Following the Trump Administration’s withdrawal from the Paris Agreement, cities, states and regions will increasingly need to lead on climate. The nine states participating in the Regional Greenhouse Gas Initiative (RGGI) have demonstrated a will to forge ahead in the absence of federal action in the past, and their leadership will make a substantial impact on the global fight against climate change; together, these states have a GDP of $2.8 trillion, representing the world’s 6th largest economy. Fortunately, the list of states taking action on climate is growing.