Short answers, pulled from the story.
The Intergovernmental Panel on Climate Change defined carbon dioxide removal in 2021 as anthropogenic activities that take CO2 from the atmosphere and store it durably. This definition excludes natural uptake not directly caused by human actions.
Direct air capture costs range from $94 to $600 per tonne while nature-based solutions remain under $50 per tonne. One direct air capture plant capturing one megaton of CO2 yearly requires land area equivalent to 46 million trees.
A private sector alliance led by Stripe announced a nearly $1 billion fund in April 2022 to reward permanent carbon capture companies. Senior employee Nan Ransohoff stated the fund was roughly 30 times larger than the 2021 market yet still 1,000 times short of 2050 needs.
Estimates suggest this method removes 0.1 to 1 gigatonnes of carbon dioxide annually at costs between $8 and $80 per tonne. Surface acidity may decrease during nutrient addition but sinking organic matter eventually increases deep ocean acidity.
Reliance on large-scale deployment of carbon dioxide removal was regarded in 2018 as a major risk to achieving less than 1.5 degrees Celsius warming. A 2019 NASEM report concluded arguments delaying mitigation because negative emission technologies provide backstops misrepresent current capacities.