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Atmospheric CO₂ concentrations varied on multidecadal timescales over the past millennium. Measurements of the carbon isotope composition of ice core CO₂ suggest climate-driven changes in land carbon stores caused these fluctuations.

The finding that feedbacks between the ocean's carbon cycle and climate may become larger than terrestrial carbon–climate feedbacks has implications for the socio-economic effects of today's fossil-fuel emissions.

Antarctic ice cores can be used to reconstruct atmospheric CO₂ concentrations, revealing significant changes during the Holocene epoch which started 11,000 years ago. Here, a highly resolved δ¹³C record is presented for the past 11,000 years from measurements on atmospheric CO₂ trapped in an Antarctic ice core. These data are combined with a simplified carbon cycle model to shed light on the processes responsible for the changes in CO₂ concentrations.

The sensitivity of the terrestrial biosphere to changes in climate constitutes a feedback mechanism with the potential to accentuate global warming. Process-based modelling experiments now indicate that under a business-as-usual emissions scenario the biosphere on land is expected to be an increasingly positive feedback to anthropogenic climate change, potentially amplifying equilibrium climate sensitivity by 22–27%.

A comprehensive model framework is used to estimate the global net direct radiative forcing of anthropogenic reactive nitrogen as being about −0.34 W m⁻², which has a cooling effect on the climate.

Bottom-up and top-down approaches are used to quantify global nitrous oxide sources and sinks resulting from both natural and anthropogenic sources, revealing a 30% increase in global human-induced emissions between 1980 and 2016.

Accurately assessing emissions reductions for various greenhouse gases to stay within temperature targets is important. Here, an adaptive approach, based solely on observations and not on model projections, allows quantification of emissions reductions required to achieve any temperature target.

The Atlantic meridional overturning circulation was shallow and weak during the Last Glacial Maximum, and water masses took time to adjust to circulation shifts during the Last Deglaciation, according to a reassessment of proxy records and model simulations.

Reconstructions of Holocene summer temperatures differ between models and vegetation-based proxies. A quantitative reconstruction for the Mediterranean region based on fossil midge assemblages suggests warm summers, in line with climate models.

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.

In the aftermath of COP21, potential post-2030 emission trajectories and their consistency with the 2 °C target are a core concern for the ocean scientific community in light of the end-century risks of impact scenarios.

Analysis of air trapped in Antarctic ice between 16,000 and 10,000 years before present yields nitrous oxide concentrations and isotopic data showing that the relative contributions from marine and terrestrial sources to nitrous oxide emission changes were equal during that period, but that terrestrial emissions dominated on centennial timescales.

Anthropogenic global warming is likely to be amplified by positive feedback from the global carbon cycle; however, the magnitude of the climate sensitivity of the global carbon cycle, and thus of its positive feedback strength, is under debate. By combining a probabilistic approach with an ensemble of proxy-based temperature reconstructions and pre-industrial CO₂ data from three ice cores, this climate sensitivity is now shown to be much smaller than previously thought.

The amount of greenhouse gas emissions that will limit the risks from such emissions has been set by the goal of keeping global warming below two degrees Celsius above preindustrial, but this study sets thresholds for sea level rise, ocean acidification and agricultural productivity as well as warming and shows that emissions need to be lowered even further.

A review of Earth system changes associated with past warmer climates provides constraints on the environmental changes that could occur under warming of 2 °C or more over pre-industrial temperatures.

A substantial amount of atmospheric carbon taken up on land is transported laterally from upland terrestrial ecosystems to the ocean. A synthesis of the available literature suggests that human activities have significantly increased soil carbon inputs to inland waters, but have only slightly affected carbon delivery to the open ocean.