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Thermal pollution, although not frequently discussed, is a problem that is also persistent and harmful to nature. A minor change in ambient temperature and oxygen levels can have a profound effect on ecosystems.

Thermal Pollution and the Environment


  • Aside from power plants and facilities, other causes of thermal pollution come from soil erosion. This elevates water and exposes it to more sunlight. Deforestation also allows more light to reach bodies of water, enabling them to absorb more heat from the ambient environment.

  • Discharge from urban runoff is heated as it passes over roads, parking lots, and other man-made surfaces, especially in the summertime. Once the water passes through the sewers and is discharged, it contributes to the heating of water bodies that it enters.

  • Thermal pollution has natural causes as well. Lava from volcanoes and other geothermal features can raise the temperature of the ocean nearby. Another natural element that adds heat to oceans is lightning, which is impossible to control since it naturally hits the Earth 8 million times per day, and can heat the air around it to more than 50,000°F.

  • Coal plants are major consumers of water. One facility can use up to 180 billion gallons per year. The Union of Concerned Scientists says 1.1 billion gallons may be consumed using such a configuration, but plants with alternative cooling systems may withdraw less.

  • When coal power plants intake water, they do not just gather water. They also draw in fish, larvae, and eggs. Many fish die even before thermal pollution in a river, lake, or ocean can have any effect on them.

  • Nuclear plants, manufacturers, research institutions, and hospitals also drain their waste into the water. This process incorporates heat materials into the water, making the water source hotter than before. Hydroelectric power may seem more sustainable, but it returns water to its source much hotter than it was before.

Biological Effects:

  • Warm water doesn’t hold as much dissolved oxygen as cooler water does, so less of it means plants and animals may succumb to the anaerobic conditions. Also, algae flourish on the surface of warm waters, which also decreases oxygen levels down below.

  • Abrupt changes in temperature can trigger mass killings of fish in the ocean. It can also affect plants, insects, and amphibians in a similar way. In fact, just a 1°C change significantly affect the metabolism and cellular biology of an organism. For other species, small increases can boost activity. However, their function and activity decrease once temperatures increase by a certain threshold.

  • High water temperatures don’t necessarily stop fish from reproducing, but they do increase the likelihood of premature hatching. Some eggs many not develop normally and newborn fish have a higher chance of defects.

  • Thermal pollution can interrupt the food chain because the increased metabolic rate that results from warmer environments accelerates enzyme activity. This, in turn, leads to a higher consumption rate of food. Organisms, therefore, eat more than what they would normally need. This can upset the balance of different species and ecosystems in general. Fish and species that can migrate to areas where they can find enough food. However, for those above them in the food chain, the impacts can be detrimental because their feeding sources are no longer available.

  • Fish are more affected by thermal pollution when biodiversity is reduced. Higher rates of feeding of and slower breeding in small fish can create food shortages. This can throw off the balance of an entire ecosystem, as species that played important roles are no longer in abundance.

  • Thermal stress is one of the contributors to coral bleaching. It increases the rate of infectious disease and, along with an influx of sediment and increased carbon dioxide and acidification, is causing many coral reefs to die off. Reduction in pH levels stunts growth and affects the structural integrity of coral formations, according to the National Oceanic and Atmospheric Administration’s assessment of how climate change is causing such trends.

Power Plants: The Old vs. the New

  • Older power plants in the U.S. withdraw a combined capacity of about 100 trillion gallons of water every year. The federal Clean Water Act enforces requirements for power plants to use technologies that minimize the impacts to the environment, while the U.S. Environmental Protection Agency has issued regulations, in effect as of 2001, that enforce less water-consuming closed-cycle cooling for use in newly built power plants.

  • They have developed some methods to cool used water. Some plants use cooling ponds. They are man-made and used resources are cooled using evaporation, radiation, or convection. Other methods include cooling towers, which transfer the heat to the atmosphere instead of into the ocean, and cogeneration that recycles the excess heat.

  • Power plants can cool water. The San Onofre Nuclear Generating Station in San Diego, California, intakes cooling waters, which circulate through the system and are subject to an additional step compared to most power plants. A series of pipes mix the discharge with regular seawater over 2,450 feet of pipe. While the water increases in temperature by 19°F on average in the system, it is returned to the ocean at a temperature rise a fraction it would otherwise be.

Sources:, Conserve Energy Future,,,, NOAA.

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