Author: Andrea Germanos| Published: July 19, 2017
Hansen is lead author of a new study that warns that there “is no time to delay” on climate change efforts and argues that they must go beyond just slashing emissions of CO2—”the dominant control knob on global temperature”—to extracting CO2 from the air, or “negative emissions.”
The team of international researchers writes that “the world has overshot appropriate targets”—a conclusion that “is sufficiently grim to compel us to point out that pathways to rapid emission reductions are feasible.”
The goal, they write, should be getting atmospheric CO2 reduced to less than 350 parts per million (ppm), as that would lead to global average temperatures decreasing to about 1 degree Celsius of warming relative to pre-industrial levels later this century. The Paris climate accord, in contrast, has a goal of keeping global average temperature increase to under 2 degrees Celsius, and an aspiration 1.5 degrees of warming. But, they argue, the problem with those
targets is that they are far above the Holocene [the epoch that began after the last Ice Age] temperature range. If such temperature levels are allowed to long exist they will spur “slow” amplifying feed-backs, which have potential to run out of humanity’s control. The most threatening slow feedback likely is ice sheet melt and consequent significant sea level rise, as occurred in the Eemian [the prior interglacial period], but there are other risks in pushing the climate system far out of its Holocene range.
For a safer scenario that limits irreversible climate impacts, what needs to happen is a “rapid phase-down of fossil fuel emissions,” bringing the rate of emissions right away to 6 percent a year, alongside reforestation and agricultural practices that draw carbon from the atmosphere into the soil.
On the other hand, if CO2 emissions grow at a rate of 2 percent a year—that’s a slower rate than the 2.6 percent they grew each year from 2000 to 2015—it could result in a costly scenario. It could rack up a CO2 extraction bill of $535 trillion by 2100—an “extraordinary cost” that “suggest[s] that, rather than the world being able to buy its way out of climate change, continued high emissions would likely force humanity to live with climate change running out of control with all the consequences that would entail,” the researchers write.
Also, technological CO2 extraction methods have “large risks and uncertain feasibility,” they point out.