User:Isonomia/Global Fuel Depletion

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[edit] Global Warming

Carbon dioxide during the last 400,000 years and the rapid rise since the Industrial Revolution; changes in the Earth's orbit around the Sun, known as Milankovitch cycles, are believed to be the pacemaker of the 100,000 year ice age cycle.

The climate system varies through natural, internal processes and in response to variations in external "forcing" from both human and natural causes. These forcing factors include solar activity, volcanic emissions, variations in the earth's orbit (orbital forcing) and greenhouse gases. The detailed causes of the recent warming remain an active field of research, but the scientific consensus identifies greenhouse gases as the main influence. The major natural greenhouse gases are water vapor, carbon dioxide, methane, and ozone.

Adding carbon dioxide (CO₂) or methane (CH₄) to Earth's atmosphere, with no other changes, will make the planet's surface warmer. Greenhouse gases create a natural greenhouse effect without which temperatures on Earth would be an estimated 30 °C (54 °F) lower, so that Earth would be uninhabitable.

[edit] Greenhouse gases in the atmosphere

Plots of atmospheric Carbon dioxide and global temperature during the last 650,000 years.

Greenhouse gases are transparent to shortwave radiation from the sun, the main source of heat on the Earth. However, they absorb some of the longer infrared radiation emitted by the Earth, thereby reducing radiational cooling and hence raising the temperature of the Earth. How much they warm the world by is shown in their global warming potential. The measure of the response to increased GHGs, and other anthropogenic and natural climate forcings is climate sensitivity. It is found by observational and model studies.^[1] This sensitivity is usually expressed in terms of the temperature response expected from a doubling of CO₂ in the atmosphere. The current literature estimates sensitivity in the range of 1.5 to 4.5 °C (2.7 to 8.1 °F).

The atmospheric concentrations of carbon dioxide and methane have increased by 31% and 149% respectively above pre-industrial levels since 1750. This is considerably higher than at any time during the last 650,000 years, the period for which reliable data has been extracted from ice cores. From less direct geological evidence it is believed that carbon dioxide values this high were last attained 40 million years ago.^{[citation needed]} About three-quarters of the anthropogenic (man-made) emissions of carbon dioxide to the atmosphere during the past 20 years are due to fossil fuel burning. The rest of the anthropogenic emissions are predominantly due to land-use change, especially deforestation.^[2]

The longest continuous instrumental measurement of carbon dioxide mixing ratios began in 1958 at Mauna Loa. Since then, the annually averaged value has increased monotonically by approximately 21% from the initial reading of 315 ppmv, as shown by the Keeling curve, to over 380 ppmv in 2006.^[3][4] The monthly CO₂ measurements display small seasonal oscillations in an overall yearly uptrend; each year's maximum is reached during the northern hemisphere's late spring, and declines during the northern hemisphere growing season as plants remove some CO₂ from the atmosphere.

Methane, the primary constituent of natural gas, enters the atmosphere both from biological production and leaks from natural gas pipelines and other infrastructure. Some biological sources are natural, such as termites or forests,^[5][6][7] but others have been increased or created by agricultural activities such as the cultivation of rice paddies.^[8] Recent evidence indicates that methane concentrations have begun to stabilize, perhaps due to reductions in leakage from fuel transmission and storage facilities.^[9]

Future carbon dioxide levels are expected to continue rising due to ongoing fossil fuel usage. The rate of rise will depend on uncertain economic, sociological, technological, and natural developments. The IPCC Special Report on Emissions Scenarios gives a wide range of future carbon dioxide scenarios,^[10] ranging from 541 to 970 parts per million by the year 2100. Fossil fuel reserves are sufficient to reach this level and continue emissions past 2100, if coal and tar sands are extensively used.^{[citation needed]}

Carbon sink ecosystems (forests and oceans)^[11] are being degraded by pollutants.^[12] Degradation of major carbon sinks results in higher atmospheric carbon dioxide levels.

Anthropogenic emission of greenhouse gases broken down by sector for the year 2000.

Globally, the majority of anthropogenic greenhouse gas emissions arise from fuel combustion. The remainder is accounted for largely by "fugitive fuel" (fuel consumed in the production and transport of fuel)^{[verification needed]} , emissions from industrial processes (excluding fuel combustion), and agriculture: these contributed 5.8%, 5.2% and 3.3% respectively in 1990.^{[citation needed]} Current figures are broadly comparable.^[13] Around 17% of emissions are accounted for by the combustion of fuel for the generation of electricity. A small percentage of emissions come from natural and anthropogenic biological sources, with approximately 6.3% derived from agriculturally produced methane and nitrous oxide.^{[citation needed]}

Positive feedback effects, such as the expected release of methane from the melting of permafrost peat bogs in Siberia (possibly up to 70,000 million tonnes), may lead to significant additional sources of greenhouse gas emissions.^[14].