Planting trees has plenty of benefits, but this popular carbon-removal method alone can’t possibly counteract the planet-warming emissions caused by the world’s largest fossil-fuel companies. To do that, trees would have to cover the entire land mass of North and Central America, according to a study out Thursday.
Many respected climate scientists and institutions say removing carbon emissions — not just reducing them — is essential to tackling climate change. And trees remove carbon simply by “breathing.” But crunching the numbers, researchers found that the trees’ collective ability to remove carbon through photosynthesis can’t stand up to the potential emissions from the fossil fuel reserves of the 200 largest oil, gas and coal fuel companies — there’s not enough available land on Earth to feasibly accomplish that.
And even if there were, if those 200 companies had to pay for planting all those trees, it would cost $10.8 trillion, more than their entire combined market valuation of $7.01 trillion. The researchers also determined that the companies would be in the red if they were responsible for the social costs of the carbon in their reserves, which scientists compute around $185 per metric ton of carbon dioxide.
“The general public maybe understand offsetting to be a sort of magic eraser, and that’s just not where we’re at,” said Nina Friggens, a research fellow at the University of Exeter who co-authored the paper published in Communications Earth & Environment, a Nature Portfolio journal.

Carbon offsetting essentially means investing in tree planting or other environmental projects to attempt to compensate for carbon emissions. Trees are one of the cheapest ways to do this because they naturally suck up planet-warming carbon. Fossil fuel corporations, along with other companies and institutions, have promoted tree-planting as key part of carbon offset programs in recent years.
For example, TotalEnergies, a global energy company, said in a statement that it is “investing heavily in carbon capture and storage (CCS) and nature-based solutions (NBS) projects.”
To do their calculations, the researchers looked at the 200 largest holders of fossil fuel reserves — the fuel that companies promise shareholders they can extract in the future — and calculated how much carbon dioxide would be released if this fuel is burned. The researchers also focused solely on tree planting because the expense and technological development needed for other forms of carbon capture are still mostly cost-prohibitive.
Forestry expert Éliane Ubalijoro, who was not involved with the research, called the study “elegant.”
It “gives people a sense of proportion around carbon,” said Ubalijoro, CEO of CIFOR-ICRAF, an international forestry research center.

But she cautioned against oversimplifying the equation by looking only at carbon capture, noting that tree planting done right can foster food security and biodiversity and protect communities from natural disasters.
The paper effectively makes the point that it's financially impossible to offset enough carbon to compensate for future fossil fuel burning, said Daphne Yin, director of land policy at Carbon180, where her team advocates for US policy support for land-based carbon removal. And the idea that companies would be required to account for the downstream emissions from the fossil fuel they extract is a “fantasy,” she said.
The idea of planting trees is appealing to the public and to politicians because it’s tangible — people can literally see the carbon being incorporated into branches and leaves as a tree grows, Friggens said. But she says other methods shouldn't be overlooked — microbes underground store carbon too, but they can't be seen.
And it's a physically and mathematically inescapable fact, illustrated in part by this study, that there's no getting around it — we have to stop emitting carbon, said Jonathan Foley, the executive director of Project Drawdown, who also was not part of the study. Carbon emissions are like an overflowing bathtub, he says: Before you start cleaning up, you have to turn off the water.
“Trees are the sponges and the mops we use to clean up the mess," he said. "But if the taps are still running and the water’s pouring out over the edges of your bathtub, destroying your bathroom and your home, maybe you’ve got to learn to turn off the taps too.”
 

PARIS: Runny nose, itching eyes, worsening asthma symptoms — the effects of hay fever are nothing to sneeze at, experts say, warning of an “explosion” of allergies as climate change lengthens and intensifies pollen seasons.
The UN’s World Meteorological Organization (WMO) has found that a shifting climate has already begun altering the production and distribution of pollen and spores.
As winter frost thaws earlier and spring weather gets warmer, plants and trees flower earlier, extending the pollen season, numerous studies have shown.
Air pollution can also increase people’s sensitivity to allergens, while invasive species are spreading into new regions and causing fresh waves of allergies.
More and more people, particularly in industrialized nations, have reported developing allergy symptoms in recent decades.
Around a quarter of adults in Europe suffer from airborne allergies, including severe asthma, while the proportion among children is 30 to 40 percent.
That figure is expected to rise to half of Europeans by 2050, according to the World Health Organization.
“We’re in crisis because allergies are exploding,” said Severine Fernandez, president of the French Allergists’ Union.
Whereas previously an allergic person would endure only what is commonly known as hay fever, albeit sometimes for years, “now that person can become asthmatic after one or two years,” Fernandez said.

‘No doubt that climate change is having an effect’

Climate change affects allergy patients in multiple ways, according to a 2023 report by the WMO.
Rising levels of carbon dioxide, one of the main heat-trapping gases produced by burning fossil fuels, boost plant growth, in turn increasing pollen production.
Air pollution not only irritates the airways of people exposed, but it also causes stress to plants, which then produce more “allergenic and irritant pollen.”
Nicolas Visez, an aerobiologist at the University of Lille, said each plant species reacted differently to a variety of factors such as water availability, temperature and CO2 concentrations.
Birch trees for example will wither as summers get hotter and drier, while the heat causes a proliferation of ragweed, a highly allergenic invasive plant.
“There’s no doubt that climate change is having an effect,” Visez said.
In a study published in 2017, researchers projected that ragweed allergies would more than double in Europe by 2041-2060 as a result of climate change, raising the number of people affected from 33 million to 77 million.
The authors suggested that higher pollen concentrations as well as longer pollen seasons could make symptoms more severe.

‘AutoPollen’ program
A Europe-wide “AutoPollen” program under development aims to provide real-time data on the distribution of pollen and fungal spores.
In Switzerland, a tie-up with MeteoSwiss allows patients and doctors to match personal allergy profiles with maps of specific allergens throughout the country.
In parts of France, authorities have planted “pollinariums,” gardens packed with the main local allergen species.
These provide information on the very first pollen released into the air so that people can start taking antihistamines and other protective measures in a timely manner.
“Hazelnuts have started to bloom as early as mid-December, which wasn’t the case before,” said Salome Pasquet, a botanist with the association behind the pollen gardens.
“That’s really because we’ve had very mild winters, so flowering has come earlier,” she said.
Some countries are taking an interventionist approach — cutting off the pollen at the source.
In Japan, the government announced a plan in 2023 to combat allergies caused by the archipelago’s many cedar trees, which includes felling cedars to replace them with species that produce less pollen.
Countries in Europe are also more mindful of species in the environment, both native ones that have been planted and invasive newcomers like ragweed.
Preference is given to species with a lower allergenic potential, such as maple or fruit trees.
“The idea is not to stop planting allergenic species,” Pasquet said, but to be mindful of creating diversity and avoiding having “places where there are rows of birch trees, as was the case a few years ago.”
It was birch trees in a client’s garden that originally set off symptoms for Simon Barthelemy, an architect who lives near Paris.
“I had a major eye allergy, and it’s been a recurring problem every year since,” he said.
“I’m on antihistamines, but if I don’t take them I get itchy eyes, I’m very tired, I cough... I can’t sleep at night.”