In this recent interview in Rolling Stone James Hansen, a leading climate scientist, covers a lot of ground from sea level rise to the inadequacy of our current actions to mitigate the impacts of climate change. Here is his response to the question of whether the Paris targets are achievable:
It’s possible, but barely. If global emissions rates fell at a rate of even two or three percent a year, you could achieve the two-degree target. People say we’re already past that, because they’re just assuming we won’t be able to reduce missions that quickly. What I argue, however, is that two degrees is dangerous. Two degrees is a little warmer than the period when sea levels were 20 to 30 feet higher. So it’s not a good target. It never had a good scientific basis.
And in this supplementary explanation he clarifies what needs to be done to not only reduce CO2 emissions but to start drawing levels back to 350 ppm. Here is a short extract.
Is it possible to store 150 GtC in the biosphere and soil? Say, even if we make all plausible efforts to employ biochar where it has other benefits and apply rock dust in conjunction with reforestation and agricultural processes where it has other benefits? We will discuss that in a later message. Here I only want to note that the 8-year delay has made the task much more difficult, increasing the magnitude of carbon extraction from 100 GtC to 150 GtC.
You can read a lot more from James Hansen here on his web site.