Forests have considerable potential to help mitigate human-caused climate change and provide society with many cobenefits. However, climate-driven risks may fundamentally compromise forest carbon sinks in the 21st century. Here, we synthesize the current understanding of climate-driven risks to forest stability from fire, drought, biotic agents, and other disturbances. We review how efforts to use forests as natural climate solutions presently consider and could more fully embrace current scientific knowledge to account for these climate-driven risks. Recent advances in vegetation physiology, disturbance ecology, mechanistic vegetation modeling, large-scale ecological observation networks, and remote sensing are improving current estimates and forecasts of the risks to forest stability. A more holistic understanding and quantification of such risks will help policy-makers and other stakeholders effectively use forests as natural climate solutions.

A systematic global stocktake of evidence on human adaptation to climate changeAssessing global progress on human adaptation to climate change is an urgent priority. Although the literature on adaptation to climate change is rapidly expanding, little is known about the actual extent of implementation. We systematically screened >48,000 articles using machine learning methods and a global network of 126 researchers. Our synthesis of the resulting 1,682 articles presents a systematic and comprehensive global stocktake of implemented human adaptation to climate change. Documented adaptations were largely fragmented, local and incremental, with limited evidence of transformational adaptation and negligible evidence of risk reduction outcomes. We identify eight priorities for global adaptation research: assess the effectiveness of adaptation responses, enhance the understanding of limits to adaptation, enable individuals and civil society to adapt, include missing places, scholars and scholarship, understand private sector responses, improve methods for synthesizing different forms of evidence, assess the adaptation at different temperature thresholds, and improve the inclusion of timescale and the dynamics of responses.

Decarbonizing the economy must remain a critical priority

Climate change mitigation policies can have significant co-benefits for air quality, including benefits to disadvantaged communities experiencing substantial air pollution. However, the effects of these mitigation policies have rarely been evaluated with respect to their influence on disadvantaged communities. Here we assess the air pollution and environmental justice implications of California's cap-and-trade mitigation program through analysis of (1) the sources of air pollution in disadvantaged communities, (2) emissions-reduction offset usage under the cap-and-trade program, and (3) the relationship between reductions in greenhouse gas emissions and reductions in co-pollutant emissions. Our analysis suggests that the cap-and-trade program has limited impacts, including limited disproportionate impacts, on air quality in disadvantaged communities. The sources of most air pollution in these communities have not been subject to the cap-and-trade program, and the use of emissions-reduction offsets is only marginally higher in disadvantaged communities than in other communities. Furthermore, reductions in greenhouse gas emissions imply smaller proportional reductions in co-pollutant emissions. While climate policies lead to important air quality co-benefits in some contexts, especially through reduced coal usage, targeted air quality policies and regulations may be more effective for reducing air pollution in disadvantaged communities in California and throughout the state.

Are forest offsets an effective way to address climate change, and do they provide other benefits? In some climate‐change mitigation policies, industries and individuals can purchase offsets that compensate for their greenhouse‐gas emissions by reducing emissions elsewhere. However, offsets may undermine mitigation efforts, by potentially giving carbon credits for emissions reductions that would have occurred even without the offset program in place. We evaluate California's forest offset program – the first‐ever legally enforceable “compliance” offset program for existing forests – to determine whether offsets (1) provide additional emissions reductions that would not have occurred without the program (called “additionality”) and (2) yield other benefits. We found that California's forest offset program, comprising a small portion of the state's mitigation portfolio, does not inhibit overall emissions reductions. Further, the program advances stringent “additionality” of emissions reductions through multiple mechanisms. Finally, mitigation through forest offsets can yield a suite of important co‐benefits. Lessons from California's experience with forest offsets can help to inform other offset programs that are increasingly being developed around the world.