Former Microsoft executive, Nathan Myhrvold, and climate scientist Ken Caldeira have produced a paper which highlights the need for a fast deployment of renewable energy in order to have any real effect on global warming. The following is lifted from an article by David Roberts on Grist (and the infographic comes from Yarra Climate Action Now).

Myhrvold and Caldeira ask the right question: What effect will deployment of clean energy have on global temperature? They take for granted that economic growth will continue as it has in the past (no small assumption, granted) and thus that 10-30 terawatts of carbon-neutral power will be needed by 2050 to meet global energy needs while limiting atmospheric CO2 concentrations to 450 ppm. (Always worth noting: 450 ppm would, according to the latest science, itself be quite dangerous.)

In their results, Myhrvold and Caldeira highlight a few poorly appreciated but crucial features of energy transitions. The first is that they take quite a while to have an appreciable effect on CO2 concentrations. The world’s oceans have considerable “thermal inertia” — it takes them a long time to absorb heat and a long time to release it. Even after CO2 concentrations start falling, it will take the oceans a while to stop releasing the excess heat they’ve already absorbed. Also, the building of a clean-energy infrastructure itself involves enormous expenditures of energy and thus CO2 emissions. For a given power source, the emissions released during its construction put it into “carbon debt” and it takes a while of generating carbon-free energy for it to work itself to the break-even point. Only then does it begin producing net reductions in CO2. Combine thermal inertia and carbon debt and you get a fairly long time lag between the energy transition and its carbon effects.

The second is that so much CO2 accumulation is already “baked in” that temperature will continue to rise for a while even in the context of rapid emission reductions. We’ve already gotten drunk on fossil fuels; there’s no way to avoid the hangover.

The consequences of this time lag are twofold. First, substantially affecting global temperature in the first half of the century is all but impossible; even to secure temperature reductions in the second half of the century, a rapid transition to clean energy needs to begin immediately. Second, lower-carbon energy — like, say, natural gas — just won’t do it. If we transitioned to something with half of coal’s emissions, it would take more than a century to produce even a 25 percent decline in CO2 relative to the status quo baseline. By then we’d be cooked.

In summary, Myhrvold and Caldeira have shown in pretty stark terms that, if we’re not willing to substantially reduce population growth or economic growth, we’re going to need an absolutely gargantuan amount of zero-carbon energy, without delay. They conclude:

Despite the lengthy time lags involved, delaying rollouts of low-carbon-emission energy technologies risks even greater environmental harm in the second half of this century and beyond. This underscores the urgency in developing realistic plans for the rapid deployment of the lowest-GHG-emission electricity generation technologies. Technologies that offer only modest reductions in emissions, such as natural gas and — if the highest estimates from the life-cycle analyses are correct — carbon capture and storage, cannot yield substantial temperature reductions this century. Achieving substantial reductions in temperatures relative to the coal-based system will take the better part of a century, and will depend on rapid and massive deployment of some mix of conservation, wind, solar, and nuclear, and possibly carbon capture and storage.