mamooth
Diamond Member
So, we had a very steep spike in temperature back then without CO2 forcing
And if anyone said that CO2 was the only factor involved in climate, that would matter.
Your logic is bad. It's basically like saying "Forest fires happened naturally in the past, so obviously humans can't cause forest fires now." The fact that climate changed naturally in the past does not preclude humans from causing it to change.
In the meantime, we had the Roman Warming Period, followed by cooling, and then a Medieval Warming Period, followed by a mini Ice Age, and back to warming for the last 400 years or so. The data, therefore, suggests a lot of natural non-anthro variation in climate.
All local variations. Noise on the signal. The globe as a whole has been slowly cooling.
We also see the stratospheric cooling, the outgoing longwave radiation decrease, the downgoing longwave radiation increase. There are no natural explanations for such directly observed data, hence such data is regarded as a smoking gun for greenhouse-gas induced global warming. Global warming theory is the only theory that explains all the observed data, therefore it is the accepted theory. If you can come up with a different theory that explains all the observed data, you'll be the first.
Your graph provides no link to a source. My guess is that it depends on amplifiers which triple the effect of CO2 if it's like other graphs I've investigated.
The source is the IPCC AR5 report, which is the summary of the current science. It displays only current forcings, and makes no assumptions about feedbacks.
Fifth Assessment Report - Climate Change 2013
Chapter 8, page 698, with the whole chapter being about how the forcings are calculated.