Ratcheting of climate pledges needed to limit peak global warming

摘要

The new and updated emission reduction pledges submitted by countries ahead of the Twenty-Sixth Conference of Parties represent a meaningful strengthening of global ambition compared to the 2015 Paris pledges. Yet, limiting global warming below 1.5 degrees C this century will require countries to ratchet ambition for 2030 and beyond. Here, we explore a suite of emissions pathways to show that ratcheting near-term ambition through 2030 will be crucial to limiting peak temperature changes. Delaying ratcheting ambition to beyond 2030 could still deliver end-of-century temperature change of less than 1.5 degrees C but would result in higher temperature overshoot over many decades with the potential for adverse consequences. Ratcheting near-term ambition would also deliver benefits from enhanced non-CO2 mitigation and facilitate faster transitions to net-zero emissions systems in major economies. Many countries have submitted updated and new emissions reduction pledges in COP26, but further ratcheting of pledges is needed to reach the 1.5 degrees C goal. Ratcheting near-term ambition through 2030 could bring the largest climate benefits and avoid potential long-term temperature overshoot.