Delta spent $137 million on carbon offsets in 2021 and promoted itself as the world's first carbon-neutral airline on in-flight napkins. By 2022 it had walked away from the claim. The voluntary carbon market has since contracted sharply, falling from $1.9 billion at its 2022 peak to $535 million in 2024, but 43% of credit retirements still came from low-rated projects. Here is what carbon offset integrity demands in practice.