Ten coupled climate-carbon cycle models were forced by historical and SRES A2 anthropogenic emissions of CO₂ for the 1850-2100 time period to study the coupling between climate change and the carbon cycle. Each model ran two separate simulations in order to evaluate the climate-carbon cycle feedback. All models agree that future climate change will reduce the efficiency of the Earth system to absorb the anthropogenic CO₂. A larger fraction of CO₂ will stay in the atmosphere if climate change is accounted for.  By the end of the 21^st century, this ranges between 20 ppm and 200 ppm depending on the model, the majority of the models lying between 50 and 100 ppm. All models simulate a negative sensitivity for both the land and the ocean carbon cycle to future climate. However there is still a large uncertainty on the magnitude of these sensitivities. Also, the majority of the models attribute most of the changes to the land. Finally, most of the models locate the reduction of land carbon uptake in the tropics. However, the attribution to changes in net primary productivity versus changes in respiration is still subject to debate amongst the models.

The effect of changes in iron supply to the ocean on CO₂ uptake is examined. Dust deposition fields from a dust model driven by output from a future climate simulation of a coupled general circulation model (GCM) were used as input to an ocean GCM with an embedded ecosystem model. In simulations using dust produced in a future climate the primary productivity of the ocean increased by 56% compared to simulations using dust from the present climate. The sinking particle flux of carbon at 100 m depth increased by 46%. The net air-to-sea flux of CO₂ was 4.1 PgC/y greater in the future dust simulation. Most of these changes occurred in the Equatorial Pacific Ocean, where the model ecosystem was iron-limited with present-day dust inputs but which received a large increase in the dust supplied from the Amazon Basin. These perturbations to the marine biogeochemical system are large compared to other potential climate effects that have been observed in the model. Although these results are preliminary, they could form a large negative feedback on global warming.

Different CO₂ stabilization scenarios and CO₂ emission scenarios have been carried out with an earth system model to investigate feedbacks between future climate change and carbon cycle. The model predicts a sensitivity of 1.6±0.1 K for an increase of 280 ppm in atmospheric CO₂ concentration. The decrease of the thermohaline circulation is predominantly controlled by an enhanced atmospheric moisture transport to high latitudes by global warming. Overall, the simulated effect of atmospheric CO₂ concentration on climate change reduces the total carbon uptake of the ocean and the land is reduced by 24-29%.

Here we use the severe heat and drought event in Europe from summer 2003 as a natural experiment to study the impact of a climatic extreme event on ecosystem physiology and its feedback to the atmosphere. The combination of continuous eddy covariance and tree growth measurements at two nearby located deciduous forests showed a large reduction in carbon uptake during the drought (-30%) and a strong carry-over effect into the next year. Both forests, however, responded differently, although climatic forcing was almost identical. Species composition and site condition of the ecosystems seemed to play a major role in the ecosystems response to the drought.

The terrestrial ecosystem carbon cycle model, Sim-CYCLE, was combined with the CCSR/NIES/FRCGC AGCM5.7b (including a land surface model: MATSIRO). That coupled model shows a reasonable distribution of the LAI, NPP and other carbon storages after the 1000yrs spin-up run. This presentation introduces the preliminary results of the coupled run in 20th century.

In recent years attention has focused on the role of terrestrial biosphere dynamics in the climate system, and the possibility of large land-atmosphere carbon cycle feedbacks under human-induced future climate warming. During the 1990s rapid development of Dynamic Global Vegetation Models (DGVMs) led a growing community to soon recognize the need for model evaluation and intercomparison. In Cramer et al. 2000 six DGVMs were run using identical forcing data based on the HadCM2 GCM climatology (1860-2100) and the IS92a emission scenario.

Increasing ocean stratification associated with global warming has been posited to serve as a positive feedback on global warming, reducing the oceanic uptake of anthropogenic carbon dioxide. We suggest that a poleward shift of westerly winds combined with future increases in atmospheric carbon dioxide may drive an increase in the CO₂ uptake in the Southern Ocean, representing a negative feedback on atmospheric anthropogenic CO₂.

This study examines the potential for feedbacks between the carbon cycle, atmospheric carbon dioxide (CO₂) increases and climate change to affect the anthropogenic emissions that are required to stabilize future levels of CO₂ in the atmosphere. Using a coupled climate-carbon cycle model, I found that positive carbon cycle-climate feedbacks reduced allowable emissions by an amount that varied with the model’s climate sensitivity.  Emissions were further reduced if CO₂ fertilization was assumed to be inactive in the model, as this removed an otherwise important negative feedback on atmospheric CO₂.