One type of CO₂ system I've heard of is as an expendable refrigerant for air-conditioning golf carts. Bottled CO₂ is evaporated through a coil on the cart; the condensing part of the cycle is done centrally elsewhere, via a Linde column I suspect. Although this releases CO₂ into the air, the CO₂ is then pulled back out for reuse; so the balance is zero. The bottles can be thought of as temporary sequestration.

Thanks for the comment,

This is the first time I've heard of CO2 being used this way ( not to mention air conditioned golf carts! ). I did some light searching and I couldn't find any mention of this on the internet, although I did learn that air conditioning in golf carts is really new. Do you know what company is working on this, or where?

I'm also wondering where CO2 is most applicable, and what properties of CO2 make it advantageous or disadvantageous in different applications. For instance, why was CO2 chosen as the refrigerant for air conditioned golf carts?

Some years after I left, Seattle Refrigeration and Mfg. Co. began producing these golf cart systems. Other than hearing about them, I am not familiar with details. It seems like an interesting niche market, though.

Dry ice production is another active, but relatively unheralded, area for CO₂ (R-744).