Abstract

Abstract. The recently developed Norwegian Earth System Model (NorESM) is employed for simulations contributing to the CMIP5 (Coupled Model Intercomparison Project phase 5) experiments and the fifth assessment report of the Intergovernmental Panel on Climate Change (IPCC-AR5). In this manuscript, we focus on evaluating the ocean and land carbon cycle components of the NorESM, based on the preindustrial control and historical simulations. Many of the observed large scale ocean biogeochemical features are reproduced satisfactorily by the NorESM. When compared to the climatological estimates from the World Ocean Atlas (WOA), the model simulated temperature, salinity, oxygen, and phosphate distributions agree reasonably well in both the surface layer and deep water structure. However, the model simulates a relatively strong overturning circulation strength that leads to noticeable model-data bias, especially within the North Atlantic Deep Water (NADW). This strong overturning circulation slightly distorts the structure of the biogeochemical tracers at depth. Advancements in simulating the oceanic mixed layer depth with respect to the previous generation model particularly improve the surface tracer distribution as well as the upper ocean biogeochemical processes, particularly in the Southern Ocean. Consequently, near-surface ocean processes such as biological production and air–sea gas exchange, are in good agreement with climatological observations. The NorESM adopts the same terrestrial model as the Community Earth System Model (CESM1). It reproduces the general pattern of land-vegetation gross primary productivity (GPP) when compared to the observationally based values derived from the FLUXNET network of eddy covariance towers. While the model simulates well the vegetation carbon pool, the soil carbon pool is smaller by a factor of three relative to the observational based estimates. The simulated annual mean terrestrial GPP and total respiration are slightly larger than observed, but the difference between the global GPP and respiration is comparable. Model-data bias in GPP is mainly simulated in the tropics (overestimation) and in high latitudes (underestimation). Within the NorESM framework, both the ocean and terrestrial carbon cycle models simulate a steady increase in carbon uptake from the preindustrial period to the present-day. The land carbon uptake is noticeably smaller than the observations, which is attributed to the strong nitrogen limitation formulated by the land model.

Highlights

  • In addition to the atmospheric radiative properties, global climate dynamics depend on the complex simultaneous interactions between the atmosphere, ocean, and land

  • The Norwegian Earth System Model (NorESM) is partly based on the recently released Community Climate System Model (CCSM4, Gent et al, 2011), which is maintained by the National Center for Atmospheric Research and is developed in partnership with collaborators funded primarily by the US National Science Foundation and the Department of Energy

  • We evaluate the carbon cycle components of the Norwegian Earth System Model (NorESM)

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Summary

Introduction

In addition to the atmospheric radiative properties, global climate dynamics depend on the complex simultaneous interactions between the atmosphere, ocean, and land. For more in-depth reviews and evaluation of the CLM4, the readers are referred to recent publications by CLM4 developers (e.g., Oleson et al, 2010; Lawrence et al, 2011; Gent et al, 2011) In this manuscript, we focus on reviewing the basic performance of the ocean and land carbon cycle components of the NorESM. 5. The Norwegian Earth System Model (NorESM) is partly based on the recently released Community Climate System Model (CCSM4, Gent et al, 2011), which is maintained by the National Center for Atmospheric Research and is developed in partnership with collaborators funded primarily by the US National Science Foundation and the Department of Energy. Since the physical components are documented in more detail by Bentsen et al (2012) and Iversen et al (2012), here, major emphasis is placed on the carbon cycle components

Atmospheric model
Ocean general circulation model
Ocean carbon cycle model
Land model
Transient global temperature
Ocean physical and biogeochemical properties
Physical fields
Biogeochemical tracers
Biological production
Sea–air CO2 fluxes
Vegetation and soil carbon pools
Terrestrial biogeochemistry
Terrestrial primary production and respiration
Transient sea–air and land–air CO2 fluxes
Summary and conclusions
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