First author

Teasing apart the various effects of global warming is tricky because there are so many variables to consider. This is especially true when assessing the effects on glaciers and ice caps. Some scientists say that global warming is making these bodies melt faster, contributing to rising sea levels. But many of these assessments have used relatively simple models of glacier and ice-cap size and so may not have captured the complexity of the dynamics involved.

Page 311 features the results of a more sophisticated model built by Sarah Raper of the Centre for Air Transport and the Environment, Manchester Metropolitan University, UK, and Roger Braithwaite at the University of Manchester. This model suggests that the global rise in sea levels caused by global warming might not be as great as some estimates have found. But it also shows that local effects, especially in high mountain areas such as Nepal, could potentially be catastrophic. Raper spoke to Nature about the results.

Were you surprised that the rise in sea level predicted by your model was up to half that predicted by others?

I didn't have previous expectations. I like this paper because I think it gives a much better framework for glacier and ice-cap melt. It is ongoing science and we are still filling in lots of gaps. We have to extrapolate to the globe what we know from only a few glaciers.

Your paper only models one aspect of sea-level change. What are some others?

We think that the other most important aspect is the thermal expansion of the ocean, in which the ocean warms up, expanding its volume and so pushing up sea level. We're not modelling that. Two other possible factors are the large ice sheets in Antarctica and Greenland, which could contribute a great deal, but it's questionable how much of an effect they would have over the next 100 years. This is actually a big unknown.

Is there any danger that your conclusions might be leapt upon and used by someone with a particular political agenda?

I am not at all belittling the importance of global warming. It's just that our estimate of one particular aspect is a bit lower.

How did you divide the work with Roger?

I approached this from a climatological point of view. Roger is more of a glaciologist; he's got much more field experience.

What's next?

We're looking for more observational data that can be easily assimilated into our model. We should look at the possible effects of changes in precipitation.