Coronavirus disease (COVID-19) has disrupted health, economy, and society globally. Thus, many countries, including China, have adopted lockdowns to prevent the epidemic, which has limited human activities while affecting air quality. These affects have received attention from academics, but very few studies have focused on western China, with a lack of comparative studies across lockdown periods. Accordingly, this study examines the effects of lockdowns on air quality and pollution, using the hourly and daily air monitoring data collected from Lanzhou, a large city in Northwest China. The results indicate an overall improvement in air quality during the three lockdowns compared to the average air quality in the recent years, as well as reduced PM2.5, PM10, SO2, NO2, and CO concentrations with different rates and increased O3 concentration. During lockdowns, Lanzhou's morning peak of air pollution was alleviated, while the spatial characteristics remained unchanged. Further, ordered multi-classification logistic regression models to explore the mechanisms by which socioeconomic backgrounds and epidemic circumstances influence air quality revealed that the increment in population density significantly aggravated air pollution, while the presence of new cases in Lanzhou, and medium- and high-risk areas in the given district or county both increase the likelihood of air quality improvement in different degrees. These findings contribute to the understanding of the impact of lockdown on air quality, and propose policy suggestions to control air pollution and achieve green development in the post-epidemic era.

Society could sustain the impact of climate change by adapting to the change and mitigating risks from adverse effects of increasing changes, so that it can continue maintaining its prospect and improving wellbeing. Nevertheless, climate change is more or less affecting society's functions at different scales, including both individuals and communities. In this review, we discuss the relationship between society and climate change in China from the aspects of the needs at different socioeconomic developing stages. The relationship as well as the current spatial pattern and future risks of the climate change impacts on societies are summarized. The complexity of social and climatic systems leads to the spatial heterogeneity of climate impacts and risks in China. To more effectively leverage increasing knowledge about the past, we advocate greater cross-disciplinary collaboration between climate adaption, poverty alleviation and Nature-based Solutions (Nbs). That could provide decision makers with more comprehensive train of thoughts for climate policy making.

Facing severe air pollution issues, China has implemented a series of clean air policies aimed to improve the country's air quality. These policies largely focused on reducing emissions of major air pollutants such as sulfur dioxide (SO2) and primary aerosols. However, changes in such pollution also affect radiative forcing. To understand the climate consequences of these clean air actions in China, we evaluate the near-equilibrium climate response to sustained changes in aerosol (and precursors) emission rates equivalent to those that occurred in China between 2006 and 2017. During this period, China's SO(2)emissions declined by similar to 70%, and black carbon emissions declined by similar to 30%. Climate simulations that used a fully coupled ocean and atmosphere climate model indicate that China's reductions in aerosol emission rates from 2006 to 2017 may exert a net increase in global radiative forcing of 0.09 +/- 0.03 W m(-2)and a mean warming of 0.12 +/- 0.01 degrees C in the Northern Hemisphere; and may also affect the precipitation rates in East Asia and in more distant regions. The success of Chinese policies to further reduce aerosol emissions may bring additional net warming, and this 'unmasked' warming would in turn compound the challenge and urgency of international climate mitigation efforts.

Part 1 of this review synthesizes recent research on status and climate vulnerability of freshwater and saltwater wetlands, and their contribution to addressing climate change (carbon cycle, adaptation, resilience). Peatlands and vegetated coastal wetlands are among the most carbon rich sinks on the planet sequestering approximately as much carbon as do global forest ecosystems. Estimates of the consequences of rising temperature on current wetland carbon storage and future carbon sequestration potential are summarized. We also demonstrate the need to prevent drying of wetlands and thawing of permafrost by disturbances and rising temperatures to protect wetland carbon stores and climate adaptation/resiliency ecosystem services. Preventing further wetland loss is found to be important in limiting future emissions to meet climate goals, but is seldom considered. In Part 2, the paper explores the policy and management realm from international to national, subnational and local levels to identify strategies and policies reflecting an integrated understanding of both wetland and climate change science. Specific recommendations are made to capture synergies between wetlands and carbon cycle management, adaptation and resiliency to further enable researchers, policy makers and practitioners to protect wetland carbon and climate adaptation/resiliency ecosystem services.

Climate change will alter ecosystem metabolism and may lead to a redistribution of vegetation and changes in fire regimes in Northern Eurasia over the 21st century. Land management decisions will interact with these climate-driven changes to reshape the region's landscape. Here we present an assessment of the potential consequences of climate change on land use and associated land carbon sink activity for Northern Eurasia in the context of climate-induced vegetation shifts. Under a `business-as-usual' scenario, climate-induced vegetation shifts allow expansion of areas devoted to food crop production (15%) and pastures (39%) over the 21st century. Under a climate stabilization scenario, climate-induced vegetation shifts permit expansion of areas devoted to cellulosic biofuel production (25%) and pastures (21%), but reduce the expansion of areas devoted to food crop production by 10%. In both climate scenarios, vegetation shifts further reduce the areas devoted to timber production by 6-8% over this same time period. Fire associated with climate-induced vegetation shifts causes the region to become more of a carbon source than if no vegetation shifts occur. Consideration of the interactions between climate-induced vegetation shifts and human activities through a modeling framework has provided clues to how humans may be able to adapt to a changing world and identified the trade-offs, including unintended consequences, associated with proposed climate/energy policies.

Although carbon dioxide emissions are by far the most important mediator of anthropogenic climate disruption, a number of shorter-lived substances with atmospheric lifetimes of under a few decades also contribute significantly to the radiative forcing that drives climate change. In recent years, the argument that early and aggressive mitigation of the emission of these substances or their precursors forms an essential part of any climate protection strategy has gained a considerable following. There is often an implication that such control can in some way make up for the current inaction on carbon dioxide emissions. The prime targets for mitigation, known collectively as short-lived climate pollution (SLCP), are methane, hydrofluorocarbons, black carbon, and ozone. A re-examination of the issues shows that the benefits of early SLCP mitigation have been greatly exaggerated, largely because of inadequacies in the methodologies used to compare the climate effects of short-lived substances with those of CO2, which causes nearly irreversible climate change persisting millennia after emissions cease. Eventual mitigation of SLCP can make a useful contribution to climate protection, but there is little to be gained by implementing SLCP mitigation before stringent carbon dioxide controls are in place and have caused annual emissions to approach zero. Any earlier implementation of SLCP mitigation that substitutes to any significant extent for carbon dioxide mitigation will lead to a climate irreversibly warmer than will a strategy with delayed SLCP mitigation. SLCP mitigation does not buy time for implementation of stringent controls on CO2 emissions.

The development of potential metrics for comparing black carbon (BC) to carbon dioxide has been requested within legislation in the United States and has been discussed at the United Nations Framework Convention on Climate Change Conference of the Parties in Poznan: therefore, it is important to further investigate the advantages and drawbacks to using such a metric. For context, we summarize the various proposed CO2 equivalent metrics and the rationales for developing them. We use BC marginal abatement curves to examine the implications of using 100-year global warming potentials to include BC in greenhouse gas (GHG) trading regimes. This idealized study demonstrates the impacts on emissions of CO2, and radiative forcing over time. Finally, we address the drawbacks of trading poorly quantified short-lived emissions with GHGs despite different physical interactions with the climate system. While the case for reducing BC for both health and climate benefits is compelling, there are reasons for limiting the use of BC metrics to illustrative analyses, such as identifying which BC mitigation actions would provide the greatest climate benefits, rather than using these metrics for trading with GHGs. Indeed, market-based mechanisms in general may not be appropriate for BC regulation at this time.

'Soot' or 'black carbon', which comes from incomplete combustion, absorbs light and warms the atmosphere. Although there have been repeated suggestions that reduction of black carbon could be a viable part of decreasing global warming, it has not yet been considered when choosing actions to reduce climatic impact. In this paper, I examine four conceptual barriers to the consideration of aerosols in global agreements. I conclude that some of the major objections to considering aerosols under hemispheric or global agreements are illusory because: (1) a few major sources will be addressed by local regulations, but the remainder may not be addressed by traditional air quality management; (2) climate forcing by carbon particles is not limited to 'hot spots'-about 90% of it occurs at relatively low concentrations; (3) while aerosol science is complex, the most salient characteristics of aerosol behavior can be condensed into tractable metrics including, but not limited to, the global warming potential; (4) despite scientific uncertainties, reducing all aerosols from major sources of black carbon will reduce direct climate warming with a very high probability. This change in climate forcing accounts for at least 25% of the accompanying CO2 forcing with significant probability (25% for modern diesel engines, 90% for superemitting diesels, and 55% for cooking with biofuels). Thus, this fraction of radiative forcing should not be ignored.