Ominous sign for Earth

Climate change and deforestation have flipped a large swathe of the Amazon basin from absorbing to emitting planet-warming CO2, a transformation that could turn humanity's greatest natural ally in the fight against global warming into a foe, researchers reported on Wednesday. 

Hundreds of high-altitude air samples collected over the last decade showed that southeastern Amazon, in particular, has shifted from a "sink" to a source of carbon dioxide, the main greenhouse gas, they reported in the journal Nature.

Terrestrial ecosystems worldwide are crucial as the world struggles to curb CO2 emissions, which topped 40 billion tonnes in 2019.

Over the last half century, plants and soil have consistently absorbed more than a quarter of those emissions, even as CO2 pollution increased by 50 percent.

The Amazon basin contains about half of the world's tropical rainforests, which are more effective at soaking up and storing carbon than other vegetation.

If Amazonia -- with 450 billion tonnes of CO2 locked in its trees and soil -- were to become a consistent source rather than a "sink" of CO2, tackling the climate crisis would be vastly more challenging.

Since 1970, the region's tropical forests have declined by 17 percent.

Climate change itself is also a key factor.  Dry-season temperatures have risen by nearly three degrees Celsius compared to pre-industrial levels.

Northwestern Amazon, they found, was in carbon balance, absorbing as much CO2 into the atmosphere as it gave off. But the eastern Amazon -- especially during the dry season -- emitted far more than it absorbe

Another recent study, using different methodology, found that the Brazilian Amazon released nearly 20 percent more CO2 over the last decade than it absorbed from 2010 to 2019.  

The Amazon rainforest is one of a dozen so-called "tipping points" in the climate system. Ice sheets atop Greenland and the West Antarctic, Siberian permafrost loaded with CO2 and methane, monsoon rains in South Asia, coral reef ecosystems, the jet stream -- all are vulnerable to point-of-no-return transitions that would radically alter the world as we know it.