On Tuesday, 15 September 2020 at 11:53:06 UTC+1, Spike wrote:
On 15/09/2020 10:27, Alastair B. McDonald wrote:

In a recent BBC R4 news programme, it was claimed that CO2 levels are
higher now than than at any time in the last 3 million years. What was
not said was that the planet has for a significant part of that time
span swung in cycles of 100,000 years from being an ice-ball for 80,000
years and a desert for 20,000 years. At the present time we are about
half-way through a warm part of the cycle. So why is there all this
concern about CO2?

Nonsense! We have been cooling for the last 6000 years. We were heading for a new glacial period, but now we are heading for the climate of the Pliocene when sea levels were 25 m higher and CO2 was at 400 ppm.

Just can't trust the BBC....

If CO2 continues to increase at the current rate of 3 ppm per year, then by 2100 CO2 will be at about 600 ppm and all the ice sheets will have gone leading to a sea level rise of 65 m, with a climate to match.
How much of London, Portsmouth, Southampton, Plymouth, Bristol, Cardiff, Swansea, Liverpool, Glasgow, Aberdeen, Dundee, Newcastle, Hull, or Cambridge at 5 m asl will be left after that?

When the temperature falls, there is little help from CO2 levels
remaining high, so what do you propose as the mechanism for your claimed
halt of the temperature drop that you mentioned?

My science does not come from the BBC.
I merely quoted what the BBC said, and asked a question based on what
they didn't say in their news item.
The BBC was just making one point - that CO2 levels are now where they were before the Pleistocene period began 3,000,000 years ago. Then the level dropped below 400 ppm and this ice age began. The ice age consists of glacial periods and interglacial, driven by the Milankovitch. Cycles in the Earth’s orbit. So the climate is not just affected by CO2. It is also affected other things such as solar radiation and water vapour.

Currently we are living in the Holocene interglacial which peaked 6000 years ago.
It comes from the scientific literature, e.g. https://science.sciencemag.org/conte.../6124/1198.ppt Which blog do you get yours from?
"Access Denied. You are not authorized (sic) to access this page"

Try this http://www.realclimate.org/images//Marcott.png from the same paper

More nonsense. When the temperature drops water vapour decreases and CO2 becomes the main greenhouse gas.
So we should be worried about water vapour rather than CO2. At what
level of water vapour does the crossover take place? How does that
relate to temperature?

At 0C water vapour is insignificant. So over the ice sheets CO2 is the main greenhouse gas. That is why the Arctic is warming three times faster than elsewhere. Gehenna the sea ice melts water vapour will take over and the NH warm even faster!