Greenhouse Gases: Causes, Sources and Environmental Effects
Dec 23, · Fluorinated gases: Hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride, and nitrogen trifluoride are synthetic, powerful greenhouse gases that are emitted from a . Apr 19, · Greenhouse gases are gases in Earth’s atmosphere that trap heat. They let sunlight pass through the atmosphere, but they prevent the heat .
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How greenhouse gases affect global warming
Jan 27, · Multiple gases contribute to the greenhouse effect that sets Earth’s temperature over geologic time. Small changes in the atmospheric concentration of these gases can lead to changes in temperature that make the difference between ice ages when mastodons roamed the Earth, and the sweltering heat in which the dinosaurs lived. Apr 19, · These heat-trapping gases can be thought of as a blanket wrapped around the Earth, which keeps it toastier than it would be without them. Greenhouse gases include carbon dioxide, methane and nitrous oxides. Greenhouse gases arise naturally, and are . Dec 29, · Human activities are responsible for almost all of the increase in greenhouse gases in the atmosphere over the last years. 1 The largest source of greenhouse gas emissions from human activities in the United States is from burning fossil fuels for electricity, heat, and transportation.
A greenhouse gas sometimes abbreviated GHG is a gas that absorbs and emits radiant energy within the thermal infrared range, causing the greenhouse effect. Hence they are almost totally unaffected by infrared radiation.
Some molecules containing just two atoms of different elements, such as carbon monoxide CO and hydrogen chloride HCl , do absorb infrared radiation, but these molecules are short-lived in the atmosphere owing to their reactivity or solubility.
Therefore, they do not contribute significantly to the greenhouse effect and often are omitted when discussing greenhouse gases.
Greenhouse gases are those that absorb and emit infrared radiation in the wavelength range emitted by Earth. In order, the most abundant [ clarification needed ] greenhouse gases in Earth's atmosphere are: . Atmospheric concentrations are determined by the balance between sources emissions of the gas from human activities and natural systems and sinks the removal of the gas from the atmosphere by conversion to a different chemical compound or absorption by bodies of water.
The annual airborne fraction is the ratio of the atmospheric increase in a given year to that year's total emissions. As of the annual airborne fraction for CO 2 was about 0. The annual airborne fraction increased at a rate of 0.
Some gases have indirect radiative effects whether or not they are greenhouse gases themselves. This happens in two main ways. One way is that when they break down in the atmosphere they produce another greenhouse gas. For example, methane and carbon monoxide CO are oxidized to give carbon dioxide and methane oxidation also produces water vapor. Oxidation of CO to CO 2 directly produces an unambiguous increase in radiative forcing although the reason is subtle.
On the other hand, the single CO vibrational band only absorbs IR at much shorter wavelengths 4. Oxidation of methane to CO 2 , which requires reactions with the OH radical, produces an instantaneous reduction in radiative absorption and emission since CO 2 is a weaker greenhouse gas than methane.
In any case, the calculation of the total radiative effect includes both direct and indirect forcing. A second type of indirect effect happens when chemical reactions in the atmosphere involving these gases change the concentrations of greenhouse gases.
For example, the destruction of non-methane volatile organic compounds NMVOCs in the atmosphere can produce ozone. The size of the indirect effect can depend strongly on where and when the gas is emitted. Methane has indirect effects in addition to forming CO 2. The main chemical that reacts with methane in the atmosphere is the hydroxyl radical OH , thus more methane means that the concentration of OH goes down. Effectively, methane increases its own atmospheric lifetime and therefore its overall radiative effect.
The oxidation of methane can produce both ozone and water; and is a major source of water vapor in the normally dry stratosphere. They remove OH from the atmosphere, and this leads to higher concentrations of methane.
The surprising effect of this is that the global warming potential of CO is three times that of CO 2. Halocarbons have an indirect effect because they destroy stratospheric ozone. Finally, hydrogen can lead to ozone production and CH 4 increases as well as producing stratospheric water vapor. The major non-gas contributor to Earth's greenhouse effect, clouds , also absorb and emit infrared radiation and thus have an effect on greenhouse gas radiative properties. Clouds are water droplets or ice crystals suspended in the atmosphere.
The contribution of each gas to the greenhouse effect is determined by the characteristics of that gas, its abundance, and any indirect effects it may cause. For example, the direct radiative effect of a mass of methane is about 84 times stronger than the same mass of carbon dioxide over a year time frame  but it is present in much smaller concentrations so that its total direct radiative effect has so far been smaller, in part due to its shorter atmospheric lifetime in the absence of additional carbon sequestration.
On the other hand, in addition to its direct radiative impact, methane has a large, indirect radiative effect because it contributes to ozone formation. Shindell et al.
When ranked by their direct contribution to the greenhouse effect, the most important are:  [ failed verification ]. A Water vapor strongly varies locally  B The concentration in stratosphere.
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. 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. Aside from water vapor , which has a residence time of about nine days,  major greenhouse gases are well mixed and take many years to leave the atmosphere.
The atmospheric lifetime of a species therefore measures the time required to restore equilibrium following a sudden increase or decrease in its concentration in the atmosphere. Individual atoms or molecules may be lost or deposited to sinks such as the soil, the oceans and other waters, or vegetation and other biological systems, reducing the excess to background concentrations.
The average time taken to achieve this is the mean lifetime. Carbon dioxide has a variable atmospheric lifetime, and cannot be specified precisely. N 2 O has a mean atmospheric lifetime of years. Earth absorbs some of the radiant energy received from the sun, reflects some of it as light and reflects or radiates the rest back to space as heat. Earth's surface temperature depends on this balance between incoming and outgoing energy.
If this energy balance is shifted, Earth's surface becomes warmer or cooler, leading to a variety of changes in global climate. A number of natural and man-made mechanisms can affect the global energy balance and force changes in Earth's climate.
Greenhouse gases are one such mechanism. Greenhouse gases absorb and emit some of the outgoing energy radiated from Earth's surface, causing that heat to be retained in the lower atmosphere. Radiative forcing quantifies in Watts per square meter the effect of factors that influence Earth's energy balance; including changes in the concentrations of greenhouse gases. Positive radiative forcing leads to warming by increasing the net incoming energy, whereas negative radiative forcing leads to cooling.
The Annual Greenhouse Gas Index AGGI is defined by atmospheric scientists at NOAA as the ratio of total direct radiative forcing due to long-lived and well-mixed greenhouse gases for any year for which adequate global measurements exist, to that present in year It is based on the highest quality atmospheric observations from sites around the world.
Its uncertainty is very low. The global warming potential GWP depends on both the efficiency of the molecule as a greenhouse gas and its atmospheric lifetime. GWP is measured relative to the same mass of CO 2 and evaluated for a specific timescale. Thus, if a gas has a high positive radiative forcing but also a short lifetime, it will have a large GWP on a year scale but a small one on a year scale.
Conversely, if a molecule has a longer atmospheric lifetime than CO 2 its GWP will increase when the timescale is considered. Carbon dioxide is defined to have a GWP of 1 over all time periods. Examples of the atmospheric lifetime and GWP relative to CO 2 for several greenhouse gases are given in the following table:. The use of CFC except some essential uses has been phased out due to its ozone depleting properties.
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, because the large natural sources and sinks roughly balanced.
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 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 midth century".
Ice cores provide evidence for greenhouse gas concentration variations over the past , years see the following section. Both CO 2 and CH 4 vary between glacial and interglacial phases, and concentrations of these gases correlate strongly with temperature.
Direct data does not exist for periods earlier than those represented in the ice core record, a record that indicates CO 2 mole fractions stayed within a range of ppm to ppm throughout the last , years, until the increase of the last years. However, various proxies and modeling suggests larger variations in past epochs; million years ago CO 2 levels were likely 10 times higher than now.
No volcanic carbon dioxide emission of comparable scale has occurred since. In the modern era, emissions to the atmosphere from volcanoes are approximately 0. Measurements from Antarctic ice cores show that before industrial emissions started atmospheric CO 2 mole fractions were about parts per million ppm , and stayed between and during the preceding ten thousand years. One study using evidence from stomata of fossilized leaves suggests greater variability, with carbon dioxide mole fractions above 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 CO 2 variability.
Since the beginning of the Industrial Revolution , the concentrations of many of the greenhouse gases have increased. For example, the mole fraction of carbon dioxide has increased from ppm to ppm, or ppm over modern pre-industrial levels. The first 30 ppm increase took place in about years, from the start of the Industrial Revolution to ; however the next 90 ppm increase took place within 56 years, from to Recent data also shows that the concentration is increasing at a higher rate.
Today, [ when? 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. Indirectly, human activity that increases global temperatures will increase water vapor concentrations, a process known as water vapor feedback.
The average residence time of a water molecule in the atmosphere is only about nine days, compared to years or centuries for other greenhouse gases such as CH 4 and CO 2. The Clausius—Clapeyron relation establishes that more water vapor will be present per unit volume at elevated temperatures. 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 assuming that the relative humidity remains approximately constant; modeling and observational studies find that this is indeed so.
Because water vapor is a greenhouse gas, this results in further warming and so is a " positive feedback " that amplifies the original warming. Eventually other earth processes [ which? Since about human activity has increased the concentration of carbon dioxide and other greenhouse gases. As of , measured atmospheric concentrations of carbon dioxide were ppm higher than pre-industrial levels. As a result of this balance, the atmospheric mole fraction of carbon dioxide remained between and parts per million for the 10, years between the end of the last glacial maximum and the start of the industrial era.
Greenhouse gases can be removed from the atmosphere by various processes, as a consequence of:. A number of technologies remove greenhouse gases emissions from the atmosphere. Most widely analysed are those that remove carbon dioxide from the atmosphere, either to geologic formations such as bio-energy with carbon capture and storage and carbon dioxide air capture ,  or to the soil as in the case with biochar.
In the late 19th century scientists experimentally discovered that N 2 and O 2 do not absorb infrared radiation called, at that time, "dark radiation" , while water both as true vapor and condensed in the form of microscopic droplets suspended in clouds and CO 2 and other poly-atomic gaseous molecules do absorb infrared radiation.