Abstract
The Paris Agreement's ratchet mechanism asks each successive Nationally Determined Contribution to represent a progression beyond its predecessor, with Article 4.3 leaving the metric, baseline, and accounting conventions for assessing progression at the discretion of each Party. This Perspective shows that this architectural latitude permits substantive regression of the absolute emissions constraint across consecutive NDCs, exercised through distinct mechanisms in major Parties to the Agreement. India's 2035 NDC raises each of its three quantitative targets above the 2030 NDC and satisfies the textual progression requirement. Under matched GDP-growth assumptions across 5-8% CAGR, however, the marginal 2030-2035 period permits faster annual absolute emissions growth than the 2030 NDC's 2020-2030 operative period, and India's required pace of intensity decline drops to half the rate the previous NDC required.Two related forms of the same latitude appear in the 2035 NDCs of China and the European Union, exercised respectively through target-reference calibration and accounting-boundary choices. The architecture as currently assessed cannot distinguish these exercises from genuine progression. The Global Stocktake's technical assessment phase will need to develop cross-vintage absolute-emissions diagnostics across Parties if the ratchet is to function as its design assumes.