SustainAbility advocates that to avoid many of the worst consequences of climate change, the increase in global average surface temperature must remain below 2°C compared with the pre-industrial era. Measures to reduce greenhouse gas emissions commensurate with this overarching ambition must be guided by the best available science. Here we explain why we continue to advocate the 2°C threshold for avoiding dangerous climate change, why we haven’t embraced a “ppm” target, and what 2°C means for policy makers and the business community.