Seen from a monitoring tower above the treetops near Manaus in the Brazilian Amazon, the rainforest canopy stretches to the horizon as an endless sea of green. It looks like a rich and healthy ecosystem, but appearances are deceiving. This rainforest — which holds 16,000 separate tree species — is slowly drying out.
Over the past century, the average temperature in the forest has risen by 1–1.5 °C. In some parts, the dry season has expanded during the past 50 years, from four months to almost five. Severe droughts have hit three times since 2005. That’s all driving a shift in vegetation. In 2018, a study reported that trees that do best in moist conditions, such as tropical legumes from the genus Inga, are dying. Those adapted to drier climes, such as the Brazil nut tree (Bertholletia excelsa) are thriving.
At the same time, large parts of the Amazon, the world’s largest rainforest, are being cut down and burnt. Tree clearing has already shrunk the forest by around 15% from its 1970s extent of more than 6 million square kilometres; in Brazil, which contains more than half the forest, more than 19% has disappeared. In the 2000s, Brazil was praised for drastically slowing forest loss, but the rate has since risen as a result of political turmoil and an economic recession. Last year, deforestation in Brazil spiked by around 30% to almost 10,000 km2, the largest loss in a decade. And last August, videos of wildfires in the Amazon made international headlines. The number of fires that month was the highest for any August since an extreme drought in 2010. Many scientists have linked these surges to the anti-environmentalist rhetoric of Brazil’s president, Jair Bolsonaro.
In the face of a warming climate, increased deforestation and fiercer fires, scientists are more worried than ever about the Amazon. Some have warned that the forest will soon reach a tipping point that could turn much of it into dry scrubland. But others say they lack the evidence to make specific forecasts about how long the rainforest can remain healthy. [Continue reading…]