252 sent when one is trying properly to parameterize them in climate modeling. Albedo feedback; Climate feedback; Noctilucent clouds; Polar stratospheric clouds.Coal fueled transportation and industry. Inefficient energy conversion, the weight of coal-fired steam engines, and massive pollution all encouraged conversion to petroleum products for most purposes other than electrical power generation in the twentieth century. These factors also constitute powerful arguments against reviving the older technologies. However, both fuel gas and oil can be produced from coal, eliminating much of the bulk and pollution associated with coal-based energy�but not the problem of carbon dioxide (CO2) emissions. According to one estimate, if early twentyfirst century trends continue, the CO2 emissions from burning coal in 2030 alone will equal about 50 percent of the total emissions from 1750 through 2000. Most of the world coal reserves accumulated during the Carboniferous (oal-bearing� age. This age, ocurring between 354 and 290 million years ago, was a very warm period when land-plant productivity greatly exceeded herbivore consumption and decomposition. The Chinese were already burning coal in the thirteenth century. The use of coal for cooking and heating in cities was well established by the middle of the eighteenth century in England, when a series of inventions enabled manufacturers to replace human and animal labor with increasingly sophisticated coal-fired steam engines. This Industrial Revolution enabled an individual worker greatly to increase productivity, leading to an overall increase in per capita consumption of the Earth renewable and nonrenewable resources at a time when population was also beginning to increase at an exponential rate. �History of Coal Consumption Coal consumption in Great Britain increased from 2.45 million metric tons per year in 1700 to 45 million metric tons per year in 1850 to 227 million metric tons per year in 1900. Annual consumption in the United States was 36 million metric tons in 1870 and 469 million metric tons in 1913. Total world consumption of coal on the eve of World War I was roughly one-tenth of its 2006 level of 5.44 billion metric tons. Global warming as an environmental concern of coal utilization is a relatively recent phenomenon. Pollution and environmental degradation due toCoal�Fossil fuels; energy Coal burning accounts for a large share of global anthropogenic CO2 output. Net carbon emissions per unit energy produced by coal exceed those of any other major energy source. The relative cheapness of coal, enormous reserves, and the concentration of those reserves in countries that are among the top energy consumers make continued growth likelynd make reducing carbon output from coal an urgent priority. �Key concepts carbon budget: the total amount of CO2 emissions that can be sustained, given a target atmospheric CO2 concentration, and the way in which those emissions are apportioned carbon-capture-and-storage (CCS) systems: processes that remove CO2 from combustion products and sequester itypically in underground storage fossil fuels: combustible products of ancient photosynthesis integrated gasification combined cycle (IGCC) systems: electrical generation technology that converts coal to combustible gas before burning it �Background Coal was the first fossil fuel to be used by humans, and it will likely be the last. Known world coal reserves are projected to last for another 250 years. Unlike petroleum and uranium, which must be transported great distances to reach oil burners and nuclear reactors, the largest concentrations of coal deposits exist within populous countries with high energy requirements. Most coal is used in contemporary society for generating electricity. Historically, solid coal also
