[cogitator]

So the burden is on the ecofreaks to establish that somehow this is different. And that is where there models fall apart on the validation problem. They have only one data point for human effect on the environment--the modern industrial era. There are no previous periods of industrialization that correlate to temperature increases (because there were no previous periods of industrialization).

Point one: the reason that now is different from any previous "then" is that a signficant increase in atmospheric CO2 is occurring during a very stable interglacial period, on a timescale for which no other natural Earth cycles will have a significant, noticeable effect. The only possible effects on this timescale are from major volcanic eruptions and changes in solar activity. As for the latter, data does not indicate a significant solar influence, though some warming in the early 20th century is attributed to an increase in solar activity.

Point two: about 55 million years ago, the Paleocene-Eocene Thermal Maximum occurred. Based on carbon isotope data, it is believed to have been caused by a major methane release over several millenia, and the methane oxidized to CO2, making the effects last longer. Though imperfect, this is the best analogy to the current situation, whereby a gas influencing Earth's radiative balance increased markedly (with no other cyclical contributions), with resultant increase in Earth's global temperature.

[ModelBreaker]

Two questions before I reply so I know if we have some common ground here.

Do you regard the chart in post 15 on this thread as a reasonably accurate representation of temperature and CO2 levels?

Where do you see us at this moment on the chart in terms of temperature and CO2?

How do you know we are in 'a very stable interglacial period?'