evidence: Climate change has led to decades of shrinking and thinning of the Arctic sea ice.[210] While ice-free summers are expected to be rare at 1.5 °C degrees of warming, they are set to occur once every three to ten years at a warming level of 2 °C.[211] Higher atmospheric CO2 concentrations cause more CO2 to dissolve in the oceans, which is making them more acidic.[212] Because oxygen is less soluble in warmer water,[213] its concentrations in the ocean are decreasing, and dead zones are expanding.[214] [...] - Stroeve, J.; Holland, Marika M.; Meier, Walt; Scambos, Ted; et al. (2007). "Arctic sea ice decline: Faster than forecast". Geophysical Research Letters. 34 (9): L09501. Bibcode:2007GeoRL..34.9501S. doi:10.1029/2007GL029703. [...] - Zhang, Jinlun; Lindsay, Ron; Steele, Mike; Schweiger, Axel (2008). "What drove the dramatic arctic sea ice retreat during summer 2007?". Geophysical Research Letters. 35 (11): 1–5. Bibcode:2008GeoRL..3511505Z. doi:10.1029/2008gl034005. S2CID 9387303.