Trees and carbon

As far as climate buzzwords go, “Net Zero” has probably become the most weaponized term. It may also be the most misunderstood.

Lots of people recognize that reaching net zero carbon emissions is key to meeting the temperature goals of the Paris Agreement. But how many of us have an accurate understanding of what that means?

A group of scientists who developed the science behind net zero 15 years ago have authored a new study, published in Nature, warning that our heavy reliance on natural carbon sinks to offset fossil-fuel emissions is a misunderstanding of the original idea. A course correction is more important than ever, particularly as developments at the 29th United Nations climate change conference, also known as COP29, will likely further incentivize the equivalence between fossil-fuel emissions and natural drawdown.

Let me break down the jargon. Net zero refers to the idea that our carbon emissions are balanced to zero, so that we’re no longer increasing the concentration of greenhouse gases in the atmosphere. There are some technical equations in the paper, but a simplified one to illustrate basic net zero would be:

Human emissions + human land-use change = 0

Now, carbon sinks — oceans, forests, peatlands — play a key role in drawing down and storing carbon. And we relying on these natural resources to balance our emissions equation leading to an equation which looks more like:

Human emissions + human land-use change — passive carbon sinks = 0

This poses some problems.

The second equation may stabilize the level of atmospheric CO2, but it also means that warming would continue. This is because the planet is currently absorbing more energy from the sun than is escaping back into space. Eventually, an equilibrium would be reached as the extra heat is absorbed by the deep oceans, but this would take a long time (think centuries), and in the meantime, we’ll get warmer. The paper notes that if atmospheric concentrations were fixed at today’s levels, the most likely eventual warming level would still exceed 2C above pre-industrial temperatures — and that would risk taking us far above the goal of the Paris Agreement.

Happily, scientists found that if passive carbon sinks were able to bring down atmospheric CO2, the continued surface warming would be canceled out.

And so carbon removal is extremely important for securing a friendly and stable climate for ourselves and our descendants. But there are two roles here — offsetting our own continuing emissions from burning oil, gas and coal, and cleaning up the mess we’ve already made. Our forests and oceans can’t do both jobs. Land is a finite resource in competition with our other needs such as food, shelter and energy, so there’s a limit to the carbon-absorbing capacity of Earth’s natural spaces.

That’s especially true as climate change is destabilizing our carbon sinks. Just look at New York, where the Jennings Creek fire has burned for more than a week. The Canadian wildfires in 2023 released more than 645 million metric tons of carbon into the atmosphere, comparable to the annual emissions of large nations.

When we burn fossil fuels, the resultant pollution is permanent — without intervention, CO2 will stay up there for somewhere between 300 and 1,000 years. We can no longer say that the carbon stored in our trees would last nearly that long.

This doesn’t mean there’s no place for any offsets in the net zero equation, but the standard needs to be higher. There should be greater distinction between “biological” removals via carbon sinks and “geological” emissions from fossil fuels in climate reporting and targets, and a ton of one shouldn’t be fungible with a ton of the other. Not a single country or company has made these distinctions — but there’s a slice of history waiting for the first entity to go beyond the current requirements.