Basically there are a few dangerous ways glaciers can react nonlinearly, raising sea level (from watching a few videos).<p>Perhaps best is to watch this long presentation by Eric Rignot from NASA JPL a few times, it&#x27;s very fascinating and also terrifying.<p><a href="https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=3p9uRxX95f4" rel="nofollow">https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=3p9uRxX95f4</a><p>Imagine two kilometers of glacier sitting on bedrock that&#x27;s 500 meters below sea level. The glacier doesn&#x27;t touch sea water because there&#x27;s higher ground between it and the sea, though still below sea level, and also that&#x27;s blocked by ice. If that blocking ice melts, the warm and salty water can then touch the big glacier that then starts melting and calving icebergs.
Or if the glacier is on higher ground, it can start directly sliding towards the sea.<p>There are multiple glaciers in Greenland and Antarctica that each could contribute one meter to sea level rise, that the scientists are watching. Eric Rignot named the parts between the glacier and the sea Flood Gates.<p>We haven&#x27;t observed ice sheet collapses, so it&#x27;s hard to know how it will play out, how long it will take, one or more centuries. We also can&#x27;t afford to wait and observe them and only then do something about it.