This article [1] in the journal Limnology and Oceanography (and others) indicates to me that we don't understand the effect of climate change on methane emissions from the Arctic and Antarctic seabed. Are emissions going up or down?

Wildfires in the western US are increasing, but we've changed the way we manage forests and forest fires in the west. The resulting accumulation of brush in forests (for one reason because we aggressively put out even small fires to protect encroaching development) makes big fires more likely. Furthermore on the scale of centuries, as long as the forests stand they will simply recycle CO2 by absorbing it as trees grow and by releasing it when they die (either through rotting and decay or by burning).

As far as the oceans not acting as CO2, the recent literature that I've read says that they are acting as CO2 sinks. The first two sentences of the abstract from a Feb. 2017 paper in Nature[2] are:

"The ocean is the largest sink for anthropogenic carbon dioxide (CO2), having absorbed roughly 40 per cent of CO2 emissions since the beginning of the industrial era. Recent data show that oceanic CO2 uptake rates have been growing over the past decade reversing a trend of stagnant or declining carbon uptake during the 1990s"

[1] Limnology and Oceanography. Effects of climate change on methane emissions from seafloor sediments in the Arctic Ocean: A review, http://onlinelibrary.wiley.com/doi/10.1002/lno.10307/full

[2] Nature. Recent increase in oceanic carbon uptake driven by weaker upper-ocean overturning. https://www.nature.com/nature/journal/v542/n7640/abs/nature2...