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A 35-year transition from fossil to renewable fuels may be possible¹, but fossil fuel emissions continue to rise. The world's largest emitter, China, is not committing to peak carbon emissions until 2030, and among developed countries, very few are aiming to end fossil fuel use by 2050. Thus, it is unlikely that fossil fuel emissions will fall in the next decade, or that they will fall by more than 80% by 2050. More likely, emissions from fossil fuels from 2015 to 2050 will exceed 250 Pg C, resulting in cumulative carbon emissions of over 400 Pg C between 2000 and 2050, and a greater-than-50% chance of exceeding a global warming of 2 °C (ref. 2). So are we already committed to a warming of 2 °C or greater? Not necessarily — absorption of carbon by tropical forests could offset much of the release of fossil fuel carbon between now and 2050, thus stabilizing and then reducing the CO₂ concentration in the atmosphere within just a few decades, and providing a bridge to a fossil-fuel-free world.

Absorption of carbon by tropical forest management is not the solution to climate change. It may be part of the solution³, but the potential for accumulating carbon in the world's forests and soils is small relative to the amount of carbon in coal, oil and gas reserves⁴. For example, the total loss of carbon from land as a result of human activity over the past centuries has been 200–300 Pg C (ref. 5), and even if all of this loss were to be recovered through reforestation, the uptake of carbon would be far from sufficient to offset unabated long-term use of fossil fuels. Further, the current net emissions of carbon from tropical deforestation and degradation account for as little as 8–15% of total annual carbon emissions, and that percentage has declined as fossil fuel use has continued to increase^{6, 7, 8}.

The conclusion that forest conservation and restoration is largely irrelevant for mitigation is incorrect, however, for two reasons. First, the relatively small net emissions of carbon from forest management hide a greater potential for carbon storage. Gross emissions from forest management are two to three times greater than net emissions⁹, suggesting that enhancing carbon uptake and reducing emissions could account for as much as 50% of total carbon emissions. Second, changes in land management can be implemented more quickly than the transition from fossil to renewable fuels.

To achieve a 75% likelihood of avoiding warming in excess of 2 °C through changes in fossil fuel emissions alone, such emissions would have to be eliminated over the next 20 years or less (Fig. 1). In contrast, the same likelihood could be achieved if, first, tropical forest management removed 5 Pg C yr⁻¹ from the atmosphere, phased in linearly over the next 10 years, and, second, fossil fuel emissions were held constant for the next 10 years and then reduced linearly to a level equal to 20% of 2014 emissions by 2050 before further linear reduction to zero by 2100. In this latter case, the cumulative reduction in net emissions over the next 50 years from fossil fuel use versus from forest management would be roughly equal.

Annual emissions of carbon from fossil fuels (solid grey line) and tropical forest management (solid green line), and total carbon emissions (solid black line), are plotted for 1850–2015. From 2015, the total emissions that are required for a 75% likelihood of avoiding warming in excess of 2 °C (dashed black line) are shown. The dashed grey line represents the fossil fuel emissions if this likelihood is achieved by fossil fuel changes alone. The orange line represents the emissions from fossil fuels if simultaneous changes in forest management are implemented (dashed green line). The hatched area represents the effect of tropical forest management on carbon emissions mitigation. Negative emissions represent the removal of carbon from the atmosphere.

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