[1] There were large interannual variations in burned area in the boreal region (ranging between 3.0 and 23.6 Â 10 6 ha yr À1) for the period of 1992 and 1995-2003 which resulted in corresponding variations in total carbon and carbon monoxide emissions. We estimated a range of carbon emissions based on different assumptions on the depth of burning because of uncertainties associated with the burning of surface-layer organic matter commonly found in boreal forest and peatlands, and average total carbon emissions were 106-209 Tg yr À1 and CO emissions were 33-77 Tg CO yr À1 . Burning of ground-layer organic matter contributed between 46 and 72% of all emissions in a given year. CO residuals calculated from surface mixing ratios in the high Northern Hemisphere (HNH) region were correlated to seasonal boreal fire emissions in 8 out of 10 years. On an interannual basis, variations in area burned explained 49% of the variations in HNH CO, while variations in boreal fire emissions explained 85%, supporting the hypotheses that variations in fuels and fire severity are important in estimating emissions. Average annual HNH CO increased by an average of 7.1 ppb yr À1 between 2000 and 2003 during a period when boreal fire emissions were 26 to 68 Tg CO À1 higher than during the early to mid-1990s, indicating that recent increases in boreal fires are influencing atmospheric CO in the Northern Hemisphere.

In an effort to increase conservation effectiveness through the use of Earth observation technologies, a group of remote sensing scientists affiliated with government and academic institutions and conservation organizations identified 10 questions in conservation for which the potential to be answered would be greatly increased by use of remotely sensed data and analyses of those data. Our goals were to increase conservation practitioners' use of remote sensing to support their work, increase collaboration between the conservation science and remote sensing communities, identify and develop new and innovative uses of remote sensing for advancing conservation science, provide guidance to space agencies on how future satellite missions can support conservation science, and generate support from the public and private sector in the use of remote sensing data to address the 10 conservation questions. We identified a broad initial list of questions on the basis of an email chain-referral survey. We then used a workshop-based iterative and collaborative approach to whittle the list down to these final questions (which represent 10 major themes in conservation): How can global Earth observation data be used to model species distributions and abundances? How can remote sensing improve the understanding of animal movements? How can remotely sensed ecosystem variables be used to understand, monitor, and predict ecosystem response and resilience to multiple stressors? How can remote sensing be used to monitor the effects of climate on ecosystems? How can near real-time ecosystem monitoring catalyze threat reduction, governance and regulation compliance, and resource management decisions? How can remote sensing inform configuration of protected area networks at spatial extents relevant to populations of target species and ecosystem services? How can remote sensing-derived products be used to value and monitor changes in ecosystem services? How can remote sensing be used to monitor and evaluate the effectiveness of conservation efforts? How does the expansion and intensification of agriculture and aquaculture alter ecosystems and the services they provide? How can remote sensing be used to determine the degree to which ecosystems are being disturbed or degraded and the effects of these changes on species and ecosystem functions?

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...

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We estimate and map the impacts that alternative national and subnational economic incentive structures for reducing emissions from deforestation (REDD+) in Indonesia would have had on greenhouse gas emissions and national and local revenue if they had been in place from 2000 to 2005. The impact of carbon payments on deforestation is calibrated econometrically from the pattern of observed deforestation and spatial variation in the benefits and costs of converting land to agriculture over that time period. We estimate that at an international carbon price of $10/ tCO 2 e, a "mandatory incentive structure," such as a cap-and-trade or symmetric tax-and-subsidy program, would have reduced emissions by 163-247 MtCO 2 e/y (20-31% below the without-REDD+ reference scenario), while generating a programmatic budget surplus. In contrast, a "basic voluntary incentive structure" modeled after a standard payment-for-environmental-services program would have reduced emissions nationally by only 45-76 MtCO 2 e/y (6-9%), while generating a programmatic budget shortfall. By making four policy improvements-paying for net emission reductions at the scale of an entire district rather than site-by-site; paying for reductions relative to reference levels that match business-as-usual levels; sharing a portion of district-level revenues with the national government; and sharing a portion of the national government's responsibility for costs with districts-an "improved voluntary incentive structure" would have been nearly as effective as a mandatory incentive structure, reducing emissions by 136-207 MtCO 2 e/y (17-26%) and generating a programmatic budget surplus.climate change | climate policy | land-use change | reducing emissions from deforestation and forest degradation A n emerging international climate policy mechanism called REDD+ would offer payments to developing countries that voluntarily reduce greenhouse gas emissions from deforestation below internationally agreed reference levels (1). Individual forested countries would decide upon the specific set of policies and measures to implement to achieve nationwide emission reductions. Accounting for these net emission reductions would ultimately take place at the national level, making national governments responsible for any internal geographical shifts of emissions (leakage), and providing incentives for systemic policy actions. However, although governments would receive payments under REDD+, it is actors at the regional, provincial, local, or household (subnational) scales who are directly responsible for many land-use change decisions. Thus, the effectiveness of REDD+ in reducing emissions and generating revenue will depend upon how national governments structure economic incentives so that subnational actors will be encouraged to reduce emissions and discouraged from increasing emissions.Emission-reduction policy in the energy and industrial sectors of developed countries has commonly been approached through mandatory, market-based incentive structures, such as cap-andtrade...