Short-lived climate forcers (SLCFs) are dubbed because of their shorter atmospheric lifetime in comparison with CO2. SLCFs are generally assumed to have only a short-term effect on the climate system: should their emission cease, so would their radiative forcing (RF). However, SLCFs have an effect on the carbon cycle through climate-carbon feedbacks.In this study, we quantify the following feedback loop: SLCF change the climate, climate change modifies land and ocean carbon sinks, impacting the atmospheric CO2, and therefore causing additional climate change. The compact Earth System Model OSCAR v2.2 is used to attribute the present-day RF of CO2 to direct CO2 emissions and to the climate-carbon feedbacks. This study illustrates and quantifies this long-term impact that short-lived species have on the climate system through the carbon cycle. It also indicates that past (and future) change in atmospheric CO2 cannot be attributed only to CO2 emissions.

Knowing the historical relative contribution of greenhouse gases (GHGs) and short-lived climate forcers (SLCFs) to global radiative forcing (RF) at the regional level can help understand how future GHGs emission reductions and associated or independent reductions in SLCFs will affect the ultimate purpose of the Paris Agreement. In this study, we use a compact Earth system model to quantify the global RF and attribute global RF to individual countries and regions. As our evaluation, the United States, the first 15 European Union members, and China are the top three contributors, accounting for 21.9 ± 3.1%, 13.7 ± 1.6%, and 8.6 ± 7.0% of global RF in 2014, respectively. We also find a contrast between developed countries where GHGs dominate the RF and developing countries where SLCFs including aerosols and ozone are more dominant. In developing countries, negative RF caused by aerosols largely masks the positive RF from GHGs. As developing countries take measures to improve the air quality, their negative contributions from aerosols will likely be reduced in the future, which will in turn enhance global warming. This underlines the importance of reducing GHG emissions in parallel to avoid any detrimental consequences from air quality policies.

Peatlands cover about 3% of the Earth’s surface and are regarded as a vital carbon (C) pool and sink. The formation of peatland is supported by continuously supplied nitrogen (N) but the sources of this N remain unclear. Here, we first review N stocks and the rate they accumulate in peatlands, then we present the sources of N, especially through biological nitrogen fixation (BNF). We found that global peatlands store 5.9–25.9 Gt N. In the past millennia, northern peatlands have a lower N accumulated rate than tropical undisturbed peatlands. BNF rate is approximately 1.9 ± 2.7 g m−2 yr−1 in northern peatlands, higher than the rate of N deposition, 0.5 ± 0.4 g m−2 yr−1. For tropical peatlands, BNF observation has hardly been reported yet and needs further investigation. This review provides a broad picture of peatland N cycling and suggests that there are large uncertainties, due to limited observations of BNF and N fluxes by inflow and outflow runoff. Therefore, we call for more efforts contributing to field observations and modelling of the N budget in peatlands.Systematic Review Registration: (website), identifier (registration number).

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