Back to the OP. I'm more interested in what expeditions can or should be doing to counter act carbon emissions that contribute to climate change. I get the 'we're all doomed' and it 'won't make a difference' or 'I don't believe in it' argument, but I'd rather hear some constructive ideas please. There have been quite a few and this discussion has given me some good ideas, thank you. Whether we like it or not, expeditions do need to think about this especially if they are applying for grants, etc.
Most of the ones I can think of substitute spending more time, or less distance getting there for the emissions from airliners.
So, explore closer to home, mainland Europe for UK people. Still a lot of cave to find. Reach it by road, train etc. The Matienzo exploration of the last 60 years is an excellent example. Reachable via a long drive across France and N Spain, or a ferry across the Bay of Biscay.
Relocate to the country where you plan to explore. A big upheaval to life, but some people do it. I know folk in China who went out and haven't come back. Also means they can help build the local caving scene to lead the exploration.
Travel slow to a destination a long way away. A literal slow boat to China, if China is your destination. This has been done for other places in the past. Overland travel to the Ghar Parau expeditions in Iran and the British expedition to
Ethiopia in the early 1970's. Both before air travel plummeted in price and there were sufficient numbers of cavers able to dedicate months on end to an expedition.
The combination that is going to be tricky, if reducing CO2 is a priority is attending an expedition a long way off for a relatively short time, weeks, not months. Flying is the only way to make mixture work. The demands of work, or other commitments in the UK that limit time away will mean choices need to be made, or future heavy green taxes on air travel make the choice for you. Cheap long haul air travel has only been around for a few decades. Probably a blip in the longer term.