Pretty clueless. CO2 isn't the problem, cheap energy is problem.
Do I need to explain how we could get to the point of harvesting solar energy from space again?
Will my idea end up costing billions of dollars- nope, trillions at least. But these the trillions aren't govermental costs, they are investment dollars which are getting a return on money spent.
Govt costs are less than 1 billion dollars [with no profits, simply spent money]. Oh it depends on how you are counting these costs (do you count the cost of a lunar program to find water into these costs, etc). But the program to get "things going" would cost about 1/2 billion dollars. Then other projects related to it could add up to a fair amount govt change, including a Manned Mars program it could be getting up there, like 50 billion or so. Anyhow, the first part, is what I call Water in Orbit. The govt buys water test payloads. This will lower launch costs.
And maybe get enough water into orbit so, this water is worth "mining". Mining the water, would have another governmental cost (certainly less than another 1/2 billion).
So as far as starting a Water in Orbit, the govt could start with 50 million budget for it. The govt offers to pay $500 per lb of water payload delivered to an orbit which will decay and re-enter in a time frame of 3-10 years. $750 for orbits which will last 11 or more years. $1000 for orbits which are beyond 10,000 miles from Earth and will also not de-orbit in less than 10 years.
Additional any water converted into LH&LOX will recieve an additional bonuses: The party launching the water test payload will receive an additional $250 per lb if water payload was orginally paid $500 (3-10 year time frame), so total payment will equal the amount given for +11 year orbit. Plus regardless of which orbit the test water payload is in it receives additional $500 per lb of water converted into LH&LOX. This $500 per lb is based on amount of water which is launched, not on how much is evenually converted into LH&LOX. The launch company would get some certified document attesting to the quanitity of the in the water payload and the mass of total payload- the inital payment (whether it's 500, 750, or 1000 dollar per lb) is based on total payload mass which is placed in orbit- wouldn't include propellent used to get to orbit (dry mass:).
Far as govt cost, lets assume 100 tons of water payload is deliver orbit higher than 10k: $200 million & this is used to make fuel: slightly less than 100 million- total cost 300 million. Or if 100 tons is delivered to LEO: $150 million plus the 100 million- total cost 250 million.
There are of course other details but generally speaking the govt should pay about 200 tons of water, this cost less than 1/2 billion. Using the water would be another aspect of it: if some party uses the water this would the same as govt buying one or more gas station for less the 1/2 billion dollars.
As I was saying you could start program for 50 million (say the year 2003), when first payload(s) is delivered- say 20 tons to LEO (3-10 years) then 20 million could be taken from 50 million and at this point congress could put more funds into program- fully fund or say another 100 million for next year or two. There is probably little risk of the water payloads exceeding the 50 million in first year, and congress could get feedback on how much future "demand" there is for paying for water payloads. And of course if no one wants to get paid for water test payloads then the govt isn't "losing" any money.

Assuming a gas station is built, it will need a fairly large quanitity of power to convert water into rocket fuel- very roughly, about 20 kw/h solar panel will make about 20 tons of rocket fuel- so 5 years to convert a 100 ton of water, or more power for short period of time. Within a few years it's possible that there would be a gas station converting 100 tons of water per year and within decade perhaps 1000 tons per year are being converted in space.

How does it start? Well, lets take Exxon Mobil, how much is it worth to this company to be associated with first gas station in orbit. Or how about a more major role such as owning it. Or said slightly differently how much is it worth not to be second or third behind some other oil companies. How much do they spend on their silly ads- aren't news stories about Exxon Mobil gas station in orbit worth more than several years worth of ads- even superbowl ads.
Would it be reasonable to assume that Exxon Mobil and/or other companies be able to put in 100 million or so- ownership, media/logo, or whatever kinds possible relationships. Now if 100 tons of water is converted into rocket fuel, you have another 100 million of money being paid by govt. Now, suppose you could manage to make a small gas station- makes 20 tons per year- which costs 200 million, and could sell the rocket fuel to cover operational cost and making a profit. With one gas station operating you get a small market in orbit for rocket fuel, if it works then, others might be will to somehow get involved (build another gas station, or use rocket fuel for something, or maybe put a small hotel near gas station, or lots of things which could be completely unrelated except that it involves creating other markets in space.