VOA慢速英语:研究表明北极地区的融化会释放出温室气体

permafrost – n. technical : a layer of soil that is always frozen in very cold regions of the world

emission -- n. something sent out or given off

unaccounted – adj. unexplained, not included in; the act of producing or sending out something (such as energy or gas) from a source

prediction – n. the action of saying something will happen; a forecast

constrain – v. to limit or restrict the scope or activity of something