In the Middle Ages, the Catholic Church offered indulgences, in which people exchanged donations for scraps of paper that promised to spend less time in purgatory after death. Less controversially, today someone indulging in the tea supply in the office might feel obligated to pay for a replacement box. Are carbon offsets more like the former or the latter?
There are many reasons why you could try to offset some of your carbon footprint, whether it’s to reduce a general sense of guilt about your lifestyle, to accurately cover a flight’s estimated emissions, or simply to do something good. do for the environment. Regardless of motivation, all these efforts are based on the belief that the money you paid will actually result in the removal of the promised amount of CO2 from the atmosphere. Otherwise you will pay for a lie – or at least get a smaller box of tea than you ordered.
Finding out if you’ve been lied to is really hard. 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, cycling between the atmosphere, oceans, ecosystems and even rock. Plants extract carbon atoms from CO2 in the air to grow. Herbivores consume plants and exhale the carbon as CO2 again. Weathered rocks attract CO2 from the sky. Volcanoes release it into the atmosphere. These are just some of the many exchanges in the carbon cycle.
Before the Industrial Revolution, these flows were in equilibrium, maintaining a stable CO concentration2 in the atmosphere. But then we discovered fossil fuels and ways to set them on fire for pleasure and profit. This cost more and more carbon that had been trapped deep underground for many millions of years and released it into the atmosphere. Some of that carbon (actually just over half) was absorbed by the oceans and terrestrial ecosystems. But the rest accumulated in the atmosphere, pushing up greenhouse gas concentrations.
To stop the rise in this greenhouse gas, our net total emissions of CO2 should reach zero. It’s that simple. We can achieve this in part by eliminating emissions from some of our operations. But we will probably also have to compensate for the ongoing emissions to reach net zero.
Some carbon offset projects help with this goal by avoiding emissions that would otherwise have occurred. Others promise to preserve something known in terms of the carbon cycle as a “sink” – a sustainable form of carbon such as forests or even mineralized carbonate in the ground. These offsets are not always identical to the avoided emissions, as they can have climate effects unrelated to carbon. For example, forests can be darker than their surroundings, so their expansion has a local warming effect because more sunlight is absorbed. But reforestation also has the potential to provide other ecosystem services, such as habitats for animals. So there are many factors other than carbon to consider.
Make like a tree and leaf
Planting trees is a temptingly simple response to climate change. (For proof, see: Reflexive Internet Commentaries.) But our ability to store carbon in this way is finite. We can undo the emissions caused by past deforestation, but we can never plant enough to cover the rampant use of fossil fuels. But even if you accept that limitation, a lot can go wrong after your seedlings are tucked into the soil.
Assuming you find a program you can rely on to actually plant the promised trees, many things will affect their impact on the carbon cycle over time. The first is the way a tree species grows. Some grow quickly and accumulate a lot of carbon per acre in the first ten years or so, providing immediate help to our carbon emissions balance. But fast-growing trees tend to be less dense than slower-growing species, so the final amount of carbon stored per hectare is lower.
Fast-growing species also have a shorter lifespan. If trees in this plantation are managed to be harvested, the end of their lifespan will occur earlier. So where does the carbon go? Some can be turned into wood, after which its value as a carbon sink depends on how long the things built with that wood will last. The leftover plant material decays or burns, releasing carbon back into the atmosphere, ending its time as a sink,
Even if the planted trees are never harvested, their carbon can be released in other ways. Old trees die and rot naturally. Insect pests can rip through forests and kill trees en masse. Wildfires can do the same. Some risks like these are increasing due to climate change, meaning that carbon storage in forests is becoming less and less safe over time in many regions.