Fossil fuel emissions may peak in two years but the fight against climate change is just beginning

Working out our fossil-carbon emissions is a relatively straightforward business. A high-school student could calculate the number of carbon atoms in a barrel of oil or a metric ton of coal, and then estimate the tonnage of carbon dioxide emitted when it’s burned. Given publicly available trade and production figures, they could produce a decent estimate of the world’s industrial carbon footprint in an afternoon.

Biological emissions are different. Does planting a biodiverse forest on a bare Scottish moorland lock away emissions, or release them? It’s a surprisingly complicated question that even experts don’t find easy to solve.

Just appraising the volume of carbon locked up in the world’s ecosystems presents formidable challenges. Working out how much is stored in the boughs and leaves of forests comes down to a series of extrapolations taken from estimates of canopy height and species mix, backed up with sample tape measurements of trunk girth taken at the chest height of whichever forester is doing the work that day.

We have even more approximate ideas of how much biomass is stored in plant roots. One 2017 study of cornfields found that traditional techniques overestimated the volume of living roots by about 67% — a significant gap when you consider that they’re reckoned to amount to about 130 billion tons of plant matter globally.

The non-plant carbon in soils is usually estimated by taking core samples and burning them to measure how much carbon dioxide is emitted. That technique, again, is subject to vast sampling errors, making it hard to be precise about a category which may lock up 2.5 billion metric tons of carbon, equivalent to 60 years of the world’s emissions.

The good news is that we may already be making progress on the natural world’s carbon ledger. About half of the world’s emissions from deforestation are being counterbalanced by the planting of new trees, according to the Global Carbon Project, a coalition of climate scientists. Land-use emissions appear to have declined from nearly 7 billion tons in 1960 to less than 4 billion now, even as we’ve added about five billion people to the global population.

It’s not impossible that further decreases in logging and increases in planting could cause that number to turn negative, meaning our ecosystems would be sequestering more carbon than they’re emitting. Indeed, we’re counting on just that change taking place: Almost all those pledges to hit net zero depend on the environment absorbing the gross bit of emissions we don’t know how to prevent.

That’s just where all the uncertainty is so troubling, however. To date, about a third of our industrial emissions have ended up locked up in land ecosystems, with another third going into the oceans. Climate change results entirely from the remaining third, 14 billion tons a year or so, that goes into the atmosphere.

Should the land and ocean carbon sinks reach saturation and stop sucking carbon out of the skies — something that may occur on land in a matter of decades — then even a reduction of our emissions may be insufficient to stop the atmosphere’s carbon concentration from going up and cooking the planet.

Changing the natural environment was the first way human technology started to bend this world to suit our needs, dating back to the dawn of fire agriculture 80,000 years or so ago. In comparison to two centuries or so of industrialisation, that ancient practice may be far harder to reverse.

David Fickling is a Bloomberg Opinion columnist covering commodities, as well as industrial and consumer companies. Views are personal, and do not represent the stand of this publication.

Credit: Bloomberg