A biogenic emissions scheme is incorporated in the global dynamic vegetation model ORCHIDEE (Organizing Carbon and Hydrology in Dynamic EcosystEms) in order to calculate global biogenic emissions of isoprene, monoterpenes, methanol, acetone, acetaldehyde, formaldehyde and formic and acetic acids. Important parameters such 5 as the leaf area index are fully determined by the global vegetation model and the influences of light extinction (for isoprene emissions) and leaf age (for isoprene and methanol emissions) are also taken into account. We study the interannual variability of biogenic emissions using the satellite-based climate forcing ISLSCP-II as well as relevant CO 2 atmospheric levels, for the 1983-1995 period. Mean global emis-10 sions of 460 TgC/year for isoprene, 117 TgC/year for monoterpenes, 106 TgC/year for methanol and 42 TgC/year for acetone are predicted. The mean global emission of all biogenic compounds is 752±16 TgC/yr with extremes ranging from 717 TgC/yr in 1986 to 778 TgC/yr in 1995, that is a 8.5% increase between both. This variability differs significantly from one region to another and among the regions studied, biogenic emis-15 sions anomalies were the most variable in Europe and the least variable in Indonesia (isoprene and monoterpenes) and North America (methanol). Year-to-year variability also reveals a strong correlation of emissions in tropical regions with El Niño events, particularly for isoprene, for which the tropical regions are a major source. Two scenarios of land use changes are considered using the 1983 climate and atmospheric 20 CO 2 conditions, to study the sensitivity of biogenic emissions to vegetation alteration, namely tropical deforestation and European afforestation. Global biogenic emissions are highly affected by tropical deforestation, with a 29% decrease in isoprene emission and a 22% increase in methanol emission. Global emissions are not significantly affected by European afforestation, but on a European scale, total biogenic VOCs emis-25 sions increase by 54%. Abstract Introduction Conclusions ReferencesTables 25 penes emissions but also methanol, acetone, acetaldehyde, formaldehyde, formic and acetic acids. In Sect. 2 of this paper, we describe the interactive biogenic emission and vegetation global dynamic vegetation model, Geophys. Res. Lett.

The existence of a feedback between climate and methane (CH₄) emissions from wetlands has previously been hypothesized, but both its sign and amplitude remain unknown. Moreover, this feedback could interact with the climate-CO₂ cycle feedback, which has not yet been accounted for at the global scale. These interactions relate to (i) the effect of atmospheric CO₂ on methanogenic substrates by virtue of its fertilizing effect on plant productivity and (ii) the fact that a climate perturbation due to CO₂ (respectively CH₄) radiative forcing has an effect on wetland CH₄ emissions (respectively CO₂ fluxes at the surface/atmosphere interface).

We present a theoretical analysis of these interactions, which makes it possible to express the magnitude of the feedback for CO₂ and CH₄ alone, the additional gain due to interactions between these two feedbacks and the effects of these feedbacks on the difference in atmospheric CH₄ and CO₂ between 2100 and pre-industrial time (respectively ΔCH₄ and ΔCO₂). These gains are expressed as functions of different sensitivity terms, which we estimate based on prior studies and from experiments performed with the global terrestrial vegetation model ORCHIDEE.

Despite high uncertainties on the sensitivity of wetland CH₄ emissions to climate, we found that the absolute value of the gain of the climate-CH₄ feedback from wetlands is relatively low (<30% of climate-CO₂ feedback gain), with either negative or positive sign within the range of estimates. Whereas the interactions between the two feedbacks have low influence on ΔCO₂, the ΔCH₄ could increase by 475 to 1400 ppb based on the sign of the C-CH₄ feedback gain.

Our study suggests that it is necessary to better constrain the evolution of wetland area and the substrate for methanogenesis under future climate change, as these are the dominant sources of uncertainty in our model

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Abstract. Land cover in sub-polar and alpine regions of northern and eastern Europe have already begun changing due to natural and anthropogenic changes such as afforestation. This will impact the regional climate and hydrology upon which societies in these regions are highly reliant. This study aims to identify the impacts of afforestation/reforestation (hereafter afforestation) on snow and the snow-albedo effect and highlight potential improvements for future model development. The study uses an ensemble of nine regional climate models for two different idealised experiments covering a 30-year period; one experiment replaces most land cover in Europe with forest, while the other experiment replaces all forested areas with grass. The ensemble consists of nine regional climate models composed of different combinations of five regional atmospheric models and six land surface models. Results show that afforestation reduces the snow-albedo sensitivity index and enhances snowmelt. While the direction of change is robustly modelled, there is still uncertainty in the magnitude of change. The greatest differences between models emerge in the snowmelt season. One regional climate model uses different land surface models which shows consistent changes between the three simulations during the accumulation period but differs in the snowmelt season. Together these results point to the need for further model development in representing both grass–snow and forest–snow interactions during the snowmelt season. Pathways to accomplishing this include (1) a more sophisticated representation of forest structure, (2) kilometre-scale simulations, and (3) more observational studies on vegetation–snow interactions in northern Europe.