Horizontal blue bars indicate the warming potential of burning the remaining global reserves of various fossil-fuel types; the red bar shows what would happen if all were burned. The vertical red line indicates how much average temperatures have already risen as a result of human carbon emissions. (Creative Commons)
[Editor's note: Welcome to final day of this course, including here a quiz you can take to test your knowledge. Pass it and you can download a certificate affirming your graduation. You can find the previous seven installments of this course and catch up by going here.]
Part 8: The Math of Carbon
The CO2 we've let loose in the atmosphere is changing our climate, and everything that relies on it, from water to food to industry and wildlife. We can ignore the risks. We can panic. Or we can stop, collect ourselves, and do what our parents might have told us to do any other time we found that we had overextended ourselves. That is to say, we can make a budget.
The goal can't be to completely eliminate any and all climate change. It's too late for that, and in any event climate will change on its own. Rather, we need to stop turning fossil fuels into atmospheric CO2 as quickly as we can, to limit further climate forcing and keep the resulting changes to a pace that we and other species can hope to adapt to.
The forcing we're feeling now resulted from the approximately 500 billion tons -- 500 gigatons (GT) -- of carbon we have released into the atmosphere so far. There are roughly 5,000 GT of carbon left in proven fossil fuel resources around the planet. We're releasing about 10 GT of that into the air every year now, and our emissions are growing. If fossil fuel consumption continues to rise we could release another 1,000-2,000 GT over the next 90 years.
Most of the 5,000 remaining gigatons of carbon is in the form of coal. If we rapidly phase out coal-fired power plants for generating electricity (instead using solar, geothermal, biomass and wind power for example), we will limit our other carbon "spending" to at most 1,200 GT. That's still probably enough however to melt the near-surface permafrost and release its own 200-400 GT of susceptible carbon. The total amount of carbon released would therefore be closer to 1,400-1,600 GT.
That is the amount projected to turn nearly a third of our farmland into desert, extinguish most species, and destabilize the entire biosphere.
Thus, while phasing out coal is necessary to change our trajectory, it's not enough.
To cut our carbon further, we can abstain from developing so-called "unconventional" oil and gas, such as oil sands, shale oil and shale gas, instead running our vehicles on, say, a combination of biofuels and electric batteries. That would cut our emissions by another 700 GT and cap our future carbon spending at 500 GT -- roughly corresponding to the remaining "conventional" oil and gas resources.
That could be enough to avoid melting the tundra.
Of course, any more forcing of the climate -- even by under 500 additional gigatons of carbon -- will be damaging and dangerous. But by limiting ourselves to conventional oil and gas, and using as little of those as possible, we can avoid carbon concentrations expected to produce extreme global drought and mass extinction.
Doing that would also give us a chance to prevent the CO2 level from peaking (very far) above 450 ppm, and therefore also a reasonable hope of bringing it back below the ~350 ppm range one day, say within a century. That in turn could be enough to prevent ice sheets from disintegrating at both poles, and sea levels from rising beyond all our ability to influence.
That doesn't ask a really tough thing of us. We're talking here about how we produce electricity, heat buildings and power our machines, not whether we should do these things. Safer, carbon-free forms of energy exist and are being deployed on a large scale already -- just not yet on anything like the massive scale at which we're currently using fossil energy.