re: #1001 EndlessBob

The 5% number is commonly accepted. You can find it anywhere from Wikipedia to here: United Nations Environment Programme - World Meteorological Organization

From the same source you cherrypicked:

As a result of this natural balance, carbon dioxide levels in the atmosphere would have changed little if human activities had not added an amount every year. This addition, presently about 3% of annual natural emissions, is sufficient to exceed the balancing effect of sinks. As a result, carbon dioxide has gradually accumulated in the atmosphere, until at present, its concentration is 30% above pre- industrial levels.

You still want to handwave away the “unknown cause” that started the previous warmings, yet have no problem accepting that once this warming started — without CO2 forcing — that 800 years later, the CO2 became the prime driver. And yet wave away again the “unknown cause” that stopped the warming and cooled the earth, allowing CO2 levels to fall again.

I don’t need to handwave anything. I have a proximate cause and mechanism for today’s trends, backed by the observations and the data. You find me a better explanation, consistent with the data.

CO2 is considered a prime forcing agent today because the GCMs have been programmed to consider it as such.

CO2 is a prime forcing agent because physics and chemistry dictates it is.

Perhaps you should research the historic geological data yourself and not just accept my — or anybody else’s — word for it.

A truly ironic statement. I know the geologic data, that is how I know why millennial and megayear cycles are not the drivers of today’s trends.