Query: The sea level was 20 to 30 feet higher than it is today, implying that the ice sheets in both Greenland and Antarctica must have partly disintegrated, a warning of what could occur in the relatively near future if the heating of the planet continues unchecked.”

Relevant passages:
Sea level rise <=SEP=> A sea level rise is an increase in the volume of water in the world 's oceans , resulting in an increase in global mean sea level . Sea level rise is usually attributed to global climate change by thermal expansion of the water in the oceans and by melting of Ice sheets and glaciers on land . Melting of floating ice shelves or icebergs at sea raises sea levels only slightly .   Sea level rise at specific locations may be more or less than the global average . Local factors might include tectonic effects , subsidence of the land , tides , currents , storms , etc. .  Sea level rise is expected to continue for centuries . Because of the slow inertia , long response time for parts of the climate system , it has been estimated that we are already committed to a sea-level rise of approximately 2.3 m for each degree Celsius of temperature rise within the next 2,000 years . IPCC Summary for Policymakers , AR5 , 2014 , indicated that the global mean sea level rise will continue during the 21st century , very likely at a faster rate than observed from 1971 to 2010 . Projected rates and amounts vary . A January 2017 NOAA report suggests a range of GMSL rise of 0.3 -- 2.5 m possible during the 21st century .   Sea level rises can considerably influence human populations in coastal and island regions and natural environments like marine ecosystems .

West Antarctic Ice Sheet <=SEP=> The Western Antarctic Ice Sheet ( WAIS ) is the segment of the continental ice sheet that covers West ( or Lesser ) Antarctica , the portion of Antarctica on the side of the Transantarctic Mountains which lies in the Western Hemisphere . The WAIS is classified as a marine-based ice sheet , meaning that its bed lies well below sea level and its edges flow into floating ice shelves . The WAIS is bounded by the Ross Ice Shelf , the Ronne Ice Shelf , and outlet glaciers that drain into the Amundsen Sea .   It is estimated that the volume of the Antarctic ice sheet is about 25.4 million km3 ( 6.1 million cu mi ) , and the WAIS contains just under 10 % of this , or 2.2 million km3 ( 530,000 cu mi ) . The weight of the ice has caused the underlying rock to sink by between 0.5 and 1 kilometres ( 0.31 -- 0.62 mi ) in a process known as isostatic depression .   Under the force of its own weight , the ice sheet deforms and flows . The interior ice flows slowly over rough bedrock . In some circumstances , ice can flow faster in ice streams , separated by slow-flowing ice ridges . The inter-stream ridges are frozen to the bed while the bed beneath the ice streams consists of water-saturated sediments . Many of these sediments were deposited before the ice sheet occupied the region , when much of West Antarctica was covered by the ocean . The rapid ice-stream flow is a non-linear process still not fully understood ; streams can start and stop for unclear reasons .   When ice reaches the coast , it either calves or continues to flow outward onto the water . The result is a large , floating ice shelf affixed to the continent .

Tipping points in the climate system <=SEP=> A tipping point in the climate system is a threshold that, when exceeded, can lead to large changes in the state of the system. Potential tipping points have been identified in the physical climate system, in impacted ecosystems, and sometimes in both. For instance, feedback from the global carbon cycle is a driver for the transition between glacial and interglacial periods, with orbital forcing providing the initial trigger. Earth's geologic temperature record includes many more examples of geologically rapid transitions between different climate states.Climate tipping points are of particular interest in reference to concerns about global warming in the modern era. Possible tipping point behaviour has been identified for the global mean surface temperature by studying self-reinforcing feedbacks and the past behavior of Earth's climate system. Self-reinforcing feedbacks in the carbon cycle and planetary reflectivity could trigger a cascading set of tipping points that lead the world into a hothouse climate state.Large-scale components of the Earth system that may pass a tipping point have been referred to as tipping elements. Tipping elements are found in the Greenland and Antarctic ice sheets, possibly causing tens of meters of sea level rise. These tipping points are not always abrupt. For example, at some level of temperature rise the melt of a large part of the Greenland ice sheet and/or West Antarctic Ice Sheet will become inevitable; but the ice sheet itself may persist for many centuries. Some tipping elements, like the collapse of ecosystems, are irreversible.