I well remember the huffing and puffing over the release of James Hansen’s paper “Target Atmospheric CO2: Where Should Humanity Aim?” :-
“…Decreasing CO2 was the main cause of a cooling trend that began 50 million years ago, large scale glaciation occurring when CO2 fell to 425 +/- 75 ppm…”
The sceptic-deniers laughed and scoffed and said things to the effect that clearly there’s nothing to worry about that the current concentration of Carbon Dioxide in the air is over 390 parts per million – it won’t melt the polar ice caps.
What the sceptic-deniers haven’t understood, or pretend not to have understood, is that it is a combination of factors that caused major lasting glaciation on Earth. Yes, the level of Carbon Dioxide in the air is important. But the rate of change of Carbon Dioxide in the atmosphere is a significant component.
If the levels of Carbon Dioxide in the atmosphere change rapidly, the heating or cooling effect is amplified, in effect. You have to take account of the relative change in levels of Carbon Dioxide, not just its level at any particular point in time.
Why does Carbon Dioxide count ? Because atmospheric Carbon Dioxide has been clearly demonstrated as being the principle temperature control of the Earth system.
People argue and argue and argue about what a safe level of atmospheric Carbon Dioxide is for long-term Climate safety, and totally neglect to consider what follows from the fact that the current rate of change of atmospheric Greenhouse Gases is far greater than most events in Earth history.
This rapidly increasing amount of Greenhouse Gas is causing the ice caps to melt – as Dr Judith Curry and others have demonstrated.
The risk is that even if the level of airborne Carbon Dioxide is controlled in the next few decades, that the melting of the ice caps will have become unstoppable because of the rapid change leading to rapid warming :-
This is why I cannot agree with Dr Judith Curry about her proposal for global Climate policy : she advocates “wait and see”, but her own Science indicates that we have no time to waste.
What we need is a rapid stabilisation of Carbon Dioxide emissions to the atmosphere, so the warming force doesn’t get any worse; followed by a strong programme of emissions reduction over the next few decades.
Delay is not an option.