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Comment by jeffbee | Hacker News Reader

Taking only 3% of California's cars off the road seems way easier.

It is, but consider the future. We need net negative emissions to stabilize the climate because we didn't decarbonize early/fast enough to achieve this goal with emissions cuts alone. The vast majority of climate progress must come from energy system decarbonization, but active carbon dioxide removal approaches like this one will be necessary to draw down the excess atmospheric CO2 accumulated so far.

"IPCC Report: Carbon Removal is Now Required to Meet Climate Mitigation Targets"

https://www.carbon-direct.com/insights/ipcc-report-carbon-re...

Also see this IPCC fact sheet about carbon dioxide removal, which includes enhanced rock weathering (the technique under discussion here):

https://www.ipcc.ch/report/ar6/wg3/downloads/outreach/IPCC_A...

Without human actives the earth is slightly net negative. We need to be more net negative than that in the short term to fix some problems (ice melt), but we don't need that forever.

> Without human actives the earth is slightly net negative

Source? AFAIK greenhouse warming has the capacity to be a runaway effect. It's not immediately obvious that if you remove all current human carbon emissions, that temperatures would level off & start declining vs continue increasing because of the feedback loop.

The Earth slowly depletes excess atmospheric CO2 due to the geological carbon cycle of silicate weathering. This is the slow, natural counterpart of the accelerated silicate weathering discussed above. It is too slow to reverse global warming on human time scales, but it means that if anthropogenic emissions ceased Earth would reach its peak temperature in less than a thousand years (ice melting and other reactions to this change would go on for several thousands of years) and gradually decline back to the pre-industrial atmospheric CO2 and climate within about 100,000 years.

My source for this recollection is David Archer's 2009 book The Long Thaw: How Humans Are Changing the Next 100,000 Years of Earth's Climate.

Humans are currently on track for around 4 degrees of warming by 2100 assuming we hit all our current emission reduction targets (i.e. reaching net zero when governments have said they would). So removals are quite necessary.

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