I'm m-m-m-m-melting... melting... MELTING!
September 18, 2007 10:25 AM Subscribe
Global Warming Filter: This might be a stupid question, but if enough polar ice has melted to open the Northwest Passage for the first time in distant memory, then why are Lake Superior's waters at an all-time low?
I thought global warming was supposed to raise water levels?
I thought global warming was supposed to raise water levels?
This would apply to oceans primarily into which polar ice melts. Lakes aren't fed by oceans but rather the other way around.
posted by vacapinta at 10:37 AM on September 18, 2007
This would apply to oceans primarily into which polar ice melts. Lakes aren't fed by oceans but rather the other way around.
posted by vacapinta at 10:37 AM on September 18, 2007
Rising sea level will be due to the melting of glaciers on land, not sea. When sea ice melts, it doesn't add volume to whatever body of water it's in because the ice was already taking up space in that basin. So the concern about rising sea level has much more to do with melting and calving in Greenland and Antarctica, for example. Since ice at the North Pole is sea ice, it won't change sea level significantly if it melts.
I don't have a clue why Lake Superior is at all time lows, but the above is why melting ice in the Arctic (open Northwest passage) won't affect sea level.
posted by HighTechUnderpants at 10:37 AM on September 18, 2007
I don't have a clue why Lake Superior is at all time lows, but the above is why melting ice in the Arctic (open Northwest passage) won't affect sea level.
posted by HighTechUnderpants at 10:37 AM on September 18, 2007
Here's an article in USA Today discussing the low water level in Lake Superior. A drought and warm weather are the immediate cause of the drop in water levels. In the past year, precipitation was 6 inches less than the average of 31 inches. The lake's southern shore had a green Christmas in 2006. The ice and snow pack that usually cover the lake arrived late, allowing water to evaporate.
posted by russilwvong at 10:38 AM on September 18, 2007
posted by russilwvong at 10:38 AM on September 18, 2007
Best answer: It's a good question, actually.
But there's quite a lot of land between the waters from melted polar ice and Lake Superior. Melting polar ice does not mean an equivalent rise in water levels everywhere - lake levels may shrink while ocean levels may rise.
Similarly, a big part of global warming is the planet getting warmer in general, not everywhere at all times. A plausible example of this would be how the 'sudden' addition of large amounts of fresh water to the oceans might cause the Gulf Stream to stop working as efficiently as it currently does, meaning some areas (such as Great Britain) may actually become colder, despite the reality of global warming.
From what I can glean from the article, global warming may be contributing to both the low levels of Lake Superior as it is to the melting of polar ice. But the world's a big place - the water just doesn't slosh around very easily and "level out" in any sort of obvious way necessarily.
posted by Dee Xtrovert at 10:38 AM on September 18, 2007
But there's quite a lot of land between the waters from melted polar ice and Lake Superior. Melting polar ice does not mean an equivalent rise in water levels everywhere - lake levels may shrink while ocean levels may rise.
Similarly, a big part of global warming is the planet getting warmer in general, not everywhere at all times. A plausible example of this would be how the 'sudden' addition of large amounts of fresh water to the oceans might cause the Gulf Stream to stop working as efficiently as it currently does, meaning some areas (such as Great Britain) may actually become colder, despite the reality of global warming.
From what I can glean from the article, global warming may be contributing to both the low levels of Lake Superior as it is to the melting of polar ice. But the world's a big place - the water just doesn't slosh around very easily and "level out" in any sort of obvious way necessarily.
posted by Dee Xtrovert at 10:38 AM on September 18, 2007
Melting off floating ice doesn't raise water levels at all. The same amount of water is displaced by the ice as is released by the melting of said ice. Its only the ice covering the polar landmasses that will raise water levels.
posted by andythebean at 10:41 AM on September 18, 2007
posted by andythebean at 10:41 AM on September 18, 2007
A more detailed article from the Detroit Free Press.
And this site is just cool... current water levels at Great Lakes. net.
posted by ormondsacker at 10:43 AM on September 18, 2007
And this site is just cool... current water levels at Great Lakes. net.
posted by ormondsacker at 10:43 AM on September 18, 2007
Response by poster: I understand that sea ice would have the same (or similar) displacement as an equivalent amount of sea water. But are you telling me global warming is only melting sea ice?
I guess... I'm just surprised that after several decades of on-going global warming, Lake Superior could now reach an all-time low? It doesn't seem to make sense.
posted by LakesideOrion at 11:00 AM on September 18, 2007
I guess... I'm just surprised that after several decades of on-going global warming, Lake Superior could now reach an all-time low? It doesn't seem to make sense.
posted by LakesideOrion at 11:00 AM on September 18, 2007
Another thing about global warming is that it changes the distribution of rainfall, and takes water vapor that evaporates from lakes and small rivers (which will happen at a faster rate if the temperature increases) and redeposits it into oceans. Bye bye potable water, hello bigger, higher oceans.
posted by rmless at 11:21 AM on September 18, 2007
posted by rmless at 11:21 AM on September 18, 2007
Best answer: But are you telling me global warming is only melting sea ice?
No. It's also melting glaciers, but there aren't any close to Lake Superior. Any water from melting glaciers that's reaching Lake Superior isn't enough to counteract other effects. From New Scientist: A rapidly warming lake is the key to understanding the change, says Jay Austin, a limnologist at the University of Minnesota Duluth's Large Lakes Observatory. Earlier this year he reported that Superior's surface waters had warmed by about 2.5 °C since 1979 - far more than average air temperatures in the region during the same period.... Austin's findings link the warming to a reduction in winter ice cover on the lake. The less ice is present to reflect sunlight, the more solar energy the lake can absorb. On average, the onset of summer warming of the lake is happening half a day earlier each year. The reduced ice cover also contributes to shrinkage by allowing more evaporation. "Most of the evaporation goes on in winter," Austin says, as cold, dry air swoops over the warmer lake. Without the ice cap to block evaporation, water losses increase.
More generally, warmer air holds more moisture. Global warming increases evaporation of moisture from land to the air, making droughts more frequent. This may also contribute to lower water levels by reducing the precipitation received by the lake.
(Global warming also makes flooding more frequent, since the increased moisture eventually comes down as precipitation. So you can get drought in one area and flooding in another area, at the same time. Or as rmless says, the precipitation can come down in the oceans.)
posted by russilwvong at 11:32 AM on September 18, 2007
No. It's also melting glaciers, but there aren't any close to Lake Superior. Any water from melting glaciers that's reaching Lake Superior isn't enough to counteract other effects. From New Scientist: A rapidly warming lake is the key to understanding the change, says Jay Austin, a limnologist at the University of Minnesota Duluth's Large Lakes Observatory. Earlier this year he reported that Superior's surface waters had warmed by about 2.5 °C since 1979 - far more than average air temperatures in the region during the same period.... Austin's findings link the warming to a reduction in winter ice cover on the lake. The less ice is present to reflect sunlight, the more solar energy the lake can absorb. On average, the onset of summer warming of the lake is happening half a day earlier each year. The reduced ice cover also contributes to shrinkage by allowing more evaporation. "Most of the evaporation goes on in winter," Austin says, as cold, dry air swoops over the warmer lake. Without the ice cap to block evaporation, water losses increase.
More generally, warmer air holds more moisture. Global warming increases evaporation of moisture from land to the air, making droughts more frequent. This may also contribute to lower water levels by reducing the precipitation received by the lake.
(Global warming also makes flooding more frequent, since the increased moisture eventually comes down as precipitation. So you can get drought in one area and flooding in another area, at the same time. Or as rmless says, the precipitation can come down in the oceans.)
posted by russilwvong at 11:32 AM on September 18, 2007
Best answer: Here's a reference to the now removed article from the Detroit Free Republic regarding the Dredging of the St. Clair. Speculation is that it has caused a permanent 1 foot drop or so in water levels.
I also remember from my water management class back in college that the Ogallala Aquifer helps feed the Great Lakes. Our rate of removal from that Aquifer has far exceeded the replenishment rate for many many years. (so more water lost there!)
Finally...[Educated Guess here]...even if the sea levels were rising and other tapping of water out of the Great Lakes were not happening, it would take a whole lot o of it to see a real effect on Lake Superior. The water flows west from the lakes to east to the Atlantic. The elevation of Lake Superior is 183 meters. Lake Erie (just before the Niagra Falls) is 173 meters. Lake Ontario (just after the falls) is 74 Meters! It would take some work to have rising sea level affect it. (The seaway itself is, of course, regulated by locks and dams and such)
posted by Wink Ricketts at 11:38 AM on September 18, 2007
I also remember from my water management class back in college that the Ogallala Aquifer helps feed the Great Lakes. Our rate of removal from that Aquifer has far exceeded the replenishment rate for many many years. (so more water lost there!)
Finally...[Educated Guess here]...even if the sea levels were rising and other tapping of water out of the Great Lakes were not happening, it would take a whole lot o of it to see a real effect on Lake Superior. The water flows west from the lakes to east to the Atlantic. The elevation of Lake Superior is 183 meters. Lake Erie (just before the Niagra Falls) is 173 meters. Lake Ontario (just after the falls) is 74 Meters! It would take some work to have rising sea level affect it. (The seaway itself is, of course, regulated by locks and dams and such)
posted by Wink Ricketts at 11:38 AM on September 18, 2007
Keep in mind that global warming isn't directly causitive of every single weather-related phenomenon on the planet.
posted by Steven C. Den Beste at 12:38 PM on September 18, 2007
posted by Steven C. Den Beste at 12:38 PM on September 18, 2007
This thread is closed to new comments.
As far as I know, they don't know for sure what is causing it - but probably all of the above.
posted by clarkstonian at 10:33 AM on September 18, 2007