The bottom figure (red curve) shows that methane started rising at around 2007 after several years of stability. (esa-ghg-cci.org)
The rates have gone up after many years of stability. (autoquotenow.com)
Fecal microbiota transplantation associated with 10 years of stability in a patient with SPMS — Seraj Makkawi — Neurology, Neuroimmunology & Neuroinflammation (microbiomedigest.com)