The
conventional wisdom has always been that the vast forests covering much of our
planet must be offsetting a great amount of anthropogenic carbon emissions. CO2
is an essential part of the photosynthetic process so an abundance of it would
“logically” provide a surplus of resources for the forest and increase rates of
photosynthesis. Generally, unless other limiting factors are present, this has proven to be true. Rates of CO2
uptake generally increase in plants when exposed to higher
atmospheric concentrations of the gas. However, in addition
to the fact that CO2 release is greatly outpacing even this
increased uptake, we may be damaging and using these forests to the point that
they are no longer net carbon sinks.
A
recent article in Nature magazine describes more recent measurements of
atmospheric carbon over arguably the world’s most iconic forest, the Amazon. According
to the research paper, the forest can vary its uptake from .02±22 Pg of carbon
during one drought year to .30±.10 Pg of C during a relatively wet year. To put
this in perspective, a petagram is one quadrillion grams of carbon. The
variation alone in carbon uptake is equal to the weight of nearly 43 million
average sized African Elephants. During the dry year, carbon released from the
forest actually greatly exceeded the uptake. Forest fires (both natural and
those started to clear forest for agriculture) released .48±.18 Pg more than
the forest absorbed. Even during the wetter year uptake and release were only
approximately even, with the average actually favoring carbon release. Given
that the Amazon absorbed an average of .4 Pg of carbon every year for the two
decades before 2005, this data is showing a potentially huge problem with our
reliance on the world’s forests as carbon sinks.
Every
year, humans release approximately 9 Pg of carbon. This is about 3 and a half
times the amount of carbon sequestered by all of the Earth’s forests (2.6±.7
Pg). Development of the third world is going to conflict with the conservation
of the existing great forests, and the widespread use of slash and burn agriculture
has the potential to throw the already damaged balance of atmospheric CO2
out the window. Conservation of the Amazon is now not only a matter of saving
the incredible amount of biological diversity, but an important part of
controlling greenhouse gas levels in the atmosphere.
Published by Stephen O'Brien
Published by Stephen O'Brien
The amount of carbon is absolutely astonishing; the scale of quadrillion grams and the variation of carbon uptake being equivalent to 43 million African elephants is insane. And it is shocking how much people release with slash and burning of forests, there's no wonder about how CO2 levels are so high; and there's definitely no way that we can hope for plants to reuptake it all to undo the mess. Really astonishing numbers here.
ReplyDeleteNicole Peterkin
The scale of things is almost impossible to wrap your head around. I can't even imagine how much area those 43 million elephants would cover. Increases levels of CO2 and other greenhouse gases are poised to become a serious problem in coming decades. Proposed solutions range from fixation factories to purifying and storing CO2 deep underground, but any real effort toward a solution is very slow in coming.
DeleteStephen O'Brien
This was a great read! It is really interesting to me that the tropical rainforests could actually be adding to the amount of carbon in the air. I wonder if this net output is accelerated by deforestation, or if the rainforests have always fluctuated between being a carbon sink and a carbon source. I would imagine that the reason the forests aren't always acting as carbon sinks has something to do with human intervention, but such a measurement would be very difficult to obtain, as I am not sure when carbon levels started being observed. I think this should really make us aware of where our paper and wood products come from.
ReplyDeleteTim Daly
Left to its own devices the forest is always a net carbon sink for any given year. Intact forest plots measured for almost 30 years put estimates at net .4 Pg of carbon per year fixed (retained as physical plant growth) by the forest. Carbon uptake fluctuates as plants can't undergo photosynthesis as well under drought conditions, but it is almost impossible in nature for a forest to be a carbon source. As far as human effect goes, in addition to the CO2 being measured Carbon Monoxide was also measured and found to be at very high levels. Carbon Monoxide in that area is almost exclusively released by the burning of forest, so it can provide an accurate measure of burning rates when supplemented by satellite data.
ReplyDeleteStephen O'Brien