Originally Posted by the_13th_redneck

As for CO2 concentration, it was higher during the Jurassic period and when the dinosaurs were around. And I don't think they had factories. And life was quite abundant. You can go through the trouble of looking that one up.

And you will notice that most life forms from that time are extinct now.

Originally Posted by perseus

Simply because you are comparing temperature changes on much longer timescales than present changes, when we know other natural effects can have large effects. It is like comparing changes in educational standards over the past few decades with the 'educational' standards 100 000 years ago when we has smaller brains. We could talk about Milankovitch cycles which are of course work on that longer timescale, but there is no need to go into that complex science stuff.

We have had 20 centuries when nothing much has changed with world temperatures. Now consider you were an alien (without any knowledge of human development and population) being given the temperature data up to 1900, and being asked this question:

What is the chance of a rise in average temperatures beyond the range of the past 2000 years over the next century?

The problem is that we cannot just measure temperature over a time span that suits our argument that would incredibly irresponsible.

Using methods that are considered accurate enough to promote the global warming argument we can see a clear cycle and we have four repetitions of it, the results we have show no shortening of the cycle nor is it showing an increase in the extremes of the cycle therefore I believe it is fair to ask why we should attribute it to mans interference.

My argument is still not to refute global warming but more to determine how much of it we can attribute to man given that we have results similar to what we have now preceding industrial man.

Originally Posted by The Other Guy

And you will notice that most life forms from that time are extinct now.

Considering it's been 70 million years, yes I'd imagine they'd be extinct. I'd be plain weird if they weren't.

Global climate change? This is how well regulated our planet is - the last ice-age was destroyed by vulcanos, remember.

Just saving ourselves will suffice; think big folks.

[quote=MontyB;445654]The problem is that we cannot just measure temperature over a time span that suits our argument that would incredibly irresponsible.quote]

The reason why 1000 or 2000 years is typically chosen for this sort of analysis isn't because there is much evidence that temperature variations were any greater in the holocene (up to around 10 000 years ago) but because the temperature evidence becomes much more suspect. (to be technical the proxies diverge, leading to a much wider confidence interval). Of course a sceptic would turn around this argument in a simplistic way ignoring evidence that suits their belief. In contrast the graph that you posted suits a sceptics scale of events totally ignoring the relative stability of temperatures on a 1000-10000 year timescale which is far more relevent to determining anthropogenic effects. It is the relative stability of the climate evidence that provides brute raw statistical evidence to man's effects, without any technical knowledge of greenhouse gases, solar radiation and the like.

However, for the sake of rigour we cannot accept anthropogenic effects on data alone, we need the theoretical and modelling to back it up and it generally does. So I would say that the raw data provides something of the order of 90% certainty, the calculations and models only add to this, that is why I think the 90% certainty statement by the IPCC is arm twisting by the politicians, it is more like 99%.