The leading cause is garbage and waste from people.
The correct answer is - the release of methane from thawed permafrost.
In the past decade it has been noticed that the levels of methane are increasing in the atmosphere, and the biggest ''producer'' of this methane is the melting permafrost. There's huge amounts of methane trapped underground bellow the permafrost. But the permafrost is melting because of the global worming, so the methane is free to come out and go up in the atmosphere.
I think you are looking for the word, Metaphase.
Answer:
B i did that to and got it right!
