Human water use, for example in irrigation, makes a substantial contribution to sea-level rise.
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By Amanda Mascarelli of Nature magazine
Climate change, with its associated melting ice caps and shrinking glaciers, is the usual suspect when it comes to explaining rising sea levels. But a recent study now shows that human water use has a major impact on sea-level change that has been overlooked.
During the latter half of the twentieth century, global sea level rose by about 1.8 millimeters per year, according to data from tide gauges. The combined contribution from heating of the oceans, which makes the water expand, along with melting of ice caps and glaciers, is estimated to be 1.1 millimeters per year, which leaves some 0.7 millimeters per year unaccounted for. This gap has been considered an important missing piece of the puzzle in estimates for past and current sea-level changes and for projections of future rises.
It now seems that the effects of human water use on land could fill that gap. A team of researchers reports in Nature Geoscience that land-based water storage could account for 0.77 millimeters per year, or 42%, of the observed sea-level rise between 1961 and 2003. Of that amount, the extraction of groundwater for irrigation and home and industrial use, with subsequent run-off to rivers and eventually to the oceans, represents the bulk of the contribution.
Taikan Oki, a global hydrologist at the University of Tokyo and an author on the paper, says that he was initially “astonished” at how well the team’s estimates of terrestrial water usage filled the deficit between the observed sea-level rise and what was accounted for by thermal water expansion and melting ice. “I didn’t expect that terrestrial water storage had such a big impact on sea level,” says Oki. And, he adds, “I didn’t expect that human extraction of groundwater would matter so much”.
Time of reckoning
Depletion of groundwater reserves has more than doubled in recent decades as a result of population growth and the increased demand on groundwater reservoirs for drinking water and the irrigation of croplands. Most of the water pumped up from deep pools is not replenished; it evaporates into the air or flows into river channels, feeding into the seas. Artificial reservoirs, such as the Hoover Dam on the Colorado River and the Three Gorges Dam on the Yangtze River in China, have the opposite effect, locking up water that would otherwise flow into the seas. Scientists once speculated that the effects cancelled each other out, but this study and other recent ones have shown that groundwater depletion has a larger net effect.
“The terrestrial contribution to sea-level rise is something that the sea-level community has to reckon with and really take into account,” says Marc Bierkens, a hydrologist at Utrecht University in the Netherlands. A study by Bierkens and his colleagues also found that groundwater depletion contributes significantly to sea-level rise. But they concluded that the contribution of groundwater use to global sea-level change was markedly lower, increasing from 0.035 millimeters per year in 1900 to just 0.57 millimeters per year in 2000.
Both teams used models to simulate the contribution from groundwater extraction, but Bierkens’ team relied on reported data whereas Oki’s team computed the total amount of groundwater pumped around the world and cross-checked its findings in certain regions. Each team acknowledges that its simulations have limitations and says that more on-site measurements of groundwater use are needed.
Nevertheless, the message is clear, says Yadu Pokhrel, a postdoctoral researcher in global hydrology at Rutgers University in New Jersey and lead author of the latest study. “When people pump groundwater, they may think it’s only having local effects. But there are huge implications. If we think about the future, what will happen if we use groundwater in the same way as we are doing today? That’s a question we have to consider if we don’t think of some kind of proper management of water resources.”
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17 Comments
Add CommentThis sounds like a flawed theory to me. Considering that dry land is only 25% of the earth's surface and the percentage of land that contains a significant amount of ground water is only a percentage of that and that ground water is only a tiny fraction of the depth of the ocean, the effect of draining all of it into the ocean would be negligible.
Reply | Report Abuse | Link to thisThe fact is, mankind has only used a fraction of the ground water so far. Much of it goes back into the ground and ground water naturally finds its way into the sea anyway by draining out through rivers, streams and springs.
I find it difficult to see how the math could show it represents a significant increase in sea level.
Haha, wow the nonsense warmists come up with. The fact they think they can measure sea levels by millimeters is about as ridiculous as it gets. The .7 millimeters missing is simply your statistical equations being not quite usable because there is no way you can have enough data to figure out what sea level is at any time.
Reply | Report Abuse | Link to thisThe only way humans could contribute to sea level rise by our use of water is if we were taking hydrogen and oxygen and making water. All other water use comes from lakes and rivers, which originated as sea water, moved to the land by precipitation and when that water gets back to the ocean, we have no change.
If anything we humans could be reducing sea level by the fact so much water that used to flow down rivers to oceans is now tied up in made made lakes like lake mead or behind the 3 gorge damn in china, among the hundreds of other massive man made lakes and rivers that no longer make it to the ocean.
Priddseren:
Reply | Report Abuse | Link to this"All other water use comes from lakes and rivers"
You're an idiot if you don't even know what an aquifer or a well is, and your "analysis" is fundamentally flawed as a result of ignoring their existence.
Your analysis seems flawed to me. Regardless of the oceans' total depths, what's being considered is an average increase of 0.7 millimeters in ocean depth over their total surface area.
Reply | Report Abuse | Link to thisThe article states that since 1950, "...global sea level rose by about 1.8 millimeters per year, according to data [extrapolated] from tide gauges. The combined contribution from heating of the oceans, which makes the water expand, along with melting of ice caps and glaciers, is estimated to be 1.1 millimeters per year, which leaves some 0.7 millimeters per year unaccounted for."
Keep in mind that the world's great ice sheets would melt to some much lessor depth of water than their current thickness of ice.
I can't do the necessary math, but I do know that increasing, enormous amounts of water is being pumped from underground sources for agricultural production around the world and to provide potable water (for drinking, flushing, showers, car washing, green lawns, etc.) for a population that has nearly tripled from 2.5 billion in 1950 (the period being considered here).
The Ogallala Aquifer under the Great Plains of the U.S. contains water that was largely deposited >2 million years ago. Its use for land irrigation only began in the 1950s.
"One of the world's largest aquifers, it covers an area of approximately 174,000 mi**2 (450,000 km**2) in portions of the eight states..."
"The USGS estimated that total water storage was about 2,925,000,000 acre feet (3,608 km**3) in 2005. This is a decline of about 253,000,000 acre feet (312 km**3) (or 9%) since substantial ground-water irrigation development began, in the 1950s."
For related maps & other info, see
http://en.wikipedia.org/wiki/Ogallala_Aquifer
Well, I haven't seen the actual article in Nature Magazine, but where's the data and citations, or peer reviews. I don't buy it. It sounds like just another politically driven agenda article that asserts that humans don't belong on this planet. Simply look at the natural cyclical and fluxuating climatic changes brought on by the solar maximum and volcanic activity to see the effects on polar melting and you'll see the reason for the increasing rise in sea levels. I see someone who is tweaking the model to fit their own theory and nothing more.
Reply | Report Abuse | Link to this9 billion people don't belong on this planet.
Reply | Report Abuse | Link to thisThis gives an interesting perspective of the amount of water on the surface of the earth:
Reply | Report Abuse | Link to thishttp://apod.nasa.gov/apod/ap120515.html
Excellent!
Reply | Report Abuse | Link to thisI know nothing about ground water nor have I read the article, but let's do some quick back-of-the-envelope calculations.
Reply | Report Abuse | Link to thisIf the total surface area of all the world's aquafers is one thousandth of the total surface of all oceans, then pumping out enough water to lower the water table by one meter and emptying it into the ocean would increase sea levels by one millimeter.
If we lowered the water table by ten meters, then the surface area of the aquafers would only need to be one ten-thousandth of the ocean surface to raise the sea level by one millimeter, etc.
The connection between ground water depletion and sea level rise doesn't look so improbable.
There is no "belonging" nor "not belonging". The question is how should we manage resources for the best outcome.
Reply | Report Abuse | Link to thisThis chain of comments highlights our greatest danger:
- that we make knee-jerk responses against any data that suggests that we should alter our resource management.
Some people seem to think that there is some sort of luddite environmentalism that drives science. Nothing could be further from the truth. I and many other biologists that I know loved fast cars, fighter jets, racing of all kinds, instruments made from exotic old-growth trees etc, but through our personal research and travel we have come to see that we need to strongly alter the way we use resources - that is if we want our children to inherit a world with wild places and fewer wars over resources.
I said dry land you foul mouthed moron. Land under lakes is not used to pump out ground water. At any rate total land mass is still only 30% of the earths surface. How you conclude that is 2/3's is no more relevant then concluding it is 1/4.
Reply | Report Abuse | Link to thisI still say this research is flawed. Ground water is replenished with the hydrologic cycle. It is a well known fact that many modern rivers have less flow into the sea then several centuries ago due to up stream diversion for agriculture and municipal use. The mighty Colorado no longer even makes it to sea.
Reply | Report Abuse | Link to thisMuch of the ground water depletion world wide is due to drought conditions that are a direct result of climate change. Nature is a much more powerful influence then man in the hydrologic cycle. In areas where rainfall has increased due to climate change, groundwater depletion is not a problem.
The unaccounted for increase in ocean levels, according to Taikin Oki is more likely due to an increase in rain fall over ocean waters caused by increased warming and the resulting increase in humidity over warming land masses. More of that rain will fall into the ocean then the land just by the simple math of the planets geography.
Certainly agricultural and municipal use is a factor in the equation, but this leap to conclusion sounds more like faulty data then a profound conclusion to me.
This theory is no more then another 'I told you so' exercise in obfuscation by the opponents of the AGW science.
I think you make a better case here, but I strongly suspect that the diverted waters of the Colorado river still run to sea, just from points further north in California. Also note that the Colorado naturally flows through arid desert valleys, where evaporation likely contributes to its depletion at its drainage point.
Reply | Report Abuse | Link to thisThe Mississippi River drainage basin covers nearly 40% of the landmass of the continental United States, and part of Canada, including the region into which the Ogallala aquifer is being pumped. It is the fifth largest river in the world by outflow.
"Withdrawals from the Ogallala Aquifer for irrigation amounted to 26 [cubic km] in 2000. As of 2005, the total depletion since pre-development [in the 1950s] amounted to... 312 [cubic km]."
http://en.wikipedia.org/wiki/Ogallala_aquifer
Unfortunately, you make a number of unsupported assertions about "ground water depletion world wide is due to drought conditions that are a direct result of climate change" and "In areas where rainfall has increased due to climate change, groundwater depletion is not a problem."
Perhaps I was confused - I don't think you intended to attribute to Dr. Oki the assertion that:
"The unaccounted for increase in ocean levels... is more likely due to an increase in rain fall over ocean waters caused by increased warming and the resulting increase in humidity over warming land masses. More of that rain will fall into the ocean then the land just by the simple math of the planets geography."
I suggest that if the increase in ocean levels is a product of increased rain fall it is because water that has long been sequestered in underground aquifers is now being added to the global water cycle, as the research suggests.
If you'd like to review the study data to identify specific "faulty data", the study's Supplementary Information is freely available at:
http://www.nature.com/ngeo/journal/vaop/ncurrent/extref/ngeo1476-s1.pdf
Please, this scientific study can be questioned on specific points, but I think you have no basis for characterizing these scientific researchers as "opponents of the AGW science." You can find the authors' affiliations at:
http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo1476.html#/author-information
I would not be playing poker with the biosphere. The risks are too high and even the payoff is negative ” (Verdicar Decarian) - on (1 sm) means change of a level of Ocean, that it is necessary to add or exclude water from the nature about (3600 км3). The size (0,7 mm) - means, that the question is quantity of water in limits (300 км3). Unfortunately, there is other point of view on a problem why the level of Ocean in the past changed in limits
Reply | Report Abuse | Link to this(1400 м) and why now the level of Ocean practically a little (thousand years) does not vary.
Annual evaporation of water on a planet is equaled (560 thousand км3), from this quantity of water
(79 %) drop out as deposits above oceans and the seas, and (109 thousand км3) drops out as deposits above continents. The area of Antarctica makes almost (10 %) a land - thus, it turns out, that a thermal stream of bowels under continent Antarctica annually
transforms into water a wall of ice in height (~ 1000 m), in the width (250 m) - this wall of ice can capture the Earth on equator. The dynamic model of the globe, has proved - why and in what limits the level of Ocean in time II, III, IV stage changed. But, as well as two centuries ago - the scientific community did not recognize axial rotation of the Earth, and repeated turn of an environment of a planet in an equatorial plane in recent times is now ignored. Thus, the call to the natural phenomenon which in the past was not taken into account is thrown, and now the second decade in general is ignored, than this game will terminate has very truly written (Verdicar Decarian)
Most recent studies indicate that there is a decrease in water flowing to the sea that is 2.5 times higher then the observed increase of flows in rivers worldwide. In other words, a net loss, not a net gain in sea level from runoff. Unless the net gain can be totally attributed to evaporation and rainfall, and that exceeds the net loss, Oki's theory is flawed.
Reply | Report Abuse | Link to thisBelow is just a few links on this subject.
https://www2.ucar.edu/atmosnews/news/854/water-levels-dropping-some-major-rivers-global-climate-changes
http://www.livescience.com/5417-rivers-losing-water-due-climate-change.html
http://www.aboutmyplanet.com/environment/major-rivers-worldwide-experience-decreased-flow/
http://hydrol-earth-syst-sci-discuss.net/6/4773/2009/hessd-6-4773-2009.pdf
It is interesting to note that I did not read any of these reports before writing my comments above. This is more of a common sense opinion from me. I am not and never claimed to be a climate scientist, however I have been a lifetime student of earth sciences and I am a world traveler. I am a firm believer that experience is more valuable then conjecture and mathematical interpolations are as flawed as the factors used.
From the article above, "The combined contribution from heating of the oceans, which makes the water expand, along with melting of ice caps and glaciers, is estimated to be 1.1 millimeters per year, which leaves some 0.7 millimeters per year unaccounted for."
Reply | Report Abuse | Link to thisFrom NASA: http://news.cnet.com/8301-11128_3-57373690-54/nasa-mission-calculates-global-ice-melt-and-rising-sea-levels/
"From 2003 to 2010, NASA satellites systematically measured all of Earth's melting glacial ice--the results added up to 4.3 trillion tons of water and a global sea level rise of half an inch."
"Of all of the ice loss measured yearly, around one quarter came from glaciers and ice caps outside of Greenland and Antarctica, which equaled about 148 billion tons or 39 cubic miles, according to the study. Melting ice from Greenland, Antarctica, and nearby caps and glaciers averaged roughly 385 billion tons, or 100 cubic miles, per year."
From the article above, "During the latter half of the twentieth century, global sea level rose by about 1.8 millimeters per year, according to data from tide gauges."
NASA calculations show that 1.75 MM a year has accumulated from 2003 to 2010. Surly the amount of melt was less in the later half of the 20th century if temperature studies show that, "Thirteen of the warmest years recorded have occurred within the last decade and a half, the UN's World Meteorological Organization said on Tuesday."
http://news.discovery.com/earth/hottest-decade-global-warming-111129.html
Now, by itself this comment proves nothing, however it clearly demonstrates that mathematical analysis is based solely on the garbage in garbage out principle if the data is flawed, and on this subject it certainly seems that is the case.
I empathize with your sentiments - I'm also generally skeptical of studies that presume too much. I'm not a climate scientists, either, but I am a retired information systems analyst who has published on computer modeling methodologies.
Reply | Report Abuse | Link to thisYour comment includes reference to many news reports based on studies that also relied on complex data analyses. There's no way from the news articles to assess the veracity of any study's data or analytical methods. However, your reference to NASA satellite data analysis indicating 1.75 mm per year seems to agree very well with this study's reference of 1.8 mm per year based on tide gauge data.
Without comparing annualized sea level data, at least, it's not valid to conclude that "Surly the amount of melt was less in the later half of the 20th century if temperature studies show..." Frankly, no method of estimating global sea levels can be precise, since there are so many factors involved and so much surface area to sample.
Regardless of any river flow data, extracting long sequestered water from underground reservoirs must contribute to the total amount of water in the global water cycle, just as melting ice sheets do also. Both of these factors must contribute to any increasing sea levels.