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By Sonya Angelica Diehn
Dams are often touted as environmentally friendly. Although they do represent a renewable source of energy, a closer look reveals that they are far from green. DW lays out the biggest environmental problems of mega-dams.
1. Dams Alter Ecosystems
Water is life — and since dams block water, that impacts life downstream, both for ecosystems and people. In the case of the Grand Ethiopian Renaissance Dam (GERD), which is being built in Ethiopia and is set to be Africa's largest source of hydroelectric power, Egypt is concerned it will receive less water for things like agriculture.
Downstream ecosystems rely not only on water, but also on sediment, both of which are held back by big dams. As solid materials build up in a manmade reservoir, downstream land becomes less fertile and riverbeds can become deeper or even erode away. Emilio Moran, a professor of geography and environment at Michigan State University in the US, described sediment loss of 30 to 40% as a result of large dams.
"Rivers carry sediment that feeds the fish, it feeds the entire vegetation along the river. So, when you stop sediment flowing freely down the streams, you have a dead river."
And ecosystems may have adapted to natural flooding, which dams take away.
Mega-dams also often have a large footprint on land upstream. Aside from displacing human communities, flooding to create a reservoir also kills plants, and leaves animals to drown or find new homes. Reservoirs can also further fragment valuable habitat and cut off migratory corridors.
2. Dams Reduce Biodiversity and Cause Extinction
Aquatic species, particularly fish, are vulnerable to the impacts of dams. Moran says the Itaipu Dam, which was constructed on the border between Paraguay and Brazil in the 1970s and 1980s, resulted in a 70 percent loss of biodiversity.
"On the Tucuruí Dam that was built in the 80s in the Amazon," he added, "there was a 60% drop in productivity of fish."
Many fish species rely on the ability to move about freely in a river, be it to seek food or return to where they were born. Migratory species are badly affected by the presence of dams. In 2016, the International Union for the Conservation of Nature (IUCN) reported a 99% drop in catches of sturgeon and paddlefish — both of which are migratory — over a period of three decades. Overfishing and river alteration were cited as major threats to the species' survival.
A 2018 study predicted that fish stocks on Asia's Mekong River could drop by 40% as a result of dam projects – with consequences not only for biodiversity, but for the people whose lives and livelihoods depend on those fish.
The stakes for biodiversity are particularly high for animals threatened with extinction. And not only for aquatic species. The Tapanuli orangutan — the Earth's rarest ape, with only 500 individuals left — could finally be pushed to the brink if a planned hydroelectric project in Sumatra, Indonesia, is completed. Dams can literally snuff out species.
3. Dams Contribute to Climate Change (and Are Affected by It)
As reservoirs fill, upstream forests are flooded, eliminating their function as carbon sinks. As the drowned vegetation decomposes, decaying plants in manmade reservoirs release methane, a powerful greenhouse gas. That makes reservoirs sources of emissions — particularly those in tropical forests, where there is dense growth. It's estimated that greenhouse gas emissions from dams amount to about a billion tons annually, making it a significant global source.
And as the climate changes, more frequent and prolonged drought means dams will capture less water, resulting in lower electricity production. Countries dependent on hydropower will be especially vulnerable as temperatures keep rising.
Moran described a vicious circle, for example in Brazil, which gets 60 to 70% of its energy from hydropower: "If you wipe out half the rainforest, there will a loss of half the rainfall. And then there won't be enough water to provide the amount of power from those dams," he explained.
4. Dams Reduce Water Quality
Manmade reservoirs trap fertilizers that run into the water from surrounding land. In addition, in some developing countries, sewage flows directly into the reservoirs. This kind of pollution can result in algae blooms that suck the oxygen out of the water, making it acidic and potentially harmful to people and animals.
Still water in large manmade lakes is warm at the top and cold at the bottom, which can also affect water quality. While warm water promotes the growth of harmful algae, the cold water that is often released through turbines from the bottom of a reservoir may contain damagingly high mineral concentrations.
In some cases, water in manmade reservoirs is of such bad quality that it is not even fit to drink.
5. Dams Waste Water
Since more surface area of the water gets exposed to the sun, reservoirs result in much more evaporation than the natural flow of the river before that dam existed. It's estimated at least 7% of the total amount of freshwater needed for human activities evaporates from the world's reservoirs every year.
This effect is made worse in hot regions, Moran pointed out. "Certainly if you had a reservoir in a tropical area with high temperatures, there is going to be a lot of evaporation," he said. And big reservoirs "are, of course, evaporating constantly."
Reservoirs are also a haven for invasive plant species, and weed-covered reservoir banks can lead to evapotranspiration — or the transfer of water from the land to the atmosphere through evaporation from soil and transpiration from plants. Such evapotranspiration amounts to six times more than the evaporation from the water's surface. And there is even evidence that dams increase water use and promote water waste by creating a false sense of water security.
In the face of dwindling global freshwater resources, some question whether dams should be reconsidered.
So What Are the Alternatives?
The evidence is damning. But if mega-dams have so many harmful environmental effects, what are the alternatives? Although some green groups point to small hydropower as being more ecologically sound, Moran is skeptical. "A dam is a dam - it's blocking the fish, it's blocking the sediment."
He pointed to the need to consider not just how to maximize energy production, but also maintain ecological productivity. One option he cited is the use of in-stream turbines.
And many environment advocates agree that other renewable energies such as solar and wind can provide clean electricity at a far lower environmental cost.
Reposted with permission from Deutsche Welle.
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By James Shulmeister
Climate Explained is a collaboration between The Conversation, Stuff and the New Zealand Science Media Centre to answer your questions about climate change.
If you have a question you'd like an expert to answer, please send it to firstname.lastname@example.org
What was the climate and sea level like at times in Earth’s history when carbon dioxide in the atmosphere was at 400ppm?<p>The last time global carbon dioxide levels were consistently at or above 400 parts per million (ppm) was around <a href="https://www.nature.com/articles/nature14145" target="_blank">four million years ago</a> during a geological period known as the <a href="http://www.geologypage.com/2014/05/pliocene-epoch.html" target="_blank">Pliocene Era</a> (between 5.3 million and 2.6 million years ago). The world was about 3℃ warmer and sea levels were higher than today.</p><p>We know how much carbon dioxide the atmosphere contained in the past by studying ice cores from Greenland and Antarctica. As compacted snow gradually changes to ice, it traps air in bubbles that contain <a href="https://www.cambridge.org/core/journals/annals-of-glaciology/article/enclosure-of-air-during-metamorphosis-of-dry-firn-to-ice/09D9C60A8DA412D16645E6E6ABC1892F" target="_blank">samples of the atmosphere at the time</a>. We can sample ice cores to reconstruct past concentrations of carbon dioxide, but this record only takes us back about a million years.</p><p>Beyond a million years, we don't have any direct measurements of the composition of ancient atmospheres, but we can use several methods to estimate past levels of carbon dioxide. One method uses the relationship between plant pores, known as stomata, that regulate gas exchange in and out of the plant. The density of these stomata is <a href="https://journals.sagepub.com/doi/abs/10.1177/095968369200200109" target="_blank">related to atmospheric carbon dioxide</a>, and fossil plants are a good indicator of concentrations in the past.</p><p>Another technique is to examine sediment cores from the ocean floor. The sediments build up year after year as the bodies and shells of dead plankton and other organisms rain down on the seafloor. We can use isotopes (chemically identical atoms that differ only in atomic weight) of boron taken from the shells of the dead plankton to reconstruct changes in the acidity of seawater. From this we can work out the level of carbon dioxide in the ocean.</p><p>The data from four-million-year-old sediments suggest that <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2010PA002055" target="_blank">carbon dioxide was at 400ppm back then</a>.</p>
Sea Levels and Changes in Antarctica<p>During colder periods in Earth's history, ice caps and glaciers grow and sea levels drop. In the recent geological past, during the most recent ice age about 20,000 years ago, sea levels were at least <a href="https://science.sciencemag.org/content/292/5517/679.abstract" target="_blank">120 meters lower</a> than they are today.</p><p><span></span>Sea-level changes are calculated from changes in isotopes of oxygen in the shells of marine organisms. For the Pliocene Era, <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2004PA001071" target="_blank">research</a> shows the sea-level change between cooler and warmer periods was around 30-40 meters and sea level was higher than today. Also during the Pliocene, we know the West Antarctic Ice Sheet was <a href="https://www.nature.com/articles/nature07867" target="_blank">significantly smaller</a> and global average temperatures were about 3℃ warmer than today. Summer temperatures in high northern latitudes were up to 14℃ warmer.</p><p>This may seem like a lot but modern observations show strong <a href="https://journals.ametsoc.org/jcli/article/23/14/3888/32547" target="_blank">polar amplification</a> of warming: a 1℃ increase at the equator may raise temperatures at the poles by 6-7℃. It is one of the reasons why Arctic sea ice is disappearing.</p>
Impacts in New Zealand and Australia<p>In the Australian region, there was no Great Barrier Reef, but there may have been <a href="https://link.springer.com/content/pdf/10.1007/BF02537376.pdf" target="_blank">smaller reefs along the northeast coast of Australia</a>. For New Zealand, the partial melting of the West Antarctic Ice Sheet is probably the most critical point.</p><p>One of the key features of New Zealand's current climate is that Antarctica is cut off from global circulation during the winter because of the big <a href="https://www.tandfonline.com/doi/abs/10.3402/tellusa.v54i5.12161" target="_blank">temperature contrast</a> between Antarctica and the Southern Ocean. When it comes back into circulation in springtime, New Zealand gets strong storms. Stormier winters and significantly warmer summers were likely in the mid-Pliocene because of a weaker polar vortex and a warmer Antarctica.</p><p>It will take more than a few years or decades of carbon dioxide concentrations at 400ppm to trigger a significant shrinking of the West Antarctic Ice Sheet. But recent studies show that <a href="http://nora.nerc.ac.uk/id/eprint/521027/" target="_blank">West Antarctica is already melting</a>.</p><p>Sea-level rise from a partial melting of West Antarctica could easily exceed a meter or more by 2100. In fact, if the whole of the West Antarctic melted it could <a href="http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.695.7239&rep=rep1&type=pdf" target="_blank">raise sea levels by about 3.5 meters</a>. Even smaller increases raise the risk of <a href="https://www.pce.parliament.nz/publications/preparing-new-zealand-for-rising-seas-certainty-and-uncertainty" target="_blank">flooding in low-lying cities</a> including Auckland, Christchurch and Wellington.</p>
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By Jo Harper
Investment in U.S. offshore wind projects are set to hit $78 billion (€69 billion) this decade, in contrast with an estimated $82 billion for U.S. offshore oil and gasoline projects, Wood Mackenzie data shows. This would be a remarkable feat only four years after the first offshore wind plant — the 30 megawatt (MW) Block Island Wind Farm off the coast of Rhode Island — started operating in U.S. waters.
Corporates Shift<p>Helping to drive offshore growth, U.S. corporate buyers <a href="https://www.dw.com/en/cities-leading-the-transition-to-renewables/a-42850621" target="_blank">are increasingly relying on wind energy to power their businesses</a>. Walmart and AT&T are the two top corporate wind buyers, while 14 newcomers entered the wind market in 2019, including Estée Lauder and McDonald's.</p><p>"Oil and gas companies have jumped into the U.S. offshore wind market, where they can transfer expertise in offshore fossil fuel development to clean energy investments," says Max Cohen, principal analyst, Americas Power & Renewable research at Wood Mackenzie. Many international oil and gas companies have already recognized this huge potential and entered the US offshore wind market, including Orsted, Equinor and Shell.</p><p>"Given the recent tumult in oil prices, fossil fuel companies may more and more be looking to diversify their portfolios, particularly with assets that are contracted or offer returns uncorrelated with oil and gas," Cohen says. "Offshore wind is an area where they may have a comparative advantage, and they can then leverage the experience with that technology to make the leap to onshore wind, solar, and other renewable technologies," he says.</p>
East Coast leads the way<p>"There is enormous opportunity, especially off the East Coast, for wind. I am very bullish," said former Interior Secretary Ryan Zinke. "Market excitement is moving towards offshore wind. I haven't seen this kind of enthusiasm from industry since the Bakken shale boom," he said.</p><p>Offshore wind initiatives require excessive upfront spending: a 250 MW venture costs about $1 billion, based on International Energy Agency data, but as costs fall the tipping point after which costs fall faster gets nearer</p><p>"The opportunity has been created by Northeastern states seeing the large price declines for offshore wind in Europe," says Cohen. Onshore wind is historically the lowest cost renewable resource, but is at its most expensive in the Northeast, he adds. "But costs are falling slower than for other technologies," he says.</p>
Jobs and Coastal Revitalization<p>U.S. wind energy now supports 120,000 US jobs and 530 domestic factories. A study by the University of Delaware predicted that the supply chain needed to build offshore turbines to feed power to seven East Coast states by 2030 would generate nearly $70 billion in economic activity and at least 40,000 full-time jobs. An American Wind Energy Association's (AWEA's) March 2020 report estimated that developing 30,000 MW of offshore wind along the East Coast could support up to 83,000 jobs and $25 billion in annual economic output by 2030.</p><p>Having said that, not all of the jobs are American jobs. The offshore wind developers with commercial leases in the US are all foreign companies. There is growing interest from the shipbuilding sector in the Gulf of Mexico in partnering with offshore wind companies to provide services. As a result, some of the US oil trade associations have submitted comments supporting certain aspects of offshore wind. "However, it is unclear to what extent offshore wind developers plan to use US vessels and crew, and the existing projects did not incorporate US vessels or labor at all," Hawkins says.</p>
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The COVID-19 pandemic has revealed both the strengths and limitations of globalization. The crisis has made people aware of how industrialized food production can be, and just how far food can travel to get to the local supermarket. There are many benefits to this system, including low prices for consumers and larger, even global, markets for producers. But there are also costs — to the environment, workers, small farmers and to a region or individual nation's food security.
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By Joe Leech
The human body comprises around 60% water.
It's commonly recommended that you drink eight 8-ounce (237-mL) glasses of water per day (the 8×8 rule).
1. Helps Maximize Physical Performance<p>If you don't stay hydrated, your physical performance can suffer.</p><p>This is particularly important during intense exercise or high heat.</p><p>Dehydration can have <a href="https://www.healthline.com/health/how-to-tell-if-youre-dehydrated" target="_blank">a noticeable effect</a> if you lose as little as 2% of your body's water content. However, it isn't uncommon for athletes to lose as much as 6–10% of their water weight via sweat.</p><p>This can lead to altered body temperature control, reduced motivation, and increased fatigue. It can also make exercise feel much more difficult, both physically and mentally.</p><p>Optimal hydration has been shown to prevent this from happening, and it may even reduce the <a href="https://www.healthline.com/health/oxidative-stress" target="_blank">oxidative stress</a> that occurs during high intensity exercise. This isn't surprising when you consider that muscle is about 80% water.<a href="https://pubmed.ncbi.nlm.nih.gov/19344695" target="_blank"><span></span></a></p><p>If you exercise intensely and tend to sweat, staying hydrated can help you perform at your absolute best.</p><p><strong>Summary</strong></p><p><strong></strong>Losing as little as 2% of your body's water content can significantly impair your physical performance.</p>
2. Significantly Affects Energy Levels and Brain Function<p>Your brain is strongly influenced by your hydration status.</p><p>Studies show that even mild dehydration, such as the loss of 1–3% of body weight, can impair many aspects of brain function.</p><p>In a study in young women, researchers found that fluid loss of 1.4% after exercise impaired both mood and concentration. It also increased the frequency of headaches.</p><p>Many members of this same research team conducted a similar study in young men. They found that fluid loss of 1.6% was detrimental to working memory and increased feelings of anxiety and fatigue.<a href="https://www.cambridge.org/core/journals/british-journal-of-nutrition/article/mild-dehydration-impairs-cognitive-performance-and-mood-of-men/3388AB36B8DF73E844C9AD19271A75BF/core-reader" target="_blank"></a></p><p>A fluid loss of 1–3% equals about 1.5–4.5 pounds (0.5–2 kg) of body weight loss for a person weighing 150 pounds (68 kg). This can easily occur through normal daily activities, let alone during exercise or high heat.</p><p>Many other studies, with subjects ranging from <a href="https://www.healthline.com/health/parenting/signs-of-dehydration-in-toddlers" target="_blank">children</a> to <a href="https://www.healthline.com/health/symptoms-of-dehydration-in-elderly" target="_blank">older adults</a>, have shown that mild dehydration can impair mood, memory, and brain performance.</p><p><strong>Summary</strong></p><p><strong></strong>Mild dehydration (fluid loss of 1–3%) can impair energy levels, impair mood, and lead to major reductions in memory and brain performance.</p>
3. May Help Prevent and Treat Headaches<p>Dehydration can trigger <a href="https://www.healthline.com/health/dehydration-headache" target="_blank">headaches</a> and migraine in some individuals.<span></span></p><p>Research has shown that a headache is one of the most common symptoms of dehydration. For example, a study in 393 people found that 40% of the participants experienced a headache as a result of dehydration.</p><p>What's more, some studies have shown that drinking water can help relieve headaches in those who experience frequent headaches.</p><p>A study in 102 men found that drinking an additional 50.7 ounces (1.5 liters) of water per day resulted in significant improvements on the Migraine-Specific Quality of Life scale, a scoring system for <a href="https://www.healthline.com/health/migraine-symptoms" target="_blank">migraine symptoms</a>.<a href="https://academic.oup.com/fampra/article/29/4/370/492787" target="_blank"></a></p><p>Plus, 47% of the men who drank more water reported headache improvement, while only 25% of the men in the control group reported this effect.<a href="https://academic.oup.com/fampra/article/29/4/370/492787" target="_blank"></a></p><p>However, not all studies agree, and researchers have concluded that because of the lack of high quality studies, more research is needed to confirm how increasing hydration may help improve headache symptoms and decrease headache frequency.<a href="https://pubmed.ncbi.nlm.nih.gov/26200171" target="_blank"></a></p><p><strong>Summary</strong></p><p><strong></strong>Drinking water may help reduce headaches and headache symptoms. However, more high quality research is needed to confirm this potential benefit.</p>
4. May Help Relieve Constipation<p><a href="https://www.healthline.com/health/constipation" target="_blank">Constipation</a> is a common problem that's characterized by infrequent bowel movements and difficulty passing stool.</p><p>Increasing fluid intake is often recommended as a part of the treatment protocol, and there's some evidence to back this up.</p><p>Low water consumption appears to be a risk factor for constipation in both younger and older individuals.</p><p>Increasing hydration may help decrease constipation.</p><p><a href="https://www.healthline.com/nutrition/mineral-water-benefits" target="_blank">Mineral water</a> may be a particularly beneficial beverage for those with constipation.</p><p>Studies have shown that mineral water that's rich in magnesium and sodium improves bowel movement frequency and consistency in people with constipation.<a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5334415" target="_blank"></a></p><p><strong>Summary</strong></p><p><strong></strong>Drinking plenty of water may help prevent and relieve constipation, especially in people who generally don't drink enough water.</p>
5. May Help Treat Kidney Stones<p>Urinary stones are painful clumps of mineral crystal that form in the urinary system.</p><p>The most common form is <a href="https://www.healthline.com/health/kidney-stones" target="_blank">kidney stones</a>, which form in the kidneys.</p><p>There's limited evidence that water intake can help prevent recurrence in people who have previously gotten kidney stones.<a href="https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD004292.pub3/full" target="_blank"></a></p><p>Higher fluid intake increases the volume of urine passing through the kidneys. This dilutes the concentration of minerals, so they're less likely to crystallize and form clumps.</p><p>Water may also help prevent the initial formation of stones, but studies are required to confirm this.</p><p><strong>Summary</strong></p><p><strong></strong>Increased water intake appears to decrease the risk of kidney stone formation.</p>
6. Helps Prevent Hangovers<p>A hangover refers to the unpleasant symptoms experienced after drinking <a href="https://www.healthline.com/nutrition/alcohol-good-or-bad" target="_blank">alcohol</a>.</p><p>Alcohol is a diuretic, so it makes you lose more water than you take in. This can lead to dehydration.</p><p>Although dehydration isn't the main cause of hangovers, it can cause symptoms like thirst, fatigue, headache, and dry mouth.</p><p>Good ways <a href="https://www.healthline.com/nutrition/7-ways-to-prevent-a-hangover" target="_blank">to reduce hangovers</a> are to drink a glass of water between drinks and have at least one big glass of water before going to bed.</p><p><strong>Summary</strong></p><p><strong></strong>Hangovers are partly caused by dehydration, and drinking water can help reduce some of the main symptoms of hangovers.</p>
7. Can Aid Weight Loss<p>Drinking plenty of water can help you <a href="https://www.healthline.com/nutrition/how-to-lose-weight-as-fast-as-possible/" target="_blank">lose weight</a>.</p><p>This is because water can increase satiety and boost your metabolic rate.</p><p>Some evidence suggests that increasing water intake can promote weight loss by slightly increasing your metabolism, which can increase the number of calories you burn on a daily basis.</p><p>A 2013 study in 50 young women with overweight demonstrated that drinking an additional 16.9 ounces (500 mL) of water 3 times per day before meals for 8 weeks led to significant reductions in body weight and body fat compared with their pre-study measurements.</p><p>The timing is important too. Drinking water half an hour before meals is the most effective. It can make you feel more full so that you <a href="https://www.healthline.com/nutrition/35-ways-to-cut-calories" target="_blank">eat fewer calories</a>.</p><p>In one study, dieters who drank 16.9 ounces (0.5 liters) of water before meals lost 44% more weight over a period of 12 weeks than dieters who didn't drink water before meals.</p>
The Bottom Line<p>Even mild dehydration can affect you mentally and physically.</p><p>Make sure that you <a href="https://www.healthline.com/nutrition/how-much-water-should-you-drink-per-day" target="_blank">get enough water each day</a>, whether your personal goal is 64 ounces (1.9 liters) or a different amount. It's one of the best things you can do for your overall health.</p>
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