20120517_JG

Source: ABC News 24

URL: http://newsroom.melbourne.edu/studio/ep-149

Date: 17/05/2012

Event: Dr Joëlle Gergis discusses the methodology behind her climate change study

Credit: University of Melbourne

People:

• Jeremy Fernandez: Journalist and presenter with ABC News
• Dr Joëlle Gergis: Climate research fellow, University of Melbourne

Jeremy Fernandez: And Dr Joëlle Gergis is a climate research fellow and scientist at the School of Earth Sciences at the University of Melbourne. She's a leader of the working group on the Australasian climate of the past 2000 years, and the lead author of the climate change study. She joins us from our studio in Melbourne. Dr Gergis, thank you for joining us. Talk us through the techniques that you used to reach these findings. You talked about tree rings, for example.

Dr Joëlle Gergis: Sure. So, what we've done is compile, for the very first time in the Australia and New Zealand region, all of our tree ring, coral and ice core records, and then compare them against direct observational temperature records, develop a statistical relationship between those records, and take that centuries back into the past.

[Caption: Scientists say they have proof the last 50 years have been the warmest in the last millennium.]

Jeremy Fernandez: Tell us about what the data has found, particularly in the last 50 years.

Dr Joëlle Gergis: Sure. So, what we've been looking at is trying to determine how unusual recent warming is, in a long-term context, and what we've been able to do is run our reconstruction 3000 times, to really mix up the different records and to get a sense of any biases that could be present in the reconstruction. And what we see is that the post-1950 period is the warmest in the last 1000 years, in the Australian region.

Jeremy Fernandez: How can you be so sure that is, in fact, a result of human activity, because, you know, 1000 years is not really a long time in the scale of, you know, the Earth's history?

Dr Joëlle Gergis: Sure, but it is an important period, because it gives us an indication of pre-industrial temperature variations, and then how the temperature has varied when we put a lot of greenhouse gases into the atmosphere. So what we've done, after we've developed our temperature reconstruction based on natural indicators, is then compare it to climate model data, to be able to get a sense of what is actually forcing those changes. So we looked at natural factors, things like solar activity, volcanic events and ocean circulation, and we also looked at the influence of greenhouse gases. And we found that the post-1950 warming that we saw in the temperature reconstruction cannot be explained by natural variability alone.

[Caption: Researchers used indicators such as ice cores and tree rings as opposed to climate modelling.]

Jeremy Fernandez: A lot of the data that comes out of climate indicators comes from the other side of the world. How much do these findings line up with what other studies are finding in other parts of the world?

Dr Joëlle Gergis: Well, the reason for doing this study is to get a better sense of what regional climate variability has been like in all different regions of the world. I've been leading the group in Australasia to try to develop a temperature reconstruction for our region, and it is showing that warming really is - late 20th century warming really is occurring in our region. And that is consistent with what we are seeing in other parts of the globe.

Jeremy Fernandez: Does the study point to what might happen in the future, I know you've looked retrospectively. But what can we tell from these results, of what is going to happen in the future?

[Caption: The scientists say the data dates back to 1910 and was cross-referenced 3,000 ways.]

Dr Joëlle Gergis: Well, the purpose of a study like this is to really try and get a better handle on the range of natural variability that our region has experienced. The next step would then be to compare with climate models that do future simulations. So the climate model that we used in our study has been looking at the past. But the next thing to look at would be to get a better estimate of the range of natural variability, to see how well we can predict the past, and therefore how well we can predict the future.

Jeremy Fernandez: How well can you predict the future, with the current models and the current techniques that are used?

Dr Joëlle Gergis: Well, I think there are a range of different climate modelling groups, and obviously modelling the climate system is a difficult process. But the sort of work that we have produced is hopefully useful, in terms of getting a better handle on natural climate variability.

Jeremy Fernandez: All right, Dr Joëlle Gergis, from the University of Melbourne, thanks so much for joining us.

Dr Joëlle Gergis: Thank you.