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We now live in a 400 parts per million world. Data from the Mauna Loa observatory, Hawaii, suggests carbon dioxide concentration levels are unlikely to consistently fall back below this level in our lifetimes.
Carbon accounting is crucial to efforts to tackle climate change, providing data on where emissions emanate and where they are absorbed. Decision-makers rely on the best information about the earth’s changing sinks and sources as they seek to constrain global emissions.
This collection brings together a selection of multi-disciplinary research and commentary from across the physical and social sciences that explores the major inputs and outputs that comprise the world’s carbon account.
Tourism is a significant contributor to the global economy, with potentially large environmental impacts. Origin and destination accounting perspectives are used to provide a comprehensive assessment of global tourism’s carbon footprint.
Traditional carbon accounting attributes gap between consumption- and production-based emissions to international trade. The authors develop a dynamic model that incorporates capital stock change and find it improves estimates for fast-developing countries.
The Paris Agreement has increased the incentive to verify reported anthropogenic carbon dioxide emissions with independent Earth system observations. Reliable verification requires a step change in our understanding of carbon cycle variability.
The decline in China’s CO2 emissions in the past few years is largely due to changes in industrial structure and a decline in the share of coal for energy production, according to a quantitative analysis of the drivers of CO2 emissions.
China has entered a new normal phase of economic development with a changing role in global trade. Here the authors show that emissions embodied in China’s exports declined from 2007 to 2012, while developing countries become the major destinations of China’s export emissions.
Fisheries generated a total of 179 million tonnes of CO2-equivalent GHG emissions in 2011 (4% of global food production). Emissions grew by 28% between 1990 and 2011, primarily driven by increased harvests from fuel-intensive crustacean fisheries.
Here emission curves are developed for advanced biofuel supply chains to enhance understanding of the relationship between biofuel supply and its potential contribution to climate change mitigation while accounting for landscape heterogeneity.
All energy generation technologies emit greenhouse gases during their life cycle as a result of construction and operation. Pehl et al. integrate life-cycle assessment and energy modelling to analyse the emissions contributions of different technologies across their lifespan in future low-carbon power systems.
Greenhouse gas emissions can be allocated to individual countries in various ways depending on where in the supply chain the emissions originated; achieving an effective and just climate policy may require multiple accounting systems.
This research presents global baseline estimates of mangrove soil C stocks enabling countries to begin to assess their mangrove soil C stocks and the emissions that might arise from mangrove deforestation.
The potential growth in terrestrial gross primary production (GPP) as a result of increasing atmospheric carbon dioxide concentrations remains poorly understood. This has led to large uncertainties in modelled estimates of terrestrial carbon storage and carbon cycle–climate feedbacks. This paper presents an estimate of GPP growth during the twentieth century, based on long-term records of atmospheric carbonyl sulfide, which responds to changes in its sources and sinks, such as uptake by plant leaves. With the help of model simulations, the authors find that the carbonyl sulfide record is most consistent with climate–carbon cycle model simulations that assume about 30 per cent growth in GPP during the twentieth century. Carbonyl sulfide analysis could provide a global-scale benchmark for modelling historical carbon cycles, the authors say.
Wetlands are the single largest global source of the greenhouse gas methane, but the contribution of the Amazon floodplain, the largest natural geographic source of methane in the tropics, remains poorly understood. Methane emission inventories underestimate the atmospheric burden of methane determined via remote sensing and inversion modelling. This paper reports on methane fluxes from the stems of Amazonian floodplain trees and finds that gas leaving the soil through wetland trees is the dominant source of regional methane emissions. The authors also provide an estimate of methane emission for the Amazon basin based on atmospheric methane profiles and find that it can be reconciled with the combined emission estimate from floodplain trees and other regional methane sources. Overall, the findings suggest that the large methane emission from trees could be what was missing from the Amazon budget.
It remains unclear whether surface water partial pressure of CO2 (pCO2) in continental shelves tracks with increasing atmospheric pCO2. Here, the authors show that pCO2 in shelf waters lags behind rising atmospheric CO2 in a number of shelf regions, suggesting shelf uptake of atmospheric CO2.
Rivers in the Western Siberian Lowland, the world’s largest peatland, play a significant role in the release of terrestrial carbon to the atmosphere, according to in situ measurements of carbon dioxide emissions from rivers.
The model–inventory discrepancy in net land-use carbon emissions mainly results from conceptual differences in estimating anthropogenic forest sinks. A revised disaggregation of global land model results allows greater comparability with inventories.
Analysis of peatland carbon accumulation over the last millennium and its association with global-scale climate space indicates an ongoing carbon sink into the future, but with decreasing strength as conditions warm.
Estimates of carbon budgets compatible with limiting warming to below specific temperature limits are reviewed, and reasons underlying their differences discussed along with their respective strengths and limitations.
The remaining carbon budget consistent with limiting warming to 1.5 °C allows 20 more years of current emissions according to one study, but is already exhausted according to another. Both are defensible. We need to move on from a unique carbon budget, and face the nuances.
Limiting warming to 1.5 °C requires staying within an allowable carbon budget. An analysis of warming and carbon budgets from the past decade shows that the median remaining budget is 208 PgC, corresponding to about 20 years of emissions at the 2015 rate.
The drivers of the increase in atmospheric methane since 2006 remain unclear. Here, the authors use satellite and in situ measurements of CO and CH4 to show that fossil fuels and biogenic sources contribute 12–19 Tg CH4per year and 12–16 Tg CH4per year respectively to the recent atmospheric methane increase.
If CO2 emissions after 2015 do not exceed 200 GtC, climate warming after 2015 will fall below 0.6 °C in 66% of CMIP5 models, according to an analysis based on combining a simple climate–carbon-cycle model with estimated ranges for key climate system properties.
The Paris Agreement is based on emission scenarios that move from a sluggish phase-out of fossil fuels to large-scale late-century negative emissions. Alternative pathways of early deployment of negative emission technologies need to be considered to ensure that climate targets are reached safely and sustainably.
Climate feedbacks associated with wetland methane emissions and permafrost-thaw carbon release substantially reduce available carbon budgets to achieve temperature targets, suggest simulations with a climate–land-surface model system.
A combination of the level and rate of human-induced warming allows estimation of remaining emission budgets to peak warming across a broad range of scenarios, suggests an analysis of emissions budgets expressed in terms of CO2-forcing-equivalent emissions.