What happens to net zero if the trees don’t survive?

When climate change undermines the climate plan

It was supposed to be a symbol of the UK’s leadership on the environment.

In 2020, a major new road near Cambridge was opened, one of the biggest infrastructure projects in the UK in recent years. And at its heart was a bold commitment: to boost the local area’s biodiversity, including planting 860,000 new trees.

Tree planting has long been one of the UK’s go-to climate solutions. And with good reason. Forests suck carbon from the air, cool overheating cities, boost biodiversity, and offer natural flood and drought defences. They touch every aspect of the sustainability transition.

Yet five years on, many of these trees have died, with one estimate putting the dieback at nearly 70% of the originally planted trees. Poor planting might be to blame. But so are climate-worsened heatwaves and disease.

This one example points to a wider problem. As the world overshoots 1.5C, the role of trees in climate strategies might become precarious. That’s because many of the escalating impacts of climate change - particularly dry conditions and fires - could kill these trees, or at least impair their ability to sequester carbon and adapt cities.

In this article, I explore how trees offer a way to understand risks to climate action - and how to manage those risks. This is a challenge affecting the whole world.

When climate undermines action

But let’s go back to the UK to understand that challenge. Like many countries, to meet its carbon reduction targets, the UK is pursuing a dual strategy: reducing the amount of carbon it emits and increasing the amount it removes from the atmosphere (sequestration). The goal is to achieve a net-zero balance by 2050.

As part of the sequestration effort, trees are expected to play a significant role, accounting for around 15% of the UK’s total carbon sequestration by 2050. To reach this target, the government’s official climate advisors - the Climate Change Committee (CCC) - have calculated that forest cover must expand from today’s 13% to at least 17%. This translates into planting approximately 30,000 hectares - or 90 to 120 million trees - every year.

So far, so sensible. But here’s the issue: climate change is no passive backdrop. It’s not just the problem to solve. It’s also increasingly a saboteur. This is what we at the Strategic Climate Risks Initiative call derailment risk. The idea that outcomes of climate change could derail our efforts to deal with its causes.

With trees, it’s stark. The climate crisis we’re trying to address through afforestation is also making forests more vulnerable. Think more wildfires, droughts, disease, floods - any of which can kill off saplings, stress mature trees, or even make some places unviable for planting.

This is already a growing problem across UK reforestation schemes. It’s not just the Cambridge road scheme. For example, in another planting project in County Durham, sapling mortality was up to 90%. Even when trees survive, their capacity to soak up carbon can shrink due to heat and water stress.

The derailment blind spot

All of this means that the calculations behind the UK’s net-zero strategy could be missing important considerations. By affecting the ability to sequester, there would be implications for the overall carbon-reduction plan.

Yet the UK’s latest climate risk assessment doesn't map how these risks might disrupt its net-zero pathway. Lose trees and you also lose their side-benefits: less cooling, less biodiversity, weaker natural buffers against extreme weather, to name a few. It’s a double hit - mitigation and adaptation capacity both suffer blows.

The risks to trees haven’t gone completely under the radar. The CCC has started assessing climate risks to planting areas. They’ve considered disease and they recommend planting various climate-adapted species and exploring mixed-species forestry to create more resilient ecosystems - all useful strategies for dealing with increasing volatility.

But here’s the problem: most of these assessments are built around fairly tame climate scenarios. They don’t touch more extreme, non-linear outcomes, like tipping points. The North Atlantic Subpolar Gyre (SPG), for example, is part of the ocean currents vital for maintaining the UK’s temperature. The SPG is one of five tipping points at imminent risk of collapse, and its consequences would bring more extreme weather to the UK, beyond that expected from climate change alone.

The implications for UK trees - and the climate plans that partly rely on them - could be considerable. Yet SPG collapse has still not been properly risk assessed and so does not feature in carbon-reduction planning.

It’s not just tipping points. Climate impacts lead to cascading shocks that send ripples throughout the whole of society. These are also often missed from climate risk assessments. Yet these ripple effects could have considerable impacts on trees. Like flooding blocking planting windows, and driving up delays and costs. Or if food shocks spike land prices, and suddenly everyone’s scrambling to convert woodland into farmland.

These risks are not guiding the approach to tree planting, which means the risk of carbon reduction plans being derailed is growing. And there’s a cautionary tale. In Finland, warming turned forests from carbon sinks into sources. The country’s decarbonisation plan leans heavily on forest absorption. With the forests becoming a carbon source, this is “​​worrying news” for Finland’s decarbonisation plan, according to Annalea Lohila, Head of the Climate System Research Unit at the University of Helsinki.

Finland's net emissions were higher in 2023 than they were in 2010, despite the fact that non-land-use CO2 emissions were 20-30 million tonnes lower. The sole cause was increased forest emissions.

Increased deforestation has contributed to weakened forest absorption capacity, but even with these heightened levels, there should still be an increase in forest area and, in theory, increased carbon uptake. With a warming climate and stressed ecosystems, this hasn’t happened.

This is a real-world example of derailment risk: climate impacts are undermining Finland’s net-zero plans, despite considerable progress in decarbonisation elsewhere.

It’s not just trees

The derailment risk for forestry sequestration is clear. Yet derailment risk doesn’t stop there.

One example comes from Zambia, where the effects of climate change are triggering what economists call a ‘climate-sovereign debt doom loop’. In recent years, severe drought has wiped out half the country's crops, forcing a reliance on costly food imports. Dwindling water levels crippled hydropower generation, causing widespread blackouts. A tanking economy led tax revenue to drop, stretching public finances to the brink at exactly the moment when more crisis spending is needed. Meanwhile, wary investors are raising risk premiums, further driving up the cost of borrowing.

All this means there’s less money to go around to invest in climate action, including adaptation. All things being equal, Zambia’s vulnerability to climate shocks has increased, so the next one could be even more costly, further eroding climate investment. This is a vicious cycle where the impacts of climate change frustrate its ability to respond to it.

There are many other examples of derailment risk, and we’ll be sharing our findings from a SCRI project soon. And derailment risk exposes a simple but urgent truth: climate change isn’t just a hazard we mitigate against. It’s an active force reshaping the landscape we’re trying to navigate. And if we don’t bake that reality into our strategies - across forestry, energy, food, and more - we’re building castles in the sand.

A new type of climate foresight

So how do we deal with this?

First, we need to plug the gaps in current risk assessments. That means accounting for cascading effects, tipping points, and other dynamic risks that could derail transition efforts - but that are still largely missing from today’s frameworks. Groups like the UK Institute and Faculty of Actuaries are already calling for this, with their report, the Climate Scorpion, arguing for:

“realistic risk assessment of climate change as a matter of urgency, taking into account the full range of outcomes, including … realistic worst-case scenarios, and the risk of ruin – the point beyond which our global society can no longer successfully adapt to climate change.”

Doing this is the critical first step, but we must go further.

Derailment risk itself needs to be made explicit. Let’s go back to UK forestry: future risk assessments, such as the government’s next Climate Change Risk Assessment (CCRA4, due in 2027), should evaluate how different climate scenarios could jeopardise decarbonisation via tree planting.

This would lay the foundation for a targeted derailment mitigation strategy - developed through NAP4 (the UK’s National Adaptation Programme, due in 2028) - to guide what kinds of trees to plant, where, how to manage them, what second-order might disrupt the strategy, and what institutions are needed to support this under growing climate volatility.

This approach shouldn’t stop at forestry or at the UK. CCRA4 could expand to assess derailment risks across the entire transition landscape, with NAP4 offering adaptive plans in response. Internationally, similar efforts are needed to prepare for the overshoot of the 1.5C target - an all but inevitable outcome. Many transition plans are based on a scenario where we stay below or near this target, and thus in a ‘safe zone’ of climate change. But new science shows that even if we limit temperature rise to 1.5C, climate change will not be in a ‘safe zone’. As we head over it, we need to ensure climate strategies can withstand the very disruptions they aimed to prevent.

Because if our transition plans can’t survive the climate crisis, then they aren’t really plans, they’re gambles. It’s time to future-proof them, or risk losing the future entirely.