PER2: K tomuhle clanku jeste napsal Michael Mann nesouhlasnej komentar
Michael E. Mann
"Point of no return" on Greenland melt? (
https://cnn.com/2020/08/14/weather/greenland-ice-sheet/index.html)
NOPE!
My Penn State College of Earth and Mineral Sciences colleague Richard Alley, one of the leading authorities in the world on ice sheet dynamics, provides context for this latest somewhat breathless claim being reported by mainstream media outlets (the result of a poorly written, over-hyped press release).
Summary of Richard's Comments:
"models show...sustained temperature above some threshold will cause..ice sheet to lose most of its mass, but...warming to date..probably not enough"
Full statement:
Greenland’s ice sheet is losing mass because of human-caused warming, will lose more mass if the modern climate is sustained because the ice sheet has not finished responding to the warming that already occurred, and will lose even more mass even faster if more warming occurs. But, the scientific literature generally indicates that we are not yet committed to loss of most or all of the ice sheet, for two reasons: changes in the shape of the ice sheet caused by the mass loss can help preserve part of it, and the ice sheet takes long enough to melt that excess warmth may be reduced before the ice sheet is gone.
Most models show that sustained temperature above some threshold will cause the ice sheet to lose most of its mass, but that the warming to date is probably not enough to cause this; how much more warming is required remains a topic of considerable interest, and probably is not too many degrees. For smaller sustained warming, the ice sheet tends to reduce its footprint (the margins retreat). The warm ocean melts ice cliffs and ice shelves or carries away icebergs today in deep fjords, but these fjords typically become shallower toward the center of the ice sheet or end entirely, so retreat of the ice front reduces mass loss, helping preserve the remaining ice.
Once the iceberg calving and ocean melting are reduced, melting the remaining ice sheet requires bringing heat to the ice in the air, which is slower (many centuries even under strong warming, and a few millennia under smaller warming), giving us time to lower the temperature. (Note, though, that changes in parts of Antarctica could possibly be faster and harder to reverse if we cross thresholds there.)