A little good news/bad news on the climate and energy front. In the Sept. 10 Science, Steven Davis and Ken Caldeira of Stanford University have a study that estimates what future carbon emissions—and consequent global warming—would be from existing energy and transportation infrastructure. (In other words, what would happen if we used all the current buildings and power plants and cars we have today to the end of their operational lifetimes, but built nothing new.) It’s a useful thought experiment, and the results are somewhat cheering. Davis and Caldeira estimated that our current, almost completely fossil-fueled infrastructure would lead to an additional 496 billion metric tons of CO2 emissions between now and 2060, which would lead to an atmospheric CO2 concentration of less than 430 parts per million and a mean warming of 1.3 C above pre-industrial levels. If we could achieve those goals, it would be a major success for climate policy—international negotiators have generally looked to keep atmospheric CO2 levels below 450 ppm and warming below 2 C. As Davis and Caldeira write in their paper (done with the help of H. Damon Matthews from Montreal’s Concordia University): “The primary threats posed by climate change are a consequence of emissions from devices that do not exist.”

Image courtesy of Stephen J. Davis

To put it simply, it’s not the cars and other fossil-fuel burning devices that we’ve already built that will push warming to edge—it’s everything we’re likely to build in the future, as the globe’s population and economy keeps growing. And that might be the bad news—it’s obvious that we’re not going to simply stop building new planes and power plants. That’s especially true in rapidly growing developing nations like China, where the mean age of power plants is just 12 years (compared to 32 years in the U.S.). And existing infrastructure doesn’t just mean cars on the road and coal power plants—highways networks with gas stations facilitate more cars, just as our network of oil refineries and drilling platforms facilitate the use of more oil. Changing all of that will be incredibly difficult—and it’s getting harder every day, as Caldeira points out:

Because most of the threat from climate change will come from energy infrastructure we have yet to build, it is critically important that we build the right stuff now – that is, low carbon emission energy technologies. We have a gas station infrastructure but not a battery recharging infrastructure. This makes it easier to sell new gasoline powered cars than new electric cars. Thus there are infrastructural commitments that go beyond our calculation of future CO2 emissions embodied in existing devices.

So we need to go beyond simply phasing out our existing fossil fuel-dependent infrastructure and starting building one that’s carbon-free. But we’ll need to facilitate A LOT of low-carbon energy, as New York University physicist Martin Hoffert argues in another Science article. Hoffert first references the familiar “wedges” scenario from Stephen Pacala and Robert Socolow of Princeton University:

Pacala and Socolow (8) analyzed a scenario that envisioned stabilizing atmospheric concentrations of CO2 at 500 ppm within 50 years. They found that reaching that goal required the deployment of seven existing or nearly existing groups of technologies, such as more fuel-efficient vehicles, to remove seven “wedges” of predicted future emissions (the wedge image coming from the shape created by graphing each increment of avoided future emissions). Those seven wedges, each of which represents 25 gigatons of avoided carbon emissions by 2054, are cited by some as sufficient to “solve” climate change for 50 years (9)

But as Hoffert points out, the “wedge” hypothesis is already looking too rosy, as carbon-heavy coal production continues to rise around the world:

The enormous challenge of making the transition to carbon-neutral power sources becomes even clearer when emissions-reduction scenarios are based on arguably more realistic baselines, such as the Intergovernmental Panel on Climate Change’s “frozen technology” scenario (11, 12). Capturing all alternate energy technologies, including those assumed within this BAU scenario, means that a total of ~18 of Pacala and Socolow’s wedges would be needed to curb emissions (13) (see the figure). And to keep future warming below 2°C, even under the Davis et al. age-out scenario, an additional 7 wedges of emissions reductions would be needed—for a total of 25 wedges.

That’s a lot of wedges and it means a lot of energy too. Hoffert estimates that maintaining global economic growth while keeping atmospheric CO2 concentrations below the magic 450 ppm number—which some environmentalists say is still too high—would require the production of approximately 30 terawatts of carbon-neutral power by 2050. (That’s terawatt as in “one trillion watts,” as in 826 times more energy than you’d need to send Marty McFly’s DeLorean back to 1985.) But we have yet to produce a single terawatt of carbon-free energy, and given the gridlock in the U.S. over climate and energy policy, I can’t say we’re moving in the right direction either, and neither does Hoffert:

Broad investment will be crucial to enabling such basic research findings to cross the “valley of death” and develop into applied commercial technologies. Carbon taxes (1) and ramped-up government research budgets (2) could help spur investments, but developing carbon-neutral technologies also requires, at the very least, reversing perverse incentives, such as existing global subsidies to fossil fuels that are estimated to be 12 times higher than those to renewable energy (18). We have to stop marching the wrong way before we can turn around.

Until we take on what the late Nobel Laureate Richard Smalley called the “terawatt challenge,” we’re just screwing around on climate change and energy. Taking the problem seriously would be a good first step.