Are young trees or old forests more important for slowing climate change?

Jeremy Kieran/Unsplash, CC BY-SA

Tom Pugh, University of Birmingham

Forests are thought to be crucial in the fight against climate change – and with good reason. We’ve known for a long time that the extra CO₂ humans are putting in the atmosphere makes trees grow faster, taking a large portion of that CO₂ back out of the atmosphere and storing it in wood and soils.

But a recent finding that the world’s forests are on average getting “shorter and younger” could imply that the opposite is happening. Adding further confusion, another study recently found that young forests take up more CO₂ globally than older forests, perhaps suggesting that new trees planted today could offset our carbon sins more effectively than ancient woodland.

How does a world in which forests are getting younger and shorter fit with one where they are also growing faster and taking up more CO₂? Are old or young forests more important for slowing climate change? We can answer these questions by thinking about the lifecycle of forest patches, the proportion of them of different ages and how they all respond to a changing environment.

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The forest carbon budget

Let’s start by imagining the world before humans began clearing forests and burning fossil fuels.

In this world, trees that begin growing on open patches of ground grow relatively rapidly for their first several decades. The less successful trees are crowded out and die, but there’s much more growth than death overall, so there is a net removal of CO₂ from the atmosphere, locked away in new wood.

As trees get large two things generally happen. One, they become more vulnerable to other causes of death, such as storms, drought or lightning. Two, they may start to run out of nutrients or get too tall to transport water efficiently. As a result, their net uptake of CO₂ slows down and can approach zero.

Eventually, our patch of trees is disturbed by some big event, like a landslide or fire, killing the trees and opening space for the whole process to start again. The carbon in the dead trees is gradually returned to the atmosphere as they decompose.

The vast majority of the carbon is held in the patches of big, old trees. But in this pre-industrial world, the ability of these patches to continue taking up more carbon is weak. Most of the ongoing uptake is concentrated in the younger patches and is balanced by CO₂ losses from disturbed patches. The forest is carbon neutral.

New trees absorb lots of carbon, old trees store more overall and dead trees shed their carbon to the atmosphere.
Greg Rosenke/Unsplash, CC BY-SA

Now enter humans. The world today has a greater area of young patches of forest than we would naturally expect because historically, we have harvested forests for wood, or converted them to farmland, before allowing them to revert back to forest. Those clearances and harvests of old forests released a lot of CO₂, but when they are allowed to regrow, the resulting young and relatively short forest will continue to remove CO₂ from the atmosphere until it regains its neutral state. In effect, we forced the forest to lend some CO₂ to the atmosphere and the atmosphere will eventually repay that debt, but not a molecule more.

But adding extra CO₂ into the atmosphere, as humans have done so recklessly since the dawn of the industrial revolution, changes the total amount of capital in the system.

And the forest has been taking its share of that capital. We know from controlled experiments that higher atmospheric CO₂ levels enable trees to grow faster. The extent to which the full effect is realised in real forests varies. But computer models and observations agree that faster tree growth due to elevated CO₂ in the atmosphere is currently causing a large carbon uptake. So, more CO₂ in the atmosphere is causing both young and old patches of forest to take up CO₂, and this uptake is larger than that caused by previously felled forests regrowing.

The effect of climate change

But the implications of climate change are quite different. All else being equal, warming tends to increase the likelihood of death among trees, from drought, wildfire or insect outbreaks. This will lower the average age of trees as we move into the future. But, in this case, that younger age does not have a loan-like effect on CO₂. Those young patches of trees may take up CO₂ more strongly than the older patches they replace, but this is more than countered by the increased rate of death. The capacity of the forest to store carbon has been reduced. Rather than the forest loaning CO₂ to the atmosphere, it’s been forced to make a donation.

So increased tree growth from CO₂ and increased death from warming are in competition. In the tropics at least, increased growth is still outstripping increased mortality, meaning that these forests continue to take up huge amounts of carbon. But the gap is narrowing. If that uptake continues to slow, it would mean more of our CO₂ emissions stay in the atmosphere, accelerating climate change.

Overall, both young and old forests play important roles in slowing climate change. Both are taking up CO₂, primarily because there is more CO₂ about. Young forests take up a bit more, but this is largely an accident of history. The extra carbon uptake we get from having a relatively youthful forest will diminish as that forest ages. We can plant new forests to try to generate further uptake, but space is limited.

But it’s important to separate the question of uptake from that of storage. The world’s big, old forests store an enormous amount of carbon, keeping it out of the atmosphere, and will continue to do so, even if their net CO₂ uptake decreases. So long as they are not cut down or burned to ashes, that is.

Tom Pugh, Reader in Biosphere-Atmosphere Exchange, University of Birmingham

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Pacific Islands must stop relying on foreign aid to adapt to climate change, because the money won’t last

Patrick Nunn, Author provided

Patrick D. Nunn, University of the Sunshine Coast and Roselyn Kumar, University of the Sunshine Coast

The storm of climate change is approaching the Pacific Islands. Its likely impact has been hugely amplified by decades of global inertia and the islands’ growing dependency on developed countries.

The background to this situation is straightforward. For a long time, richer developed countries have been underwriting the costs of climate change in poorer developing countries, leaving them reliant on Western solutions to their climate-related issues.

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But as rising sea water continues to encroach on these low-lying Pacific islands, inundating infrastructure and even cemeteries, it’s clear almost every externally sponsored attempt at climate adaptation has failed here.

And as the costs of adaptation in richer countries escalate, this funding support to developing countries will likely taper out in future.

We’ve researched climate change adaptation in the Pacific for more than 50 years. We argue this trend is not merely unsustainable, but also dangerous. Pacific Island nations must start drawing from traditional knowledge to adapt to climate change, rather than continue to rely on foreign funds.

High waves destroyed this sea wall on Majuro Atoll (Marshall Islands).
Patrick Nunn, Author provided

Western solutions don’t always work

On a global scale, climate adaptation strategies have largely been either ineffective or unsustainable.

This is especially the case in non-Western contexts, where Western science continues to be privileged. In the Pacific Islands, this is often because these Western strategies invariably subordinate, even ignore, funding recipients’ culturally grounded worldviews.

A good example is the desire of foreign donors to build hard structures, such as sea walls, to protect eroding coasts. This is the preferred strategy in richer nations.

However it does not embrace nature-based solutions such as replanting coastal mangroves, which can be more readily sustained in poorer contexts.

A likely scenario

The availability of external financial assistance means developing countries have become more dependent on their richer counterparts for climate change adaptation.

For example, between 2016 and 2019, Australia provided A$300 million to help Pacific Island nations adapt to climate change, committing to a further $500 million to 2025. This left little need or incentive for these countries to fund their own adaptation needs.

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Pacific Island nations will no longer stand for Australia’s inaction on climate change

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But imagine this climate change scenario. Ten years from now, unprecedented rainfall is dumped on Australia’s east coast over a prolonged period. Several cities become flooded and remain so for weeks.

In the aftermath, the Australian government scrambles to make recently flooded areas liveable once more. They build a series of massive coastal dikes – structures to prevent the rising sea from flooding populated areas.

The cost is exorbitant and unanticipated – like COVID-19 – so the government will look for ways to shuffle money around. This may well include reducing financial aid for climate change adaptation in poorer countries.

Plunging international aid

Economic modelling shows nations will incur massive costs this century to adapt to climate change within their own borders. So it’s almost inevitable wealthier countries will rethink the extent of their assistance to the developing world.

Recent and projected Australian GDP and adaptation aid to Pacific Island.
countries.
Patrick Nunn, Author provided

In fact, even before the pandemic, Australia’s foreign aid budget was projected to decrease in real terms by nearly 12% from 2020 to 2023.

These factors do not bode well for developing countries, which will be facing higher climate adaptation costs and dwindling foreign aid assistance.

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Building autonomy with ‘cashless adaptation’

Leaders of developing countries should anticipate this situation now, and reverse their growing dependence on outside assistance.

For example, rural communities in regions like the Pacific Islands could revive their use of “cashless adaptation”. This means developing ways of adapting livelihoods to climate change that cost nothing.

These methods include the intentional planting of surplus crops, the use of traditional methods of food preservation and water storage, the use of free locally-available materials and labour for constructing sea defences. And it perhaps even includes the recognition that living along coastal fringes exposes you unnecessarily to weather-related change.

Prior to globalisation, this is how it was for decades, even centuries, in places like the rural Pacific islands. Then, adaptation to a changing environment was sustained by cooperation with one another and the use of freely available materials, not with cash.

Researchers have also argued for such “looking forward to the past” strategies regarding Hawaii’s climate adaptation.

And research from last year in Fiji showed more rural communities still have and use a stock of traditional methods for anticipating and withstanding disasters, such as flood and drought.

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We can take this argument further. Perhaps it’s time for Pacific Island nations to rediscover traditional medicines, at least for primary health care, to supplement western medicine.

Greater production and consumption of locally grown foods, over imported foods, is also an important and valuable transformation.

The future of the developing world

Dirak faluw (‘men’s house’) at Wanyaan Village on Yap (Micronesia) was.
constructed by community labour using local-available materials.
Roselyn Kumar, Author provided

The need for nations to adapt to unanticipated phenomena like climate change and COVID-19 encourages de-globalisation – including that countries depend less on cross-border aid and economic activity. So it seems inevitable that under current global circumstances, smaller economies will be forced to become more efficient and self-reliant.

Restoring traditional adaptation strategies would not only drive effective and sustainable climate change adaptation, but also would restore residents’ beliefs in their own time-honoured ways of coping with environmental shocks.

This not only means finding ways to reduce costs through cashless adaptation, but also to explore radical ways of reducing dependency and increasing autonomy. An appeal to past practice, and traditional ways of coping, is well worth considering.

Patrick D. Nunn, Professor of Geography, School of Social Sciences, University of the Sunshine Coast and Roselyn Kumar, , University of the Sunshine Coast

This article is republished from The Conversation under a Creative Commons license. Read the original article.