* The melting of permafrost in the Arctic is releasing large amounts of methane, a potent greenhouse gas. (This emphasizes the environmental impact of permafrost thaw.)
* Scientists are studying how permafrost thaw could affect infrastructure and ecosystems in the far north. (This highlights the practical implications of permafrost change.)
* The construction of buildings in areas with permafrost requires special techniques to avoid damage. (This shows the challenges of building on permafrost.)
* Permafrost is a frozen layer of soil found in cold climates, and it is vital for supporting the Arctic ecosystem. (This provides a simple definition of permafrost and its importance.)
* The thawing permafrost is revealing ancient artifacts and even woolly mammoth remains. (This illustrates the archaeological significance of permafrost.)
You can choose the sentence that best fits the context you are writing in.