The study’s key takeaway is that unless CO2 emissions peak right about now—which they are clearly not doing—in just a few more years we will lock in a 2°C rather than a 1°C temperature rise. That will set climate impacts in motion for the next thousand years or so, barring advances in technology that are currently largely discredited as either too expensive or too impractical on the scale necessary to reverse the warming that’s already baked into the system.

Why emissions need to start falling now

As we reported recently, the UN has endorsed a carbon “budget”—a maximum of one trillion tonnes of carbon emitted into the atmosphere to keep warming below 2°C. To stay below 1°C, Hansen et al argue that the world can burn only half this amount.

To achieve this, they say, global CO2 emissions would need to peak immediately and decline three times faster than the rate currently being discussed for inclusion into the next global climate treaty—a 90% reduction by 2030. The current UN plan (dotted line in the chart on the left below) won’t even be implemented until 2020 at the earliest. Even if by some miracle Hansen’s plan (the solid line in the chart on the left) took effect this week, he says we’d still have only a 50/50 shot at staying under 1°C.

But the cost of waiting is enormous. If global CO2 peaks in 2013—that is, sometime in the next week or so—followed by drastic reductions, we’re still locked in to climate change of 1°C or so until about 2100. If we delay this peak until 2030 (the green line in the chart on the right above), Hansen projects extensive climate-change impacts will continue for a further two centuries. If we delay until 2050 (the red line), dangerous climate change will be locked in until past the year 3000.

Basically, if we wait even a few years to implement anything less than a fossil-fuel starvation diet, momentum already built into the system nearly guarantees the climate is toast. To quote the study:

The inertia of energy system infrastructure, (i.e., the time required to replace fossil fuel energy systems) will make it exceedingly difficult to avoid a level of CO2 that would have highly undesirable consequences.

Why revolution is the only way

Hansen and his associates admonish the environmental community for doing the same things over and over again—advocating for renewable energy, recycling, and hybrid cars—and expecting different results. The change that is produced in this way is much, much too slow, they say. Their study concludes with what can only be characterized as a call to arms: a global challenge akin to the anti-slavery and civil rights movements, begging the world’s young people to disrupt their governments and demand immediate action on climate change.