What's all This About Melting Ice?
I just plain stole the following copy from the homepage of Pete Stevens, another blogger who writes on a wide variety of topics. I can't say it any better than he can. The scaremongering about Greenland Ice melting by 2050 is impossible. The scaremongering about it sliding off into the ocean is simply not happening and is pretty much impossible. The ocean will not rise to overwhelming levels if the ice sheet melts. The rate of heating would have to 300 times faster than today to possibly manage to do such a thing by 2050. At today's rate of heating it will take 10000 years or more to achieve a full melt (we'll be back in the next ice age by then).
The sad part is - he just did the math. And you can too.
Just slipped this in to give some perspective on world water distribution.
To help lessen my guilt, I've attached Pete's blog site on the button below and then copied his post on the Greenland ice sheet melting in its entirety below that. Hope that gives credit where credit is due.
*The Greenland ice sheet isn't melting anywhere near as fast as you think.
A repeated assertion I've heard from many people who are worried about climate change is that the greenland ice sheet is going to melt in the near future - 20-30 years and that the whole world will sink. I think people have mistaken the statement that the arctic ocean could be ice free by 2050 with the statement tha the greenland ice cap will melt by 2050.
The greenland ice sheet won't melt by 2050. Here's why.
NASA says' it's melting really quickly
Lots of people quote this NASA press release, Loss of ice is 220 cubic kilometers per year, or 264 billion gallons of water. The important questions are :-
How big is the greenland ice sheet.?
Very. Wikipedia and other sources suggest about 2.85million cubic kilometres.
How long will it take to melt at current rates
So, divide, 2 850 000 by 220 and you get 13000 years.
To put it another way, if the rate of ice melt in Greenland accelerates by a factor of 300 and remains at that level for the next 43 years the icecap will finish melting in 2050.
Update (2019 - 13 years after original publication in 2006)
Average loss of ice from 2002 to 2016 has been slightly higher, at 280 GT, roughtly 300 cubic kilometres. From 1900-2000 Greenland lost 9TT of ice, 90GT/year or 1/4 the current rate of ice loss. That alters the timescale to less than 10,000 years. Still not 2050 though.
Latent heat of ice
To melt greenland you need to provide enough energy for all the ice to melt. You need 334kJ/kg to melt ice. The ice sheet is about 2.85 * 10^6 km^3 = 2.85*10^15m^3 which is 2.85*10^18kg of ice. So that's pretty much 10^21kJ of energy. Let's suppose you paint it black and stick it in the sahara with the sun directly overhead. The surface area is about 1.7*10^12m^2 which nets you about 2x10^12kW. Divide one by the other and you get pretty much 5*10^8s = 16 years.
The more observant among you will notice that the sun doesn't shine at night, integrating out for over the whole day we get 1/4 the energy you do at peak which gives us 64 years.
To put it another way, were we to pick up the greenland ice sheet and relocate it to the sahara, paint it in a perfect absober, replace the atmostphere overhead with something as transparent as a vacuum, assuming the ice sheet temperature is 0C and we can dispose of all the water at 0C without accidently heating it up, and there is not a cloud for the next 64 years and we can distribute the suns energy perfectly evenly over 1700000000000m^2 we could melt the greenland ice sheet in only 50% more time than the scaremongers suggest.
A vague accounting estimate, for greenland being at 72 degrees latitude (30% of the sunshine), ice is reflected (80% reflected energy), you start scaling that estimate up towards 500 years. Fortunately the ice sheet doesn't radiate any energy away to space. Oh, hang on a minute...
What about the gulf stream.
Wikipedia suggests the gulf stream supplies about 1.4*10^15W of heat. Assuming all that can be delivered to the greenland ice sheet with perfect efficiency we get to recycle the sahara argument but with a source energy flow of 1.4*10^12kW instead of 2*10^12kW. You would get to grow another ice sheet over northern europe though.
D'uh. It's going to break up and float out to sea.
The distance from the centre of greenland to the sea is 550km. To do it in the 43 years we have remaning, it needs to crack in the centre and travel at a uniform speed of 12.7km/year towards the ocean in all directions.
There is a glacier in Greenland (Jakobshavn Isbrae) which has been measured moving this quickly at it's fastest point (2005), and Kangerdlugssuaq even faster (14.6km/s in the summer of 2005) for a short period.
In order for the ice sheet to disappear in time, the centre of the ice sheet needs to start moving now at the same rate as the fastest ice flow in the world. Since the rest of the ice sheet is in the way and gravity means you can't go over it, the whole ice sheet needs to start moving. This should be pretty obvious - by 2010 there will be a 75km wide ice free hole exactly in the middle of the Greenland ice sheet, by 2020 it will be 330km wide, 2030 584km wide, 2040 838km wide, 2050 1100km wide covering the whole of Greenland.
Update in 2019
There isn't a 330km ice free area in the middle of Greenland.
How much did the sea level rise ?
220km^3 = 53miles^3. The ocean is about 360000000 square miles, we get 1.5*10^-7 miles = 0.2mm. Scary stuff indeed!
Isn't that terrifyingly fast?
Maybe. 20000 years ago the sea level was 125m below what it is today, that's an average rise over the last 20000 years of 6mm/year, about twice as fast as the sea level is rising today. That doesn't necessarily mean the current rise isn't concerning though.
Many thanks to Nick Barnes for pointing out some errors, in particular regarding ice sheet flow.
*SO, WHAT IF WE WERE TO APPLY THIS REASONING TO THE TOTAL ICE MASS PRESENTLY ESTIMATED TO BE IN THE WORLD?
I drew the following numbers from the reference below. I converted them because I didn't like the way they reported their numbers. For example, instead of giving us ice volumes in a simple term such as cubic kilometers they reported it as SLE (sea level equivalents) - huh! Then ice loss is given as gigatonnes / year without mentioning that 1 gigatonne is equivalent to a cubic kilometer. They compare "oranges to apples" in a manner that makes the data look more fearsome and in which it is impossible to compare or to draw perspective. I've converted their numbers to simple cubic kilometers and you can see just how much we are "losing" worldwide in simple, understandable language. *
AREA SLE (m) = CU. KM. LOSS GT. = LOSS CU. KM. YRS. TO MELT
GREENLAND 7.36 3,000,000 250 250 12,000 yrs.
ANTARCTIC 57.80 24,000 000 200 200 120,000 yrs.
GLACIERS / CAPS .43 200,000 230 230 869 yrs.
* numbers were calculated and rounded off for simplicity. True table given in reference below. Good luck.
*Now, some more gleanings.
Consistent with not taking any credit for the information in this blog, I include a number of "cut and pastes" that I undertook off my Google search requests. I've collated and blended them, then smoothed to make a readable story. The goal is to repeat information that's out there for people in a way that they can read and appreciate the size and scale of the ice sheets that are a part of the Earth and to give perspective to the alarming reports being circulated about our potential to "melt all the ice" and flood the world due to sea level rise.
So, to begin, I've given the NASA real time readout for Ice Sheets in the Antarctic and Greenland which also displays average melt rates over given periods of time for perspective. (values are also given for other parameters such as Carbon Dioxide, Global Temperature, Arctic Sea Ice, Sea Levels).
World Measurements of Climate Parameters by NASA.
With a warning about their contentious validity!
Do we read these numbers as simply portending disaster - or do we have to scrutinize the techniques, calculations, assumptions, corrections, interpretations, correlations, applied to data in order to prepare these conclusions? The purpose of this blog is to do report on work that has done just that and in this spirit we copy the article below makes some damming accusations about manipulation of this data by NASA and NOAA.
And so, perhaps our best summary of the present situation is as follows:
1. The Greenland Ice Sheet is a vast body of ice covering 1,710,000 square kilometres, roughly 80% of the surface of Greenland. In addition to the large ice sheet, isolated glaciers and small ice caps cover between 76,000 and 100,000 square kilometres around the periphery.The ice sheet has covered large parts of Greenland for the last 2-3 million years, but active glaciers and constant melting have meant that the ice has been recycled many times. The aging ice sheet is only a few metres thick at the ice fringe, but more than 3,200 metres thick at its highest point. The total volume of Greenland's ice sheet is about 2,900,000 cubic kilometers. Much attention is being given to the claim that the warm air and water being seen in today's climate is leading ice sheets to melt at unprecedented rates.
Greenland ice constitutes roughly 9% of the world ice mass. If the entire Greenland ice sheet were to melt, (calculated at around 10000 years at today's "hotter" melt rate) it would mean an 8 metre rise in sea level, on average.
2. The Antarctic Ice Sheet extends almost 14 million square kilometers (7 times the area of Greenland), and roughly the area of the contiguous United States and Mexico combined. The Antarctic Ice Sheet contains 24 million cubic kilometers of ice (8 times more ice than Greenland). The mean thickness of the Antarctic ice sheet is 2.16 km; the maximum known thickness of the ice sheet is 4776 m. Without the ice, Antarctica may be the lowest lying continent; the greatest known depression of bedrock is the Byrd Subglacial Basin, at 2538 m below sea level.
90 % of the world's ice mass is found in the Antarctic and 9% to Greenland leaving only 1% to assign to all other sources of ice such as land based glaciers, snowfall, frozen lakes, etc. If massive Antarctica were to melt sea levels would rise by as much as 58 meters (also known as the sea level equivalent SLE).
MELT RATES - at the present rate of melt, Greenland would lose ALL of its ice in approximately 10000 years (see above). Antarctic ice melt would require over 120,000 years but melting is not so much a problem in Antarctica as is ice movement from the land to the sea. There is more concern today that underlying warmer waters are encouraging the ice to slide off the land mass into the oceans. The resulting glaciers would contribute to sea level rise as the ice was on land before sliding into the ocean.
WILL MELT RATE INCREASE ? - well, that's the question isn't it? We are presently being bombarded with just that possibility in the media and monthly melt figures are being quoted (eg. 160 gigatons for July) as in the attached CNN article to scare the public (they didn't mention that this summer melt only occurs for 3 to 4 months by the way). Remember the calculations above though - melt rate would have to increase 300 times the present day's rate in order to melt the Greenland sheet by 2050.
The following reference, although lengthy, does a credible job of estimating the present conditions regarding total sea level rise / year (from all ice) . If you scroll through there are tables that not only give their estimates but also several other authours as well. These estimates indicate present rise at somewhere between .9 mm and 1.7 mm / year. 30 years to 2050 would be 27 to 60 mm (that's 3 to 6 cm) at these varied rates (but of course, this assumes the next 30 years will continue to be hot - see cycle 25 blog). Quite a range. How high do you build the dyke ?
and also -
Keep perspective everyone and don't let articles like the following attached scare you into submission because cutting your carbon footprint isn't going to stop this rollercoaster ride.
AND FINALLY, HAS THE "TIDE ALREADY TURNED" - SEEMS IT'S SNOWING UP NORTH.
AND DOWN SOUTH.
Please note: these images and the discussions surrounding them are easily found on Google. I'm not even going to attempt to make a bibliography because this isn't a scientific paper, it's an opinion piece. If you doubt me go search them out. The exercise is quite revealing.