What is the most difficult change humans will have to make to combat climate change?
Getting rid of gasoline-powered cars.
Probably the most difficult change for people to make to reduce greenhouse gas emissions would be switching to cars powered by alternative fuels, such as electric, hydrogen, natural gas, or nuclear. All of the above would be alternative fuel forms that produce little to no greenhouse gas emissions. Hydrogen cars, for example, emit only water vapor as exhaust.
The reason such a change would be difficult is because of infrastructure. There aren't really hydrogen, natural gas, or nuclear refilling stations, so it'd be rather inconvenient for people to have these types of cars but to have no way to refill them. Electric charging stations are becoming more popular, though. Once the infrastructure to support alternative fuel cars is developed, people would readily switch over.