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

[GliderGuider]

24. Stopping the extrapolation at 2015 leaves far too much wiggle room for the diminishers.

They can always claim that the divergence of our actual emissions from the A1FI scenario is not too great, that the curves in that time frame are basically similar, and so the gap could be closed in a decade or two following 2015.

Running out the curves for a few decades makes it clear that there are fundamentally different forces driving the two cases. It also plants the idea that it might take more than a snap of the fingers and some windmills to align ourselves with the IPCC - even with their worst case +4C scenario. And since the temperatures are given for the end of the century, it helps to think about what our situation couldl probably be like at that point.

Now, there is a lot of variability in the projection, especially depending on the chosen starting point. I started at 1990, and got emissions of 80 GtC in 2100. If I start at 1980 I get 60 GtC in 2100, and starting at 1985 gives me 70, using the same class of curves. What this indicates to me, beyond the prosaic ±15% variation, is that the emissions curve is growing steeper with time. Metaphorically, we have our carbon legs under us and are sprinting for home. Looking out to 2100 in that context makes even more sense to me.