claim: Methane plays a minor role in global warming but could get much worse if permafrost starts to melt.
evidence: For instance, a 2016 study led by Jim Hansen concluded that based on past climate change data, sea level rise could accelerate exponentially in the coming decades, with a doubling time of 10, 20 or 40 years, respectively, raising the ocean by several meters in 50, 100 or 200 years.