Facing a climate of uncertainty

SCIENTISTS agree to disagree at a conference on global warming.

Climate change

IT was a long way from picture postcard blue skies in Cairns yesterday as the nation's top 450 climate scientists gathered to take stock of global warming.

The tropical rainstorm may pale alongside the political cyclone that has been unleashed by the federal government's talk about a carbon tax. But the continued wet weather may prove relevant to this week's scientific discussions, which are expected to have a heavy focus on how much there is still to understand about climate change.

For Australia, whether the north can expect to get more or less rainfall because of global warming remains one of the great unknowns.

The Cairns meeting is Australia's peak biannual conference at which climate scientists meet to discuss the state of research.

And while organisers of Greenhouse 2011 say participants represent a broad church, the uniform view is undeniably one of a warmer future for the planet.

Beyond that, everything from atmospheric carbon, feedback cycles, ocean temperatures, sea levels, carbon sinks, mitigation and adaptation are on the table for discussion.

Delegates will even be told how emotional responses to climate change represent a missing link to behaviour, with those who accept man-made climate change motivated to act by fear. Others who believe the climate is changing naturally are likelier to feel irritation and refuse to engage or respond.

CSIRO principal research scientist Kevin Hennessy says understanding the causes, both natural and human, of climate change is central to the conference agenda, as is consideration of future projections of climate change globally and regionally.

Surprisingly, a key theme through the conference will be the state of scientific uncertainty.

This does not mean that sceptics have crashed the CSIRO-sponsored climate change party, however.

"These are the real uncertainties as opposed to the uncertainties that some of the sceptics might claim are important," Hennessy says.

The uncertainties include things such as the various causes of regional climate change and extreme weather events, uncertainty about the future level of greenhouse gas emissions, the rate of global warming, the rate of future sea level rises and the scale and impact of future extreme weather events.

"When we are talking about global warming it is not about whether there will be global warming but about the rate of change," Hennessy says.

The approach reflects a new approach by the climate science community after the issue lost significant momentum in the lead-up to the 2009 Copenhagen conference following claims of exaggerated research claims.

The new caution was reflected in an updated statement issued by Britain's Royal Society last year summarising the scientific evidence on climate change and its drivers.

The statement highlighted the areas where the science is well established, where there is still some debate and where substantial uncertainties remain.

The Royal Society even held a two-day discussion meeting in March last year on handling uncertainty in science.

The Australian conference agenda reflects the new approach has been taking place elsewhere ahead of the release of a new data from global modelling that will form the basis of the International Panel of Climate Changes update due in 2013.

Hennessy says by its nature the science has always been uncertain.

"The 2007 IPCC report estimated a range of global warming by the end of this century of between one and six degrees," Hennessy says.

"That incorporated uncertainty in future greenhouse gas emissions as well as uncertainty you get from 20-odd different climate models.

"When you get to sea level rises, that in turn depends on the rate of warming, but it critically depends on uncertainty around the rate of melting of the polar ice sheets.

"It is trying to get a better understanding of the magnitude of these changes, but we are highly confident of the direction of change in temperature and sea level."

This week's conference will hear that carbon dioxide emissions are tracking the mid to upper end of the IPCC predictions.

Average global temperatures are tracking in the upper to mid IPCC projections and sea level rises at the upper end of forecasts.

CSIRO sea-level specialist John Church will tell the conference Australia's tropical oceans are becoming steadily warmer and more acidic under the influence

of greenhouse gases such as carbon dioxide, which is affecting marine life in our oceans and on coastlines.

He says most scientific evidence has concluded that pushing sea temperatures to 2C above their pre-industrial values will cause a decline in ecosystems such as the Great Barrier Reef.

"At the moment it is looking like the upper half of the IPCC projections is more likely than the lower half," Hennessy says.

Penny Whetton, a senior scientist with the CSIRO's Centre for Australian Weather and Climate Research, says there are two ways to deal with the uncertainty.

"One is trying to reduce it," she says. "The other is working with uncertainty and communicating it because we have to decide how to deal with the climate change issue while the information is somewhat uncertain.

"There are some things we know with great certainty in our climate change understanding and some things we know with less certainty, and we really need to make that clear in our communications as well.

"The best example is that we are expecting increasing temperatures in future and the only uncertainty associated with that is how much and exactly how rapid it will be.

"If you move to another variable such as rainfall change, although we are reasonably certain about decreased rainfall in southern Australia we don't actually know the direction of rainfall change in northern Australia.

"As we go forward, some of that growth in knowledge creates new uncertainties while clarifying the certainties we have been previously working with."

Whetton is involved in the collation of the next set of national climate projections for the 21st century, which are planned for release in 2014.

The projections are for a range of factors including sea levels, seasonal-average temperatures, rainfall, as well as extreme weather events such as heatwaves, fires, droughts, floods and cyclones.

Whetton is looking to the upcoming release of updated global climate modelling to remove some of the uncertainties, particularly with regard to regional variation.

"We will get twice the number of models and 50 or 60 times the amount of data we got the last time we went through this exercise," Whetton says.

"I will be most interested in what the models show about the change in temperatures over Australia, changes in precipitation patterns, changes in extreme events such as very hot days and extreme rainfall events."

Clarification is also needed on what global warming means for rainfall in the tropical north.

"I will be particularly interested to see what the new crop of models are showing for rainfall in northern Australia because that has been a major source of uncertainty," Whetton says.

"Many lines of evidence over many years have pointed towards decreases in rain in southern Australia.

"But it has been more uncertain about how precipitation will change in the north, with some models showing decrease and some showing increase," she says.

From this week's conference, Whetton says she is looking forward to more information on some of the processes taking place in the atmosphere that drive climate change.

"I am expecting to come away from here with a better understanding of what drives changes in climate in a particular direction in a particular location as opposed to another," she says.

"I am expecting better understanding on how climate drives the El Nino and La Nina systems and how climate change may affect tropical cyclone occurrence."

Research is still under way to establish what role, if any, climate change has had on the most recent extreme rainfall events in Queensland.

Climate scientists generally say it is not possible to identify a climate change signal in any particular weather event.

And the higher than average rainfall in eastern Australia last year is consistent with the La Nina weather pattern.

But the question of whether the La Nina system was strengthened by associated climate change phenomena is contested, just as there is global discussion about the extent to which natural feedback mechanisms, such as cloud and air-borne particulate matter, complicate the task of modelling effectively.

One of the reasons global climate models differ from one another on how much warming they show relates to different feedback processes operating in those models.

Water vapour feedback is well understood as a positive feedback, reinforcing warming.

Aerosols tend to have a cooling effect, but the amount of aerosol in the atmosphere is expected to decrease, limiting their beneficial effect.

While high cloud is understood to reinforce warming, there is uncertainty about the extent to which low cloud has a cooling effect.

According to Hennessy, it is OK to disagree.

"This is a conference where the latest science is put on show and I would expect a broad range of people to be attending, both those who are sceptical and those who are more of an advocate than others," he says.

"There has been some very robust discussion. That is the sort of thing we expect in a conference in this area."