Do you want to offset your carbon footprint? Here’s what you need to know

In the Middle Ages, the Catholic Church offered indulgences, allowing people to exchange gifts for scraps of paper that promised a reduction in time in purgatory after death. Less controversial today, someone who indulges excessively in office tea sourcing might feel pressured to pay for a replacement tin. Are carbon offsets more like the first or the second?

There are many reasons why you might be looking to offset a portion of your carbon footprint, whether it’s to allay a general feeling of guilt for your lifestyle, to precisely cover the estimated emissions of a flight, or just to to do something beneficial for the environment. Regardless of the motivation, all of these efforts are based on the belief that the money you paid will truly lead to the elimination of the amount of CO promised.₂ of the atmosphere. Otherwise, you’re paying for a lie – or at least to get a smaller box of tea than the one you ordered.

Knowing if you’ve been lied to is really difficult. Here’s what you need to know.

Downshifting the carbon cycle

Carbon dioxide in the atmosphere is part of a bio-geo-chemical dance called the carbon cycle. Carbon regularly changes shape and area code, circulating between the atmosphere, oceans, ecosystems and even bedrock. Plants take carbon atoms from CO₂ in the air to grow. Herbivores consume plants and exhale carbon as CO₂ again. Aging rocks attract CO₂ out of the air. Volcanoes release it into the atmosphere. These are just a few of the many exchanges in the carbon cycle.

Before the industrial revolution, these flows were in equilibrium, maintaining a stable concentration of CO₂ in the air. But then we found out about fossil fuels and the ways to ignite them for fun and profit. It was taking more and more carbon that had spent millions of years locked deep underground and released it into the atmosphere. Some of this carbon (a little over half, in fact) was taken up by oceans and terrestrial ecosystems. But the rest has accumulated in the atmosphere, pushing up greenhouse gas concentrations more and more.

To stop the increase in this greenhouse gas, our total net CO emissions₂ must reach zero. It’s that simple. We can do this in part by eliminating the emissions caused by some of our operations. But we will probably also have to offset current emissions to reach net zero.

Some carbon offset projects contribute to this goal by preventing emissions that would otherwise have occurred. Others promise to preserve something which in terms of the carbon cycle is known as a “sink” – a sustainable form of carbon like forests or even carbonate mineralized in the soil. These offsets are not always identical to the avoided emissions, as they can have climate effects distinct from carbon. Forests, for example, can be darker than their surroundings, so their expansion has a local warming effect as more sunlight is absorbed. But reforestation also has the potential to provide other ecosystem services such as animal habitats. There are therefore many factors other than carbon to take into account.

Make like a tree and a leaf

Planting trees is an extremely simple response to climate change. (For evidence, see: Instinctive Internet comments.) But our ability to store carbon in this way is limited. We could cancel the emissions caused by past deforestation, but we will never be able to plant enough to cover the rampant use of fossil fuels. But, even if you accept this limitation, a lot can go wrong once your seedlings are stuck in the ground.

Assuming you find a reliable schedule for planting the promised trees, there are many factors that will influence their impact on the carbon cycle over time. The first is the way tree species grow. Some are growing rapidly, accumulating a lot of carbon per acre over the past decade, which provides immediate help to our carbon footprint. But fast-growing trees are generally less dense than slower-growing species, so the ultimate amount of carbon stored per acre is lower.

Faster-growing species also tend to have a shorter lifespan. If the trees on this plantation are managed for harvest, end of life will occur sooner. So where does the carbon go? Some, could be turned into lumber, how much of its value as a carbon sink depends on the lifespan of things built with that wood. Leftover plant material decomposes or burns, releasing carbon into the wood. ‘atmosphere, which ends up like a sink,

Even if the trees planted are never harvested, their carbon could be released in other ways. Old trees die and rot, of course. Insect infestations can tear forests apart, killing trees en masse. Forest fires can do the same. Some risks like these are increasing due to climate change, which means that forest carbon storage is becoming less and less secure over time in many regions.