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The first phase of the 350 campaign has been a wild success. ”350” is now an international symbol of emergency climate stabilization. More importantly, the 350 target reflects a scientifically-grounded assessment of what global climate protection really means. But what would it actually take to bring the atmospheric carbon-dioxide (CO2) concentration back to 350 parts per million?

This paper provides a quick, up-to-date overview of the issues here, which are significant to any plausible emergency emissions-reduction effort. It focuses on the extremely limited size of the global CO2 budget that would remain to us in a 350 ppm future, and on the shape of the emissions pathway that’s needed if we’re to keep within that budget. In particular, it specifies a representative emissions pathway consistent with a 350 ppm concentration target. By way of context, it then compares this 350 pathway to an emission pathway consistent with a 2°C temperature target, and to other, supposedly 2°C-compliant pathways that have significantly lower odds of actually satisfying their target.

Finally, it offers a brief glimpse of the challenges that all true emergency climate-reduction targets raise in this North / South divided world.

A 350 ppm Emergency Pathway

The atmospheric CO2 concentration is now about 389 ppm. Average out seasonal variations, look just a bit ahead, and call it 390 ppm and rising fast. With current concentrations already so high above the 350 target, some observers are inevitably proclaiming 350 to be impossible1, especially given the political context of fraught and faltering global negotiations. Given these realities, “350” is a call to a new politics – a scientifically well-grounded politics that can draw upon our ever clearer understanding of what it would it actually take to bring concentrations back to 350 ppm.

Jim Hansen and his colleagues have taken important steps toward establishing this understanding, by way of a number of studies2 designed to motivate a 350 target and explore its emission implications. Here, we’ve built on their principal 350 emissions pathway, updating it to capture the modest (and no doubt temporary) 2007-2009 downturn in global emissions caused by the recent financial crisis, and adapting it to yield essentially the same outcome in terms of projected atmospheric CO2 concentrations. The result, shown in Figure 1 below, is our representative 350 emissions pathway – an extremely stringent pathway that has emissions dropping to zero by 2050, and returns atmospheric CO2 concentrations to 350 ppm by approximately 2100. For comparison, we also show the International Energy Agency’s latest (2009) business-as-usual projection, one in which 2030 emissions are eight times higher than they would need to be in the 350 pathway.  Alternate Link.

A 350 ppm Emergency Pathway