As announcements of seasonal low concentrations of CO2 emerge, understanding of the anthropogenic and natural factors affecting this balance continues to develop. Decision-makers rely on the best information about the Earth's changing sinks and sources as they seek to constrain global emissions. This is why Nature Climate Change has launched a new online collection, Carbon Accounting (

Earlier this year, a Commentary by Richard Betts et al. (Nat. Clim. Change 6, 806–810; 2016) predicted that atmospheric CO2 concentrations at Mauna Loa observatory, Hawaii, would fail to fall below 400 parts per million (ppm) at any time during the year as a consequence of natural and anthropogenic drivers. Given the time-lag in the relationship between reducing emissions and altering that concentration, the authors concluded that the concentration is unlikely to dip below this level again in our lifetimes.

The 400-ppm level is a milestone. Passing 400 ppm serves as a reminder of how far-reaching, fast, and deep efforts to reduce emissions must be. Carbon accounting provides the foundations for efforts to tackle climate change by providing data on where greenhouse gases are released into the atmosphere, and where they are removed.

There are three strands to the Collection. The first includes scholarship on methods to calculate the balance of the carbon account. Developing nuanced means of attributing emissions to different sources is crucial for understanding which countries, companies, or activities are responsible for rapidly spending the world's carbon budget.

The second strand presents the latest research on carbon sinks. Significant progress has been made in this area in recent years and knowing how much CO2 the world's forests, oceans, and other natural and engineered sinks can absorb is essential to balancing the carbon account.

Finally, the Collection presents research on the world's carbon sources. As some countries intensify emissions to develop, others decarbonize, and consumption patterns change, as do the major sources of anthropogenic emissions. Understanding how these emissions interact with natural sources and create additional warming can allow policymakers to target mitigation policies.

This evolving Collection will bring together a selection of multi-disciplinary research and commentary from across the natural and social sciences that explores the major inputs and outputs that comprise the world's carbon account. We hope it will prove a useful resource to inform decision-makers about what ecosystems need protecting, which resources can be used, and how responsibility for these should be shared, if the world is going to rapidly decarbonize.