Global Carbon Storage Research Articles

Historical variations in terrestrial biospheric carbon storage

Changes in carbon storage in terrestrial ecosystems are a consequence of shifts in the balance between net primary production (NPP) and heterotrophic respiration (RH). Historical climatic variations which favored NPP over RH may have led to increased ecosystem carbon storage and might account for at least part of the “missing” sink required to balance the current century's global carbon budget. To test this hypothesis, we employed a georeferenced global terrestrial biosphere model of 0.5° spatial resolution. The model was driven from an assumed equilibrium in 1900 using gridded historical time series of monthly temperature and precipitation and the historical record of changes in atmospheric CO2 concentration. Interannual variability in climate induced interannual changes in terrestrial biospheric carbon storage and net carbon exchange with the atmosphere of the order of 1–2 Gt C yr−1. With climate change alone, global biospheric carbon storage declined by 1% (23 Gt C) over the period 1900–1988. With the addition of a moderate CO2 fertilization response, biospheric carbon storage increased by 3% (57 Gt C), primarily as a consequence of changes in NPP and litter inputs to the soil system. With CO2 fertilization, the model's cumulative carbon sink for the period 1900–1988 accounts for about 69% of the missing sink derived by deconvolution. For the period 1950–1988, the modeled sink is about 56% of the missing sink. Our results suggest that the temporal evolution of the missing sink over the period 1900–1988 could be a response of the terrestrial biosphere to changes in climate and atmospheric CO2 or perhaps climate change alone. The discrepancy in the magnitudes of the modeled and deconvolved sinks may be due to limitations of the biospheric model or to overestimates of the land‐use source flux.

Linking a global terrestrial biogeochemical model and a 2-dimensional climate model: implications for the global carbon budget

We used the terrestrial ecosystem model (TEM, version 4.0) to estimate global responses of annual net primary production (NPP) and total carbon storage to changes in climate and atmospheric CO2, driven by the climate outputs from the 2-dimensional MIT L-O climate model and the 3-dimensional GISS and GFDL-q atmospheric general circulation models (GCMs). For contemporary climate with 315 ppmv CO2, TEM estimates that global NPP is 47.9 PgC/yr and global total carbon storage is 1658 PgC: 908 PgC of vegetation carbon and 750 PgC of reactive soil organic carbon. For climate change associated with a doubling of radiative forcing and an atmospheric level of 522 ppmv CO2, the responses of global NPP are + 17.8% for the MIT L-O climate, + 18.5% for the GFDL-q climate and + 20.6% for the GISS climate. The responses of global total carbon storage are + 6.9% for the MIT L-O climate, + 8.3% for GFDL-q climate and + 8.7% for the GISS climate. Among the three climate change predictions, the changes in latitudinal distributions of cumulative NPP and total carbon storage along 0.5° latitudinal bands vary slightly, except in high latitudes. There are generally minor differences in cumulative NPP and total carbon storage for most of the 18 biomes, except for the responses of total carbon storage in boreal biomes for the 2-D MIT L-O climate change. The results demonstrate that the linkage between the TEM and the 2-D climate model is useful for impact assessment and uncertainty analysis within an integrated assessment framework at the scales of the globe, economic regions and biomes, given the compromise between computational efficiency in the 2-D climate model and more detailed spatial representation of climate fields in 3-D GCMs.

The Potential Response of Terrestrial Carbon Storage to Changes in Climate and Atmospheric CO 2

We use a georeferenced model of ecosystem carbon dynamics to explore the sensitivity of global terrestrial carbon storage to changes in atmospheric CO2 and climate. We model changes in ecosystem carbon density, but we do not model shifts in vegetation type. A model of annual NPP is coupled with a model of carbon allocation in vegetation and a model of decomposition and soil carbon dynamics. NPP is a function of climate and atmospheric CO2 concentration. The CO2 response is derived from a biochemical model of photosynthesis. With no change in climate, a doubling of atmospheric CO2 from 280 ppm to 560 ppm enhances equilibrium global NPP by 16.9%; equilibrium global terrestrial ecosystem carbon (TEC) increases by 14.9%. Simulations with no change in atmospheric CO2 concentration but changes in climate from five atmospheric general circulation models yield increases in global NPP of 10.0–14.8%. The changes in NPP are very nearly balanced by changes in decomposition, and the resulting changes in TEC range from an increase of 1.1% to a decrease of 1.1%. These results are similar to those from analyses using bioclimatic biome models that simulate shifts in ecosystem distribution but do not model changes in carbon density within vegetation types. With changes in both climate and a doubling of atmospheric CO2, our model generates increases in NPP of 30.2–36.5%. The increases in NPP and litter inputs to the soil more than compensate for any climate stimulation of decomposition and lead to increases in global TEC of 15.4–18.2%.

Carbon storage along a latitudinal transect in Alaska

Global warming is anticipated to have a significant impact on high-latitude ecosystems which store large amounts of C in their soils and have a predominance of permafrost. The purpose of this study was to estimate the total C storage of different ecosystems along a north-south transect in Alaska. Soil pedons from three Alaska climate zones were studied. These zones were the arctic slope with continuous permafrost and vegetation predominantly tussock tundra and coastal marsh, Interior Alaska with discontinuous permafrost and vegetation predominantly spruce forest on the upland and tundra or bog in the lowland, and Southern Alaska free of permafrost with the vegetation predominantly mixed hardwood and conifers with moss bogs. Soil samples were taken from the representative ecosystems of these zones for carbon storage analysis. In the Arctic and Interior Alaska zones, many soils are cryoturbated and as a result the horizons are warped and often broken. These conditions made it impractical to use the common method for estimating C storage that is used for soils with roughly parallel horizons. For this study the linear proportion of each horizon in the cryoturbated pedon was digitized by using a Geographic Information System (GIS) and the irregular horizons were collapsed to form a simulated profile with parallel horizons. The carbon content of each pedon was then calculated based on the linear proportions. These carbon stores based on the whole soil (1 m deep) approach were compared to other available estimates from the literature. Calculations for pedons from selected ecosystems in Alaska ranged from 169 MgC/ha to 1292 MgC/ha. The organic carbon storage of the arctic coastal marsh pedon amounted to 692 MgC/ha, and that of the arctic tundra pedon amounted to 314 and 599 MgC/ha. The carbon storage of interior forest pedons was 169 and 787 MgC/ha, and the associated organic soil stored nearly 1300 MgC/ha. The carbon storage in the mixed forest and coastal forest pedons was 240 and 437 MgC/ha, respectively. The bog associated with the mixed and coastal forest stored 1260 MgC/ha. Soils with the thickest organic layers were bogs associated with the tundra and boreal forest. These soils had the largest carbon storage. Carbon stores estimated from the whole pedon approach are 30 to 100% higher than those from the literature from the same zones. These data suggest that the global carbon storage estimates based in part on literature values from the N. latitudes, may be underestimated.

Biotic feedbacks in the global climatic system: will the warming feed the warming?

Part I: Global Warming: Perspectives from Land and Sea 1. Biotic feedbacks from the arming of the earth 2. Climatically important biogenic gases and feedbacks on global climatic change Part II: Biotic Processes and Potential Feedbacks 3. Plant physiological responses to elevated CO temperature, air pollution and UV-B radiation 4. On the potential for a CO fertilization effect in forest trees: An assessment of 58 controlled-exposure studies and estimates of the biotic growth factor 5. Indicators of climatic and biospheric change: Evidence from tree-rings 6. Global climate change: Disturbance regimes and biospheric feedbacks of temperate and boreal forests 7. Permafrost and vegetation response to global warming in North Eurasia 8. Soil respiration and change in soil carbon stocks 9. The biogeochemistry of Northern peatlands and its possible responses to global warming 10. Methane output from natural and quasi-natural sources 11. Linkages between carbon and nitrogen cycling and their implication for storage of carbon in terrestrial ecosystems 12. Biofeedback in the ocean in response to climate change 13. Net carbon metabolism of oceanic margins and estuaries 14. Biogenic dimethyl sulphide, marine aerosol and climate 15. Implications of increased solar UVB for aquatic ecosystems Part III. Global Carbon Budgets, Models and Geophysical Constraints 16. Modelling interactions of carbon dioxide, forests, and climate 17. Vegetation geography and global carbon storage changes 18. CO climate feedbacks 19. Effects of land-use change 20. Storage versus flux budgets 21. Perturbations to the biospheric carbon cycle Part IV: Biotic Feedbacks in the Global Climatic System 22. What we need to know 23. Will the arming feed the warming Index

The potential response of global terrestrial carbon storage to a climate change

The potential response of global terrestrial carbon storage to a climate change

Modelling Global Vegetation Patterns and Terrestrial Carbon Storage at the Last Glacial Maximum

Global patterns of potential natural vegetation were simulated for present and last glacial maximum (LGM) climates. The LGM simulation showed good agreement with available evidence, most importantly in the humid tropics. Simple calculations based on these simulations indicate that terrestrial carbon storage increased by 300-700 Pg C after the LGM. The range is due to uncertainties in the mean carbon storage values for different biomes, and in the amount of carbon in boreal peats. These results are consistent with the global change in ocean 8'3C, inferred from measurements on benthic foraminifera, reflecting the increased storage of isotopically light carbon on land.

Biomass and carbon storage of the North American deciduous forest

Field measures of tree and shrub dimensions were used with established biomass equations in a stratified, two-stage cluster sampling design to estimate above-ground ovendry woody biomass and carbon storage of the eastern deciduous forest of North America. Biomass averaged 8.1 ± 1.4 (95% C.I.) kg/m2 and totaled 18.1 ± 3.1 (95% C.I.) gigatons. Carbon storage averaged 3.6 ± 0.6 (95% C.I.) kg/m2 and totaled 8.1 ± 1.4 (95% C.I.) gigatons. These values are lower than previous estimates commonly used in the analysis of the global carbon budget which range from 17.1 to 23.1 kg/m2 for biomass and 7.7 to 10.4 kg/m2 for carbon storage. These new estimates for the deciduous forest, together with earlier work in the boreal forest begin to reveal a pattern of overestimation of global carbon storage by vegetation in analyses of the global carbon budget. We discuss reasons for the differences between the new and earlier estimates, as well as implications for our understanding of the global carbon cycle.

The response of terrestrial c storage to climate change: Modeling C dynamics at varying temporal and spatial scales

The response of terrestrial C storage to GCM derived climate change scenarios was investigated over a range of temporal and spatial scales. The potential changes in the global distribution of major ecosystem complexes were examined by combining changes in land cover and corresponding soil type with C storage estimates for each of the ecosystem types. All scenarios consistently showed an overall increase in global carbon storage. On a more regional basis, the potential impacts of climate change on the structure, composition and biomass dynamics of major forest types within the North American Boreal zone were investigated using individual based stand models. Biomass fluxes were found to be dependent on the tree species, site and GCM parameters. A method to simulate corresponding changes in intra- and interannual patterns of CO2 flux by combining a gap model with an ecosystem model which incorporates photosynthesis, respiration (both canopy and decomposer) and transpiration is demonstrated.

The global carbon cycle and climate change: Responses and feedbacks from below-ground systems

According to most global climate models, a continued build-up of CO 2 and other greenhouse gases will lead to significant changes in temperature and precipitation patterns over large parts of the Earth. Below-ground processes will strongly influence the response of the biosphere to climate change and are likely to contribute to positive or negative biospheric feedbacks to climate change. Current global carbon budgets suggest that as much as 2000 Pg of carbon exists in soil systems. There is considerable disagreement, however, over pool sizes and flux (e.g. CO 2, CH 4) for various ecosystems. An equilibrium analysis of changes in global below-ground carbon storage due to a doubled-CO 2 climate suggests a range from a possible sink of 41 Pg to a possible source of 101 Pg. Components of the terrestrial biosphere could be managed to sequester or conserve carbon and mitigate accumulation of greenhouse gases in the atmosphere.