Renewable energy sources such as hydropower, wind power, and solar energy are on the rise as many countries seek sustainable alternatives to fossil fuels, but the harmful impact these activities may have on fragile environments is often overlooked or poorly understood.
Human-driven climate change is almost certain to cause catastrophic harm worldwide, and the need to utilise clean energy and minimise global carbon emissions is undeniable. Yet a newly-published review of the biodiversity impacts of three types of green energy in Trends in Ecology and Evolution warns that we must still be mindful of the environmental effects these activities do have, and strive to implement them both wisely and well. Upon closer examination of these “clean” energy sources, it becomes abundantly clear that “sustainable” does not always mean “does no harm.”
The past several years have seen the construction or approval of thousands of hydroelectric dams worldwide, particularly in developing nations. These dams rely on the power of falling water from a large manmade reservoir to rotate a turbine and generate electricity. No fossil fuels are directly burned, yet the reservoir water does release greenhouses gases as a consequence of being held back by a dam.
“Despite being touted as a clean energy source,” lead author Dr Luke Gibson and his colleagues write, “hydropower causes substantial emissions of greenhouse gases such as CO2, methane (CH4), and nitrous oxide (N2O).”
Gibson’s research found that hydropower reservoirs in tropical regions are the worst offenders, such as the Curua-Una Dam in Para, Brazil. Studies show that this dam releases over three times the amount of greenhouse gases annually than would be produced by generating the same energy from fossil fuels.
In addition, the creation of a dam necessarily means flooding a large area of riparian land — and that can be devastating for biodiversity. “Globally, hydroelectric reservoirs cover an area of 340,000 km2, nearly the size of Germany, replacing important lowland and riverine forest and grassland habitats used by countless species,” the research team reports.
Even the habitat that remains after flooding often experiences biodiversity loss as well, as remaining populations are fragmented from each other. For example, when an enormous hydropower reservoir was built in Venezuela, so many species went extinct or were deeply affected on the lake’s remaining islands that conservationists referred to the event as an “ecological meltdown.”
In addition to flooding a large area, the construction of a hydroelectric dam also requires building a network of supporting roads that can further destroy or fragment natural habitat. Dams also create barriers to sediment flow, block animals migrating upstream or downstream, contribute to increased saltwater intrusion, and disrupt natural flow cycles. Adding insult to injury, the resulting stagnation almost always favours non-native species over natives, allowing invasives to thrive.
Despite these concerns, the construction of hydroelectric reservoirs is on the rise across the world and is often touted as a “sustainable solution.”
“Overall,” Gibson’s research team grimly warns, “the substantial greenhouse gas emissions and pronounced disruption of terrestrial and aquatic ecosystems from hydropower dams raise serious questions as to whether they should be considered “green energy” at all.”
Solar energy is becoming increasingly popular with both private homeowners and governments, and is arguably the fastest-growing renewable energy of today. Yet it is not without its downsides, as Gibson and team point out.
Large-scale solar power facilities need a considerable amount of water for cooling and clearly require significant areas of land. Solar facilities are best suited to deserts in order to take full advantage of the minimal cloud cover, but deserts can be surprisingly fragile ecosystems and are still vulnerable to biodiversity impacts.
For example, one obvious region for efficient solar power is the American Southwest, with its miles of seemingly-barren desert landscape. Gibson’s study warns of the harmful impact of solar facilities in this area on the important Agassiz desert tortoise, an ecological-engineer species that digs burrows which many other desert species depend upon. These burrows are often destroyed by the construction of a solar facility and its supporting roads. In addition, the researchers found, solar facilities create substantial dust emissions that can harm desert plants, while the sex ratios in species that use incubation temperature to determine hatchling sex can be thrown out of balance by the facility’s heat emissions.
One obvious solution to these challenges, says Gibson and colleagues, is to follow the old adage “location, location, location.”
“Although ample space exists to develop solar facilities outside areas of high conservation value,” they write, “much development has occurred in core ecological habitats, which could affect desert wildlife.”
As they pointed out in their study, “There are currently 1.1 billion ha of degraded lands globally, and at current capacity <0.1% of the available degraded lands would be necessary to double the current solar PV capacity – even without accounting for advances in the efficiency of solar energy.”
Wind farms have the definite potential to generate efficient, renewable energy with a relatively small physical footprint. Although the sight of wind turbines dotting the landscape may give the impression that they require a lot of space, in reality the actual base of the turbine itself is not large; therefore, the area can simultaneously be used for other purposes, such as agriculture (unlike with hydroelectric dams or solar facilities).
However, wind farms do pose a biodiversity threat to winged species unfortunate enough to fly too close. Although bird mortality from wind turbines is much lower than mortality from power lines, building collisions, or feral cats, Gibson’s study points out that the impacts can still be significant, particularly for endangered or vulnerable populations. The study shows the presence of wind farms can also displace migratory or breeding populations from their usual routes or layovers, as they are forced to go “the long way around” to avoid wind farms.
Offshore wind farms are not immune from these impacts either – seabirds are also vulnerable to collisions and route disruptions, and the underwater noise generated by offshore wind farms can mask the communications of marine mammals and, as research increasingly shows, that of fish as well.
Fortunately, this new research also provides some solutions. Gibson and team’s analysis of wind turbine studies suggests that rotor diameter doesn’t matter very much for preventing collisions, but tower height does, with taller towers resulting in more deaths for birds and bats.
“By building wind turbines at the lowest height feasible, mortality of birds and bats can be markedly reduced,” Gibson argues, “although there may be tradeoffs between having a smaller number of large turbines versus many smaller turbines.”
Once again, placement is also crucial, and construction of wind farms near important migratory routes, ridgelines, or habitats of threatened species should be strongly avoided. The noise and heat generated by turbines can be improved as the technology progresses – but only if governments prioritise and invest in renewable research and development.
The researchers ultimately conclude, “Given that wind energy requires a smaller footprint than either solar or hydropower, and that its impacts are more easily addressed, wind is likely the safest form of green energy in terms of biodiversity.”
What to do?
Based on these results, it would appear that hydropower is the “green” energy with the worst environmental impact, and that wind power has the potential to be the least harmful. However, all three types of renewable energy clearly require much more research into their environmental impacts and a more concerted effort by governments and energy companies to mitigate their harmful effects. In addition, this study was not able to analyse the impacts of geothermal energy or bioenergy from agricultural crops – a good opportunity for future research.
Investing in renewable energy is obviously a worthy goal – yet Gibson’s study shows we cannot afford to be too lax and fall into the trap of believing all renewable energy is inherently “good for the environment” and free from harmful biodiversity impacts. Yet with foresight and scientific consultation, many of the potentially harmful impacts can be minimised.
“Renewable energy, a vital component of our global climate change mitigation strategy, needs to be considered within the broader context of biodiversity and ecosystem protection,” Gibson and his fellow researchers urge. “Recent policy changes targeting carbon emissions – including the landmark Paris Agreement – could trigger an avalanche of renewable energy projects, and concerted research efforts and practical planning guidelines will be necessary to help ensure that such developments are truly as “green” as possible.”
Gibson, L. et al. (2017). “How Green is ‘Green’ Energy?” Trends in Ecology and Evolution Vol 32, No. 12. DOI: https://doi.org/10.1016/j.tree.2017.09.007
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