Gases absorbing and emitting radiation within the thermal infrared range in the atmosphere are called greenhouse gases. They are responsible for the greenhouse effect. The main greenhouse gases are carbon dioxide, methane, nitrous oxides and fluorinated gases or, in short, F-gases.
The relative contribution of each of these greenhouse gases to climate change depends roughly on three main factors:
1. The amount of a respective gas in the atmosphere.
2. The duration of stay in the atmosphere.
3. The intensity of their impact on the global temperature.
For each of these gases a Global Warming Potential (GWP) has been calculated which is a measure of the total energy that a gas absorbs over a particular period of time compared to carbon dioxide. Besides, it is also based on the degradation rate of the respective gas. Thus the GWP describes the ability of a gas to trap heat in the atmosphere. The larger the GWP the bigger the effect of the particular gas on global warming.
As shown in the figure below, the GWPs (100 years) of the primary greenhouse gases differ significantly. Since the GWP is calculated in relation to carbon dioxide, the GWP of carbon dioxide is defined as 1. The 100 year GWP for methane is 25 implying that methane will trap 25 times more heat than carbon dioxide over the next 100 years.

Carbon dioxide is the main greenhouse gas emitted by human activities. As part of the Earth’s carbon cycle, carbon dioxide is also naturally present in the atmosphere: It is constantly exchanged between the atmosphere, ocean and land surface as it is produced and absorbed by many microorganisms, plants and animals. But human activities affect the carbon cycle by adding more carbon dioxide to the atmosphere and by damaging natural sinks, for example forests which would otherwise remove carbon dioxide from the atmosphere.
Nitrous Oxide, like carbon dioxide, is also naturally present in the atmosphere as it is part of the global nitrogen cycle: Nitrogen circulates between the atmosphere, plants, animals and bacteria breaking it down in the oceans and soils. Even though it has a variety of natural sources, human activities such as wastewater management or nitrogen fertilization increase the amount of nitrous oxide in the atmosphere. These molecules stay in the atmosphere for about 120 years but can be removed by certain types of bacteria or even destroyed by chemical reactions or ultraviolet radiation.
In contrast to other greenhouse gases, fluorinated gases do not have natural sources and only arise from human activities. F-gases are emitted through different industrial processes and many of them have a very high global warming potential in comparison to other greenhouse gases. Therefore, even very small atmospheric concentrations can have great effects on global temperatures. Additionally they have very long atmospheric lifetimes, lasting up to thousands of years. F-gases are removed from the atmosphere only when they get destroyed by sunlight in the far upper atmosphere. In general, fluorinated gases are the most potent and longest lasting sort of greenhouse gases emitted by humans.
Methane is the second most important greenhouse gas. It is emitted by several natural sources such as wetlands but also by different human activities like leakage from natural gas and livestock farming. Methane can be removed from the atmosphere by natural processes in soil and chemical reactions in the atmosphere. As its lifetime in the atmosphere is, compared to other greenhouse gases, quite short (~12 years), targeting methane emissions as a means of reducing the overall greenhouse gas emissions in a relatively short period of time is a reasonable approach to reduce global warming.
Globally around 60% of all methane emissions originate from human activites like industry, agriculture and waste management.

Even though the total methane emissions decreased by around 10% between 1990 and 2012 the emissions associated with agricultural activities did not. This is mostly due to the intensification of livestock farming. Methane is set free in the course of digestion in ruminant animals like cattle and emitted into the atmosphere. Therefore, by increasing livestock production methane emissions are increased as well.

Methane is formed in a process called methanogenesis which, for example, takes place in the rumen of cattle. However, the methane is not further utilized by any of the microorganisms living in the animal’s digestive tract nor by the animal itself, so it gets exhaled to the atmosphere and thus contributes to global warming. Read here (LINK) what has been done in the past against these emissions, or here (LINK) how exactly methanogenesis takes place.

The Greenhouse Effect is a well known phenomenon describing the synergy of several gases in the atmosphere of our earth, which leads to positive as well as negative consequences. Without greenhouse gases the earth would be a very cold place and life would not be possible the way we know it. Nevertheless, due to increasing emission of gases like methane and carbon dioxide the effect is further enhanced and thus causes global warming. Among other things the greenhouse gas methane is a product of the natural digestion of cows. Because the consumption of dairy products and meat is increasing mass husbandry is widely spread. Hence, the emission of methane attributed to cows rises to unnatural dimensions. Since most people are not willing to change their daily nutrition and reduce their consumption of several products significantly (see our survey) an elimination of methane emissions caused by cows would be useful. However, former approaches merely regard either the methanotrophs responsible for methane production or the substrates they need. Our project idea is to reduce global methane emission right at one of the sources, the rumen of cows, without affecting resident organisms. Our idea is to provide the digestive tract with a specially modified microorganism, named E. cowli, which is planned to metabolise the methane before its emission and, therefore, prevents the enhanced greenhouse effect and global warming.