text: Present day global emissions of volcanic gases to the atmosphere can be classified as eruptive or non-eruptive. Although all volcanic gas species are emitted to the atmosphere, the emissions of CO (a greenhouse gas) and SO have received the most study. 
  It has long been recognized that eruptions contribute much lower total SO emissions than passive degassing does. Fischer et al (2019) estimated that, from 2005 to 2015, SO emissions during eruptions were 2.6 teragrams (Tg or 10g or 0.907 gigatons Gt) per year and during non-eruptive periods of passive degassing were 23.2 ± 2Tg per year. During the same time interval, CO emissions from volcanoes during eruptions were estimated to be 1.8 ± 0.9 Tg per year and during non-eruptive activity were 51.3 ± 5.7 Tg per year. Therefore, CO emissions during volcanic eruptions are less than 10% of CO emissions released during non-eruptive volcanic activity.  
  The 15 June 1991 eruption of Mount Pinatubo (VEI 6) in the Philippines released a total of 18 ± 4 Tg of SO. Such large VEI 6 eruptions are rare and only occur once every 50 – 100 years. The 2010 eruptions of Eyjafjallajökull (VEI 4) in Iceland emitted a total of 5.1 Tg CO. VEI 4 eruptions occur about once per year. 
  For comparison, Le Quéré, C. et al estimates that human burning of fossil fuels and production of cement processed 9.3 Gt carbon per year from 2006 through 2015, creating up to 34.1 Gt CO2 annually.
  Some recent volcanic CO emission estimates are higher than Fischer et al (2019). The estimates of Burton et al. (2013) of 540 Tg CO/year and of Werner et al. (2019) of 220 - 300 Tg CO/year take into account diffuse CO emissions from volcanic regions.