Methane emissions are down a total of 15% from 1990 to 2013--mostly due to the reduction of exploration when it comes to natural gas and petroleum products. However, it has increased in agriculture as domestic livestock produce methane through their daily digestive processes. Another large contributor is landfills. We all throw away large amounts of trash and it decomposes in landfills that produce emissions that are hazardous.
So far there have been no findings that there are long term effects caused by methane, but it is highly flammable and can cause oxygen deficiency in humans.
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