Actual Carbon Emissions vs. IPCC Scenarios - how far away is safety?

[GliderGuider]

4. That's your prerogative - this thumbnail assessment isn't the Truth.

I agree that other curves could be fitted. However, in order to have a chance to escape a +4C hell, we're probably limited to looking at sigmoid/logistic curves with some sort of built-in saturation effect. Do human needs for energy saturate? There are external events that can suppress them, but I don't know of any organic reason why that should be so. Energy use and CO2 emissions have grown at a faster rate than population for the last 100 years, which is a good indication that the curve is open-ended.

See this post for my look at open-ended, super-linear scaling.

Human population growth does in fact appear to be following a sigmoid curve (even though it's going to saturate too late for comfort), but the growth of energy and CO2 does not. That's worrying, because if it doesn't stop rising on its own we will depend on external forces like political policy-making to modify its trajectory. Or just wait for events to modify it for us.

Anyway, the main point of this graph was to show that we would not necessarily "run out of" fossil fuels before we hit extremely dangerous climate territory, and that the possibilities definitely include us blowing well past even the most pessimistic IPCC scenario.