Stormy forecast in climate crystal ball

Earlier this year CSIRO Atmospheric Research released a report Climate Change under Enhanced Greenhouse Conditions in Northern Australia. Savanna Links interviewed one of the authors, Senior Research Scientist Dr Kevin Walsh .

Is there a connection between the high temperatures around the world at the moment (see graph) and climate change?

This graph from NOAA illustrates how July 1998 was the warmest month worldwide in the historical record. Printed with permission of the National Oceanic and Atmospheric Administration (NOAA)

It's been in the news that July 1998 was the warmest month worldwide in the historical record. I think it's fair to say that we haven't detected an unambiguous human contribution to this trend but on the other hand if Greenhouse gases were causing the world to warm then this is exactly the sort of effect you might expect.

But can you say that the longer term temperature rises we've seen are due to Greenhouse gases and not just natural variation ó such as more radiation from the sun?

Several studies have come out recently which have reinforced the conclusion that it is at least partly due to Greenhouse gases.

How can they tell?

Firstly, Greenhouse gases produce a characteristic warming across the globe—more at poles than at the equator—and secondly Greenhouse gases warm more in the upper troposphere than lower troposphere (the troposphere is the 8km thick layer of constantly moving air closest to the earth). These telltale warming patterns have indeed been detected.

Is there a link with the flooding here and overseas?

The thing about the impact of flooding is that it is so dependent on climate variability from year to year and human trends like population increases in flood-prone areas. The jury is still out on links to climate change.

Moving on to the North Australia Study, what aspects of climate change are important up here?

In north Australia the variation in rainfall is the important factor.

So what are your predictions for the changes in rainfall in the north?

We had great difficulty in coming up with predictions for summer rainfall in the north that's linked to ENSO (El Nino Southern Oscillation) variations. We don't know what's going to happen to ENSO under climate change. The latest models give us different results for rainfall change than the earlier models ó unusually the Australian region is the only major region in the world where this is true.

Why?

Because our rainfall is dependent upon sea surface temperatures in the Pacific, and those in turn are related to ocean circulation changes which we don't have a really good understanding of yet.

Can you say something about expected changes in rainfall intensity?

One of the things that we suggested might occur would be increased intensity of rainfall events in the north Australian summer.

What about the dry-season winter rainfall?

That's interesting because for winter rainfall the older models and newer models agree for northern Australia and predict slightly less rain in the future.

Is there a link between climate change and the record wet seasons and "wet" dry seasons that parts of the north have been getting lately?

It's difficult to make extrapolations for a long forecast from just the past few years. Again it is a question of local effects being influenced by year-to-year changes in climate rather than long-term ones, so I don't know if you should read too much into that at the present time.

Anything you want to add to finish up?

I think it's important to realise that some climate change is now inevitable. Even if we stopped producing Greenhouse gases tomorrow the oceans' temperature are still adjusting to the Greenhouse gases that have already been put into the atmosphere so that will keep on warming into the middle of next century.

Interview Peter Jacklyn

For a special north Australian forecast go to the Savanna Links story below.