Nitrogen and phosphorous limitations significantly reduce future allowable CO2 emissions

Allowable CO2 emissions are the emissions of CO2 allowed in order to follow a prescribed atmospheric CO2 concentration pathway. Allowable emissions depend on the uptake rates by the land and ocean and carbon-climate interaction. Few Earth System Models used for estimating allowable emissions include nitrogen limitation on land, and none include phosphorus. We provide the first estimate of how nitrogen and phosphorus limitations alter the allowable emissions between 2006 and 2100 for two representative concentration pathways (RCPs). We show that nutrient limitations on land have little influence on ocean carbon uptake but reduce the land carbon uptake and allowable emissions by 69 Pg C (21%) for RCP2.6 and by 250 Pg C (13%) for RCP8.5 by 2100, as compared with the emissions estimated using integrated assessment models. We therefore demonstrate the importance of nutrient limitations in estimating future CO2 emissions to achieve the climate change limits implied by RCPs.