The machete-wielding scientists ventured into the Amazon, hacking through dense jungle as the mid-morning temperature soared past 100 degrees Fahrenheit (38 C). Soaked in sweat, the small group of men and women sawed and tore trees limb from limb. They drilled into the soil and sprayed paint across tree trunks. This is vandalism in the name of science. In the trees about 90 km (55 miles) from Rondônia state capital Porto Velho, the Brazilian researchers are seeking to learn how much carbon can be stored in different parts of the world’s largest rainforest, helping to remove emissions from the atmosphere that foment climate change. “It’s important because we are losing forests globally,” said Carlos Roberto Sanquetta, a forestry engineering professor at the Federal University of Paraná in Brazil. “We need to understand what is the role that forests play,” both in absorbing carbon when they are left intact and releasing it when they are destroyed. Sanquetta led the weeklong research expedition in November, overseeing a team including a botanist, agronomist, biologist and several other forestry engineers to take myriad samples of vegetation – living and dead – for analysis. It’s rigorous and elaborate work, often in humid and insect-infested conditions, involving chainsaws, spades, corkscrews and calipers. “These are not white-coat scientists just lecturing people,” Raoni Rajão, who specializes in environmental management at the Federal University of Minas Gerais and is not involved with Sanquetta’s team. “These are hardworking people that get their hands dirty.” HOLISTIC APPROACH The Brazilian team is just one contingent among hundreds of researchers seeking to measure carbon in the complex and environmentally crucial Amazon rainforest ecosystem, which sprawls across more than six million square kilometers in nine countries. Some research seeks only to quantify carbon in trees, but Sanquetta says his team’s approach is holistic, measuring carbon in underbrush, soil and decomposing plant matter as well. In addition, his team is looking beyond primary forest, examining reforested areas to shed new light on how much carbon they hold – information key to incentivizing restoration efforts. Carbon dioxide (CO2) is the most prevalent of the greenhouse gases, which lock heat into the earth’s atmosphere. Trees soak up carbon dioxide from the atmosphere and store it as carbon, one of the cheapest and easiest ways to absorb greenhouse gas. The process also works in reverse, however. When trees are chopped down or burned – often to make way for farms or cow pastures – the wood releases CO2 back into the atmosphere. “Every time there is deforestation, it’s a loss, an emission of greenhouse gas,” said Sanquetta, who is a member of the U.N. Intergovernmental Panel on Climate Change, the world’s top climate science authority. At current emission rates, global temperatures are expected to rise about 2.9 degrees Celsius by 2100, according to nonprofit consortium Climate Action Tracker, far surpassing the 1.5- to 2-degree limit needed to avert catastrophic changes to the planet. Climate change raises sea levels, intensifies natural disasters and can spur the mass migration of refugees. Deforestation in the Amazon has accelerated during the administration of Jair Bolsonaro, the right-wing president of Brazil. Since he took office in 2019, at least 825 million tonnes of CO2 have been released from Brazilian Amazon deforestation. That’s more than emitted by all U.S. passenger cars in a year. In a statement, the office of Brazilian Vice President Hamilton Mourão, who leads the government’s Amazon policy, said the rise in deforestation predated the current administration and that the government has been working around the clock to thwart destructive mining and lumber trafficking. “We have not achieved the desired degree of success, but it could have been worse,” the statement said. METICULOUS MEASUREMENTS Key to understanding and addressing the climate threat is bringing more precision to carbon measurements in receding forests. “Everyone wants this information,” said Alexis Bastos, project coordinator of the nonprofit Rioterra Study Center, a Brazilian organization that provides financial support and several scientists to Sanquetta’s team. Today there are scientists measuring forest carbon on nearly every continent. Aside from Sanquetta’s team, for instance, the Amazon Forest Inventory Network with its more than 200 partner scientists is trying to standardize carbon and other measurements, garnering huge amounts of data to “quantify” the forest. The challenge is “there’s differences in species across the Amazon. In Peru in the southwest versus Guyana in the northeast, there’s virtually no species overlap at all, so it’s completely different plants in exactly the same climate,” said Oliver Phillips, the network’s coordinator and a tropical ecologist at the United Kingdom’s University of Leeds. The network’s partners use precise parameters to capture the major carbon reservoirs, including in dead plant matter and soil. For instance, if a tree is on the border of a plot, it should be measured only if more than 50% of its roots are in the plot. No one team could hope to sample enough of the vast rainforest for an exact count of carbon harbored by the Amazon. It’s also a moving target: The Amazon rainforest, which varies from tangled jungle to more open, riverine spaces, is constantly shifting, as more trees are chopped down while restoration efforts are accelerating. Sanquetta’s team began its current line of research in 2016, relying on support from Rioterra, which itself received funding from Petróleo Brasileiro SA (Petrobras), the Brazilian state-owned oil firm. At the time, Rioterra was replanting destroyed areas of rainforest, and wanted to know how much carbon was being sequestered.