Slashdot Mirror
NASA Study Shows Antarctic Ice Sheet Shrinking
deman1985 writes "A recently released NASA study has shown that the Antarctic ice shelf is shrinking at an alarming rate of 36 cubic miles per year. The study, run from April 2002 to August 2005, indicates that the melting accounted for 1.2 millimeters of global sea level rise for the period. From the article: 'That is about how much water the United States consumes in three months and represents a change of about 0.4 millimeter (0.01575 inch) per year to global sea level rise, the study concluded. The study claims the majority of the melting to have occurred in the West Antarctic ice sheet."
because of the properties of ICE vs Liquid Water the melting of the Artic ice sheet actually lowers water world wide..
Errr... WHAT?
Time to do the math again, I guess. Every now and then this bit of ugly science rears its ugly head.
Useful numbers:
Density of Seawater: 1025kg/m^3.
Density of Freshwater: 1000kg/m^3 (rounded up from 999.98 at freezing point)
Density of Ice: 916kg/m^3 [same source].
Things to know:
The vast majority of icebergs are not frozen seawater, they break off from land glaciers and float out to sea.
Buoyancy tells us that X will float in Y if X displaces a volume of Y where the mass of the displaced volume equals the mass of X.
Hollowed out shapes can contain more volume than a solid block of mass (this is why metal boats float).
So, lets say we have a solid, convex iceberg floating in an ocean ever so slightly above freezing, consisting of exactly 1025kg of ice right about to melt. To float, this iceberg must displace 1025kg of saltwater, which by sheer coincidence is exactly one cubic meter. Thus, when this iceberg broke off the glacier and fell into the water, the sea level increased by the height of one cubic meter spread out really thin across the entire surface. If you lifted the iceberg out without letting it melt, that one cubic meter would come back and fill the hole where it was.
Naturally, the sea being ever so slightly above freezing and the ice being ever so slightly below, the ice absorbs heat from the ocean and melts. Thanks to wonderful conservation of mass, we know we now have 1025kg of fresh water at ever so slightly above freezing, with a density of 1000kg/m^3. Thus, we have 1.025 cubic meters of fresh water to fill that 1 cubic meter hole where the iceberg used to be.
So because the iceberg fell into the ocean and melted, the sea level is now 1.025 cubic meters (spread out real thin over the entire ocean) higher than it used to be. Even if the ice started in the ocean (as in the Arctic), it's still 0.025 cubic meters high! It gets worse if the ice is sitting on the bottom of the ocean (then there is more ice than displaced water)! Even if you assume that the seawater is less dense in the Arctic (a fallacy, as the freezing action actually increases the saline content of the water around the ice), as long as the density of the seawater is greater than the density of the water you get from melting the ice (almost always freshwater), you will get an increase in sea level from melting the ice.
Incidentially, arctic ice is not all frozen seawater, much of it is from precipitation falling on top of the frozen seawater, so you can't even claim that the water in the ice came directly from the ocean in the first place (not that that claim would really help any, because that water has been locked up for thousands and thousands of years, returning it to water would definitely raise the ocean level beyond anything in written history). Plus, once the water is liquid and continues to heat, it will continue to expand: at 30C freshwater is only 995.65kg/m^3.
Since I whipped out the math anyway, 1025kg of ice is 1025kg*(1m^3/916kg)=1.119 m^3. Since it's solid and convex we know that there must be 0.119 m^3 of ice above sea level. This shows that roughly 10% of the 1.119 m^3 of ice is above sea level, thereby supporting the old adage that 9/10 of the iceberg is below the waterline.
If I have been able to see further than others, it is because I bought a pair of binoculars.
The last 5 yaers are the hottest in recorded history. I'm sorry, but how far back do our climate records go? Not that far in the grand scheme of things.
e rature_Comparison.pnga variety of different sources, from glaciers, to ice cores, to tree rings, but there is pretty good general agreement. That latest such study, putting together data from a wide variety of difference sources to cross reference temperatures for the last 1200 years showed the previous century was the warmest. For records going further back there are the Greenland ice cores with detailed data going back 120,000 years. Further back than that we have the Antarctic Vostok and DomeC ice cores which provide data going back 650,000 years. That gives a pretty good general picture of temperature historically at least over a large chunk of human history, and in the end its human history that counts: whether the planet continues on its merry way matters little to us - what matters is the impact any warming has on humans.
We have a number of temperature reconstructions going back about 2000 years. They do vary because they use http://en.wikipedia.org/wiki/Image:2000_Year_Temp
Change is the natural way of things. I think it's pretty presumptious of us to think we're causing it.
Well there are the remarkable correlations between atmospheric carbon dioxide and temperature, even over the 650,000 years spanned by Antarctic ice cores. Combine that with the present spike in carbon dioxide, which is verifiably anthropogenic, and the absorption spectra of carbon dioxide which makes it an effective greenhouse gas, together with the close correlation between the recent spike in atmospheric carbon dioxide and temperature, and you have some good reasons to start thinking we may be causing it. Is that conclusive? No. But then there's plenty more evidence than what I can pack into a quick paragraph.
Volcanoes put out far more greenhouse gasses than anything humans do.
This one is just a bizarre bit of disinformation that keeps getting circulated. It is quite false. Volcanoes put out around 130 to 230 teragrams of carbon dioxide a year. The US alone puts out around
5844 teragrams. Atmospheric carbon dioxide from volcanoes is less than 1% of the amount from human activities. Please, put this particular myth to bed.
Jedidiah.
Craft Beer Programming T-shirts
Wrong. There is widespread scientific consensus on the existence of global warming, and that human activity is contributing to it. A 2004 Survey of 928 peer-reviewed research articles related to climate change from 1993-2003 concluded that:
"Many details about climate interactions are not well understood, and there are ample grounds for continued research to provide a better basis for understanding climate dynamics. The question of what to do about climate change is also still open. But there is a scientific consensus on the reality of anthropogenic climate change. Climate scientists have repeatedly tried to make this clear. It is time for the rest of us to listen."
Noteworthy is that none of the articles dissented with the consensus opinion. None of them. Not much of a controversy, at least among people who know what they are talking about.