Current climate change reports最新文献

Purpose of review: This special issue on "Bridging Research and Policy on Climate Change and Conflict" brings together the results of a 2018 workshop organized by the Peace Research Institute, Oslo (PRIO) and the Wilson Center with six papers that address different aspects of the translation of the research on climate change and conflict to policy and practice. Here, we provide an overview of the workshop and papers to highlight key opportunities and challenges to linking the climate-conflict scholarship with pressing issues in diplomacy, development, and security.

Recent findings: Multiple methods, especially comparative case studies, should be applied to elucidate the more complex mechanisms of the climate-conflict link. This approach may also enhance engagement with the policymakers who draw on examples and narratives. There is also a need for both predictive models that capture contextual factors and policy interactions as well as decision-support tools, such as integrated assessment models, that can be used to test the implications of different theories and models in the literature.

Summary: Scholars should engage the policy community to formulate research questions that are more policy relevant, such as the effectiveness of interventions. There is also the need for models and frameworks that help practitioners synthesize the academic results. Practitioners are encouraged to leverage the comparative advantages of academic researchers in new policy and projects to inform data collection and future analysis of effectiveness.

Purpose of review: Some aerosols absorb solar radiation, altering cloud properties, atmospheric stability and circulation dynamics, and the water cycle. Here we review recent progress towards global and regional constraints on aerosol absorption from observations and modeling, considering physical properties and combined approaches crucial for understanding the total (natural and anthropogenic) influences of aerosols on the climate.

Recent findings: We emphasize developments in black carbon absorption alteration due to coating and ageing, brown carbon characterization, dust composition, absorbing aerosol above cloud, source modeling and size distributions, and validation of high-resolution modeling against a range of observations.

Summary: Both observations and modeling of total aerosol absorption, absorbing aerosol optical depths and single scattering albedo, as well as the vertical distribution of atmospheric absorption, still suffer from uncertainties and unknowns significant for climate applications. We offer a roadmap of developments needed to bring the field substantially forward.

Purpose of review: The observed substantial loss of Arctic sea ice has raised prospects of a seasonally ice-free Arctic Ocean within the foreseeable future. In this review, we summarize our current understanding of the most likely trajectory of the Arctic sea-ice cover towards this state.

Recent findings: The future trajectory of the Arctic sea-ice cover can be described through a deterministic component arising primarily from future greenhouse gas emissions, and a chaotic component arising from internal variability. The deterministic component is expected to cause a largely ice-free Arctic Ocean during summer for less than 2 ^∘C global warming relative to pre-industrial levels. To keep chances below 5 % that the Arctic Ocean will largely be ice free in a given year, total future CO₂ emissions must remain below 500 Gt.

Summary: The Arctic Ocean will become ice free during summer before mid-century unless greenhouse gas emissions are rapidly reduced.

Purpose of review: This paper reviews sea level contributions from land ice across the Arctic, including Greenland. We summarize ice loss measurement methods, ice loss mechanisms, and recent observations and projections, and highlight research advances over the last 3-5 years and remaining scientific challenges.

Recent findings: Mass loss across the Arctic began to accelerate during the late twentieth century, with projections of continued loss across all future greenhouse gas emission scenarios. Recent research has improved knowledge of ice hydrology and surface processes, influences of atmospheric and oceanic changes on land ice, and boundary conditions such as subglacial topography. New computer models can also more accurately simulate glacier and ice sheet evolution.

Summary: Rapid Arctic ice loss is underway, and future ice loss and sea level rise are guaranteed. Research continues to better understand and model physical processes and to improve projections of ice loss rates, especially after 2050.

Increasing atmospheric CO₂ is having detrimental effects on the Earth system. Societies have recognized that anthropogenic CO₂ release must be rapidly reduced to avoid potentially catastrophic impacts. Achieving this via emissions reductions alone will be very difficult. Carbon dioxide removal (CDR) has been suggested to complement and compensate for insufficient emissions reductions, through increasing natural carbon sinks, engineering new carbon sinks, or combining natural uptake with engineered storage. Here, we review the carbon cycle responses to different CDR approaches and highlight the often-overlooked interaction and feedbacks between carbon reservoirs that ultimately determines CDR efficacy. We also identify future research that will be needed if CDR is to play a role in climate change mitigation, these include coordinated studies to better understand (i) the underlying mechanisms of each method, (ii) how they could be explicitly simulated, (iii) how reversible changes in the climate and carbon cycle are, and (iv) how to evaluate and monitor CDR.

Purpose of review: Dynamic manifestations of climate change, i.e. those related to circulation, are less well understood than are thermodynamic, or temperature-related aspects. However, this knowledge gap is narrowing. We review recent progress in understanding the causes of observed changes in polar tropospheric and stratospheric circulation, and in interpreting climate model projections of their future changes.

Recent findings: Trends in the annular modes reflect the influences of multiple drivers. In the Northern Hemisphere, there appears to be a "tug-of-war" between the opposing effects of Arctic near-surface warming and tropical upper tropospheric warming, two predominant features of the atmospheric response to increasing greenhouse gases. Future trends in the Southern Hemisphere largely depend on the competing effects of stratospheric ozone recovery and increasing greenhouse gases.

Summary: Human influence on the Antarctic circulation is detectable in the strengthening of the stratospheric polar vortex and the poleward shift of the tropospheric westerly winds. Observed Arctic circulation changes cannot be confidently separated from internal atmospheric variability.