Final answer:
The greatest concern with the drying of Northern peatlands is the release of methane, which is a more immediate and concerning impact due to its significant contribution to global warming.
Step-by-step explanation:
The greatest concern with the drying of Northern peatlands is a) Release of methane. Peatlands in the Northern hemisphere represent a significant carbon sink; they store a substantial amount of carbon that has accumulated over thousands of years. When these peatlands dry, the stored carbon is exposed to the air and can be decomposed by microorganisms, which release methane, a potent greenhouse gas, into the atmosphere. This process exacerbates climate change because methane has a much greater warming potential than carbon dioxide. While soil erosion, loss of biodiversity, and increased forest growth are also issues related to the changing dynamics of the Northern peatlands, the release of methane is the most immediate and concerning impact of their drying due to its significant contribution to global warming, as reflected in question 35 regarding significant contributors to global warming.