You need someone who doesn't know about Climate Change or doesn't exist in(side) time itself
So, one big problem with time traveling is the fact than causality can bite you in the balls, but you have some ways to do a work around it:
A) Send a traveler who doesn't know about Climate Change but travels with a mission give it by some otherworldy over-temporal entity who happend to exist beyond time.
So that way the traveler doesn't affect the events than lead him to be sended in the first time, because the entity who send him exist outside and over time.
B) Make him have an artifact than make him (the traveler) exist beyond time like in the X-men animated series, where time travelers use some bracelets than allow them to exist beyond the impact of time, allowing them to modify time without being afected for causality.
After you fix that problem, i would argue than:
Send a group of time independant traveler to make an intervention in the time before the napoleonic wars
You see, before the napoleonic wars, there was france and england having capitalistic economics reforms than opose to the agrarian concept of richness very common in nation back in the day.
This reforms actualy help to make both nations industrial (or pre-industrial if you want) change them shift to investing resources in production as a way to generate more wealth.
So, what you need is actualy reeplace both economical characters by time travelers, being themselfs second hand of the arguibly most powerfull "kings" on earth in that time they will propose somewhat different economical policys than make a turn for the enviroment, without anyone ever knew them.
If the changes are right, then, the napoleonic wars can happend as it should, but your agents probably already make the change in the timeline just enough to make sure than the oil and coal industry never see his zenith. because you gave that zenith to another, cleaner industry before.
Like, i don't know, send your travelers with vastly electric independant railroads or send very efficient solar panels together with very powerfull Electric engines to reeplace the steam machines much earlier than the moment they become the stars of the movie, and make your main characters make investment policies and recomendation than clearly benefit that tecnologys instead of the steam and coal tecnologys developed back then.
To prevent a technological causality problem just make sure than research is still done about this steam engines, but doesn't give them any chance of being used in industrial production, maybie make them work in ships or some other masive transportation method, than because of massivity is not so frecuent like a car or a train.