Clean Freshwater Can Slow Down Global Warming

We will also save $7.5–81 trillion in the process.

New developments in the field of water science have enabled researchers to calculate for the first time the quantity of global methane (CH₄) emissions caused by eutrophication. This is the human-driven enrichment of inland waters with nutrients and minerals and will cost us a fortune as a planet by 2050.

Clean surface water is a vital resource on our planet, supporting ecosystems and human life. But despite its importance, cost-benefit analyses so far have indicated that the costs of preserving local water quality are simply not worth it. How can it be so? One reason might be that previous calculations have not considered all the possible benefits and contributing factors, one of which is eutrophication.

Eutrophication: a previously ignored phenomenon

The accumulation of nutrients and minerals in surface waters is a natural process but is being accelerated by anthropogenic activities, such as agricultural practices or the release of sewage in lakes and reservoirs. Within the next century, the eutrophication of inland waters will increase almost 5-fold due to the growth in population, agricultural activity (and the use of fertilizers), the temperature of surface waters, storms, runoff, and others.

Eutrophication generates greenhouse gases, such as CH₄, which amounts to 75% of all emissions related to lakes, rivers, and reservoirs. That is a trillion kilograms of methane. In the words of the authors of the Nature Communications paper, the methane emissions related to eutrophication have “an influence on climate change comparable to about 20% of the current emissions from fossil fuel combustion.”

Economic models are finally applied for eutrophication

In their study published on May 11th, 2021, researchers from the University of Minnesota and University of Wyoming compared for the first time the quantifiable costs and benefits of eutrophication-driven methane emissions and applied the same models to a case study of Lake Erie.

The theoretical framework is based on simple Integrated Assessment Models (IAMs), which join socioeconomic and climate factors, benefits and damages, and discount rates — these reflect the present value of costs and benefits in the future. To put it more bluntly, this rate shows how much value we place on future generations (a high rate means less value).

Considering these factors, the researchers ran first an optimistic scenario: assuming that the amount of annual eutrophication-driven CH₄ emissions is at the lower end of estimations and will remain constant. Using a 5% discount rate, the present value of these emissions for the period 2015–2050 is $7.5 trillion. The ingredients of a more pessimistic scenario are high current emissions that grow at a high rate over time with a 2.5% discount rate applied (placing a bit more value on future generations), which yields the astonishing number of $81 trillion in global social costs.

Local water pollution also has immediate health consequences

The negative effects of polluting our rivers and lakes are not limited to methane emissions. Harmful algal blooms (HABs) are known to thrive in waters with an excess of phosphorus from agricultural activities. The CDC’s website has an entire page dedicated to HAB-related illnesses and defines HABs as “the rapid growth of algae or cyanobacteria that can cause harm to people, animals, or the local ecology. Harmful algae or cyanobacteria can look like foam, scum, paint, or mats on the surface of water and can be different colors. These blooms can produce toxins that make people and animals sick.”

Situated at the border between Canada and the United States, Lake Erie is the eleventh-largest lake globally and supports a substantial fishing activity. However, HABs have been affecting the quality of its water. The researchers applied an integrated assessment model to compare the costs and benefits of reducing the phosphorus load by 40% and found that the global climate benefits exceed by an order of magnitude the estimated recreational benefits to Ohio anglers ($3.1 billion versus $0.12 billion, respectively).

In 2014, a water crisis in Toledo left locals without drinking water as a consequence of harmful algal blooms, which rendered drinking water toxic due to microcystin. The Ohio Environmental Council says that “[m]icrocystin is the most toxic of all cyanotoxins and ranks higher than cyanide, DDT or PCBs. This toxin causes liver and kidney damage, and is particularly dangerous to small children, the elderly and pets.”

In fact, a 2019 study in the state of Michigan, Ohio found that this same cyanotoxin was correlated with low birth weight and shorter gestation periods in infants of exposed mothers, although the toxin levels were below the current water advisory guidelines.

Limitations

Some limitations to these calculations exist. For example, it is difficult to estimate the damages of possible future catastrophic events caused by climate change. These models are highly empirical, and the way parameters are chosen is sometimes arbitrary. However, this should not be interpreted as not having to take any precautions against the effects of global warming but as a cautionary note that more work needs to be done to get an accurate idea of the numbers.

However surprising, the quality of freshwater sources, such as lakes, rivers, and reservoirs, is not only a local or regional issue but a global one. Using economic models to run cost-benefit analyses, it is now possible to quantitatively prove that keeping our waters clean is not only a sensible objective but also a financially effective one in the long term.

© Gianina Buda, PhD 2021

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