Geothermal energy

Geothermal energy is energy obtained by tapping the heat of the earth itself, both from kilometers deep into the Earth’s crust in some places of the globe or from some meters in geothermal heat pump in all the places of the planet . It is expensive to build a power station but operating costs are low resulting in low energy costs for suitable sites. Ultimately, this energy derives from heat in the Earth’s core.

Three types of power plants are used to generate power from geothermal energy: dry steam, flash, and binary. Dry steam plants take steam out of fractures in the ground and use it to directly drive a turbine that spins a generator. Flash plants take hot water, usually at temperatures over 200 °C, out of the ground, and allows it to boil as it rises to the surface then separates the steam phase in steam/water separators and then runs the steam through a turbine. In binary plants, the hot water flows through heat exchangers, boiling an organic fluid that spins the turbine. The condensed steam and remaining geothermal fluid from all three types of plants are injected back into the hot rock to pick up more heat.



Most hydroelectric power comes from the potential energy of dammed water driving a water turbine and generator. In this case the energy extracted from the water depends on the volume and on the difference in height between the source and the water’s outflow. This height difference is called the head

The amount of potential energy in water is proportional to the head. To obtain very high head, water for a hydraulic turbine may be run through a large pipe called a penstock.Pumped storage hydroelectricity produces electricity to supply high peak demands by moving water between reservoirs at different elevations. At times of low electrical demand, excess generation capacity is used to pump water into the higher reservoir. When there is higher demand, water is released back into the lower reservoir through a turbine. Pumped storage schemes currently provide the only commercially important means of large-scale grid energy storage and improve the daily capacity factor of the generation system. Hydroelectric plants with no reservoir capacity are called run-of-the-river plants, since it is not then possible to store water.

A tidal power plant makes use of the daily rise and fall of water due to tides; such sources are highly predictable, and if conditions permit construction of reservoirs, can also be dispatchable to generate power during high demand periods. Less common types of hydro schemes use water’s kinetic energy or undammed sources such as undershot waterwheels


Solar energy

Solar energy, radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation, along with secondary solar-powered resources such as wind and wave power, hydroelectricity and biomass, account for most of the available renewable energy on earth. Only a minuscule fraction of the available solar energy is used. 

The Earth receives 174 petawatts (PW) of incoming solar radiation (insolation) at the upper atmosphere. Approximately 30% is reflected back to space while the rest is absorbed by clouds, oceans and land masses. The spectrum of solar light at the Earth’s surface is mostly spread across the visible and near-infrared ranges with a small part in the near-ultraviolet.

Earth’s land surface, oceans and atmosphere absorb solar radiation, and this raises their temperature. Warm air containing evaporated water from the oceans rises, causing atmospheric circulation or convection. When the air reaches a high altitude, where the temperature is low, water vapor condenses into clouds, which rain onto the Earth’s surface, completing the water cycle. The latent heat of water condensation amplifies convection, producing atmospheric phenomena such as wind, cyclones and anti-cyclones Sunlight absorbed by the oceans and land masses keeps the surface at an average temperature of 14 °C. By photosynthesis green plants convert solar energy into chemical energy, which produces food, wood and the biomass from which fossil fuels are derived.


Wind power

Wind power is the conversion of wind energy into a useful form of energy, such as using wind turbines to make electricity, wind mills for mechanical power, wind pumps for pumping water or drainage, or sails to propel ships.At the end of 2008, worldwide nameplate capacity of wind-powered generators was 121.2 gigawatts (GW). , which is about 1.5% of worldwide electricity usage; and is growing rapidly, having doubled in the three years between 2005 and 2008. Several countries have achieved relatively high levels of wind power penetration (with large governmental subsidies), such as 19% of stationary electricity production in Denmark, 13% in Spain and Portugal, and 7% in Germany and the Republic of Ireland in 2008. As of May 2009, eighty countries around the world are using wind power on a commercial basis. 

Large-scale wind farms are connected to the electric power transmission network; smaller facilities are used to provide electricity to isolated locations. Utility companies increasingly buy back surplus electricity produced by small domestic turbines. Wind energy as a power source is attractive as an alternative to fossil fuels, because it is plentiful, renewable, widely distributed, clean, and produces no greenhouse gas emissions. However, the construction of wind farms is not universally welcomed because of their visual impact and other effects on the environment.

Wind power is non-dispatchable, meaning that for economic operation, all of the available output must be taken when it is available. Other resources, such as hydropower, and standard load management techniques must be used to match supply with demand. The intermittency of wind seldom creates problems when using wind power to supply a low proportion of total demand.


The greenhouse effect

Greenhouse gases are gases in an atmosphere that absorb and emit radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The main greenhouse gases in the Earth’s atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone. In our solar system, the atmospheres of Venus, Mars and Titan also contain gases that cause greenhouse effects. Greenhouse gases greatly affect the temperature of the Earth; without them, Earth’s surface would be on average about 33 °C (59 °F) colder than at present.

The burning of fossil fuels since the Industrial revolution has increased the levels of greenhouse gases in the atmosphere.

Greenhouse effects in Earth’s atmosphere

Modern global anthropogenic Carbon emissions.
In order, Earth’s most abundant greenhouse gases are:

• water vapor

• carbon dioxide

• methane

• nitrous oxide

• ozone

• chlorofluorocarbons

The contribution to the greenhouse effect by a gas is affected by both the characteristics of the gas and its abundance. For example, on a molecule-for-molecule basis methane is about eight times stronger greenhouse gas than carbon dioxide, but it is present in much smaller concentrations so that its total contribution is smaller. When these gases are ranked by their contribution to the greenhouse effect, the most important are:

• water vapor, which contributes 36–72%

• carbon dioxide, which contributes 9–26%

• methane, which contributes 4–9%

• ozone, which contributes 3–7%

It is not possible to state that a certain gas causes an exact percentage of the greenhouse effect. This is because some of the gases absorb and emit radiation at the same frequencies as others, so that the total greenhouse effect is not simply the sum of the influence of each gas. The higher ends of the ranges quoted are for each gas alone; the lower ends account for overlaps with the other gases. The major non-gas contributor to the Earth’s greenhouse effect, clouds, also absorb and emit infrared radiation and thus have an effect on radiative properties of the greenhouse gases.
In addition to the main greenhouse gases listed above, other greenhouse gases include sulfur hexafluoride, hydrofluorocarbons and perfluorocarbons (see IPCC list of greenhouse gases). Some greenhouse gases are not often listed. For example, nitrogen trifluoride has a high global warming potential (GWP) but is only present in very small quantities.

Atmospheric absorption and scattering at different electromagnetic wavelengths. The largest absorption band of carbon dioxide is in the infrared.
Scientists who have elaborated on Arrhenius’s theory of global warming are concerned that increasing concentrations of greenhouse gases in the atmosphere are causing an unprecedented rise in global temperatures, with potentially harmful consequences for the environment and human health. Although contributing to many other physical and chemical reactions, the major atmospheric constituents, nitrogen (N2), oxygen (O2), and argon (Ar), are not greenhouse gases. This is because molecules containing two atoms of the same element such as N2 and O2 and monatomic molecules such as Ar have no net change in their dipole moment when they vibrate and hence are almost totally unaffected by infrared light. Although molecules containing two atoms of different elements such as carbon monoxide (CO) or hydrogen chloride (HCl) absorb IR, these molecules are short-lived in the atmosphere owing to their reactivity and solubility. As a consequence they do not contribute significantly to the greenhouse effect and are not often included when discussing greenhouse gases.
Late 19th century scientists experimentally discovered that N2 and O2 did not absorb infrared radiation (called, at that time, „dark radiation”) and that water as a vapour and in cloud form, CO2 and many other gases did absorb such radiation. It was recognized in the early 20th century that the greenhouse gases in the atmosphere caused the Earth’s overall temperature to be higher than it would be without them.
Natural and anthropogenic

400,000 years of ice core data

The amount of net carbon increase in the atmosphere, compared to carbon emissions from burning fossil fuel.
Aside from purely human-produced synthetic halocarbons, most greenhouse gases have both natural and human-caused sources. During the pre-industrial Holocene, concentrations of existing gases were roughly constant. In the industrial era, human activities have added greenhouse gases to the atmosphere, mainly through the burning of fossil fuels and clearing of forests.

The 2007 Fourth Assessment Report compiled by the IPCC (AR4) noted that „changes in atmospheric concentrations of greenhouse gases and aerosols, land cover and solar radiation alter the energy balance of the climate system”, and concluded that „increases in anthropogenic greenhouse gas concentrations is very likely to have caused most of the increases in global average temperatures since the mid-20th century”. In AR4, „most of” is defined as more than 50%.
Ice cores provide evidence for variation in greenhouse gas concentrations over the past 800,000 years. Both CO2 and CH4 vary between glacial and interglacial phases, and concentrations of these gases correlate strongly with temperature. Before the ice core record, direct data does not exist. However, various proxies and modelling suggests large variations; 500 million years ago CO2 levels were likely 10 times higher than now. Indeed higher CO2 concentrations are thought to have prevailed throughout most of the Phanerozoic eon, with concentrations four to six times current concentrations during the Mesozoic era, and ten to fifteen times current concentrations during the early Palaeozoic era until the middle of the Devonian period, about 400 Ma. The spread of land plants is thought to have reduced CO2 concentrations during the late Devonian, and plant activities as both sources and sinks of CO2 have since been important in providing stabilising feedbacks. Earlier still, a 200-million year period of intermittent, widespread glaciation extending close to the equator (Snowball Earth) appears to have been ended suddenly, about 550 Ma, by a colossal volcanic outgassing which raised the CO2 concentration of the atmosphere abruptly to 12%, about 350 times modern levels, causing extreme greenhouse conditions and carbonate deposition as limestone at the rate of about 1 mm per day.] This episode marked the close of the Precambrian eon, and was succeeded by the generally warmer conditions of the Phanerozoic, during which multicellular animal and plant life evolved. No volcanic carbon dioxide emission of comparable scale has occurred since. In the modern era, emissions to the atmosphere from volcanoes are only about 1% of emissions from human sources.
Anthropogenic greenhouse gases

Global anthropogenic greenhouse gas emissions broken down into 8 different sectors for the year 2000.

The projected temperature increase for a range of greenhouse gas stabilization scenarios (the coloured bands). The black line in middle of the shaded area indicates ‘best estimates’; the red and the blue lines the likely limits. From the work of IPCC AR4, 2007.
Since about 1750 human activity has increased the concentration of carbon dioxide and other greenhouse gases. Measured atmospheric concentrations of carbon dioxide are currently 100 ppmv higher than pre-industrial levels.    Natural sources of carbon dioxide are more than 20 times greater than sources due to human activity, but over periods longer than a few years natural sources are closely balanced by natural sinks such as weathering of continental rocks and photosynthesis of carbon compounds by plants and marine plankton. As a result of this balance, the atmospheric concentration of carbon dioxide remained between 260 and 280 parts per million for the 10,000 years between the end of the last glacial maximum and the start of the industrial era.
It is likely that anthropogenic warming, such as that due to elevated greenhouse gas levels, has had a discernible influence on many physical and biological systems. Warming is projected to affect various issues such as freshwater resources, industry, food and health.

The main sources of greenhouse gases due to human activity are:

• burning of fossil fuels and deforestation leading to higher carbon dioxide concentrations. Land use change (mainly deforestation in the tropics) account for up to one third of total anthropogenic CO2 emissions.

livestock enteric fermentation and manure management, paddy rice farming, land use and wetland changes, pipeline losses, and covered vented landfill emissions leading to higher methane atmospheric concentrations. Many of the newer style fully vented septic systems that enhance and target the fermentation process also are sources of atmospheric methane.

• use of chlorofluorocarbons (CFCs) in refrigeration systems, and use of CFCs and halons in fire suppression systems and manufacturing processes.
• agricultural activities, including the use of fertilizers, that lead to higher nitrous oxide (N2O) concentrations.

The seven sources of CO2 from fossil fuel combustion are (with percentage contributions for 2000–2004):

1. Solid fuels (e.g., coal): 35%
2. Liquid fuels (e.g., gasoline, fuel oil): 36%
3. Gaseous fuels (e.g., natural gas): 20%
4. Flaring gas industrially and at wells: <1%
5. Cement production: 3%
6. Non-fuel hydrocarbons: < 1%
7. The „international bunkers” of shipping and air transport not included in national inventories: 4%
The US Environmental Protection Agency (EPA) ranks the major greenhouse gas contributing end-user sectors in the following order: industrial, transportation, residential, commercial and agricultural. Major sources of an individual’s greenhouse gas include home heating and cooling, electricity consumption, and transportation. Corresponding conservation measures are improving home building insulation, installing geothermal heat pumps and compact fluorescent lamps, and choosing energy-efficient vehicles.
Carbon dioxide, methane, nitrous oxide and three groups of fluorinated gases (sulfur hexafluoride, HFCs, and PFCs) are the major greenhouse gases and the subject of the Kyoto Protocol, which came into force in 2005.
Although CFCs are greenhouse gases, they are regulated by the Montreal Protocol, which was motivated by CFCs’ contribution to ozone depletion rather than by their contribution to global warming. Note that ozone depletion has only a minor role in greenhouse warming though the two processes often are confused in the media.
On December 7, 2009, the US Environmental Protection Agency released its final findings on greenhouse gases, declaring that „greenhouse gases (GHGs) threaten the public health and welfare of the American people”. The finding applied to the same „six key well-mixed greenhouse gases” named in the Kyoto Protocol: carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride.
Role of water vapor
Main article: water vapor

Increasing water vapor in the stratosphere at Boulder, Colorado.

Water vapor accounts for the largest percentage of the greenhouse effect, between 36% and 66% for water vapor alone, and between 66% and 85% when factoring in clouds. However, the warming due to the greenhouse effect of cloud cover is, at least in part, mitigated by the change in the Earth’s albedo. According to NASA, „The overall effect of all clouds together is that the Earth’s surface is cooler than it would be if the atmosphere had no clouds.” (cf. NASA Clouds and Radiation) Water vapor concentrations fluctuate regionally, but human activity does not significantly affect water vapor concentrations except at local scales, such as near irrigated fields. According to the Environmental Health Center of the National Safety Council, water vapor constitutes as much as 2% of the atmosphere.

The Clausius-Clapeyron relation establishes that air can hold more water vapor per unit volume when it warms. This and other basic principles indicate that warming associated with increased concentrations of the other greenhouse gases also will increase the concentration of water vapor.
When a warming trend results in effects that induce further warming, the process is referred to as a „positive feedback”; this amplifies the original warming. When the warming trend results in effects that induce cooling, the process is referred to as a „negative feedback”; this reduces the original warming. Because water vapor is a greenhouse gas and because warm air can hold more water vapor than cooler air, the primary positive feedback involves water vapor.

This positive feedback does not result in runaway global warming because it is offset by other processes that induce negative feedbacks, which stabilizes average global temperatures. The primary negative feedback is the effect of temperature on emission of infrared radiation: as the temperature of a body increases, the emitted radiation increases with the fourth power of its absolute temperature.

Other important considerations involve water vapor being the only greenhouse gas whose concentration is highly variable in space and time in the atmosphere and the only one that also exists in both liquid and solid phases, frequently changing to and from each of the three phases or existing in mixes. Such considerations include clouds themselves, air and water vapor density interactions when they are the same or different temperatures, the absorption and release of kinetic energy as water evaporates and condenses to and from vapor, and behaviors related to vapor partial pressure. For example, the release of latent heat by rain in the ITCZ drives atmospheric circulation, clouds vary atmospheric albedo levels, and the oceans provide evaporative cooling that modulates the greenhouse effect down from estimated 67 °C surface temperature.

See also water, water (molecule).
Greenhouse gas emissions
Main articles: List of countries by carbon dioxide emissions and List of countries by greenhouse gas emissions per capital
Measurements from Antarctic ice cores show that before industrial emissions started atmospheric CO2 levels were about 280 parts per million by volume (ppmv), and stayed between 260 and 280 during the preceding ten thousand years. Carbon dioxide concentrations in the atmosphere have gone up by approximately 35 percent since the 1900s, rising from 280 parts per million by volume to 387 parts per million in 2009.

One study using evidence from stomata of fossilized leaves suggests greater variability, with carbon dioxide levels above 300 ppm during the period seven to ten thousand years ago, though others have argued that these findings more likely reflect calibration or contamination problems rather than actual CO2 variability. Because of the way air is trapped in ice (pores in the ice close off slowly to form bubbles deep within the firn) and the time period represented in each ice sample analyzed, these figures represent averages of atmospheric concentrations of up to a few centuries rather than annual or decadal levels.

Recent year-to-year increase of atmospheric CO2

Since the beginning of the Industrial Revolution, the concentrations of most of the greenhouse gases have increased. For example, the concentration of carbon dioxide has increased by about 36% to 380 ppmv, or 100 ppmv over modern pre-industrial levels. The first 50 ppmv increase took place in about 200 years, from the start of the Industrial Revolution to around 1973; however the next 50 ppmv increase took place in about 33 years, from 1973 to 2006.

Recent data also shows the concentration is increasing at a higher rate. In the 1960s, the average annual increase was only 37% of what it was in 2000 through 2007.

The other greenhouse gases produced from human activity show similar increases in both amount and rate of increase. Many observations are available online in a variety of Atmospheric Chemistry Observational Databases.
Relevant to radiative forcing

Gas Current (1998) Amount by volume Increase (ppm)
over pre-industrial (1750) Increase (%)
over pre-industrial (1750) Radiative forcing (W/m2)

Carbon dioxide

365 ppm
(383 ppm, 2007.01) 87 ppm
(105 ppm, 2007.01) 31%
(38%, 2007.01) 1.46
(~1.53, 2007.01)


1745 ppb
1045 ppb 67% 0.48
Nitrous oxide
314 ppb 44 ppb 16% 0.15
Relevant to both radiative forcing and ozone depletion; all of the following have no natural sources and hence zero amounts pre-industrial
Gas Current (1998)
Amount by volume Radiative forcing
268 ppt
533 ppt 0.17
84 ppt 0.03
Carbon tetrachloride
102 ppt 0.01
69 ppt 0.03
(Source: IPCC radiative forcing report 1994 updated (to 1998) by IPCC TAR table 6.1 ).
Recent rates of change and emission

Greenhouse gas intensity in 2000 including land-use change

Per capita responsibility for current anthropogenic atmospheric CO2

Major greenhouse gas trends
The sharp acceleration in CO2 emissions since 2000 to more than a 3% increase per year (more than 2 ppm per year) from 1.1% per year during the 1990s is attributable to the lapse of formerly declining trends in carbon intensity of both developing and developed nations. Although over 3/4 of cumulative anthropogenic CO2 is still attributable to the developed world, China was responsible for most of global growth in emissions during this period. Localised plummeting emissions associated with the collapse of the Soviet Union have been followed by slow emissions growth in this region due to more efficient energy use, made necessary by the increasing proportion of it that is exported. In comparison, methane has not increased appreciably, and N2O by 0.25% y−1.

The direct emissions from industry have declined due to a constant improvement in energy efficiency, but also to a high penetration of electricity. If one includes indirect emissions, related to the production of electricity, emissions from industry in Europe are roughly stabilized since 1994.


Atmospheric levels of CO2 continue to rise, partly a sign of the industrial rise of Asian economies led by China.] Over the 2000–2010 interval China is expected to increase its carbon dioxide emissions by 600 Mt, largely because of the rapid construction of old-fashioned power plants in poorer internal provinces.
See also: Asian brown cloud
United Kingdom
The UK set itself a target of reducing carbon dioxide emissions by 20% from 1990 levels by 2010, but according to its own figures it will fall short of this target by almost 4%.
United States

Main articles: Greenhouse gas emissions by the United States and United States federal register of greenhouse gas emissions.

The United States emitted 16.3% more greenhouse gas in 2005 than it did in 1990. According to a preliminary estimate by the Netherlands Environmental Assessment Agency, the largest national producer of CO2 emissions since 2006 has been China with an estimated annual production of about 6200 megatonnes. China is followed by the United States with about 5,800 megatonnes. The per capita emission figures of China are about one quarter of those of the US population, but the per GDP emission figures of China are about four times those of the US due to the varying size of the nations population and GDP.

Relative to 2005, China’s fossil CO2 emissions increased in 2006 by 8.7%, while in the USA, comparable CO2 emissions decreased in 2006 by 1.4%. The agency notes that its estimates do not include some CO2 sources of uncertain magnitude. These figures rely on national CO2 data that do not include aviation. Although these tonnages are small compared to the CO2 in the Earth’s atmosphere, they are significantly larger than pre-industrial levels.

See also: Climate change in the United States
Relative CO2 emission from various fuels
Pounds of carbon dioxide emitted per million British thermal units of energy for various fuels[49]

Fuel name
CO2 emitted (lbs/106 Btu)
CO2 emitted (g/106 J)

Natural gas
117 50.30
Liquefied petroleum gas
139 59.76
139 59.76
Aviation gasoline
153 65.78
Automobile gasoline
156 67.07
159 68.36
Fuel oil
161 69.22
Tires/tire derived fuel
189 81.26
Wood and wood waste
195 83.83
Coal (bituminous)
205 88.13
Coal (subbituminous)
213 91.57
Coal (lignite)
215 92.43
Petroleum coke
225 96.73
Coal (anthracite)
227 97.59

Removal from the atmosphere and global warming potential

Natural processes

Greenhouse gases can be removed from the atmosphere by various processes:

• as a consequence of a physical change (condensation and precipitation remove water vapor from the atmosphere).
• as a consequence of chemical reactions within the atmosphere. For example, methane is oxidized by reaction with naturally occurring hydroxyl radical, OH• and degraded to CO2 and water vapor (CO2 from the oxidation of methane is not included in the methane Global warming potential). Other chemical reactions include solution and solid phase chemistry occurring in atmospheric aerosols.
• as a consequence of a physical exchange between the atmosphere and the other compartments of the planet. An example is the mixing of atmospheric gases into the oceans.
• as a consequence of a chemical change at the interface between the atmosphere and the other compartments of the planet. This is the case for CO2, which is reduced by photosynthesis of plants, and which, after dissolving in the oceans, reacts to form carbonic acid and bicarbonate and carbonate ions (see ocean acidification).
• as a consequence of a photochemical change. Halocarbons are dissociated by UV light releasing Cl• and F• as free radicals in the stratosphere with harmful effects on ozone (halocarbons are generally too stable to disappear by chemical reaction in the atmosphere).