Complex sentence: Palin agreed that he had been busy "polluting this environment on almost every conceivable form of carbon-emitting vehicle" but he claimed that his adventures reduced overall greenhouse gas emissions by encouraging people to remain on their sofas.
Split into simpler sentences: Palin agreed that he had been busy "polluting this environment on almost every conceivable form of carbon-emitting vehicle". He also commented that his adventures reduced overall greenhouse gas emissions by encouraging people to remain on their sofas.