It's not as bad as we've been told so far. A comprehensive study of the behavior of ice sheets has shown that by 2100, their melting will add no more than 36.8 cm to sea level. In other words, growth in this century will not exceed 69 cm.
Water rises because it heats up with the planet and expands, and also because glaciers and ice sheets melt and slide into the ocean. The rate of sea level rise remains unknown, as predicting how much ice will be lost and when has proven to be very difficult. A large group of scientists called Ice2sea claims its estimate is the most accurate.
If carbon dioxide emissions continue to grow rapidly until the end of the century, melting and mixing of ice sheets will add 3.5 to 36.8 cm to the sea by 2100. “This is the most likely assumption,” says project coordinator David Vaughan of the British Antarctic Survey. "We are confident that this is the best forecast for today."
Add this result to the expansion of water and we get that sea level will rise by 16-69 cm by 2100. Almost the same estimate is indicated in the latest report of the UN Intergovernmental Panel on Climate Change: 18-59 cm.
Then, in 2007, this forecast was considered overly optimistic, because in the absence of good physical models of the flow of the ice sheets of Greenland and Antarctica towards the ocean, the IPCC had to exclude them from the calculations. Subsequently, various research groups took this point into account, and they got a rise in sea level by an entire meter or even two. But, as it turns out, the authors of that report were on the right track.
Mr. Vaughan admits that the main unknowns were the amount of heat that warm oceans can transfer to the edges of the ice sheets, and the rate of retreat of those edges. To understand this, the Ice2sea collaboration has developed more sophisticated models of how changes in the atmosphere affect the ocean and how it affects the ice sheets. “We are the first to connect these things,” emphasizes Mr. Vaughan. It turned out that a lot in the life of ice really depends on the temperature of the sea.
And another factor that was considered important turned out to be insignificant. Melt water can seep down to the base of ice sheets and glaciers, lubricating them and allowing them to slide further into the sea. However, this happens in short bursts. “Yes, this is a factor, but far from the main one,” says Mr. Vaughan.
In fact, there is nothing to rejoice in, because the rise in sea level will continue for more than one century. In the past, when the Earth was only a few degrees warmer than today, the sea level was tens of meters higher. Probably the same thing awaits us - in the long run.
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