“Savannization”

                                                                                                           Chris Linder

Deforestation of the Amazon is creating an entirely new climate for the region.  A regional climate that will have a massive impact on the global climate, while devastating the regions agricultural capacity. Profound climate impact combined with crippling social dislocation.  

… it is where Brazilian and American scientists are keeping watch for the long-predicted tipping point – the moment when the Amazon, the world’s largest rainforest, begins a process of runaway degradation, when so much forest has been lost that the transition to savanna is irreversible. That will be the moment when the Amazon ceases to be a carbon sink that helps protect the planet from climate change, and turns into a global source for carbon emissions.

Deforestation is dramatically raising local temperatures. The air over the farm is on average 5 degrees Celsius hotter than in the forested reserve over the fence: 34 degrees C, rather than 29 degrees C. The difference rises to a staggering 10 degrees at the end of the dry season, says Coe.

And the dry season is lengthening. Across the Xingu Basin and through the southern Amazon region known as the “arc of deforestation,” it lasts almost four weeks longer than half a century ago.

Trees in the Amazon rainforest, don’t just convert CO2 into O2, they also generate water through a process called transpiration.  A process that not only creates water, but removes heat from the forest.

Transpiration requires large amounts of energy, taken from solar radiation. “Every square meter of forest removes the heat equivalent of about two 60-watt [light] bulbs burning 14 hours per day,” Coe calculated in one study. So it cools the air of intact forest. But take away the forest, and the air is instantly much hotter.

The transpiration of a typical large Amazon tree also releases around 500 liters of water a day into the atmosphere. The moisture creates clouds and rain that sustain the forest.

When the closed looped processes that the rainforest drives are disrupted, even in areas that haven’t been directly impacted by deforestation, the reduction in moisture can result in a process of “savannization” – where the dense, cool rainforest becomes an open dry grassland with far fewer trees.  Savannas have nowhere near the same impact on CO2 conversion than do rainforests. 

Nobre argued in 2007 that there could come a point where savannization is unstoppable across large swaths of the Amazon. He said the tipping point could occur if 40 percent of the forest was lost. More recently he has warned that, with the background global rise in temperatures, that threshold could be much closer – at between 20 and 25 percent loss. With Brazilian government scientists putting the current loss at 19.7 percent, the doomsday could be close.

The clock is ticking towards midnight in the world's largest rainforest.  Its collapse won't just drive global warming.  It will also have a profound impact on the global food supply.