Reposted from Pakalolo by angelajean
The Amazon rainforest is the source of one-fifth of all fresh water on the planet, it is also the lungs of the planet or a carbon sink. It is called that because it sucks up the global emissions of carbon dioxide from things like cars, planes and power stations to name just a few. The Amazon rain forests hydrological system plays a critical function in regulating the global and regional climate. Water condensation, evaporation, and transpiration over the Amazon are key drivers of the global atmospheric circulation, affecting precipitation across South America and much of the Northern Hemisphere.
From Climate Central:
Professor Fu of the University of Texas, and her colleagues say the water stored in the forest soil at the end of each wet season is all that the trees have to last them through the dry months. The longer that lasts – regardless of how wet the wet season was – the more stressed the trees become and the more susceptible they are to forest fires.
Findings from a recent study show that since 1979, the dry season in southern Amazonia has stretched about a week longer per decade.
They say the most likely explanation for the lengthening dry season in recent decades is human-caused greenhouse warming, which inhibits rainfall in two ways: It makes it harder for warm, dry air near the surface to rise and freely mix with cool, moist air above; and it blocks incursions by cold weather fronts from outside the tropics which could trigger rainfall.
The team says the IPCC’s climate models represent these processes poorly, which might explain why they project only a slightly longer Amazonian dry season.
The Amazon rainforest normally acts as a carbon sink, removing atmospheric carbon dioxide and storing it. But during a severe drought in 2005 it went into reverse, releasing 1 petagram of carbon (1 billion tons – about one-tenth of annual human emissions) to the atmosphere.
Fu and her colleagues estimate that if dry seasons continue to lengthen at just half the rate seen in recent decades, the 2005 Amazon drought could become the norm rather than the exception by the end of this century.
Recently, 2 droughts have raised alarm bells on the health of the Amazon. Not only is the forest susceptible to drought and has increased forest fires as a result the problem is being exacerbated by logging and ranching and other agricultural uses.A 2005 drought is estimated to have turned the rainforest from a net absorber of about two billion tonnes of carbon dioxide to an exporter of some five billion tonnes of carbon dioxide, which is almost as much as the 5.4 billion tonnes emitted annually by the US.
The 2005 drought:
Throughout 2005unusually high sea temperatures prevailed in the North Atlantic. These exceptionally warm waters also powered the most destructive hurricane season on record, which included Hurricane Katrina. In Amazonia, and especially its western and southern regions, the subsiding air from the Atlantic convection dried the forest, helping make the 2005 dry season the driest ever in many locations.
In 2010 the drought was more widespread and more intense than the earlier drought, with a far bigger impact on the growth and death of trees, which is why the scientists expect the overall release of carbon dioxide from dead and decaying organic matter to reach eight billion tonnes.
In normal years the forest absorbs nearly 2 billion tonnes of carbon dioxide. The drought caused a loss of more than 3 billion tonnes. The total impact of the drought - 5 billion extra tonnes of carbon dioxide in the atmosphere - exceeds the annual emissions of Europe and Japan combined.
RAINFOR, the sole research organization dedicated to examining the rainforests of the Amazon reports:
Without this “carbon sink” the world’s ability to lock up carbon will be reduced, compounding the effects of global warming.