By Carlyn Kranking
To control Earth’s mounting climate emissions, we really have our work cut out for us.
First, greenhouse gas emissions must be reduced to nearly zero by 2050 to prevent massive sea level rise, drought and heat waves. But that isn’t enough, since already-emitted carbon dioxide lingers in the atmosphere for millennia. To meet climate goals, this harmful gas must be removed from the air in a process called “negative emissions,” according to scientists at the virtual Comer Climate Conference this fall.
“There’s no scenario that keeps us under even 2 degrees [Celsius of warming] without negative emissions,” said physicist Raymond Pierrehumbert, a professor at the University of Oxford.
That is, no realistic scenario, he added.
“If you wave a magic wand” to erase CO2 emissions, that would prevent catastrophic warming, Pierrehumbert said in an email.
Though there’s no magic wand, the Earth does have a few defenses against changing climates. Some natural chemical reactions take carbon dioxide from the atmosphere and store it away. On their own, these methods take many thousands of years, but they would remove CO2 much more quickly if humans could accelerate them.
To succeed, though, the world must dramatically reduce emissions with green energy alternatives such as solar and wind. That way, the negative emissions techniques remove CO2 that’s already accumulated in the atmosphere.
Chemical reactions with rocks
If it weren’t for silicate weathering, Earth would be a hot, almost Venus-like hellscape. Carbon dioxide mixes with rain and causes the weathering, or breakdown, of rocks. This sets in motion chemical reactions that remove CO2 from the atmosphere and store it as minerals hidden away on the ocean floor.
This process has helped control Earth’s temperature throughout history.
“If it gets hotter, the silicate weathering goes faster, and it pulls CO2 out of the atmosphere. And if it cools down, silicate weathering slows down, so CO2 builds up,” said R.J. Graham, a doctoral student at the University of Oxford. “So it sort of acts as a thermostat for Earth’s climate.”
But now, human-forced climate change is warming Earth too quickly for it to be controlled by natural silicate weathering, which can take hundreds of thousands of years to work. To have a larger impact, Graham said we’d have to use enhanced weathering to speed up the process.
A silicate rock called olivine is particularly good for removing CO2 through weathering. If people mined olivine, broke it into tiny pieces to increase its surface area and distributed it on land or in the oceans, it would get weathered at high rates and remove lots of CO2.
“[This idea] hasn’t really had as much attention paid to it as I think it deserves,” Graham said.
Enhanced weathering has…