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Avoiding catastrophic climate change requires rapid decarbonization and improved ecosystem stewardship. To achieve the latter, ecosystems should be prioritized by responsiveness to direct, localized action and the magnitude and recoverability of their carbon stores. Here we show that a range of ecosystems contain 'irrecoverable carbon' that is vulnerable to release upon land use conversion and, once lost, is not recoverable on timescales relevant to avoiding dangerous climate impacts. Globally, ecosystems highly affected by human land-use decisions contain at least 260 gigatonnes of irrecoverable carbon, with particularly high densities in peatlands, mangroves, old-growth forests and marshes. To achieve climate goals, we must safeguard these irrecoverable carbon pools through an expanded set of policy and finance strategies. Main TextScientific assessments provide increasingly strong evidence that global warming in excess of 1.5 ˚C above pre-industrial levels may trigger irreversible changes to the Earth system, with far-reaching social and economic costs for human societies around the world 1 . Limiting warming to 1.5 ˚C, according to the Intergovernmental Panel on Climate Change (IPCC), requires the world to slow global emissions immediately and reach net zero carbon dioxide (CO 2 ) emissions by around 2050.To do this, the IPCC estimates that our remaining carbon budget as of 2017, or the amount of CO 2 we can add to the atmosphere between now and mid-century, is about 420 gigatonnes (Gt), equal to about 114 Gt of carbon, for a two-thirds chance of staying below 1.5 ˚C1 . Given emissions have not slowed since 2017, as of 2020, this carbon budget will be spent in approximately eight years at current emissions rates 2 . Staying within this carbon budget will require a rapid phase-out of fossil fuels in all sectors as well as maintaining and enhancing carbon stocks in natural ecosystems, all pursued urgently and in parallel 3-6 . Natural climate solutions, which promote conservation, restoration, and improved land management to increase carbon sequestration or reduce emissions from ecosystems and agricultural lands, could provide a quarter or more of the cost-effective mitigation (i.e. ≤USD100 / t CO 2 e) needed by 2030 [7][8][9] .These natural climate solutions focus on either turning down the 'dial' of emissions, for example by preventing the conversion of ecosystems to other land-uses, or turning up the dial on ecosystems' ability to remove CO 2 from the atmosphere via restoration or enhanced productivity. Yet uncertainty remains regarding the responsiveness of various ecosystem carbon stocks to management actions and regarding the relative reversibility of their loss. Are there ecosystem carbon stocks that, if lost, could not recover within a time scale meaningful to the remaining carbon budget? Any loss of such 'irrecoverable' carbon stocks would represent an effectively permanent debit from our remaining carbon budget. Ecosystems containing irrecoverable carbon may thus warrant distinct and unwavering conser...

Avoiding catastrophic climate change requires rapid decarbonization and improved ecosystem stewardship at a planetary scale. The carbon released through the burning of fossil fuels would take millennia to regenerate on Earth. Though the timeframe of carbon recovery for ecosystems such as peatlands, mangroves and old-growth forests is shorter (centuries), this timeframe still exceeds the time we have remaining to avoid the worst impacts of global warming. There are some natural places that we cannot afford to lose due to their irreplaceable carbon reserves. Here we map ‘irrecoverable carbon’ globally to identify ecosystem carbon that remains within human purview to manage and, if lost, could not be recovered by mid-century, by when we need to reach net-zero emissions to avoid the worst climate impacts. Since 2010, agriculture, logging and wildfire have caused emissions of at least 4.0 Gt of irrecoverable carbon. The world’s remaining 139.1 ± 443.6 Gt of irrecoverable carbon faces risks from land-use conversion and climate change. These risks can be reduced through proactive protection and adaptive management. Currently, 23.0% of irrecoverable carbon is within protected areas and 33.6% is managed by Indigenous peoples and local communities. Half of Earth’s irrecoverable carbon is concentrated on just 3.3% of its land, highlighting opportunities for targeted efforts to increase global climate security.

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While we don’t tend to think about it, healthy ecosystems provide a variety of critical benefits. Ecosystem goods, the physical items an ecosystem provides, are obvious. Forests provide timber; coastal marshes provide shellfish. While less visible and generally taken for granted, the services underpinning these goods are equally important. Created by the interactions of living organisms with their environment, ecosystem services provide the conditions and processes that sustain human life.1 If you doubt this, consider how to grow an apple without pollination, pest control, or soil fertility. Once one realizes the importance of ecosystem services, three points quickly emerge: (1) landscapes provide a stream of services ranging from water quality and flood control to climate stability—the economic value of which can be significant; (2) the vast majority of these services are public goods and not exchanged in markets, so landowners have little incentive to provide these positive externalities; and (3) we, therefore, need to think creatively about creating markets for these services so they are not under-provided. This is the basis of the policy approach known as Payments for Ecosystem Services (“PES”).