Carbon dioxide (CO₂) and methane (CH₄) have been recognized by the International Panel of Climate Change as the most important of the Earth’s greenhouse gases whose concentration has been directly modified by human activities.

Methane has an estimated global warming potential per molecule 28 times greater than CO₂ over a 100 year horizon and 84 times greater over a 20 years horizon and, despite its much lower abundance, thus is the second most significant anthropogenic greenhouse gas. The main anthropogenic emissions of methane originate from livestock breeding, the energy sector, rice agriculture, landfills/waste disposal, and biomass burning. The predominant natural sources are wetlands, geological sources, termites, wild animals, hydrates from the oceans and wildfires.

The CO₂ concentration in the atmosphere is mainly determined by the emissions from combustion of fossil fuels and by CO₂ uptake and release by the Earth’s oceans and terrestrial biosphere. Currently 91% of the total emissions are caused by fossil fuel combustion and cement production and 9% by land use change.

Large uncertainties in their budget, however, and feedback mechanisms which are, if at all, only partly understood, limit the accuracy of climate change projections. In order to reliably predict the climate of our planet, and to help constrain political conventions on greenhouse gas avoidance, adequate knowledge of the sources and sinks of these greenhouse gases and their feedbacks is mandatory. In spite of the recognized importance of this issue, our current understanding about sources and sinks of the gases CO2 and CH₄ is still inadequate.

The overarching objective of CoMet is to improve our understanding and to better quantify the carbon dioxide and methane cycles. Through analyzing the CoMet data, scientists will accumulate new knowledge on the global distribution and temporal variation of the greenhouse gases. These findings will help to better understand the global carbon cycle and its influence on climate. These new findings will be utilized for predicting future climate change and assessing its impact.

The measurement strategies will be chosen to provide the best possible synergy of the instruments. In general, the remote sensors will measure the GHG columns between the ground and flight level. The flight paths will be chosen to fly along projected gradients of the greenhouse gas columns.

On smaller scales such gradients will occur in the vicinity of well-known emission sources such as coal mines, coal-burning power plants, landfills, volcanoes (e.g. Mt. Etna) etc. The flight pattern will be chosen to fly downwind of these emission sources.

On larger scales the hemispheric gradient should be perceivable for example on flights from central Europe towards the sub-tropics. This is the region on Earth where the gradients are largest.