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The Role of Reforestation in Tackling the Climate Crisis

Every second counts Combatting the climate crisis is of the utmost importance. Both our society and our planet are being destroyed, and with every fraction of a degree of global warming, the consequences grow significantly more alarming. The Paris Agreement set to keep the temperature rise below 2°C (with the ambitious goal of 1.5°C), but we are not on track to reaching this target; the global commitment remains largely insufficient and unfulfilled. When it comes to stopping the crisis, time is the essential ingredient – and we are running short of it. While reducing our greenhouse gas (GHG) emissions in the first place is crucial, there is rising optimism associated with sucking the carbon down from the atmosphere, and into deposits called carbon sinks. Ecosystem restoration is gaining vast attention as a carbon-sequestering mechanism, with the UN even declaring it the mission of this decade. A huge chunk of the debate is centered around none other than trees. Indeed, restoring the Earth’s forests presents a major hope for our future. In this article, I will introduce you to the global tree-planting efforts, celebrating its ups and warning of its downs. While I aim at providing an unbiased read, I would hereby like to acknowledge that for many years now, I have been an Ambassador tree-planting initiative Every zero counts Tree-planting dates as far back as human civilizations go. Yet, the globally coordinated effort of planting trees for climate crisis mitigation is relatively recent. Knowing the power of planting, Wangari Maathai, a Nobel Peace Prize laureate, founded the African Green Belt Movement back in 1977. Wangari Maathai eventually planted over 30 million trees with women across Africa, which inspired the United Nations Environment Programme (UNEP) to start the Billion Tree Campaign in 2006 – an ambitious reforestation plan in response to global warming. Around the same time, children started to plant trees and raise climate change awareness as part of the initiative Plant-for-the-Planet. In 2011, the UNEP handed over the management of the Billion Tree Campaign to Plant-for-the-Planet, voicing ambitions not for a billion-tree reforestation, but instead a restoration of 1 trillion trees worldwide. But what do all these numbers mean? What chances do millions, billions, or even trillion trees present? And how do these perplexing digits fit within the bigger picture? The children of Plant-for-the-Planet asked these questions, and a team of scientists from Yale and ETH Zurich answered, providing us with a ground-breaking study in 2015. Combining technology and fieldwork, the team led by a young ecologist Thomas Crowther estimated that there are roughly 3 trillion trees currently on Earth. Shockingly, that represents just half of the 6 trillion trees Earth had before human civilization. In 2019, Crowther followed up with a study that sparked hope and attention across global media – the study of Tree Restoration Potential, which claims that 1.2 trillion trees across the planet can still be planted. Adding such a number of trees to the existing 3 trillion could then see a carbon sequestration of over 200 gigatonnes, which translates into more than a decade of cumulative anthropogenic GHG emissions. This not only sheds light on how unambitious the original UNEP Billion Tree Campaign really was, but also shows how spot on the new Trillion Tree Campaign is, which Plant-for-the-Planet launched a year before the study by Crowther got published. With scientific evidence and built-up momentum, the 2020 World Economic Forum gave birth to the One Trillion Tree Initiative, which now aims at uniting people, governments, and businesses for the reforestation target that can win us the time we need for fight against the climate crisis. At the Forum, the reforestation effort received voiced support not just from the well-established environmentalists, but also from the then-president Donald Trump, showing that reforestation also has the power of bringing people together – even climate deniers. Every tree counts

Having the numbers surrounding reforestation established, it is clear how crucial a role reforestation plays within the strategy to combat the climate crisis. As an extremely effective carbon capture, the trillion tree campaign sparks hope of giving us some valuable extra years for reducing our emissions and reaching the goals we so ambitiously set in Paris in 2015. Moreover, tree-planting presents numerous other benefits for sustainable development as a whole – it can help protect and enhance biodiversity, and its socio-economic impact could very well be the necessary push for overcoming poverty traps in underdeveloped regions. As the Crowther study indicated, the biggest reforestation potential lies within tropical regions, where most underdeveloped countries are located. Reforesting those areas would create the conditions for a healthy environment, a prosperous economy, and a happy society. With that in mind, we can project a positive correlation between tree-planting and each of the 17 Sustainable Development Goals. Not to mention that trees in well-managed ecosystems also act effectively in reducing the local impacts of the climate crisis, thus being both a mitigation and an adaptation tool. Every criticism counts too As you may have guessed by now, it all sounds a bit too optimistic and easy, right? Let’s just all pick up the shovels and plant a trillion trees by next year, shall we? Well, no. Capturing carbon by trees might not be a complicated technological mechanism – if it were, Elon Musk would have donated $100M to it by now – but that does not mean its implementation is easy. While planting one tree is a task that can easily be carried out by any of us within half an hour, planting a trillion trees with the goal of mitigating the climate crisis will be difficult, and as a wave of criticism towards the trillion-tree study pointed out, reckless reforestation could do us more harm than good. After the ground-breaking study by Thomas Crowther got published, the scientific community quickly pointed out several of its misunderstandings: anthropogenic emissions are consistently subject to uptake from both ocean and land carbon sinks. Having misinterpreted the numbers of tons of anthropogenic carbon currently stuck in the atmosphere with the total carbon that we have emitted changes the perspective of how big a fraction of our emissions the trillion trees could absorb. Doing so, the study overestimated the tree-sequestration potential by half. Furthermore, the study simplified the characteristics of different forest ecosystems across the globe, again overestimating the carbon uptake potential for several biomes. Overall, it is possible that the impact of a trillion trees has been overestimated by a factor of 5. Lastly, the study did not address possible negative consequences of such a massive reforestation, such as impacts on water availability. This criticism further emphasizes the fact that whatever the positive impacts of reforestation are, it still is only part of the solution and will only delay the climate crisis, not stop it. Shedding light on tree-planting at the expense of reducing our emissions in time could, therefore, truly present a burden. The team behind Crowther’s research stands by its original estimates. Yet, the scientific discussion on the topic is full of question marks, implying that further research is needed on the barely-understood carbon cycles within vegetation. Crowther and his team admit the number of uncertainties that had to be omitted in order to calculate the potentials of tree-reforestation. The debate and criticism over the recent years has provided us with the lessons needed for an effective reforestation. It is crucial that trees are planted only in places, where their sequestration potential is significantly higher than the impact of their sun-absorbing albedo – in the tropics. The prefix “re” in the word reforestation is not to be omitted, as avoiding negative consequences of tree-planting is best done when we only plant trees where trees are supposed to naturally exist – as for the other areas, instead of planting new trees (afforestation), we should always just copy nature and restore whatever ecosystem there once were. Without a doubt, putting biodiversity first is imperative – never plant monocultures, as it is the rich forests that draw the most carbon and attract the most life. In every corner of the world, the strategy for a successful reforestation will be different, and it is thus vital that such efforts incorporate the local communities for individual project assessments. This will take us a long time, but it’s better we do it right than with a hasty and careless centralised approach. The time of trees Trees have been symbols of life and prosperity for thousands of years. They have accompanied us on our journey to where we are today, and it is clear that they will continue accompanying us if we are to survive the climate crisis – for that, we need to understand them and respect them above all. We have recently seen quite a development: from Wangari Maathai, to the children of Plant-for-the-Planet, to the discovery that we could add a trillion trees to the existing three trillion. Yet, the journey has just started. The momentum around trees is as never-before and without doubt, this decade will see other major discoveries in regard to the potential impact of reforestation, and both the successful and failed reforestation projects will provide us with valuable lessons. What is clear now, however, is that trees are not the ultimate solution to the climate crisis. They will not save us from ourselves. The solution to the climate crisis lies within many puzzling pieces of unique strategies with GHG-reductions at their core. What trees can do is give us time to act while making our whole lives a bit better – but that is only the case if we do it right. The Crowther Lab continues to examine the relationship between carbon and various ecosystems – forests, in particular. Using machine learning and technology by Google, they are building up the Restor platform, which utilises open data from all around the world in order to provide a complex ecosystem restoration strategy that will efficiently combat the climate crisis. You can learn more about it in Crowther’s speech for last year’s TED Countdown event. While Restor is still in development, there are already several reforestation projects across the globe that have got the strategy right – you can support those on the Plant-for-the-Planet platform. Find out more about the journey towards the trillion trees at WEF’s And know one thing for certain: everybody – from individuals to governments to scientists to businesses – everybody can be a part of the trillion-tree restoration.

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