Typically, climate scientists run big, complicated models about the most economically optimal ways to decarbonize. “That envisions this very technocratic, manicured, highly granular transition,” Hanna says, “which doesn't really reflect the way transitions actually occur in reality.” So Hanna and his colleagues sketched out an alternate vision: Imagine what would happen if humanity invested in DAC like we’d invest in another world war.The researchers broke their modeling into three parts. The first was an estimate of how much governments would need to pay for DAC plants. This would include appropriating crisis-level funding to pay private firms to build the facilities, and to pay the companies for storing the carbon they’d be capturing. The second piece of the modeling looked at how fast the plant rollout could scale using already-existing energy supplies like hydropower. (You wouldn’t want to use fossil fuels to run them, obviously.) And the last part was a climate model, representing the entire Earth system, including oceans and the atmosphere. This showed how global temperatures would change if a mass deployment of DAC facilities turned down the amount of CO2 hanging around in the atmosphere.
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The researchers found that with an annual investment of between 1 and 2 percent of the global gross domestic product, humanity could scale up a DAC network to remove around 2.3 gigatons of CO2 annually by the year 2050. (For perspective, total global emissions are currently around 40 gigatons a year.)That’s about 400 times the amount of CO2 humanity currently sequesters, so we’re talking about a massive scale-up. Still, “relative to what the integrated assessment models tell us we should do by 2050, it's actually quite small,” says Hanna. We need to remove something like 5 to 9 gigatons of CO2 per year by 2050 to meet the Paris agreement’s 1.5 degrees C goal. “What that tells us is that we need more than just a single means of negative emissions,” Hanna adds. For instance, we could also bolster wetlands and plant trees to naturally sequester carbon.