It is generally understood that trees are good for the environment. That the forest will be an important ally in preventing global warming is a less known fact. The European Union (EU), however, seems bound to change that.

Deforestation and fossil fuel use result in the annual emission of 7-8 billion metric tons of greenhouse gases. While the earth is capable of sequestering, or storing, some of those gases, roughly half, or 3.5 billion metric tons, remains trapped in the atmosphere, causing the gradual but certain warming of the planet.

In response to this warming, the EU has implemented far-reaching mechanisms to prevent further climate change. Aggressive emission-reduction goals set for 2050, requirements for renewable energy portfolio investments, and a cap-and-trade system that remains unrivalled are a few examples of the impressive goal-setting by EU’s leadership. In the cap-and-trade system, businesses and countries buy and trade emission credits. The concept, in theory, is simple: cut emissions below your limit, then receive credits to sell to those emitting above their limit.

Cap-and-trade, however, is not perfect. As critics note, it allows business to continue belching while buying offsets, benefiting the environment very little. While offsets will not save the planet, however, they are a start. That the United States has yet to follow suit is testament to how much industry resists cap-and-trade because it doesn’t want to assign a cost to carbon.

Improvements to cap-and-trade thus are welcome and necessary given that it remains an evolutionary process. The EU, for example, is considering integrating an important element into their global warming prevention scheme: the forest. The forest’s ability to sequester carbon is real: growing trees absorb the air’s carbon, storing it as sugar, starch, or cellulose, thus removing the greenhouse gas from the atmosphere. What is less recognized within the cap-and-trading community is the capacity of the soil beneath, particularly in old-growth forests, to sequester even larger amounts of carbon.

While younger forests are more frequently credited with higher levels of daily carbon intake, the secret carbon storage capacity of old-growth forests lies in the soil beneath. What do old-growth stands have that the young stands lack? A fungus called mycorrhizal that is especially adept at storing carbon, and lots of it.

Arbuscular mycorrhizal fungi, located in the forest’s underground root systems, appear to be the only producers of a sticky protein called glomalin. According to a University of Maryland study, glomalin accounts for almost a third of all the carbon stored in soil. Factor this with scientific estimates that soil has the potential to sequester 40-80 billion metric tons of carbon over the next century and the conclusion is simple: protect old-growth forests. The soil found in old-growth forests may be one of our most valuable assets in our efforts to slow climate change.

Protecting existing old-growth stands, therefore, and safeguarding future old-growth stands, will need to be a critical component of the climate change agenda of the EU and the rest of the world. Embracing an EU-wide forest credit system will immediately benefit Sweden, Norway, and Finland, given their remaining stands, and provide incentives to others to preserve their nearly-old forests. Constructing a worldwide trading system, if one emerges post-Kyoto, will make it more profitable for the US, Canada and Russia, big emitters with ample old growth, to preserve their remaining stands.

Undoubtedly cultivating and protecting old trees is a time-intensive process. Yet it remains a more natural and surefire way to cool the planet than mirrors in space, projectiles on ocean surfaces, or cloud-making — all of which are intended to deflect solar rays. Geo-engineering is risky business. No amount of short-term testing can prove long-term impacts. Forests, however, have proven their worth over time.

The EU must consider offering emissions credits for forest owners. The soil beneath may well be what saves us from an overheated planet.