Abstract
Most proposals for mitigating climate change assume that economic demand should grow without constraints so depend primarily on technology innovations to substitute today's activities with emissions-free alternatives. However, the potential for such "invisible technology substitutions", which could allow high-resource lifestyles to continue unchanged, is often overstated and disguised by burden-shifting. For example, plans may depend on synthetic fuels without accounting for its supply, or on negative emissions technologies without accounting for their power or land area requirements. Here, we show that all net-zero plans depend fundamentally on three resources: emissions-free electricity, biomass, and carbon storage. Using a comprehensive calculator, we reveal the high risk of shortages of these fundamental resources by comparing aggregated demands of net-zero plans, published by business, government, and industry bodies, against likely global availability in 2050. The calculator builds on physical models of 170 processes derived from an extensive literature search. Our results demonstrate that most climate policy proposals, which depend primarily on "invisible technology substitutions", require an improbable expansion of the fundamental resources in the time available, indicating significant risks of under-delivery. We demonstrate an alternative mitigation plan built on a credible forecast of resource availability, revealing overlooked opportunities for innovations in policy, service supply, and financing: feasible zero-emission futures necessitate end-user participation and changed economic demand, which are largely disregarded in current international policy discussions.