Showing papers on "Atmospheric carbon cycle published in 1989"

Environmental Factors and Ecological Processes in Boreal Forests

Abstract: This paper reports on the boreal forest, a broad, circumpolar mixture of cool coniferous and deciduous tree species which covers over 14.7 million km{sup 2}, or 11%, of the earth's terrestrial surface. At these latitudes, a strong correlation exists between the seasonal dynamics of atmospheric carbon dioxide and the seasonal dynamics of the greenness of the earth. A possible causal relation, in which the dynamics of the forests at these latitudes regulates the atmospheric carbon concentrations, appears to be consistent with the present-day understanding of ecological processes in these ecosystems. Along with its familiar role in plant photosynthesis, carbon dioxide is a greenhouse gas that markedly affects the heat budget of the earth. Thus the possibility that boreal forests may actively participate in the dynamics of atmospheric carbon dioxide is of considerable significance, especially since the climatic response to elevated atmospheric carbon dioxide concentrations seems to be strongly directed to the boreal forests of the world.

Modeling the geochemical carbon cycle

Abstract: The authors have modeled the slow, long-term cycle in which geochemical processes transfer carbon among land, sea, and atmosphere. The model suggests that the earth may have been warmed in the past when buildups of atmospheric carbon dioxide enhanced the greenhouse effect. The model predicts that the slow natural fluctuations of atmospheric carbon dioxide may rival or even exceed the much faster changes that arise from human activities or from the biological carbon cycle. The main purpose in modeling the geochemical carbon cycle is to expose how little is known about the rates of important global processes and how seemingly unrelated processes (such as tectonism and climate) are linked.

Forests: a tool to moderate global warming

Abstract: Earth's climate may be growing warmer in response to atmospheric accumulation of greenhouse gases, predominantly but not exclusively stemming from human-induced emissions of carbon dioxide (CO/sub 2/) into the atmosphere. Once in the atmosphere, CO/sub 2/ traps heat that would otherwise radiate into space. Each year the Earth's atmosphere takes up approximately 2.9 billion tons of the 4.8 to 5.8 billion tons of carbon that are emitted from various sources. The rest is removed from the atmosphere by natural processes in carbon sinks - places like oceans or forests where carbon is removed from the atmosphere and stored. In addition, changes in land use that have eliminated terrestrial biomass, including tropical forests, have released into the atmosphere the carbon that was captive in the vegetation. Humankind can respond to the prospective global climate change by adapting to the warming, attempting to limit the warming by preventing or mitigating the buildup of atmospheric carbon, or by some combination of the above. Forests can play a critical role in any attempt to mitigate the warming because they are able to capture and store large amounts of carbon from the atmosphere.

Carbon flows in the biosphere: present and future

Abstract: The atmosphere, biosphere and ocean surface layers contain approximately equal amounts of carbon (the deep ocean contains over 50 times as much). The flux of carbon between these pools is dominated by the process of photosynthesis which is itself influenced by the CO 2 concentration of the atmosphere. Over the last 200 years deforestation and now fossil fuel combustion have added CO 2 to the atmosphere to increase the concentration by 27%—half the increase occurred over the last 30 years. The resulting greenhouse effect has been accompanied by an increase in the global average temperature of about 0.5°; other 9greenhouse gases9 (N 2 O 1 O 3 , CFCs, CH 4 ) are also contributing to the warming. Present uncertainties with estimating carbon flows result from the disputed contribution of deforestation, the level of increased plant productivity and carbon storage due to CO 2 fertilization, and problems with estimating net primary production. Uncertainties in estimating future carbon balances arise from the extent of fossil fuel use especially by USA, USSR and China, the degree of control of greenhouse gas emissions, the CO 2 fertilization effect on plant productivity and vegetation responses (including moisture availability) and the rate of change of the climatic factors resulting from changing carbon fluxes.

The greenhouse effect

Abstract: Atmospheric concentrations of greenhouse gases such as carbon dioxide affect the radiative heat balance and surface temperature of the earth. In the next 80 to 130 years, concentration of carbon dioxide is expected to double and the rest of the greenhouse gases to contribute half as much again to the greenhouse warming. Also, oceans have a large heat capacity and absorb half of any additional carbon dioxide emitted into the atmosphere. This will cause greenhouse warming to lag many decades behind increases in concentrations of greenhouse gases and cause a rise in sea level. Large complex computer models are used to simulate the present climate and to predict future changes. However, in these models, treatment of feedback mechanisms such as the influence of clouds on radiation will need to be improved to narrow the range of predictions and to provide firm guidance for remedial action.

Carbon Dioxide, Soil Moisture, and Future Crop PRODUCTION1

Abstract: Model simulations of the effects of increases in atmospheric carbon dioxide on air temperature, precipitation, and soil moisture suggest that the resultant “greenhouse effect” will be bad for agriculture. Experimental evidence, however, indicates otherwise, demonstrating that plants can more than compensate for the predicted adverse climatic changes. Indeed, recent evidence from around the globe suggests that a carbon-dioxide-induced stimulation of the biosphere is already in progress.

Carbon oxidation state in the early atmosphere: CO2 or CO?

Abstract: Atmospheric scientists have argued for the last several years that the earth's primitive atmosphere consisted primarily of CO2, N2, and H20, with smaller amounts of reduced species such as H 2 and CO, and only minute concentrations of CH 4 (Walker, 1977; Holland, 1984; Kasting et al., 1983, 1984; Walker, 1986; Zahnle, 1986). The constituent of interest here, carbon, was predicted to be present mostly in its highest oxidation state, as CO 2. This belief was based on two observations: i) CO 2 is the dominant carbon compound released from volcanos today and should have been so in the past if the upper mantle redox state has not varied greatly with time (Walker, 1977; Holland, 1984). And, 2) CH~ and CO can be photochemically oxidized to CO 2 by OH radfcals produced from water vapor photolysis, even in an anoxic atmosphere (Kasting et al., 1983, 1984; Zahnle, 1986). In a typical model model calculation (Kasting et al., 1984), some 0.3 bar of CO~ is presumed to have been present to counteract the ~limatic effects of reduced solar luminosity~ and the predicted CO/CO 2 ratio is on the order of I0 -~. Methane is much less abundant than CO unless a large CHa source is assumed to exist at the surface (Kasting et al., 1983; Zahnle, 1986). Photochemical model calculations that I have performed recently now indicate that the above argument is flawed and that there may be physically plausible conditions under which the dominant carbon compound in the atmosphere was CO, rather than CO 2. In particular, such conditions could have pertainea if the atmosphere was relatively dense (i.e. it contained 2 bar or more of CO + CO~), and if the rate of CO input to the atmosphere was substantially higher than today. A high rate of CO input could have resulted from an enhanced volcanic outgassing rate or from the reaction of atmospheric CO 2 with elemental iron contained in late-impacting planetes = imals. These new calculations are not complete at the

Carbon dioxide releases from fossil-fuel burning: Statement before the Senate Committee on Energy and Natural Resources

Abstract: Discussion of the anthropogenic emissions of carbon dioxide to the atmosphere is given. There are three kinds of human activity that are currently resulting in net release of carbon dioxide (CO/sub 2/) to the atmosphere: burning fossil fuels, converting tropical forest area to other land use, and manufacturing cement. Although it is a comparatively small source of CO/sub 2/, cement manufacture involves the calcining of limestone (calcium carbonate) to produce calcium oxide. The associated CO/sub 2/ emissions are included in the figures that follow. Production of one metric ton of cement results in the release of 0.136 metric tons of carbon as CO/sub 2/. (This does not count the fuel used in the processing). When forest area is cleared and converted to land uses that have smaller inventories of carbon in the biota and in the surface liter and soil, there is a net release of carbon to become CO/sub 2/ in the atmosphere. Every cubic meter of timber burned releases about 0.26 metric tons of carbon as CO/sub 2/ to the atmosphere, and forest clearing generally results in a release of additional carbon from the soil and surface litter. When fossil fuels are burned, carbon that has been longmore » stored in the earth is oxidized and released to the atmosphere as CO/sub 2/. Because fossil-fuel burning releases heat from the oxidation of both carbon (to produce carbon dioxide) and hydrogen (to produce water), and because the different fuel forms contain different ratios of carbon to hydrogen, the amount of CO/sub 2/ produced per unit of energy released is different for the various fuel forms. 14 figs.« less