of atmospheric methane compared to carbon dioxide from the atmosphere would result in a similar climate impact. With background levels of atmospheric Since the beginning of the Industrial Revolution (around 1750), the methane concentration in the atmosphere has increased by about 160%, and human activities almost entirely caused this increase. Since 1750 methane has contributed 3% of greenhouse gas (GHG) emissions in terms of mass but is responsible for approximately 23% of radiative or climate forcing. By 2019, global methane concentrations ha T… These 2005 NASA computer model simulations—calculated based on data available at that time—illustrate how methane is destroyed as it rises. As air rises in the tropics, methane is carried upwards through the troposphere—the lowest portion of Earth's atmosphere which is 4 miles (6.4 km) to 12 miles (19 km) from the Earth's surface, into the lower stratosphere—the ozone layer—and then the upper portion of the stratosphere. This atmospheric chemical process is the most effective methane sink, as it removes 90% of atmospheric methane. This global destruction of atmospheric methane mainly occurs in the troposphere. Methane molecules react with hydroxyl radicals (OH)—the "major chemical scavenger in the troposphere" that "controls the atmospheric lifetime of most gases in the troposphere". Through this CH4 oxidation process, atmospheric methane is destroyed and water vapor and carbon dioxide are produced. While this decreases the concentration of methane in the atmosphere, it is unclear if this leads to a net positive increase in radiative forcing because both water vapor and carbon dioxide are more powerful GHGs factors in terms of affecting the warming of Earth. This additional water vapor in the stratosphere caused by CH4 oxidation, adds approximately 15% to methane's radiative forcing effect. By the 1980s, the global warming problem had been transformed by the inclusion of methane and other non-CO2 trace-gases—CFCs, N2O Their new RF calculations which significantly revised those cited in earlier, successive IPCC reports for well mixed greenhouse gases (WMGHG) forcings by including the shortwave forcing component due to CH4, resulted in estimates that were approximately 20–25% higher. Collins et al. said that CH4 mitigation that reduces atmospheric methane by the end of the century, could "make a substantial difference to the feasibility of achieving the Paris climate targets", and would provide Methane's radiative forcing (RF) of climate is direct, and it is the second largest contributor to human-caused climate forcing in the historical period. Methane is a major source of water vapour in the stratosphere through oxidation; and water vapour adds about 15% to methane's radiative forcing effect. The global warming potential (GWP) for methane is about 84 in terms of its impact over a 20-year timeframe, and 28 in terms of its impact over a 100-year timeframe. CH4 has been measured directly in the environment since the 1970s. The Earth's atmospheric methane concentration has increased 160% since preindustrial levels in the mid-18th century. Since methane oxidation consumes OH (hydroxyl radicals), higher methane concentrations can reduce global mean OH levels and slightly increase methane's atmospheric lifetime (originally approximately 9 years). This creates a positive feedback between methane sources and sinks that is explicitly considered in contemporary atmospheric chemistry–climate studies. Carbon isotope analysis allows scientists to identify the source of the carbon in a methane sample by carefully measuring the ratio of the most common form of carbon, carbon-12, and its stable isotope, carbon-13 (13C), which has one extra neutron and is thus heavier. That means 13C is ever so slightly heavier than 12C. By analyzing the isotopic composition of methane in the atmosphere, it is possible to distinguish between microbial, thermal, and combustion sources of methane in atmospheric observations and inversion models. Another major natural sink is through oxidation by methanotrophic or methane-consuming bacteria in Earth's soils. These 2005 NASA computer model simulations—calculated based on data available at that time—illustrate how methane is destroyed as it rises. Through this CH4 oxidation process, atmospheric methane is destroyed and water vapor and carbon dioxide are produced. While this decreases the concentration of methane in the atmosphere, it is unclear if this leads to a net positive increase in radiative forcing because both water vapor and carbon dioxide are more powerful GHGs factors in terms of affecting the warming of Earth. This additional water vapor in the stratosphere caused by CH4 oxidation, adds approximately 15% to methane's radiative forcing effect. NASA researchers in 2001, had said that this process was enhanced by global warming, because warmer air holds more water vapor than colder air, so the amount of water vapor in the atmosphere increases as it is warmed by the greenhouse effect. Their climate models based on data available at that time, had indicated that carbon dioxide and methane enhanced the transport of water into the stratosphere. Atmospheric methane could last about 120 years in the stratosphere until it is eventually destroyed through the hydroxyl radicals oxidation process. === Mean lifespan === There are different ways to quantify the period of time that methane impacts the atmosphere. Methane oxidation allows methanotrophic bacteria to use methane as a source of energy, reacting methane with oxygen and as a result producing carbon dioxide and water. CH4 + 2O2 → CO2 + 2H2O Forest soils act as good sinks for atmospheric methane because soils are optimally moist for methanotroph activity, and the movement of gases between soil and atmosphere (soil diffusivity) is high. With a lower water table, any methane in the soil has to make it past the methanotrophic bacteria before it can reach the atmosphere.