[1] This paper presents a global model-based country-scale quantification of urban N and P mass flows from humans, animals, and industries and their waste N and P discharges to surface water and urban waste recycling in agriculture. Agricultural recycling was practiced commonly in early twentieth century Europe, Asia, and North America. During the twentieth century, global urban discharge to surface water increased~3.5-fold to 7.7 Tg yr -1 for N and~4.5-fold to 1.0 Tg yr -1 for P; the major part of this increase occurred between 1950 and 2000. Between 1900 and~1940, industrial N and P flows dominated global surface water N and P loadings from urban areas; since~1940, human wastes are the major source of urban nutrient discharge to both surface water and agricultural recycling. During the period 1900-2000, total global recycling of urban nutrients in agriculture increased from 0.4 to 0.6 Tg N yr -1 and from 0.07 to 0.08 Tg P yr -1. A large number of factors (the major ones related to food consumption, urban population, sewer connection, and industrial emissions) contribute to the uncertainty of À18% to +42% for N and À21% to +45% for P around the calculated surface water loading estimate for 2000.

Abstract. The ocean carbon cycle is a key player in the climate system through its role in regulating the atmospheric carbon dioxide concentration and other processes that alter the Earth's radiative balance. In the second version of the Norwegian Earth System Model (NorESM2), the oceanic carbon cycle component has gone through numerous updates that include, amongst others, improved process representations, increased interactions with the atmosphere, and additional new tracers. Oceanic dimethyl sulfide (DMS) is now prognostically simulated and its fluxes are directly coupled with the atmospheric component, leading to a direct feedback to the climate. Atmospheric nitrogen deposition and additional riverine inputs of other biogeochemical tracers have recently been included in the model. The implementation of new tracers such as “preformed” and “natural” tracers enables a separation of physical from biogeochemical drivers as well as of internal from external forcings and hence a better diagnostic of the simulated biogeochemical variability. Carbon isotope tracers have been implemented and will be relevant for studying long-term past climate changes. Here, we describe these new model implementations and present an evaluation of the model's performance in simulating the observed climatological states of water-column biogeochemistry and in simulating transient evolution over the historical period. Compared to its predecessor NorESM1, the new model's performance has improved considerably in many aspects. In the interior, the observed spatial patterns of nutrients, oxygen, and carbon chemistry are better reproduced, reducing the overall model biases. A new set of ecosystem parameters and improved mixed layer dynamics improve the representation of upper-ocean processes (biological production and air–sea CO2 fluxes) at seasonal timescale. Transient warming and air–sea CO2 fluxes over the historical period are also in good agreement with observation-based estimates. NorESM2 participates in the Coupled Model Intercomparison Project phase 6 (CMIP6) through DECK (Diagnostic, Evaluation and Characterization of Klima) and several endorsed MIP simulations.

Abstract. The ocean carbon cycle is a key player in the climate system through its role in regulating atmospheric carbon dioxide concentration as well as other processes that alter the Earth's radiative balance. In the second version of the Norwegian Earth System Model (NorESM2), the oceanic carbon cycle component has gone through numerous updates that include, amongst others, improved process representations, increased interactions with the atmosphere, and additional new tracers. Oceanic dimethyl sulfide (DMS) is now prognostically simulated and its fluxes are directly coupled with the atmospheric component, allowing for a direct feedback to the climate. Atmospheric nitrogen deposition and additional external inputs of other biogeochemical tracers through riverine are recently included in the model. The implementation of new tracers such as 'preformed' and 'natural' tracers enables a separation of physical from biogeochemical drivers as well as of internal from external forcings and hence a better diagnostic of the simulated biogeochemical variability. Carbon isotope tracers have been implemented and will be relevant for studying long-term past climate changes. Here, we describe these new model implementations and present the evaluation of the model's performance in simulating the observed climatological states of water column biogeochemistry as well as in simulating the transient evolution over the historical period. Compared to its predecessor NorESM1, the new model's performance has improved considerably in many aspects. In the interior, the observed spatial patterns of nutrients, oxygen, and carbon chemistry are better reproduced, reducing the overall model biases. A new set of ecosystem parameters and improved mixed layer dynamics improves the representation of upper ocean processes (biological production and air-sea CO2 fluxes) at seasonal time scale. Transient warming and air-sea CO2 fluxes over the historical period are also in good agreement with observation-based estimates. NorESM2 participates in the Coupled Model Intercomparison Project phase 6 (CMIP6) through DECK (Diagnostic, Evaluation and Characterization of Klima) and several endorsed MIP-simulations.