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Carbon Accounting

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.

Footprints and accounting

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.

Article | | Nature Climate Change

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.

Comment | | Nature Climate Change

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.

Article | | Nature Climate Change

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.

Article | | Nature Energy

Sources and sinks

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.

Letter | | Nature

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.

Letter | | Nature

Budget approaches

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.

Comment | | Nature Geoscience

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.

Article | Open Access | | Nature Communications

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.

Comment | | Nature Climate Change