Melting Ice

I was struggling to summarize the seven articles and one editorial on melting glaciers in this week’s Science magazine, when RealClimate did it for me. This summary of their summary contains some background and extra material.

The RealClimate piece looks at the changes we are seeing in Greenland and Antarctic ice sheets today. The Greenland ice is producing ice quakes measured on seismometers worldwide, as ice lubricated by water lurches over obstacles. The Antarctic ice sheets are showing mass loss of 150 +/- 80 cu km/year. A cu km is a block one km by one km by one km, about the amount of water used by Los Angeles each year.

The two biggies are the articles that look at the last time the Earth was warmer than today. Or at least the northern hemisphere was. The tilt of the axis (now in the middle of the cycle) changes between 22 and 25 degrees over a 41,000-year cycle. The spinning Earth wobbles on its axis like a spinning top, changing the axis direction when closest to the sun over a 22,000 year cycle – now the southern axis points almost directly at the sun at perihelion, so southern summers are warmer and winters colder. Earth’s orbit changes as well. All these differences added about 130,000 years ago to make the southern hemisphere approximately today’s temperature and the northern hemisphere a few degrees C warmer.

The sea level rose by 4 to 6 m or even more, half or more from the Greenland melt, and the remainder from Antarctica, presumably from the effects of sea level rise and a warmer ocean, as air temperatures did not change.

The sea level is now increasing at about 3 mm/year (a little over an inch/decade), but in the last interglacial, sea level increased as much as 10 mm/year (4 inch/decade). By 2100, Greenland’s temperature may exceed its maximum temperature from that period 130,000 years ago. Unmentioned is that Antarctica’s temperature is likely to be warmer in 2100 than during the last interglacial.

It may still take millennia for the sea level to rise to its maximum from global warming. It is still thought that sea level rise will be less than a meter this century. Alaska is already being affected by increases in sea level and storms, which together have forced several coastal villages to move. This century, in addition to the loss of some Pacific Island states, Florida, Louisiana, the Netherlands, and Bangladesh will be among the areas suffering land loss from sea level rise. Even in areas where land loss is not important this century, flooding will increase: New York City’s hundred year floods will occur once every 4 years with a sea level increase of 1 m. Note to those who worry about unfunded mandates: infrastructure changes are costly.

Comments that go beyond praise and nays Sherwood notes other alternatives to cars in his comment on the last blog: bicycles and motorscooters.

Some people worry about the danger of bicycling, but this can be minimized by practicing safe cycling. Perhaps there are classes in your area? Even with all its dangers, and the mortality rate of very young males, cyclists have a higher life expectancy, plus it is fun, plus it is wonderful to know your body can get you around. Did I mention that it is fun? Well, the first little bit of getting used to them can be hard for those of us not in shape, but afterwards!

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