Saturday, March 20, 2010

Modelling climate change

Radio National's Saturday Extra program this morning had a discussion on modelling climate change with Kevin Judd, a mathematician involved with the recent Universities Australia climate forum. It was a good discussion, and I left the following comment on the guest book afterwards:

Thanks for your discussion of climate modelling and the confidence we can have in its predictions.

What I think needs to be said is that while modelling is improving, which we can judge in part by its ability to reproduce past observations using known data, it's not the only way we can predict the likely effects of increasing greenhouse gases in the atmosphere. NASA's James Hansen, perhaps the world's most renowned climate scientist, considers we need only look to the past 'paleoclimate' record.

By studying the known climate forcings and resulting temperature changes between past glacial periods, Hansen has determined that climate sensitivity - the warming we can expect from a doubling of pre-industrial atmospheric carbon dioxide - is about 3 degrees Celsius. No models are necessary, in his view, to establish that the emissions trajectory of business as usual will lead us to 3 degrees and beyond, with consequent disastrous sea-level rise, and species extinction to which we will be unlikely to adapt.

To those who argue that climate has undergone rapid transformations in the past, Hansen responds that these have not matched the current rate of change, and even then have been associated with mass-extinction events. Our current climate trend places us on a path towards the sixth such event on record.

That said, I think your guest did a good job explaining just what are the uncertainties and strengths of current modelling.

One of the strengths is indeed the basic science. The basic mechanism of warming needs to be more broadly understood. That includes the insight that greenhouse gases do not impede the sunlight hitting the earth, but they do impede that portion of its energy that isn't reflected straight back as light, but is instead radiated as infrared radiation or heat. That happens when sunlight, instead of hitting a reflective surface, hits and is absorbed by a darker surface - such as the ocean - which itself warms, but also sheds the incoming energy as heat into the atmosphere. That's what is trapped by greenhouse gases, increasing quantities of which are emitted by human activities, trapping ever more heat.

On the expertise of climate commentators, I write a bit about climate change and am not a climate scientist. I don't think you need to be, if you make the effort to read the science and base what you say upon it.

As far as scientists speaking out, I believe they have been painfully reticent almost to the point of negligence. Imagine if a deep space probe detected an incoming asteroid that scientists determined was on a collision course with earth. Would we think it reasonable if they remained silent to avoid 'politicisation' despite a considered view that action by government was too slow to meet the threat?

We criticise 'politicised' scientists mainly because they bring an unpleasant but urgent message - one that is attacked by vested interests such as the coal lobby, who want to keep their profits while sharing the catastrophic warming with everyone on this planet.

Thanks for the links to Nature and to the Universities Australia forum.

Finally, I invite the ABC (not Maurice Newman) to convene a citizens' climate change panel, where ordinary people describe what they think climate change is, and then have their understanding clarified by an expert panel of articulate climate scientists.

The program referred listeners to the Universities Australia climate forum, and to the climate coverage in the February edition of Nature.

No comments:

Post a Comment

Comments are most welcome on any of the posts at Northcote Independent. I encourage feedback - positive or negative. Feel free to disagree, but remember that posts are moderated to ensure they are on the topic and in the spirit of open debate, as outlined in my editorial policy.