Russ Steele
Please read Anna’s comments here before reading this post. This a rather long answer, and I have been asked not to post long replies on NCFocus. So, here is my long answer.
Dear Anna:
If your religion does not allow you to believe in a Medieval Warm Period, that is fine with me. I find significant data in the ice cores and and sea floor cores to indicate there was a warm period over a range of years centered around 800-1300, dispersed over the globe. The real question is was it warmer then, than today? I agree that question may still be an open issue, the proxy data is not precise enough to know for sure.
Since we now know that 1934 was now the warmest year, not 1998 or 2006, when the CO2 was much less then, than it is today. This raises the question what was the role of CO2 in causing the higher temperature in the 1930s? Or for that matter in the 40-70s when it was cooling. Four of the top ten years were in the 1930s: 1934, 1931, 1938 and 1939 and only three of the top ten in the last ten: 1998, 2006, 1999. As for that matter what happened to 2000, 2002, 2003, 2004, that were cooler than 1900. So, if every increasing CO2 is the problem, why are we not seeing a steady increase in temperatures, they seem to be all over the map. Why is that?
You wrote: “What do you think is the probability that global warming really is being caused by increasing CO2 levels and is a grave danger that's very much worth taking major steps to address?”
My reply: I think that CO2 is making a very small contribution to global warming, but it is being swamped by the activity of the sun. Or, I should say the lack of sunspot activity. I would say there is a higher danger of global cooling over the next 30 years than global warming. The southern hemisphere is having a really tough winter with record breaking cold temperatures. We are having a mild summer, even breaking local records. But, this is just the weather. We need 30 years of weather for a climate trend to emerge. Where as, 300 years of sunspot trends indicate we maybe in for an extended cooling trend, with a tiny mitigation by increasing CO2.
And an extended cooling period would more dangerous to large segments of the population than extended warming, crop failures and increased energy demands. During the Dalton Minimum 1790 to 1820 California experiences long periods of drought, the longest being 13 years, when there was little moisture and the there were insufficient degree days for the wheat to mature and the corn came late, with smaller ears than normal. Native americans move in to the Spanish villages and the warmth of adobe buildings. Life was tough during the Dalton Minimum. Tougher than it would have been if it were a few degrees warmer. Let’s hope the sun returns to a normal sunspot cycle, sooner rather than latter.
Best regards,
Russ