Sentence:  The heat input to polar areas prevents this global <WSD>cold trap</WSD> catastrophe from happening, but during ice ages, signifcant capture of the Earth's water in polar areas will occur. 
Meaning of the word marked with <WSD> tags:  An atmospheric layer that is significantly colder than the adjacent layers both deeper and higher. It keeps ascending gases that have high melting points from escaping the atmosphere by freezing them to a solid which then drops back to the planet surface.