I understand about global warming melting the ice and glaciers, causing the ocean levels to rise. I know that there is a considerable amount of water tied up in this frozen medium that can melt and cause a considerable and detrimental effect.
But I have heard for years about the ongoing depletion of fresh water sources also. Aquifers are being pumped low or dry, large fresh water lakes have dried up or vastly receded, and many rivers, yearly snowfalls and surface water reservoirs are but a small volume of their former capacities.
If all this fresh water hasn’t gone into the oceans (and risen the levels), and there can only be so much cloud and water vapor in the atmosphere, then where has the water gone?
Is it now stored up in man-made structures and materials? Has it been converted into another form that isn’t readily apparent to me?
I’m sure the fresh water depleted is not as great as the water locked up in glaciers and ice caps, but I would think if it had been released from its normal sources to find its way to the sea, that the sea levels would be affected to some extent.
Most human water use is from agriculture, and almost all of it is wasted–it evaporates, soaks into the ground, runs off into the ocean, etc. More efficient agriculture would be by far the single biggest thing that people could do to reduce water use. The amount actually contained in the final food product is almost infinitesimal compared to the amount that was used in production.
The fresh water that causes sea level rise is not accessible to people. Basically, it’s Antarctica. That’s way more water than is available in our lakes and rivers. It’s not practical to transport it. Agricultural runoff is a significant waste but not a worry when it comes to sea levels.
In short, the freshwater problem is because our industry transports it to the oceans where it is no longer freshwater. It is possible to slow this process without affecting industrial output, but we need the will for it.
Very large areas of this country and others depend on deep aquifers that took thousands or more years to build up their supply. We are taking the water out much faster than it can be replaced and it is perfectly possible to exhaust them completely without having an equivalent replacement available. The problem with fresh water is that it needs to be both consistent and accessible. Rain falling on dry farmland can water the crops for a few days but it does nothing to recharge the aquifers deep underground that support agriculture even during times of little rain let alone drought. Like many things, it is a distribution problem. There can still be just about as much fresh water today as there was centuries ago but it can become an extreme problem if that water becomes less consistently available for use.
Precisely. That’s the whole problem with climate change overall. The earth is quite capable of recycling all the pollutants we spew, the problem is we’re spewing it faster than it can be recycled.
The same with fresh water, as Shagnasty said. The planet has the same amount of water it’s always had (excepting that amount that might come from falling space debris – someone more knowledgeable about that can speak better than I), it’s just that it gets recycled. We’re screwing things up faster than they can be fixed.
If we slowed down on our overall pollution, that would give the earth a chance to catch up. The question is, is it too late or do we still have time to slow it down enough?
It should be noted that about half of the sea level rise over the last century has been due to thermal expansion of the oceans (warmer water takes up more space) rather than melting of ice caps and glaciers.
Fresh ground water makes up less than one percent of the total mass of water on the planet, and the reductions, even if regionally important, are a tiny part of that. Lakes, both fresh and saline, make up less than 2 hundreths of a percent, and the most dramatic change in that, the drying up of the Aral sea changed this by about half a percent.
So “some extent” is actually “not practicably measurable”.
The Antarctic ice sheet and the Greenland ice sheet in contrast make up 1.62% and 0.17% of all total water all by themselves, and the changes predicted to change sea levels are significant portions of those volumes.
So no, the water depleted from fresh water sources hasn’t gone anywhere special, it’s just not a whole lot of water compared to the oceans and to the big depots of ice.
Well, the amount of water on Earth is increasing right now. You’ve heard of all that oil we’re burning for fuel? The main products from burning gasoline, diesel fuel, and home heating oil are carbon dioxide and water. Those hydrogens in the exhaust water were tied up in crude oil for millions of years.
Is that enough water to make a difference in any way? I don’t know.
There are also places where if we don’t use the water it just flows into the sea, the aquifers under Long Island NY is a prime example, that catchment basin includes most of New England and far into Canada, all that water just heading off the coast into the Atlantic Ocean. I’ve heard it said in a hydrology class that if it never rained again and LI withdraws water at their current peak rate continuously they would have water for 1000 years.
It does seem somewhat reasonable to intercept ground water right before it flows into the ocean, but then again their might be some life forms that depend on that ‘zone’ between fresh and salt.
One other number to think about. The planet is about 70% ocean and 30% land. The water that evaporates falls again as rain, true. But 70% of all that fresh water falls back onto the ocean. Reclaiming it through desalinization is expensive and high energy.
But even getting 30% of the rain is not realistic. Only about one-quarter of the land surface is arable land. That’s now around 7% of the total. We require more so we have to use up stored water from times where we we’re pumping it.
That’s another way of saying that it’s the distribution rather than total that counts, but it’s also a reminder of how small humanity is compared to the planet.
This recent article from the New York Times says according to a study by UC Irvine that “nearly a third of the world’s 37 largest aquifers are being drained faster than they are being replenished” and that these aquifers are in regions that produce food for up to two billion people.
Of course one primary reason that land is “arable” is that it gets sufficient water so perhaps the one-quarter of the land that’s arable land gets more than one quarter of the precipitation.
Possible, sure. These are the roundest of round numbers.
It wasn’t clear from the sources I looked at whether cities are included in arable land. If so, that’s a large confounding factor. Most rain that falls on cities and suburbs doesn’t get to a tap or do anything useful in our sense other than water lawns and parks.
Once you have a few facts, and a little perspective, the answer is that the missing non-frozen water is a tiny fraction of the water out there, so its depletion would never be as noticable as possible ice-melt volume.
I thought this most likely, but would have figured that the missing fresh water might have been more noticable.
I like this question.
It seemed more obvious than it is.
I think there is a big issue of time lag involved. Connected to the various ways that “fresh” water is procured and used.
Water wells are a human technology. Bringing sequestered water back into the evaporate and precipitate cycle much faster. There are water sources being brought to the surface that are prehistoric. I hear a lot of what is happening because of that. But now I am wondering, what if we were not doing that? Would areas above an underground water reservoir eventually become swamp? Then begin releasing that water back into the cycle? Of course there are all sorts of geological dynamics below the surface. Some aquifers might flow underground to other outlets.
But in the long term, wouldn’t all the water, that could eventually overfill an aquifer, be freed at the surface to enter the cycle? We are short circuiting the time frame of that cycle. But we are not putting into place the structures to short circuit the water directly to our uses, before evaporation or sequestration. The water is going slowly back underground to fill up what we took. While we want it right now from a well. We should be building more water control and collection systems. To even out the flow cycle to our demands.
Of course this includes giving a great big finger to a lot of other natural systems. But maybe we could care enough to build that in too?
Also.
When aquifers are drained, the land often subsides. Will that destroy the aquifer for all time? Can a compacted layer be refilled, or will the water that used to go into it, find new paths?
Is the amount of water produced by burning hydrocarbons more than the amount that is consumed to make concrete? Most water uses do end up with water being returned to the ecosystem, but not concrete making. It reacts with the other ingredients to harden them, which locks the water molecules into hydrated compounds.