Effects of fuel and forest conservation on future levels of atmospheric carbon dioxide.
Effects of fuel and forest conservation on future levels of atmospheric carbon dioxide.
复制标题
燃料和森林保护对未来大气二氧化碳水平的影响。
DOI：
10.1016/0031-0182(92)90207-l
复制
发表时间：
1992
影响因子：
3.9
通讯作者：
J. Kasting
中科院分区：
文献类型：
--
作者：
James C. G. Walker;J. Kasting
我们开发了一个全球碳的地球化学循环的数值模拟，其工作时间从几年到几百万年不等。海洋的代表是温暖和寒冷的浅水水库，温跃层水库，以及大西洋，印度洋和太平洋的深层水库。大气层的特点是只有一个碳库，全球生物区系的特点是只有一个生物量库。模拟包括岩石周期，区分陆架碳酸盐和远洋碳酸盐沉淀，在三个深海水库不同的溶跃层深度。溶解的远洋碳酸盐在响应减少溶跃层深度包括在内。模拟调整，以重现原子武器试验所观察到的放射性碳记录。它也被调整，以再现海洋水库之间的溶解磷酸盐和总溶解碳的分布，以及海洋和大气中13C和14C的碳同位素比值。模拟再现合理以及二氧化碳分压的历史记录，以及在过去200年的大气同位素比for13C和14C，因为这些都发生了变化，响应化石燃料燃烧和土地利用的变化，主要是森林砍伐。观察和计算之间的一致性涉及二氧化碳施肥效应的假设，其中生物质的生产率随着二氧化碳分压的增加而增加。目前，增加二氧化碳的施肥效应超过了森林砍伐的影响，因此生物群包括一个整体的大气二氧化碳汇足够大，使预算接近balanced.This模拟是用来检查二氧化碳的未来演变和它的敏感性，对化石燃料燃烧率和森林砍伐的假设。在长达数千年的时间里，结果对岩石周期的形成和深海碳酸盐沉积物的溶解不敏感。只要化石燃料以相当高的速度燃烧，大气中的二氧化碳就会继续增加，因为化石燃料产生二氧化碳的速度远远超过地球化学过程从大气中去除二氧化碳的速度。大气中二氧化碳的最大浓度取决于化石燃料的燃烧总量，但对燃烧速度的影响很小。然而，大气中二氧化碳的未来过程是非常敏感的命运的森林在这个模拟中，因为分配给二氧化碳施肥的植物生长速度的重要作用。森林砍伐不仅通过将生物质转化为大气二氧化碳，而且更重要的是通过降低生物群隔离化石燃料二氧化碳的能力来增加大气二氧化碳。在这个模拟中，如果化石燃料燃烧率立即从目前的5 × 1014米/年减少到0.2 × 1014米/年（减少25倍），并且停止进一步的森林砍伐，大气中的二氧化碳水平可以无限期地维持在百万分之500以下。如果这两个条件都不满足，如果我们消耗了世界上大部分的化石燃料储备，那么在未来几个世纪内，二氧化碳浓度可能达到1000 - 2000 ppm的峰值。
We develop a numerical simulation of the global biogeochemical cycles of carbon that works over time scales extending from years to millions of years. The ocean is represented by warm and cold shallow water reservoirs, a thermocline reservoir, and deep Atlantic, Indian, and Pacific reservoirs. The atmosphere is characterized by a single carbon reservoir and the global biota by a single biomass reservoir. The simulation includes the rock cycle, distinguishing between shelf carbonate and pelagic carbonate precipitation, with distinct lysocline depths in the three deep ocean reservoirs. Dissolution of pelagic carbonates in response to decrease in lysocline depth is included.The simulation is tuned to reproduce the observed radiocarbon record resulting from atomic weapon testing. It is tuned also to reproduce the distribution of dissolved phosphate and total dissolved carbon between the ocean reservoirs as well as the carbon isotope ratios for both13C and14C in ocean and atmosphere. The simulation reproduces reasonably well the historical record of carbon dioxide partial pressure as well as the atmospheric isotope ratios for13C and14C over the last 200 yr as these have changed in response to fossil fuel burning and land use changes, principally forest clearance. The agreements between observation and calculation involves the assumption of a carbon dioxide fertilization effect in which the rate of production of biomass increases with increasing carbon dioxide partial pressure. At present the fertilization effect of increased carbon dioxide outweighs the effects of forest clearance, so the biota comprises an overall sink of atmosph ric carbon dioxide sufficiently large to bring the budget approximately into balance.This simulation is used to examine the future evolution of carbon dioxide and its sensitivity to assumptions about the rate of fossil fuel burning and of forest clearance. Over times extending up to thousands of years, the results are insensitive to the formulation of the rock cycle and to the dissolution of deep sea carbonate sediments. Atmospheric carbon dioxide continues to increase as long fossil fuel is burned at a significant rate, because the rate of fossil fuel production of carbon dioxide far exceeds the rates at which geochemical processes can remove carbon dioxide from the atmosphere. The maximum concentration of carbon dioxide achieved in the atmosphere depends on the total amount of fossil fuel burned, but only weakly on the rate of burning. The future course of atmospheric carbon dioxide is, however, very sensitive to the fate of the forests in this simulation because of the important role assigned to carbon dioxide fertilization of plant growth rate. Forest clearance drives up atmospheric carbon dioxide not only by converting biomass into atmospheric carbon dioxide but more importantly by reducing the capacity of the biota to sequester fossil fuel carbon dioxide. In this simulation, atmospheric carbon dioxide levels could be sustained indefinitely below 500 parts per million (ppm) if fossil fuel combustion rates were immediately cut from their present value of 5 × 1014m/y to 0.2 × 1014m/y (a factor of 25 reduction) and if further forest clearance were halted. If neither of these conditions is met and if we consume most of the world's fossil fuel reserves, peak carbon dioxide concentrations of 1000–2000 ppm are probable within the next few centuries.