemics, tsunami, drought and soil erosion, failure to predict the future can mean death, suffering and loss for thousands.

These events are hard to study because they occur over long time scales, in hidden places and in sudden, erratic episodes. But they all have telltale buildup signs which, correctly interpreted, can help us to zero in on the timing and scale of the impending event – and provide those who might be affected with early warning, says ‘Siva’ Sivapalan of the University of Western Australia in Perth.

This exciting new field of science is known as ‘threshold and pattern dynamics’, because it involves understanding when a vital threshold (to a catastrophe or major change) is crossed – and recognising patterns in the things that are driving it. Australian and international scientists met in Perth, Western Australia recently at a Sir Mark Oliphant Conference on the Frontiers of Science, to compare notes and polish their latest high-tech ‘crystal balls’.

There are thresholds in human affairs too – booms and crashes in the money markets, sudden shifts in public opinion, changes in community behaviour, the explosion in the World Wide Web, even the outbreak of wars.

Threshold and pattern dynamics uses mathematics and computers to build a model of the factors driving uncommon and important events, Sivapalan explains. “By running these models forward in time, it becomes possible to predict when vital thresholds will be crossed – when things will shift dramatically from their present state to another, possibly dangerous or unstable one.

“For example, if you think about rain falling on the soil, it reaches a point where the soil has absorbed as much water as it can, a threshold is crossed, and the water begins to run off and cause flooding,” he says. “Another example of a threshold is erosion, when the power of the wind or floodwater reaches a point where it can dislodge soil particles and sweep them away. A third case is when an apparently stable environment like farmland is hit by rising saline groundwater – and everything suddenly dies.”

Some thresholds are reversible, others are not – or are extremely hard to re-cross, according to Sivapalan. Hence the importance of having good predictive tools. “The build-up to many of these things is extremely hard to observe, perhaps because it takes place somewhere it is not easy to take measurements. Then the challenge is to identify telltale things we can observe, and see if we can identify patterns in them which point to a future threshold being crossed.”

The task, which scientists around the world are working on, is immensely complex and challenging, but in fields like earthquake prediction, there are encouraging signs of progress.

The science of threshold and pattern dynamics has its roots in the efforts of scientists over the last 20 years to predict earthquakes. Geologists can measure the build-up of giant stresses along critical rock fractures (or faults) deep in the Earth, and estimate the accumulated energy – but knowing exactly when the rocks will slip and how much energy will be released has proven a huge challenge.

A team led by John Rundle at the University of California in Davis has developed computer-based methods that forecast earthquakes with much greater precision. “Most people would say that earthquakes can’t be predicted or forecast and, indeed, there have been many notable failures,” he says. However, his team has overcome the main obstacle to prediction: time. Humans live for a few decades, but large quakes recur over hundreds of years – outside our ability to accurately observe and remember.

By using a computer to simulate the whole fault system, it is possible to see thousands of years of geological activity, Rundle explains. His program simulates the tectonic plates in a fault moving away from each other at a constant rate. After a century or so a threshold is reached where the stresses on the fault are so great that the rocks slip – and a quake occurs. This temporarily lowers the stress on the fault, and the process starts again.

The team still cannot predict the precise time of an upcoming earthquake, “but we can now say that it is likely to happen in one of a small number of areas within a certain time window,” says Rundle.

Research into thresholds has many possible uses, he adds. “For example: why do countries go to war? Take the United States where, in 1941, it wasn’t really until Pearl Harbour that some sort of a social threshold was reached when people en masse decided: ‘We’re not going to stand for this. We are going to war’.”

A similar pattern occurred with the World Wide Web, which didn’t achieve widespread use until a certain level of connectivity was reached. “It looks more and more like this was a sudden process, a threshold. You had to reach some critical level in connections between the computers of the world before the usefulness of the Web became apparent to most people,” says Rundle.

Michael Raupach, an atmospheric scientist with Australia’s research agency, the CSIRO, is analysing past abrupt climate changes – from ice ages to salinity – to try and identify the external forces that might cause our present climate patterns and ecosystems to collapse. “With salinity, for a long time while the saline groundwater is rising, you see nothing,” he says. “But when the salty water reaches the surface or root zone of plants and trees – the threshold – you see sudden death across a wide area. This is due to a relatively subtle shift in the level of the groundwater.”

Another example is the drought which has lately afflicted eastern Australia. The subtle difference from past dry periods was the interaction between drought and warming. While this drought was similar to past events in lack of rainfall, a new feature this time was heat: it was by far the hottest drought on record, because of global warming. This combination pushed many parts of the landscape, including deep-rooted trees, beyond the threshold of no return.

By identifying the external forces that drive such events, it may be possible to predict critical changes and either prevent them or else manage the consequences, says Raupach. His research uses well-understood systems – like fires and stockmarkets – and analyses them to understand the drivers. It has revealed hallmarks common to other complex systems, an indication that there may be universal factors that can be used to analyse all systems.

Raupach’s research asks four questions: Are there thresholds? How will things be different if we cross the threshold? What drives the threshold? Can we manage the system to lower the possibility of bad outcomes?

“One of the fundamental questions is: ‘Can we identify what the crucial interactions are so we can get some idea of how likely this is?’,” he explains. “We might be able to figure out how close we are to the threshold and determine the probability of tipping our climate into a different state.”

His research opens the way to better manage human actions that do the greatest damage to the environment and natural ecosystems. “This will mean we are not completely powerless in influencing the trajectory of man-made climate change,” says Raupach.

According to Ian Prosser of the CSIRO, drought intensifies the impact of flooding on Australia’s water and land-based ecosystems. Heavy floods cause severe erosion of the land and degrade water quality, which in turn can cause havoc in both freshwater and marine environments.

The damage is caused when soil is swept up off the land by floodwaters and deposited in rivers, lakes and dams. The removal of sediment from the land exposes infertile and unworkable soils, while their dumping in rivers or the sea can lead to outbreaks of algal blooms or the smothering of coral reefs.

To understand how this system works Prosser, has studied the history of floods and erosion in Australia over thousands of years. “We looked into gully erosion in the past 10,000 years and found that it is a natural process of the continent,” he says. “But in the past 200 years it has increased in intensity and frequency.”

With climate change expected to bring more floods it is the condition of the land that will determine their impact, says Prosser. “Good vegetation cover is the key to preventing erosion. A landscape with very good grass cover and vegetated valleys can withstand a one-in-100 year flood event and resist the effect of erosion.”

But fires, drought and overgrazing cause the loss of protective vegetation. These degraded habitats take years to recover their natural resistance to erosion and during this time are at high risk of losing their soil. Special care and management is needed to prevent this.

Prosser’s latest research aims to predict the impact of flood events so that their risks can be better managed. It aims to identify the point at which flooding reaches sufficient strength to move soil particles and so erode the landscape. Predicting when this threshold will be crossed is now greatly assisted by threshold and pattern dynamics.

“The ideal way for a drought to break is with gentle winter rains and steady vegetation growth,” says Prosser. “But if major floods occur, they can have severe effects anywhere that land cover is poor. In these conditions there need to be changes in land management practices to offset the increased risks posed by floods under climate change.”

John Finnigan of the CSIRO says human relationships are now recognised as a vital ingredient in complex systems such as disease epidemics, protected marine areas or salinity outbreaks. His research explores how the relationships between people form a single connected network – and how the patterns within networks control what the group might do and how they interact with their environment. This new approach sidesteps the very difficult problem of trying to predict the behaviour of large groups of people.

Landscapes with people in them are very complicated social, biological and economic systems, Finnigan says. “Individual actions add up and can impact the whole system. Even with the best intentions, the results of many individual decisions can be almost impossible to predict.

“We are now starting to understand that the pattern of connections between people through friendships, family ties or economic transactions can put strong bounds on what happens in a particular region.”

This novel way of looking at systems is giving scientists new tools to predict, control and sometimes prevent disastrous events like disease epidemics or algal blooms which are usually the result of a system reaching a threshold.

The foot and mouth disease (FMD) outbreak in England – in which tens of thousands of animals were slaughtered – was due primarily to a drastic increase in contacts between livestock herds across the U.K., says Finnigan. More animals were being trucked longer distances to other farms or to fewer abattoirs. This meant that distant farms become so interlinked that when one animal contracted FMD the infection could spread rapidly through the whole herd. The livestock network had passed a ‘connectivity threshold’ and the disease was able to become rampant.

Finnigan says that while network theory can’t predict the likelihood of an initial disease outbreak, it can determine how quickly it can spread and how difficult it may be to stop it. It can also identify where and how the outbreak can be intercepted.

In future, network theory may help prevent a global epidemic – such as Asian bird flu – by predicting whether it is possible to stop the disease. “If it tells you that once a disease has started spreading you will never catch it, then you might be advised to start changing the network now, so as to keep the epidemic contained,” says Finnigan.

Australian scientists, with their strengths in Earth sciences and complex systems science, are making a potent contribution to world advances in threshold and pattern dynamics theory, says Sivapalan. “These two areas are bringing the theoretical tools and analytical wisdom needed to attack problems in this field.

“These problems are so complex they cannot be solved by one or two fields of science alone, but they need a multi-disciplinary approach from many creative people with new ideas and insights. That is one of Australia’s strengths,” he says. “Threshold and pattern dynamics is an area of huge potential, and we are at the forefront. We must be sure we maintain our efforts.”

Julian Cribb is a science journalist and Adjunct Professor of Science Communication at the University of Technology in Sydney.

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