Tennis courts serve up an unexpected climate solution

A new study has found that tennis courts made of green clay are able to absorb large amounts of carbon dioxide via a process called enhanced rock weathering. In the US alone, green clay courts sequester more than 25,000 metric tons of CO2 per year. And 80% of green clay courts generate net negative emissions within 10 years, according to the study published in the journal Applied Geochemistry.

Enhanced rock weathering (ERW) is an emerging strategy to address climate change. It is based on a geological process by which silicate rocks such as basalt react with CO2 and store it as carbonate minerals. That natural rock weathering happens over millions of years.

To speed up this process, ERW involves spreading crushed silicate rocks on agricultural and other land so they can react with CO2 in rainfall. Recent studies have shown that EWR has the potential to lock away many gigatons of CO2.

Turns out, green clay tennis courts in the US are made of metabasalt, known as greenstone. It is a type of rock with properties to basalt in terms of their reaction with CO2. So oceanographer Frank Pavia of the University of Washington and earth scientist Jonathan Lambert at the New York University decided to analyze just how much CO2 green clay courts sequester.

There are 698,034 tennis courts in the world, according to the International Tennis Federation. Over 91% of those are outdoor courts; over 55% are hard concrete courts, which are topped with acrylic paint, while almost 26% are clay courts.

From a database of courts in the US, the researchers analyzed data for 17,178 green clay courts. They modeled carbon removal by these courts by factoring the type of basalt used, grain size of the rocks, the court temperature, and chemical composition.

They took into account carbon emissions during mining and processing, transportation of materials to court locations, court construction, and maintenance. They also used similar models to estimate the emissions from hard courts. Clay courts have substantially lower emissions even during construction than hard courts, before you even consider EWR benefits.

According to the calculations, not only do clay courts remove about 25,000 metric tons of CO2 per year, the median time for a green clay court to become net negative for emissions is approximately 3.5 years.

Replacing existing hard courts with green clay courts could be a promising way to sequester additional CO2. “For new court construction, building a green clay court appears to have less climate impact than a hard court,” Lambert said in a press release. “This provides a great opportunity to organizations and facilities that want to reduce their emissions.”

Source: Frank J. Pavia and Jonathan E. Lambert. Carbon dioxide removal by enhanced weathering on American green clay tennis courts. Applied Geochemistry, 2026.

Art: based on image by Frankie S./Deposit Photos