The Potential Effects of Elevated Co2 and Climate Change on Tropical Forest Soils and Biogeochemical Cycling

Tropical forests are responsible for a large proportion of the global terrestrial C flux annually for natural ecosystems. Increased atmospheric CO₂ and changes in climate are likely to affect the distribution of C pools in the tropics and the rate of cycling through vegetation and soils. In this paper, I review the literature on the pools and fluxes of carbon in tropical forests, and the relationship of these to nutrient cycling and climate. Tropical moist and humid forests have the highest rates of annual net primary productivity and the greatest carbon flux from soil respiration globally. Tropical dry forests have lower rates of carbon circulation, but may have greater soil organic carbon storage, especially at depths below 1 meter. Data from tropical elevation gradients were used to examine the sensitivity of biogeochemical cycling to incremental changes in temperature and rainfall. These data show significant positive correlations of litterfall N concentrations with temperature and decomposition rates. Increased atmospheric CO₂ and changes in climate are expected to alter carbon and nutrient allocation patterns and storage in tropical forest. Modeling and experimental studies suggest that even a small increase in temperature and CO₂ concentrations results in more rapid decomposition rates, and a large initial CO₂ efflux from moist tropical soils. Soil P limitation or reductions in C:N and C:P ratios of litterfall could eventually limit the size of this flux. Increased frequency of fires in dry forest and hurricanes in moist and humid forests are expected to reduce the ecosystem carbon storage capacity over longer time periods.     

Future Expansion Of Agriculture and Pasture Acts to Amplify Atmospheric CO<Subscript>2</Subscript> Levels in Response to Fossil-Fuel and Land-Use Change Emissions

The expansion of crop and pastures to the detriment of forests results in an increase in atmospheric CO₂. The first obvious cause is the loss of forest biomass and soil carbon during and after conversion. The second, generally ignored cause, is the reduction of the residence time of carbon when, for example, forests or grasslands are converted to cultivated land. This decreases the sink capacity of the global terrestrial biosphere, and thereby may amplify the atmospheric CO₂ rise due to fossil and land-use carbon release. For the IPCC A2 future scenario, characterized by high fossil and high land-use emissions, we show that the land-use amplifier effect adds 61 ppm extra CO₂ in the atmosphere by 2100 as compared to former treatment of land-use processes in carbon models. Investigating the individual contribution of each of the six land-use transitions (forest &#x02194; crop, forest &#x02194; pasture, grassland crop) to the amplifier effect indicates that the clearing of forest and grasslands to arable lands explains most of the CO₂ amplification. The amplification effect is 50% higher than in a previous analysis by the same authors which considered neither the deforestation of pastures nor the ploughing of grasslands. Such an amplification effect is further examined in sensitivity tests where the net primary productivity is considered independent of the atmospheric CO₂. We also show that the land-use changes, which have already occurred in the recent past, have a strong inertia at releasing CO₂, and will contribute to about 1/3 of the amplification effect by 2100. These results suggest that there is an additional atmospheric benefit of preserving pristine ecosystems with high turnover times.     

Future Expansion Of Agriculture and Pasture Acts to Amplify Atmospheric CO2 Levels in Response to Fossil-Fuel and Land-Use Change Emissions

The expansion of crop and pastures to the detriment of forests results in an increase in atmospheric CO₂. The first obvious cause is the loss of forest biomass and soil carbon during and after conversion. The second, generally ignored cause, is the reduction of the residence time of carbon when, for example, forests or grasslands are converted to cultivated land. This decreases the sink capacity of the global terrestrial biosphere, and thereby may amplify the atmospheric CO₂ rise due to fossil and land-use carbon release. For the IPCC A2 future scenario, characterized by high fossil and high land-use emissions, we show that the land-use amplifier effect adds 61 ppm extra CO₂ in the atmosphere by 2100 as compared to former treatment of land-use processes in carbon models. Investigating the individual contribution of each of the six land-use transitions (forest &#x02194; crop, forest &#x02194; pasture, grassland crop) to the amplifier effect indicates that the clearing of forest and grasslands to arable lands explains most of the CO₂ amplification. The amplification effect is 50% higher than in a previous analysis by the same authors which considered neither the deforestation of pastures nor the ploughing of grasslands. Such an amplification effect is further examined in sensitivity tests where the net primary productivity is considered independent of the atmospheric CO₂. We also show that the land-use changes, which have already occurred in the recent past, have a strong inertia at releasing CO₂, and will contribute to about 1/3 of the amplification effect by 2100. These results suggest that there is an additional atmospheric benefit of preserving pristine ecosystems with high turnover times.     

The role of land surface dynamics in glacial inception: a study with the UVic Earth System Model

The first results of the UVic Earth System Model coupled to a land surface scheme and a dynamic global vegetation model are presented in this study. In the first part the present day climate simulation is discussed and compared to observations. We then compare a simulation of an ice age inception (forced with 116 ka BP orbital parameters and an atmospheric CO₂ concentration of 240 ppm) with a preindustrial run (present day orbital parameters, atmospheric [CO₂] = 280 ppm). Emphasis is placed on the vegetations response to the combined changes in solar radiation and atmospheric CO₂ level. A southward shift of the northern treeline as well as a global decrease in vegetation carbon is observed in the ice age inception run. In tropical regions, up to 88% of broadleaf trees are replaced by shrubs and C₄ grasses. These changes in vegetation cover have a remarkable effect on the global climate: land related feedbacks double the atmospheric cooling during the ice age inception as well as the reduction of the meridional overturning in the North Atlantic. The introduction of vegetation related feedbacks also increases the surface area with perennial snow significantly.     

Global transport and inter-reservoir exchange of carbon dioxide with particular reference to stable isotopic distributions

A two-dimensional model of global atmospheric transport is used to relate estimated air-to-surface exchanges of carbon dioxide (CO₂) to spatial and temporal variations of atmospheric CO₂ concentrations and isotopic composition. The atmospheric model coupled with models of the biosphere and mixed layer of the ocean describes the gross features of the global carbon cycle. In particular this paper considers the change in isotopic composition due to interreservoir exchanges and thus the potential application and measurement requirements of new isotopic observational programs.A comparison is made between the model-generated CO₂ concentration variation and those observed on secular, interannual and seasonal time scales and spatially through the depth of the troposphere and meridionally from pole-to-pole.The relationship between isotopic and concentration variation on a seasonal time-scale is discussed and it is shown how this can be used to quantitatively estimate relative contributions of biospheric and oceanic CO₂ exchange. Further, it is shown that the interhemispheric gradient of concentration and isotopic ratio results primarily from the redistribution of fossil fuel CO₂. Both isotopic and concentration data indicate that tropical deforestation contributes less than 2 Gt yr^-1 of carbon to the atmosphere.The study suggests that changes in the rate of change of the ratio of ¹³C to ¹²C in the atmosphere of less than 0.03 yr^-1 might be expected if net exchanges with the biosphere are the cause of interannual variations of CO₂ concentrations.     

Historical and experimental evidence for enhanced concentration of artemesinin,a global anti-malarial treatment,with recent and projected increases in atmospheric carbon dioxide

Although the role of rising atmospheric carbon dioxide concentration [CO₂] on plant growth and fecundity is widely acknowledged as important within the scientific community; less research is available regarding the impact of [CO₂] on secondary plant compounds, even though such compounds can play a significant role in human health. At present, Artemisia annua, an annual plant species native to China, is widely recognized as the primary source of artemesinin used in artemesinin combination therapies or ACTs. ACTs, in turn, are used globally for the treatment of simple Plasmodium falciparum malaria, the predominant form of malaria in Africa. In this study, artemesinin concentration was quantified for multiple A. annua populations in China using a free-air CO₂ enrichment (FACE) system as a function of [CO₂]-induced changes both in situ and as a function of the foliar ratio of carbon to nitrogen (C:N). The high correlation between artemesinin concentration and C:N allowed an historical examination of A. annua leaves collected at 236 locations throughout China from 1905 through 2009. Both the historical and experimental data indicate that increases in artemesinin foliar concentration are likely to continue in parallel with the ongoing increase in atmospheric [CO₂]. The basis for the [CO₂]-induced increase in artemesinin is unclear, but could be related to the carbon: nutrient hypothesis of Bryant et al. (1983). Overall, these data provide the first evidence that historic and projected increases in atmospheric [CO₂] may be associated with global changes in artemesinin chemistry, potentially allowing a greater quantity of drug available for the same area of cultivation.     

Determination of tropospheric mean carbon dioxide concentration from satellite high spectral resolution IR-sounder data

In view of the importance of studying a global carbon cycle and inadequacy of a ground-based network of observations of the atmospheric carbon dioxide (CO₂) concentrations and its fluxes, the feasibility of remote sensing of the atmospheric CO₂ concentration obtained from the satellite high-spectral resolution IR-sounder data is studied. In reference to the AIRS infrared-sounder measurements (the EOS Aqua satellite) the satellite data informativeness is analyzed, and a subset of most sensitive channels in respect to the CO₂ concentration variations is selected. A method of retrieving the carbon dioxide concentration \(X_{CO_2 } \) averaged over height from the AIRS data (in the middle and upper troposphere) is suggested and tested. The method is based on a numerical solution of an inverse problem. The comparison of satellite estimates of \(X_{CO_2 } \) averaged over a month with the aircraft (in situ) data on observations over the areas of boreal forests (the Novosibirsk region) and ecosystems (the region of Surgut) for 10 months of 2003 confirms the possibility to trace a seasonal trend of \(X_{CO_2 } \) with an error not worse than 1%.     

RESPONSES OF A GLOBAL CGCM TO CO2 INCREASE

The responses of the climate system to increase of atmospheric carbon dioxide(CO₂)arestudied by using a new version of the Bureau of Meteorological Research Centre(BMRC)globalcoupled general circulation model(CGCM).Two simulations are run:one with atmospheric CO₂concentration held constant at 330 ppm,the other with a tripling of atmospheric CO₂(990 ppm).Results from the 41-year control coupled integration are applied to analyze the mean state,seasonal cycle and interannual variability in the model.Comparisons between the greenhouseexperiment and the control experiment then provide estimations of the influence of increased CO₂on climate changes and climate variability.Especially discussed is the question on whether theclimate changes concerned with CO₂ inerease will impact interannual variability in tropical Pacific,such as ENSO.     

Global climatic change,hurricanes, and a tropical forest

Most, if not all forests in the Caribbean are subject to occasional disturbances from hurricanes. If current general circulation model (GCM) predictions are correct, with doubled atmospheric CO₂ (2 × CO₂), the tropical Atlantic will be between 1 °C and 4 °C warmer than it is today. With such a warming, more than twice as many hurricanes per year could be expected in the Caribbean. Furthermore, Emanuael (1987) indicates that in a warmed world the destructive potential of Atlantic hurricanes could be increased by 40% to 60%. While speculative, these increases would dramatically change the disturbance regimes affecting tropical forests in the region and might alter forest structure and composition. Global warming impacts through increased hurricane damage on Caribbean forests are presented.An individual tree, gap dynamics forest ecosystem model was used to simulate the range of possible hurricane disturbance regimes which could affect the Luquillo Experimental Forest in Puerto Rico. Model storm frequency ranged from no storms at all up to one storm per year; model storm intensity varied from no damage up to 100% mortality of trees. The model does not consider the effects of changing temperature and rainfall patterns on the forest. Simulation results indicate that with the different hurricane regimes a range of forest types are possible, ranging from mature forest with large trees, to an area in which forest trees are never allowed to reach maturity.     

The increasing CO2 concentration in the atmosphere and its implication on agricultural productivity

The increasing concentration of CO₂ in the atmosphere should result in a general increase in the net primary productivity of most cultivated species and forest species, assuming no counterproductive climatic changes occur. The photosynthetic rate of C₃ plants is most responsive to increasing concentration of CO₂ in the ambient air. C₄ plants demonstrate a stomatal closure that causes reduced transpiration. In the case of both types of plants, the water use efficiency (photosynthesis/transpiration) is likely to be improved.It has been suggested that photosynthetic production may be limited today more by shortages of water and nutrients than by shortages of carbon dioxide. The author speculates that the inadvertant CO₂-fertilization now occurring could, in itself, cause a moderate release from these constraints.Physiological responses to an increased atmospheric CO₂ concentration are easily demonstrated in controlled environment studies. Because of the difficulty in maintaining artifically enriched air near the crop against the forces of turbulent transfer, studies in the open field have been inconclusive. The observation of decreased photosynthetic rate in a perennial crop during that part of the growing season when CO₂ concentration is naturally low suggests a technique by which it may be possible to infer what will happen in the real world of agricultural fields if a CO₂-rich environment, such as is predicted in the coming decades, materializes. Inferences from the very limited set of data available support the view that net photosynthetic production will be increased.Published as Paper No. 6123, Journal Series, Nebraska Agricultural Experiment Station. The work reported was conducted under Regional Research Project 11–33 and Nebraska Agricultural Experiment Station Project 1149.George Holmes Professor of Agricultural Meteorology, Center for Agricultural Meteorology and Climatology, Institute of Agriculture and Natural Sources, University of Nebraska-Lincoln, Lincoln, NE 68583, U.S.A.     

Detecting a Terrestrial Biosphere Sink for Carbon Dioxide: Interannual Ecosystem Modeling for the Mid-1980s

There is considerable uncertainty as to whether interannual variability in climate and terrestrial ecosystem production is sufficient to explain observed variation in atmospheric carbon content over the past 20–30 years. In this paper, we investigated the response of net CO₂ exchange in terrestrial ecosystems to interannual climate variability (1983 to 1988) using global satellite observations as drivers for the NASA-CASA (Carnegie-Ames-Stanford Approach) simulation model. This computer model of net ecosystem production (NEP) is calibrated for interannual simulations driven by monthly satellite vegetation index data (NDVI) from the NOAA Advanced Very High Resolution Radiometer (AVHRR) at 1 degree spatial resolution. Major results from NASA-CASA simulations suggest that from 1985 to 1988, the northern middle-latitude zone (between 30 and 60°N) was the principal region driving progressive annual increases in global net primary production (NPP; i.e., the terrestrial biosphere sink for carbon). The average annual increase in NPP over this predominantly northern forest zone was on the order of +0.4 Pg (10¹⁵ g) C per year. This increase resulted mainly from notable expansion of the growing season for plant carbon fixation toward the zonal latitude extremes, a pattern uniquely demonstrated in our regional visualization results. A net biosphere source flux of CO₂ in 1983–1984, coinciding with an El Niño event, was followed by a major recovery of global NEP in 1985 which lasted through 1987 as a net carbon sink of between 0.4 and 2.6 Pg C per year. Analysis of model controls on NPP and soil heterotrophic CO₂ fluxes (R_h) suggests that regional warming in northern forests can enhance ecosystem production significantly. In seasonally dry tropical zones, periodic drought and temperature drying effects may carry over with at least a two-year lag time to adversely impact ecosystem production. These yearly patterns in our model-predicted NEP are consistent in magnitude with the estimated exchange of CO₂ by the terrestrial biosphere with the atmosphere, as determined by previous isotopic (¹³C) deconvolution analysis. Ecosystem simulation results can help further target locations where net carbon sink fluxes have occurred in the past or may be verified in subsequent field studies.     

Sensitivity of terrestrial carbon storage to CO2-induced climate change: Comparison of four scenarios based on general circulation models

The potential impacts of CO₂-induced climate change on terrestrial carbon storage was estimated using the Holdridge Life-Zone Classification and four climate change scenarios derived from general circulation models. Carbon values were assigned to life-zones and their associated soils from published studies. All four scenarios suggest an increase in area occupied by forests although details of predicted patterns vary among the scenarios. There is a poleward shift of the forested zones, with an increase in the areal extent of tropical forests and a shift of the boreal forest zone into the region currently occupied by tundra. Terrestrial carbon storage increased from 0.4% (8.5 Gt) to 9.5% (180.5 Gt) above estimates for present conditions. These changes represent a potential reduction of 4 to 85 ppm on elevated atmospheric CO₂ levels.     

Impact of anthropogenic CO 2 on the next glacial cycle

The model of Paillard and Parrenin (Earth Planet Sci Lett 227(3–4):263–271, 2004) has been recently optimized for the last eight glacial cycles, leading to two different relaxation models with model-data correlations between 0.8 and 0.9 (García-Olivares and Herrero (Clim Dyn 1–25, 2012b)). These two models are here used to predict the effect of an anthropogenic CO ₂ pulse on the evolution of atmospheric CO ₂, global ice volume and Antarctic ice cover during the next 300 kyr. The initial atmospheric CO ₂ condition is obtained after a critical data analysis that sets 1300 Gt as the most realistic carbon Ultimate Recoverable Resources (URR), with the help of a global compartmental model to determine the carbon transfer function to the atmosphere. The next 20 kyr will have an abnormally high greenhouse effect which, according to the CO ₂ values, will lengthen the present interglacial by some 25 to 33 kyr. This is because the perturbation of the current interglacial will lead to a delay in the future advance of the ice sheet on the Antarctic shelf, causing that the relative maximum of boreal insolation found 65 kyr after present (AP) will not affect the developing glaciation. Instead, it will be the following insolation peak, about 110 kyr AP, which will find an appropriate climatic state to trigger the next deglaciation.     

The warming of the industrialized middle latitudes 1985–2050: Causes and consequences

The dominant influence on global climate for the indefinite future is expected to be a warming in the middle and high latitudes of both hemispheres. The speed of the warming is uncertain. The warming in winter may exceed 1.0 degree per decade. The warming in summer is expected to be less. The cause is the accumulation of infra-red absorptive gases, especially CO₂ and CH₄, in the atmosphere. The sources are the combustion of fossil fuels, the destruction of forests and their soils, and, possibly, the warming itself, which can be expected to stimulate decay of organic matter in soils. The warming in these latitudes is expected to be accompanied by increased precipitation as climatic zones migrate generally poleward. A 1 °C change in mean temperature is equivalent to a change in latitude of 100–150 km. The changes expected are rapid enough to exceed the capacity of forests to migrate or otherwise adapt. Forest trees will die at their warmer and drier limits of distribution more rapidly than forests can be regenerated in regions where climates become favorable. The destruction of forests will add further to the releases of C to the atmosphere. There is no equivalent countervailing storage that has been identified. The result suggests that a significant enhancement of the warming beyond current predictions is to be expected. An open-ended, accelerating warming of the Earth at rates that bring rapid changes in climatic zones, drive forests to impoverishment, and raise sea level rapidly is beyond the limits of simple adjustments of the human enterprise. Steps to stabilize the atmospheric composition seem inevitable. Because the total emissions of C to the atmosphere are not known, the current rate of transfer from the atmosphere to the oceans is uncertain. But whatever the current total release to the atmosphere, the annual atmospheric increase is about 3.0 G-tons of C as CO₂. At least three possibilities exist for reducing or eliminating the imbalance and moving toward long-term stability:

1. a reduction in the use of fossil fuels globally, now estimated as the source of about 5.6 G-tons of C annually;
2. a reduction or cessation of deforestation, now estimated as releasing 1–3 G-tons annually;
3. a vigorous program of reforestation that would remove from the atmosphere into storage in plants and soils about 1 G-ton of C annually for each 2 × 10⁶ km² tract reforested.

Further adjustments in emissions will be appropriate as experience accumulates. Such steps are appropriate now and possible. They will bring widespread ancillary benefits to the human enterprise.     

Effects of Climate Change on Carbon Storage in Boreal Forests of China: A Local Perspective

The BIOME3 model was used to simulate the distribution patterns and carbon storage of the horizontal, zonal boreal forests in northeast and northwest China using a mapping system for vegetation patterns combined with carbon density estimates from vegetation and soils. The BIOME3 prediction is in reasonable good agreement with the potential distribution of Chinese boreal forests. The effects of changing atmospheric CO₂ concentration had a nonlinear effect on boreal forest distribution, with 3.5–10.8% reduced areas for both increasing and decreasing CO₂. In contrast, the increased climate together with and without changing CO₂ concentration showed dramatic changes in geographic patterns, with 70% reduction in area and disappearance of almost boreal forests in northeast China. The baseline carbon storage in boreal forests of China is 4.60 PgC (median estimate) based on the vegetation area of actual boreal forest distribution. If taking the large area of agricultural crops into account, the median value of potential carbon storage is 6.92 PgC. The increasing (340–500 ppmv) and decreasing CO₂ concentration (340–200 ppmv) led to decrease of carbon storage, 0.33 PgC and 1.01 PgC respectively compared to BIOME3 potential prediction under present climate and CO₂ conditions. Both climate change alone and climate change with CO₂ enrichment (340–500 ppmv) reduced largely the carbon stored in vegetation and soils by ca. 6.5 PgC. The effect of climate change is more significant than the direct physiological effect of CO₂ concentration on the boreal forests of China, showing a large reduction in both distribution area and carbon storage.     

Present and future surface climate in the western USA as simulated by 15 global climate models

We analyze results of 15 global climate simulations contributed to the Coupled Model Intercomparison Project (CMIP). Focusing on the western USA, we consider both present climate simulations and predicted responses to increasing atmospheric CO₂. The models vary in their ability to predict the present climate. In the western USA, a few models produce a seasonal cycle for spatially averaged temperature and/or precipitation in good agreement with observational data. Other models tend to over-predict precipitation in the winter or exaggerate the amplitude of the seasonal cycle of temperature. The models also differ in their ability to reproduce the spatial patterns of temperature and precipitation in the USA. Considering the monthly mean precipitation responses to doubled atmospheric CO₂, averaged over the western USA, we find some models predict increases while others predict decreases. The predicted temperature response, on the other hand, is invariably positive over this region; however, for each month, the range of values given by the different models is large compared to the mean model response. We look for possible relationships between the models temperature and precipitation responses to doubled CO₂ concentration and their ability to simulate some aspects of the present climate. We find that these relationships are weak, at best. The precipitation response over the western USA in DJF and the precipitation response over the mid- and tropical latitudes seem to be correlated with the RMS error in simulated present-day precipitation, also calculated over the mid- and tropical latitudes. However, considering only the responses of the models with the smallest RMS errors does not provide a different estimate of the precipitation response to a doubled CO₂ concentration, because even among the most accurate models, the range of model responses is so large. For temperature, we find that models that have smaller RMS errors in present-climate temperature in the north eastern Pacific region predict a higher temperature response in the western USA than the models with larger errors. A similar relation exists between the temperature response over Europe in DJF and the RMS error calculated over the Northern Atlantic.     

Climate models and CO2-induced climatic changes

This article is a review of the modeling of potential CO₂ effects on climate, intended for an interdisciplinary audience of mathematically oriented scientists and engineers. The carbon dioxide (CO₂) content of the atmosphere has shown a systematic increase each year since regular measurements began in 1958. A major source of CO₂ is the combustion of fossil fuels. A number of studies of the sensitivity of climate to increases in the CO₂ content of the atmosphere have been published. This report is an assimilation of the results of some of these studies. The climate sensitivity problem is introduced through a discussion of the various atmospheric feedbacks and the ice albedo feedback. The most recent estimates of the various feedbacks are used to estimate upper and lower bounds of the globally averaged temperature increase that would accompany a doubling of atmospheric CO₂ content. The results of a CO₂ doubling experiment using a simple general circulation model are reviewed, and the possible response of the cryosphere is discussed.     

Time-scale and state dependence of the carbon-cycle feedback to climate

Climate and atmospheric CO₂ concentration are intimately coupled in the Earth system: CO₂ influences climate through the greenhouse effect, but climate also affects CO₂ through its impact on the amount of carbon stored on land and in the ocean. The change in atmospheric CO₂ as a response to a change in temperature ( $\varDelta CO_{2}/\varDelta T$ ) is a useful measure to quantify the feedback between the carbon cycle and climate. Using an ensemble of experiments with an Earth system model of intermediate complexity we show a pronounced time-scale dependence of $\varDelta CO_{2}/\varDelta T$ . A maximum is found on centennial scales with $\varDelta CO_{2}/\varDelta T$ values for the model ensemble in the range 5–12 ppm °C^?1, while lower values are found on shorter and longer time scales. These results are consistent with estimates derived from past observations. Up to centennial scales, the land carbon response to climate dominates the CO₂ signal in the atmosphere, while on longer time scales the ocean becomes important and eventually dominates on multi-millennial scales. In addition to the time-scale dependence, modeled $\varDelta CO_{2}/\varDelta T$ show a distinct dependence on the initial state of the system. In particular, on centennial time-scales, high $\varDelta CO_{2}/\varDelta T$ values are correlated with high initial land carbon content. A similar relation holds also for the CMIP5 models, although for $\varDelta CO_{2}/\varDelta T$ computed from a very different experimental setup. The emergence of common patterns like this could prove to usefully constrain the climate–carbon cycle feedback.     

Carbon budget of managed forests in the Russian Federation in 1990–2050: Post-evaluation and forecasting

Considered are the contribution of managed forests in the Russian Federation to the climate change softening and the forecast of their carbon-depositing potential in the period till 2050 under different scenarios of the forest management. The sink of CO₂ to managed forests is estimated using the flow balance method. The CBM-CFS3 model worked out in the Canadian Forestry Service is used for predicting the carbon budget. It is found out that managed forests absorb 473.8 Mt of CO₂ per year. The carbon sink is caused by the reduction of the volume of the forest use and by the regeneration of cutover stands of previous years. Depending on the conditions of the forest use, by 2020 the CO₂ sink to managed forests will amount to 466–632 Mt/year and will be able to compensate from 21 to 29% of industrial emissions of greenhouse gases. The carbon absorption by managed forests will decrease to 105–235 Mt/year by 2050. To maintain and increase the carbon-depositing potential of managed forests, the Russian Federation needs the development of the system of purposeful activities on strengthening the protection against forest fires and on the intensification of forest reproduction.     

Correlations among combustion effluent species at Barrow,Alaska: Aerosol black carbon,carbon dioxide,and methane

As part of the second Arctic Gas and Aerosol Sampling Program (AGASP II) continuous measurements of atmospheric aerosol black carbon (BC) were made at the NOAA/GMCC observatory at Barrow, Alaska (71°19N, 156°36W) during the period March 21–April 22, 1986. Black carbon is produced only by incomplete combustion of carbonaceous materials and so is a particularly useful atmospheric indicator of anthropogenic activities. The BC data have been analyzed together with the concurrent measurements of carbon dioxide (CO₂), methane (CH₄), and condensation nuclei (CN) that are routinely made at the observatory. All four species showed elevated and highly variable concentrations due to local human activities, principally in the township of Barrow, 7 km to the southwest, and at the DEW Line radar installation 1 km to the northwest. We distinguish between those periods of the record that are affected by local activities and those that are not, on the basis of the short-term (periods of up to 1 hour) variability of the continuous CO₂ and CN records, with large short-term variabilities indicating local sources. We identified seven periods of time (events) with durations ranging from 13 to 37 hours when the BC, CO₂, and CH₄ concentrations changed smoothly over time, were highly correlated with each other, and were not influenced by local activities. These events had BC/CO₂ ratios in the range (50–103)×10^–6. These ratios are dimensionless since we convert the CO₂ concentrations to units of ng m^–3 of carbon. Such values of BC/CO₂ are characteristic of the combustion effluent from large installations burning heavy fuel oil or coal, automobiles, and domestic-scale natural gas usage. We conclude that these events are indicative of air masses that have been polluted with combustion emissions in a distant location and then transported to the Arctic. In the absence of species-selective loss mechanisms, these air masses will maintain their combustion effluent signatures during the transport. The BC/CO₂ ratios found for the local combustion activities are consistent with those expected from known combustion processes.