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The mechanisms behind the 20 ppm pre-industrial rise in atmospheric CO2 since 6000 BC have been the focus of considerable debate in recent years. Some studies suggest that natural processes, such as a decline in global forests, calcite compensation, and warming ocean temperatures, can explain the increase in CO2. Others have argued that, because the CO2 increase did not occur during previous interglacial periods, it is an indication of an early human influence on the climate. In this paper, we investigate several facets of the natural carbon cycle of the past 8000 years related to ocean circulation patterns and ice shelf configuration using the University of Victoria Earth System Climate Model (v. 2.9), which includes a representation of the climate system with dynamic vegetation and an interactive carbon cycle. The fully simulated earth system for various freely evolving atmospheric carbon scenarios since 6000 BC failed to recreate the observed rise in CO2 and consistently produced a decline in CO2 throu...

Identifying the drivers of changing continental runoff is key to understanding current and predicting future hydrological responses to climate change. Potential drivers of runoff change include changes in precipitation and evaporation caused by climate warming, physiological responses of vegetation to elevated atmospheric CO2 concentrations, increases in lower-atmosphere aerosols and anthropogenic land-cover change. In this study, we present a series of simulations using an intermediate-complexity climate and carbon cycle model to assess the contribution of each of these drivers to historical and future continental runoff changes. We present results for global runoff, in addition to northern latitude runoff that discharges into the Arctic and North Atlantic oceans, to identify any potential contribution of increased continental freshwater discharge to changes in North Atlantic deep-water formation. Between 1800 and 2100, the model simulated a 26% increase in global runoff and a 32% runoff increase in the ...

Terrestrial carbon fluxes are an important factor in regulating concentrations of atmospheric carbon dioxide (CO2). In this study, we use a coupled climate model with interactive biogeochemistry to benchmark the simulation of net primary productivity (NPP) and its response to elevated atmospheric CO2. Short-term field experiments such as Free-Air Carbon Dioxide Enrichment (FACE) studies have examined this phenomenon but it is difficult to infer trends from only a few years of field data. Here, we employ the University of Victoria's Earth System Climate Model (UVic ESCM) version 2.8 to compare simulated changes in NPP due to an elevated atmospheric CO2 concentration of 550 ppm to observed increases in NPP of 23% ±2% from four temperate forest FACE studies between 1997 and 2002. We further compare two scenarios: elevated CO2 with climate change, and elevated CO2 without climate change, the latter being consistent with FACE methodology. In the climate change scenario global terrestrial and forest-only NPP in...

A new earth system climate model of intermediate complexity has been developed and its climatology compared to observations. The UVic Earth System Climate Model consists of a three‐dimensional ocean general circulation model coupled to a thermodynamic/dynamic sea‐ice model, an energy‐moisture balance atmospheric model with dynamical feedbacks, and a thermomechanical land‐ice model. In order to keep the model computationally efficient a reduced complexity atmosphere model is used. Atmospheric heat and freshwater transports are parametrized through Fickian diffusion, and precipitation is assumed to occur when the relative humidity is greater than 85%. Moisture transport can also be accomplished through advection if desired. Precipitation over land is assumed to return instantaneously to the ocean via one of 33 observed river drainage basins. Ice and snow albedo feedbacks are included in the coupled model by locally increasing the prescribed latitudinal profile of the planetary albedo. The atmospher...