Thanks for that, Poirot, but I found it unconvincing for a couple of reasons. First, it doesn't tell us anything about what the response of the climate to the increase in free energy (heat) will be. It assumes that the long-term response is predictable from data accumulated on an extremely short baseline, which is not a reasonable assumption in a metastable system that has oscillating variables at every time scale. Therefore, to claim that a 2 degree temperature rise is "virtually certain" is not a reasonable conclusion based on that data.

Second, even with a simplified model, including just some of the parameters, the range of uncertainty is enormous, meaning the model is effectively useless as a predictive tool over even short timeframes, as the disjoint between modelling and observation over the last decade or so has demonstrated. If we can't predict what's going to happen next year, how can we hope to predict what will happen in 100 or 100 years?

I'm not suggesting we do nothing, just take it carefully, rather than committing to actions that will have negative impacts in other ways, including economically and socially, which may limit our ability to muster a proper response in future.

We should also be aware that there are larger cyclic variations operating on longer timeframes which we understand even less.

It seems a pretty obvious thing to do to reduce anthropogenic atmospheric contributions to as small as possible, but intuitive responses aren't always the best, especially when dealing with complexity. Make haste slowly is my advice.

Luciferase, with population pressure growing rapidly, food and water security are going to be major issues whatever the climate does. The penultimate generation in a petri dish culture is well fed and has room to expand - the last ones drowns in its own excrement or starves. The question that we have to answer on that is how close we are to filling the petri dish that houses our species. I guess we'll find out in time, because it's very unlikely we'll stop expanding our numbers until we do.

Antiseptic,

You may also be interested in this, which relies on empirical real world data and not global climate models.

http://www.columbia.edu/~jeh1/mailings/2012/20120803_DicePopSci.pdf

And we already know what's happening in the Arctic.

http://www.youtube.com/watch?v=YgiMBxaL19M

Antiseptic, have you ever wondered why some projections (not predictions) in some metrics start to stabilise (say mid-century) then decline thereafter?

There are some pretty smart cookies out there working on it - political ideologues tend to stuff it.

Poirot, what's happening in the Arctic is not unique to our times, it's just that we haven't directly observed it before, so it is impressive.

It's a big leap from "wow, I haven't seen that before", to "wow, that looks bad, I must have done something to cause it".

The whole of large-scale human interaction with climate has occurred over a hundred or 2 years. The growth of human population is itself an example of how interactions of systems can produce emergent outcomes not predictable from looking at earlier trends.

If an alien scientist had done a study of human population for the entire time from the evolution of the species to just before the time of the pharaohs he'd have seen that it was pretty static and had started a small exponential growth trend due to technological advances increasing food availability.
If he'd then taken that data and extrapolated it for the next 5500 years, he might have concluded the population today would be at most 500 million but probably much lower.

He simply had no way of knowing how the variables were going to interact to produce the conditions for the population to be heading for 9 or 10 billion based on his observations, especially variables which were themselves emergent,like technological innovation. He may have had a rate term for that in his model, but it would have been a simple one of small effect and would have been a pretty good fit right up until the last few hundred years when it would have failed completely.

That's a pretty simple system, readily modelled by a smooth curve for the most part, which cannot reliably extrapolate the curve about 2% further in time because there are emergent factors which are unpredictable.

The climate data shows no smooth curves on any time scale.

We need more data.

Poirot, you may be interested in "Negotiating our future: Living scenarios for Australia to 2050."

Media release:

http://www.science.org.au/news/media/21february13.html

Volumes 1 & 2:

http://www.science.org.au/policy/australia-2050/volume1.html

http://www.science.org.au/policy/australia-2050/volume2.html

Select a drink of your choice, cosy up and click the embedded chapters at your leisure.

Sadly, the contents would go over the top of most OLO'ers.

My last post, good-bye.

Thank you, qanda.

Adieu

: )