AVOIDing dangerous climate change. Can Global Warming be Limited to Two Degrees?

[OldLeatherneck]

If the world continues to burn fossil fuels at the current rate, global warming will rise 2 degrees Celsius by 2036, crossing a threshold that many scientists think will hurt all aspects of human civilization: food, water, health, energy, economy and national security.

--M. Mann

http://www.scientificamerican.com/article/mann-why-global-warming-will-cross-a-dangerous-threshold-in-2036/

Wili,

Below is the chart that Dr. Mann included in the article you referenced.  It scares me to think that the 2^o(C) might be reached as early as 2036.  Even worse, I see no significant efforts on the horizon to start reducing our emissions.  I feel sorry for the younger generations who will live to see the upper extremes of the warming. 

[ccgwebmaster]

During a wet year, the Amazon forests were roughly carbon-neutral: Forests “inhaled” more carbon dioxide than they “exhaled,” but biomass burning, which releases carbon dioxide, compensated for the difference. In contrast, during a very dry year forest growth stalled and biomass burning increased, resulting in the region “exhaling” substantial amounts of carbon dioxide to the atmosphere.

So then the Amazon is already a net carbon emitter? That's a big positive (exacerbating) feedback to tip!

I'm not sure if one can assume that just yet - since one of the years was 2010 - a statistically bad drought year (1 in 100 if memory serves). At best though, it would seem the forest is essentially neutral - holding carbon dioxide in but not really sinking a lot (wouldn't seem surprising with how long the forest was there, you're bound to reach equilibrium).

Start to dry it out though - and you're in trouble.

I'm slightly curious to what extent human impact factors in to the observations as it's still being actively burned and logged? I would think that will also tend to skew the region towards being a net emitter? (albeit one might term it land use changes more than a natural effect).

Isn't the main concern with the Amazon that if it dwindles too much it's finished - as it essentially relies upon itself to maintain it's rainfall? Therefore it's potentially subject to a tipping point if it diminishes too much to maintain itself. It reminds me of the Greenland Ice Sheet - stable but only because it's already there. Mess with it - and it's not coming back later.

[JimD]

ccg

A major factor determining what happens to the Amazon is what happens in the Cerrado and vice  versa.  The vast tropical savannah (the most diverse in the world) which sits next to the Amazon and is under heavy development by agriculture.

The Cerrado gets most of its moisture from rains which were generated by transpiration in the Amazon.  If the Cerrado gets drier is promotes agriculture further intruding into the Amazon which makes the Amazon drier.  If this cycle gets underway at a more intense level than what used to be the natural variations it could be one of Wili's tipping points and drag the combined ecosystem down and push the whole area into being a carbon emitter.

What happens when the next big Amazon drought happens?

http://en.wikipedia.org/wiki/Cerrado

http://www.nature.org/ourinitiatives/regions/southamerica/brazil/placesweprotect/cerrado.xml

http://www.wwf.org.uk/what_we_do/safeguarding_the_natural_world/forests/forest_conversion/cerrado.cfm

EDIT:  I also meant to point out that droughts in the Amazon tend to occur during El Nino's.

[TenneyNaumer]

Jim, do you have any data on whether or not there was a sustained drought in the Amazon during the 97/98 El Nino?

I was living in Bahia at the time, and the drought there was quite extraordinary.  As I recall, the rains didn't come back until 1999.  Even the cactus turned brown and died.  There was not a speck of green as far as the eye could see.

After that, we had good enough rains until 2011.  In the meantime, the city I lived in (Vitoria da Conquista) had doubled in size to roughly 400,000, and city water was available only during certain hours of the evening, and not every day.

It is not only the cerrado south of the Amazon that is dependent on transpiration from the Amazon rainforest, but also the sertão of the northeast, the Pantanal, and the farmland in southern Brazil because the flow of water vapor is from the Amazon all the way down to Argentina.

In fact, if the Amazon driesout, nearly all of eastern South America will be in huge trouble.

[JimD]

Tenney

The answer is yes there was.

Google

Amazon drought 1998

and you will get dozens of articles and research papers.  The last 3 big droughts were 1998, 2005 & 2010.  One could naturally be concerned about a drought with the coming El Nino.

[jai mitchell]

Jeff Masters at Wunderblog has a good post on this from 2010

http://www.wunderground.com/blog/JeffMasters/amazon-rainforest-recovering-from-its-second-100year-drought-in-5-yea

The importance of the Amazon to Earth's climate
We often hear about how important Arctic sea ice is for keeping Earth's climate cool, but the Amazon may be even more important. Photosynthesis in the world's largest rainforest takes about 2 billion tons of carbon dioxide out of the air each year. However, in 2005, the drought reversed this process. The Amazon emitted 3 billion tons of CO2 to the atmosphere, causing a net 5 billion ton increase in CO2 to the atmosphere--roughly equivalent to 16 - 22% of the total CO2 emissions to the atmosphere from burning fossil fuels that year. According to Phillips et al., 2009, "The exceptional growth in atmospheric CO2 concentrations in 2005, the third greatest in the global record, may have been partially caused by the Amazon drought effects documented here." The Amazon stores CO2 in its soils and biomass equivalent to about fifteen years of human-caused emissions, so a massive die-back of the forest could greatly accelerate global warming. In late 2009, before the 2010 drought, the World Wildlife Federation released a report, Major Tipping Points in the Earth's Climate System and Consequences for the Insurance Sector,(link:  http://www.worldwildlife.org/climate/Publications/WWFBinaryitem14354.pdf  )which suggested that odds of extreme 2005-like droughts in the Amazon had increased from once every 40 - 100 years, to once every 20 years. The study projected that the extreme droughts would occur once every two years by 2025 - 2050. This year's drought gives me concern that this prediction may be correct. The occurrence of two extreme droughts in the past five years, when no El Niño conditions were present and record warm Atlantic sea surface temperatures occurred, are suggestive of a link between global warming and extreme Amazon drought. If the climate continues to warm as expected, the future health of Earth's greatest rainforest may be greatly threatened, and the Amazon may begin acting to increase the rate of global warming. According to Rosie Fisher, a scientist at the National Center for Atmospheric Research in Boulder, Colorado who specializes in interactions between climate and forests, "I'm genuinely quite alarmed by this. In some ways it kind of reminds me of when they figured out than the Greenland ice sheet was melting much faster than the climate models predicted it would."