Suppose Consumption of Fossil Fuels Were to Peak in 2030

Even though, so far, they appear to be peaking due to the levelling off of demand, due to the ramp-up of renewables and because of affordability and financial reasons, like too high a debt load.

Source: Sam Caranas, Arctic News.

But if the did, a certain Grebulocities figured out a possible end point for atmospheric carbon content and posted it a a response to the post "Dark Ages America: Climate" at The Archdruid Report blog, in which the archdruid, John Michael Greer, suggested that fossil fuel emissions might peak in 2030 -- this was on July 30, 2014 mind you:

Now if only I could somehow find a time machine or a longevity potion and see if you're right... 

I just made a crude spreadsheet in Excel to see what type of CO2 concentration we might peak at under the assumption that the rate of change of the CO2 concentration peaks around 2030, falling to 0 by 2100. Under my model, the CO2 concentration rises by 0.55% this year (roughly equal to its average growth rate over the last decade) and the growth rate increases by 0.01% per year from now until 2029 (at 0.7%/year), then falls by 0.01%/year until it bottoms out at 0 by 2099. 

The peak concentration under these assumptions is "only" 562 ppm, obviously reached in 2099, conveniently about double the preindustrial level where temperatures were 0.8 C cooler than present. If the mean of most model estimates of equilibrium climate sensitivity is correct, we see about 3 C/doubling. So under these really crude assumptions, we've got a world 2.2 C warmer than present. Of course the error bars are huge, and they're larger on the warmer side. But if this is roughly where we end up, we're in the mid-Pliocene warm period at about 3.3 Ma, or perhaps a little worse. This is inconvenient because sea levels were 25 m higher than present, with no West Antarctic ice sheet and little or no Greenland ice sheet, but the East Antarctic ice sheet still existed and contained most of its current mass.

Well the CO₂ did rise by about 2.25 ppm on average from 2014 through 2015.by about 0.57% which is roughly on target with his prediction of 0.55%. But from 2015 through 2016? Well we don't have the minimum yet, but the CO₂ rise according to the graph maxima was about 3.5 ppm or about 0.88% according to the 2015 average content. And that's not even accounting for the fact that CO₂ content for 2016 finally peaked out at around 408 ppm in April - May, shown below.

Annual CO₂ pulse on Keeler Curve through July 2016.
Source: Mauna Loa Observatory, NOAA.

It appears that the 3.5 ppm rise is now being maintained. Although we're just coming off an El Niño, it's possible, especially when compared to the graph at the top, that we are having increased positive feedbacks or less negative feedbacks or both from natural sources, because it appears we did not have a nearly as big a Carbon Dioxide increase the last time we had an El Niño as strong as the one we've just had, i.e., the one in 1997-1998.

So will the atmosphere's Carbon Dioxide content be as little as 560 ppm? Don't know. But given the present rate of fossil fuels burning through 2030 and a new normal of 3.5 ppm for annual Carbon Dioxide content increase, we could be looking at 450 ppm or so around 2030, which makes the terminal content that much larger. Robertscribbler reports that under Business as Usual (IPCC's RCP 8.5) it could be as high as 936 ppm with a average planetary temperature increase at that time of around 4 to 5 degrees Celsius (7 to 9 Fahrenheit). Will it actually get that bad? Don't know.

But I DO know that global warming is NOT a myth!