Researchers from NASA's Goddard Space Flight Center in Maryland worked with scientists at the Brazilian Agricultural Research Corporation and the Federal University of Western Pará in a "painstaking effort to measure downed branches and trees," according to a recent statement from NASA, which released the video. As Brazilian researchers studied the rainforest from the ground, NASA Goddard researchers flew a plane over the canopy (the treetops) and used pulses of laser light to measure the fallen branches and trees over the course of several years.
Drought brought on by climate change can cause large trees in a rainforest to die. To obtain a 3D view of dying trees, NASA scientists mounted light detection and ranging (lidar) technology onto an airplane. Pulsing 300,000 times per second, the lidar tech swept over two 30-mile (50 kilometers) swaths of the Amazon rainforest near Santarém, Brazil. One was a section of the Tapajós National Forest, and the other was an area of privately owned forests that were "fragmented by a range of land uses," NASA officials said.
From that information, scientists could estimate how much carbon dioxide failed to be absorbed as a result of dead vegetation in the multi-layered rainforest.
The researchers found that tree and branch mortality was 65 percent higher during the El Niño drought period from 2014 to 2016, totaling about 65,000 square miles (168,000 square km). And if tree decline continues, more carbon dioxide subsequently gets left in Earth's atmosphere, which, in turn, feeds the greenhouse cycle that can cause more droughts in the future, NASA officials said.
The researchers published a paper on their findings in March in the journal New Phytologist.