In 2010, the second 100 year drought in 5 years killed "in the low billions" of trees more than the 4 billion average lost yearly in the Amazon Basin.
The 2010 drought was even more devastating than the destructive 2005 drought that was so strong the dead trees drove up global atmospheric CO2 levels.
57% of the Amazon basin suffered from drought in the 2010 dry season, compared to 37% in the devastating drought in 2005.
Researchers investigating the effects of the droughts calculated that an enormous amount of carbon, 1.6 ×10^15 grams, was released from dead trees in 2005. They forecast 2010 emissions to be an even larger 2.2 × 10^15 grams. The Amazon may rapidly turn into a source of carbon to the atmosphere, instead of one of the world's largest sinks.
But that's just part of a bigger problem.
The record hurricane season of 2005 and the very active hurricane season of 2010 are directly related to the droughts in the Amazon. In 2005 exceptionally warm water temperatures in the north Atlantic, north of South America spawned a number storms in an area, at very low latitude, where they rarely form. A zone of intense convergence of moist low level tropical air north of south America triggered storm after storm.
The strong upward convection of moist warm air over the tropical north Atlantic intensified the subsidence of hot dry air over the Amazon basin. Both the intense hurricane season and the intense drought of 2005 were related to much warmer than normal sea surface temperatures in the tropical north Atlantic and cool temperatures south of the equator.
Sea surface temperatures hit record levels in the tropical north Atlantic in 2010, triggering another intense hurricane season and the severe drought in the Amazon basin.
The bigger problem is that studies of the climate of south America over the past 170,000 years show that warming of the north Atlantic can lead to long-term drought in tropical south America. Studies of ancient lake beds in south America indicate that tropical south America is suffers long-term droughts when the sea surface temperatures are warmer than normal in the tropical north Atlantic compared to the tropical south Atlantic. When the tropical north Atlantic is cool, tropical south America is wet.
Alternating mud and salt layers in a high Bolivian lake showed alternating wet and dry periods in the tropical south American climate over the past 170,000 years. Gamma ray logs show muddy layers with high radioactivity associated with lakes. Salty sediments and low gamma levels are associated with dry periods.
These long-term shifts from wet to dry were associated with shifts form cool to warm sea surface temperatures in the tropical north Atlantic ocean. When sea ice (and glaciers) had its greatest extent tropical south America was very wet. When sea ice retreated, the tropical north Atlantic warmed and tropical south America got drier.
The tropical north Atlantic hit record high temperatures in the summer of 2010. The area of warm tropical and subtropical water is expanding in the north Atlantic as sea ice retreats. Now we are seeing record low sea ice levels.
The heating of the north Atlantic may be a direct response to global warming. We may be observing a long term climate shift that will lead to more hurricanes forming in the intensifying tropical convergence zone north of south America. The dry season in the Amazon basin may intensify in response to the intensifying convection north of south America.
If we are witnessing the beginning of a long-term climate shift we may be also watching the beginning of the rapid death of much of the Amazon rain forest. Reports from the Amazon this October were shocking.
In a press release on 22 Oct (Seca pode bater recorde na Amazônia / Drought may hit record in the Amazon), Brazil's Amazon Environmental Research Institute (Instituto de Pesquisa Ambiental da Amazônia or IPAM) said:
"The drought of 2010 still hasn’t ended in the Amazon and could surpass that of 2005 as the region’s worst during the past four decades. In the Western Amazon, the Solimões River reached its lowest level in recorded history. In Manaus, the level of the Rio Negro (Black River) is approaching that of 1963 – the lowest in a century. Even if this doesn’t occur, the forest will have already experienced three extreme dry spells in just 12 years, two of which occurred during the past five years: 1998, 2005 and 2010. And this is not including the drought of 2007, which affected only the Southeastern Amazon and left 10 thousand sq. km. of forest scorched in the region...`The Amazon that had wet seasons so well-defined that you could set your calendar to them – that Amazon is gone,' says ecologist Daniel Nepstad of IPAM..."
The conclusion in last week's brief report in Science magazine was also shocking. The Amazon may be rapidly shifting from a region that stores carbon to a region that releases CO2 to the atmosphere. The decline of the Amazon rain forest may trigger a feedback loop that accelerates the heating of tropical south America and the planet.
The two recent Amazon droughts demonstrate a mechanism by which remaining intact tropical forests of South America can shift from buffering the increase in atmospheric carbon dioxide to accelerating it. Indeed, two major droughts in a decade may largely offset the net gains of ~0.4 Pg C year−1 in intact Amazon forest aboveground biomass in nondrought years. Thus, repeated droughts may have important decadal-scale impacts on the global carbon cycle.
Droughts co-occur with peaks of fire activity (5). Such interactions among climatic changes, human actions, and forest responses represent potential positive feedbacks that could lead to widespread Amazon forest degradation or loss (7). The significance of these processes will depend on the growth response of tropical trees to increases in atmospheric carbon dioxide concentration, fire management, and deforestation trends (3, 7). Nevertheless, any shift to drier conditions would favor drought-adapted species, and drier forests store less carbon (8). If drought events continue, the era of intact Amazon forests buffering the increase in atmospheric carbon dioxide may have passed.