The Siberian permafrost carbon stock has been studied using a newly developed soil model, which takes into account soil freezing/thawing and organic matter decomposition in the form of soil respiration and methanogenesis. The results show that the soil response to a rapid external warming can be a self-sustaining process involving permafrost melting, deep-soil respiration with associated heat generation, and methanogenesis. Most of the soil carbon is thus consumed until there is not enough of it to feed intense respiration and/or methanogenesis. This behavior is manifested only at sufficiently warm climate established after the warming. Carbon consumption in the extremely carbon-rich Yedoma Ice Complex region appears to be moderate due to cold climatic conditions.

Despite their relative small extension, wetlands are important as sources or sinks of C. But, due to their intermediate position between land and permanent water, they have been modified in the name of “health” or “productivity.” Such changes have altered substantially their ability to store/produce C greenhouse gasses but the main point is to establish until which point this changes are “structural” (implying the intrinsic environmental mechanisms), and therefore unrecoverable, or “casual” (implying not the environment processes but its “external”–not directly implied in the C storage/emission- components), and consequently recoverable. Temperate wetlands are strongly dependant on water availability due to their position but, on the other hand, use to be occupied by resistant species able to survive hard conditions. The example shown below presents a case of intense human activity on a Mediterranean wetland that has caused very intense changes in the flooded area but not so evident and perdurable in the main ecological relations implied in the C cycle.

In order to investigate the long-term and inter-annual variations in the atmospheric CO₂ concentration record obtained by aircraft measurements over Japan, we have conducted numerical experiments using a transport model with a process-based ecosystem model. The climate-induced anomalies of net biospheric flux account for a significant part of the inter-annual variations in the CO₂ growth rate. The results indicate that year-to-year change in observed vertical CO₂ gradient is mainly caused by the inter-annual variability in atmospheric transport, likely related to El Niño events.

Results from recent models in the coupled carbon cycle climate model intercomparison project (C4MIP) indicate a positive feedback to global warming from the interactive carbon cycle, but the magnitude varies widely. A typical model simulates an additional increase of 90 ppmv in the atmospheric CO₂, and 0.6 degree additional warming due to this feedback, but some model can be as large as 250ppm. Using a liner perturbation framework, we analyze what might have caused such large discrepancy in the models, with a focus on land where the largest uncertainties lie. Change in NPP such as different sensitivity to the CO₂ fertilization effect is one where in some models it is modest largely due to the multiple limiting factors constraining terrestrial productivity and carbon loss. The large differences among the models are also manifestations of other poorly constrained processes such as the turnover time and rates of soil decomposition.

Increased winter temperatures associated with the observed positive trend in the winter Arctic Oscillation can partially explain trends towards earlier spring leafout in the northern hemisphere.  Increased spring drawdown associated with earlier leafout, coupled with increased winter respiration due to warmer temperatures, indicate the trend in the winter Arctic Oscillation can help explain observed increases in the seasonal amplitude of atmospheric CO₂ concentration.

The MC1 Dynamic General Vegetation Model (DGVM) was used to assess the impacts of global warming on North American ecosystems, north of Mexico, under 6 future climate scenarios (3 General Circulation Models X 2 emission scenarios).  The simulations were begun in 1900 using observed climate and CO₂ until 2000, then transferring to the future scenarios to 2100.  Carbon sequestration over the continent occurred in the late 20^th century and for a short period into the 21^st century, being fostered largely by increased precipitation, enhanced water-use efficiency and mild temperature increases.  However, these ‘greening’ processes were overtaken by the exponential effects of increasing temperature on evaporative demand and respiration, producing a subsequent decline. Simulation experiments suggested that fire suppression could significantly mitigate the carbon losses, yet many ecosystems were still forced to a lower carrying capacity.

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.