Jim D
You ask specific questions.
Let me respond with specific answers.
where do you draw the line for “natural phenomena” as an alternative “explanation”.
Over most of our planet’s history, the significant swings in its climate have been caused by “natural phenomena”. As a result, this is the “null hypothesis” of climate change.
Does it have to be an “explanation” first or just a word for “I don’t know” but not CO2. That’s what I am complaining about. It is like saying “it can’t be CO2, but I don’t know what else it could be either.” This is just lazy denialist talk, the way it comes across.
It is simply a statement of the “null hypothesis”: climate changes as a result of natural phenomena.
Could CO2 also be a factor? Why not? We just do not know enough to be able to say for sure that CO2 has been a significant factor in the past or will be a significant one in the future.
Paleo data (to be taken with a grain of salt) tell us that the Ordovician “ice-ball Earth” period occurred when atmospheric CO2 levels were at several thousand ppmv.
Earlier warm and cold periods since historical times have all occurred without any significant change in CO2 levels.
We see that there was a mid-20thC period of cooling despite increasing post-WWII CO2 emissions and rapidly rising concentrations.
We see that there has been a current lull in warming despite unabated CO2 emissions and concentrations reaching record levels.
These observations raise some doubt regarding the “CO2 control knob” hypothesis. But, yes, CO2 could be a factor – or it might not be a significant one. We just don’t know, Jim.
And that’s not “lazy denialist talk”.
Max
