The correct answer is 1, 2, and 3, as all statements regarding methane hydrate deposits are accurate and interlinked. Firstly, global warming can destabilize methane hydrates, leading to the release of methane, a potent greenhouse gas, thereby exacerbating climate change. Secondly, significant reserves of methane hydrate are indeed located in Arctic tundra regions and beneath ocean floors, making them critical in understanding both energy resources and climate dynamics. Lastly, once released into the atmosphere, methane tends to oxidize into carbon dioxide over a period of one to two decades, contributing to long-term atmospheric carbon levels and global warming effects. Understanding these interconnections is vital for comprehending climate change implications, as emphasized in standard UPSC-level materials.