Thomas Crowther (ecologist)


Thomas Ward Crowther is a British scientist specialising in ecosystem ecology and the chief scientific advisor to the UN's Trillion Tree Campaign. He is a tenure-track professor of Global Ecosystem Ecology at ETH Zürich where he formed the Crowther Lab. His work aims to generate a holistic understanding of the global scale ecological systems which regulate the Earth's climate.

Research career

After his PhD, Crowther received a postdoctoral fellowship from the Climate and Energy Institute at Yale University. In 2015, Crowther was awarded a Marie Curie fellowship to research the impact of carbon cycle feedbacks on climate change at the Netherlands Institute of Ecology. In 2017, Crowther started a tenure track professorship at ETH Zürich. His ongoing research is supported through a unique partnership with DOB Ecology, a private foundation supporting projects which protect and restore threatened ecosystems across the globe.

Three Trillion Trees

During his post-doctoral research, Crowther was recognized for mapping the distribution and diversity of trees across the world for the first time. This research estimated that there are approximately 3.04 trillion trees on Earth, 46% fewer than at the onset of agriculture about 12,000 years ago. Previous estimates had suggested there may have been only be 400 billion trees on Earth.
Crowther was inspired to conduct his tree study by Plant-for-the-Planet, the youth-led NGO leading the UN's Billion Tree Campaign. According to a textbook to be distributed at global Plant-for-the-Planet Academies, "Tom was teased over the years by his fellow Professors for being the 'tree counter'. But Tom stuck with it and on 2 September 2015, his findings were published in the Journal Nature, the most prestigious paper in his field".
With the knowledge that there were now three trillion trees on Earth, Plant-for-the-Planet increased their restoration targets and transformed the Billion Tree Campaign into the Trillion Tree Campaign. Crowther is now the lead science advisor to Plant-for-the-Planet. As part of his tree study Crowther was able to compile one of the largest inventories of tree data ever recorded. In 2016 he co-founded the Global Forest Biodiversity Initiative – a foundation which manages the world's largest tree-level forest inventory database with 1.2 million plots from more than 70 countries.

Climate Change Ecology

Whilst at NIOO Crowther's research found that a 1 °C increase in temperatures could release an additional 55 billion tonnes of soil carbon, not previously accounted for by scientists, into the atmosphere by 2050. Further, his research suggested that warming generally stimulates decomposition more than photosynthesis. Increased activity of microbes and soil animals, such as worms, would be the source of the additional carbon emissions, which could accelerate global warming by 17%. Prof Ivan Janssens, seen as one of the godfathers in the global change ecology field commented "the research had provided essential data to climate change models". The study's data was since incorporated into ongoing work by the UN's Intergovernmental Panel on Climate Change. In a more recent scientific review of research on soil carbon feedback, Crowther's work was highly cited as the "new finding of a statistical dependence of decomposition on the initial carbon content of the soil may prove to be a useful benchmark for simulations".
Whilst Crowther acknowledges humanity has passed the "point of no return" in reversing the effects of climate change, he does believe action to dampen these effects is possible. He was outspoken about Donald Trump's decision to remove the United States from the Paris Agreement, calling it "catastrophic for humanity". Crowther also criticised the Trump administration for lifting the moratorium on the coal industry, noting that "renewable energies employ more people" and calling the decision "ridiculously short term and short sighted".
In July 2016, Crowther provided an expert declaration on the carbon cycle, and the sequestration potential of forests and soil for the Western Environmental Law Center to support the proposed Clean Air Rule to limit greenhouse gases in Washington. He went on to give a keynote address at the FAO's 2017 Global symposium on soil organic carbon alongside Nobel Prize winner Dr. Rattan Lal.
In May 2019 Crowther co-authored research on global mycorrhizal fungal networks, revealing that 60% of trees are connected by ectomycorrhizal fungi but, as temperatures rise, these fungi - and their associated tree species - will decline and be replaced by arbuscular mycorrhizal fungi. Whilst EM fungi support huge carbon stores, the transition to AM fungi could increase the release of carbon into the atmosphere. The research estimated that if there isn't a reduction in carbon emissions by 2100, there could be a 10% reduction in EM - and the trees that depend on them.

Geospatial Mapping

Crowther's ongoing research employs location intelligence and mapping technologies to convey the status of Earth's terrestrial ecosystems. Through the latest machine learning approaches they generate predictive models for a detailed understanding of the biosphere's spatial and temporal patterns.
In October 2018 he delivered a keynote address at the 2018 conference for the Association for Forest Spatial Analysis Technologies, hosted by the NASA Goddard Space Flight Center and the University of Maryland. In February 2019, at the American Association for the Advancement of Science, Crowther announced that scientists had established there was room for an additional 1.2 trillion trees, noting that such a scale of reforestation could be one of the most powerful tools in the fight against climate change.

One Trillion Trees

In July 2019 the Crowther Lab published a major paper on ''. They identified a global area of 0.9 billion hectares available for tree restoration. Studying nearly 80,000 high resolution satellite photographs they analysed tree cover in protected areas largely unaffected by human activity across Earth's ecosystems, from arctic tundra to equatorial rainforest. They used machine learning to identify correlations with key soil and climactic variables in Google Earth Engine to predict the natural level of tree cover which could potentially exist in each ecosystem.
In January 2020 the Crowther Lab was appointed as scientific advisor to the UN Decade on Ecosystem Restoration, a global initiative highlighting the need for greatly increased global cooperation to restore degraded and destroyed ecosystems, contributing to efforts to combat climate change and safeguard biodiversity, food security, and water supply. On 22 January the World Economic Forum, in partnership with Marc and Lynne Benioff, announced the launch of . With the support of Jane Goodall, Inger Andersen, Thomas Crowther and others, it was announced that the platform aimed to facilitate the conservation and restoration of one trillion trees within the decade.
Like any grand-scale venture, Crowther cautions that there are inherent risks to consider in order to realize a positive impact for biodiversity, human well-being, and climate change. In a letter to The Guardian he identified some basic principles that any organisation peddling to the trillion tree campaign should uphold :
  1. Cutting fossil fuel emissions is the priority for climate action. There is not enough room on Earth to offset all of our carbon emissions with trees. In combination with decarbonising, ecosystem restoration can be valuable for drawing down some of the excess atmospheric carbon.
  2. Global restoration must be ecologically responsible. Restore the right diversity of native tree species where they naturally exist. Planting trees in unsuitable ecosystems could result in unintended adverse consequences. Natural forests, grasslands, shrublands and wetlands serve as vital repositories of carbon and biodiversity to be preserved and restored. Monoculture plantations of exotic species will not likely yield the desired benefits.
  3. Global restoration must be socially responsible. It is crucial to uphold the rights of indigenous people and local communities, building on fair and sustainable economic models, and avoiding competition with food production. Only when local communities benefit from the economic and ecological benefits that new ecosystems provide can restoration be sustainable.
  4. Conserve existing ecosystems. We are losing old forests at an alarming rate. Conserving and sustainably managing ecosystems we already have must be at the core of a global restoration movement