I think the main downside is that we are quite sure what would happen. The primary effect (a giant fucking algae bloom) is pretty well known. But the secondary effects are hard to predict and could be very negative.
Running experiments on the planet we live on is usually frowned upon.
> Running experiments on the planet we live on is usually frowned upon.
We are in a big fucking experiment right now: what happens if we release fucktons of CO2 into the atmosphere? Most of the developed world doesn't give a fuck.
Purely anacdotal of course, but most of the really bad incidents I've been involved in with production systems were actually caused by a rushed response to an initial problem that seemed serious at the time....
Nobody is pushing for a rushed response. Just some fucking common sense, and scientifically literate people. And nobody can cry 'rushed response' anyway because the effects have been known (more or less accurately) for dozens of years.
If a sufficiently large mass of people can be convinced of something that's where everyone is going. So the result is that if a small group of people want to get somewhere all they have to do is convince a larger group. Sounds difficult but with today's tech and money concentration it's not hard to convince someone that "more CO2 is better".[0]
Regular people can't draw their own conclusions based on self study and own research. Scientifically literate is not enough when you rely on someone else's data and conclusions. So the only way is to present some evidence (plausible stuff) and the conclusion in a loud enough and convincing fashion. What you end up with is a great number of people who are genuinely convinced that global warming is a farce. They have scientists on their side so who are they to argue?
Most of the world signed the Paris Agreement. The majority of the developed world thinks man-made climate change is real and is a threat. Conflicting priorities and systems of government that are set up for short term decisions make progress much slower than it should be, but saying that we don't care is very unfair to most of the developed world.
Indeed, and you don't need to start with a half-tanker, especially if you are not aiming for an ice age. You can start with a half-bucket and work your way up to a half-kayak, half-fishing-boat, maybe half-trawler.
Oh, wait. Some guy did just that in 2012 [1]. Some people claim it was an absolute success, while some others claim that more studies are needed (but they are not willing to fund them!), or we should not play with the only planet we have, etc, etc.
I know settling to the sea floor is the intended result, but locking up more carbon in the steady state biomass of creatures would do the trick too. If we did this continuously could we just grow the biosphere?