Have Global Forests Become A Source Of Carbon, Not A Sink?

Climate change and talk of carbon can be confusing at the best of times. It doesn’t then help that things keep changing as new research is done and, as the name implies, the climate debate changes. For example, a recent Carbon Brief report states tropical forests are now a source of carbon into the atmosphere, rather than, as previously believed, a sink. You’re probably now confused!

So, to put that confusion at rest Andrew Mitchell, Ecosphere+ Senior Advisor and expert in forest canopy research, provides an explanation.

Why are forests so important?

Instead of being a backwards step for forest conservation, the research discussed in the Carbon Brief report actually makes the case that stopping deforestation is even more important for beating climate change than experts previously thought.

Rainforests sequester carbon from the atmosphere at about a rate of one tonne of CO₂ per hectare per year. There are roughly one billion hectares of rainforest left, so very roughly about one billion tonnes of CO₂ are absorbed by them, per year.

When rainforests are cut down, the carbon stored in their branches, trunks, and often soil, gets released by either burning or oxidation of the soil, such as from peatlands in Indonesia. Because forests store between 100 – 400 tonnes of carbon per hectare, and one tonne of carbon converts to 3.66 tonnes of CO₂ when burnt, then that means when they are cleared and burned between 366 – 1,462 tonnes of C0₂ are released.

That’s why burning the ‘store’ is so bad, and why protecting it is so much better than, say planting a new plantation. That’s because a plantation takes many decades to build up an equivalent ‘store’ of carbon at the scale of an ancient living rainforest. So, burning the ‘store’, and planting a new one, is no solution in the short or medium term.

Deforestation vs degradation

The challenge with calculating emissions from burning forests, lies in what can be seen by satellites from space, that monitor deforestation.  On the one hand, a pristine standing rainforest can be recognised easily. On the other, a totally cleared forest replaced with beef cattle or soy or palm oil trees, can also be recognised easily from space. So, gross ‘deforestation’ can be calculated each year. Simple enough.

However, what lies in between is ‘degraded’ forest, and that is much harder to quantify and where problems ensue. A degraded forest is one where trees may have been taken out invisibly under the canopy, by farmers for say cocoa and coffee farming, or loggers for lumber, charcoal and firewood. This kind of degradation happens everywhere in the forest margins, especially in Africa. In some cases, the forest can be almost hollowed out, appearing full of trees from above but in fact much of its carbon has been removed and probably burnt.

What the study discussed in the Carbon Brief report has done, for the first time, is to make an estimate of carbon loss from this form of deforestation i.e. ‘degradation and disturbance’. In the past, scientists knew this was a big number but had effectively ignored it because the number was too hard to calculate. The research team have had a crack at it. Although other scientists will inevitably disagree with their research, it is a start and a step in the right direction. What was found is that degradation could account for almost 70% of the total carbon lost from forests. That’s huge, and much larger than previously thought, although not all of it will be burnt and so contribute to carbon emissions.

So what?

What their study tells us is that the loss of carbon from tropical forests is much greater than previously thought, because it now adds in that amount lost through ‘degradation’, to what we already knew was being lost, from wholesale forest clearance. Two conclusions are then drawn:

1. The amount of CO₂ getting into the atmosphere from tropical forest conversion is likely to be much bigger than we previously thought.

2. Rainforests are releasing more CO₂ into the atmosphere than they are absorbing. (That’s the headline) i.e. They are no longer to be thought of as net sinks of carbon, but are a net source.

However, that is not because they are no longer absorbing CO_2, they are – a billion tonnes a year as above! But this study shows that what is being released in total through deforestation (wholesale clearance + degradation) is larger than what was previously estimated.

It must be stressed that the paper does not say that forests should be forgotten about because they are a source of carbon and not a sink. The sink and store function remains big, it’s just that deforestation is causing more CO₂ to be released than we had thought.

Huge potential of forests for addressing climate change

The final conclusion of all this, they state, is that there is an even bigger amount of CO₂ from deforestation that could be stopped from entering the atmosphere than we thought before. That’s because if we could call a halt to deforestation tomorrow, we could stop all the CO₂ from both ‘deforestation’ (wholesale clearance), plus ‘degradation’, stuffing up our atmosphere! We now have the number – before we did not.

This means, from a climate stabilisation perspective, stopping deforestation has an even bigger role to play in keeping the world below a 2-degree temperature rise than estimated before, not the reverse.

As the Carbon Brief report states:

“The findings suggest that curbing deforestation and protecting existing forests could be instrumental in removing greenhouse gases from the atmosphere and fighting future climate change.”

The take home message here is not that we should give up with rainforests and that they are detrimental to climate change. Quite the opposite – it makes an even stronger case for the conservation of rainforests and their potential in the fight to curb climate change and achieve the 2-degree change set out by the Paris Agreement.

There is a final point. Deforestation is often stated to contribute about 10% of the global carbon emissions pie. That may not sound so big. But what is misunderstood is that tropical forest and agricultural landscapes (where most deforestation is occurring) can offer 30-50% of the global emissions reductions needed, to stay below 2-degrees in the next two decades.

That’s because you can save the store from being burnt + keep it absorbing carbon + stop landscape degradation + restore degraded land with new trees + reduce emissions fromagriculture – these five things are a huge contribution to the climate challenge. PLUS, you get all the “co-benefits” i.e. water, food and energy security, a better economy for the poor. Taken together – that’s VAST and something that is too important to turn our backs on.