Observations suggest the global reflectivity of Earth changed during recent decades. Although there is some ambiguity surrounding these findings, it is clear that, should there be changes in clouds or scattering aerosols, a change in the total solar radiation received at the surface and the fraction of diffuse light could result. Intriguingly, the d¹⁸O of CO₂ time series measured at Mauna Loa shows variability during the 1990s that does not match secular trends in CO₂ concentration or d¹³C. While a decrease in total solar radiation alone would reduce biospheric productivity, an increase in diffuse light can increase productivity, as has been argued for the period following the eruption of Pinatubo. Moreover, since the changes in radiation affect the surface latent energy exchange, the isotopic composition of terrestrial water with which CO₂ interacts (specifically leaf and soil water) will be modified and can thus drive a change in isotopic fluxes.

The carbon cycle has undergone changes from 1998-2003 as a result of extensive droughts.  The CO₂ seasonal amplitude at MLO halted its increase, and the CO₂ growth rate accelerated as a result of a slowing down of the North American carbon sink.  In a series of coupled carbon-climate model experiments, we show a greater probability of drier soils in the 21^st century, especially in the tropics and in mid-latitude summers as temperature-driven evapotranspiration exceed precipitation, and a positive feedback between the carbon cycle and climate. This positive feedback reduces the land and ocean’s capacity to store fossil fuel CO­_2­ and accelerates the warming. A fossil fuel emission accelerating rapidly as the sink capacities decrease leads to further increases in the airborne fraction of fossil fuel CO₂.

Is the massive Amazon forest a CO₂ sink, a source or is it in equilibrium?  

There is a large uncertainty in carbon fluxes estimates for the tropics as a whole and in particular for the Amazon region in South America, bringing the attention to the lack of information to call the region a carbon source or sink. The production of scientific consistent and long term data series for the region is a process that has to advance step by step.

Using discrete air sampling, atmospheric CO₂ and its stable carbon (d¹³C) and oxygen (d¹⁸O) isotopic ratios have been measured since 1994 in a cool-temperate deciduous forest in central Japan influenced strongly by the Asian monsoon. In this paper, the results are shown and the temporal variations on different time scales are discussed.

This paper examines two key feedbacks that operate between the terrestrial carbon cycle, atmospheric carbon dioxide (CO₂) and climate: the positive carbon cycle-climate feedback and the negative CO₂ fertilization feedback.  Both feedbacks affect strongly the growth rate of future atmospheric CO₂, and interact in such a way that the effect of one is notably modified in the absence of the other.

A Time Dependent Inverse (TDI) model is used to estimate CO₂ fluxes for 64 regions of the globe from atmospheric data in the period January 1988–December 2001. These estimated are then used for understanding interannual variability in fluxes and simulating the CO₂ concentrations at various sites. The NIES/FRCGC transport model driven by interannually varying meteorology is used in both part of the analysis. Estimated atmospheric CO₂ concentrations agree closely with those observed at various sites globally.

Soil moisture measurements in an Australian tropical savanna show accumulating soil water under three years of Free Air CO₂ Enrichment (FACE).  Most of this accumulation is occurring below the rooting depth of grasses.  Although this increase in stored soil water is only a fraction (< 0.3% yr^-1) of annual rainfall, it is cumulative and may advantage deep-rooted woody plants.

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.