Hello and welcome to Just Have Another Think - our twice monthly look at the environmental
ecological and social impacts of our 21st century climate emergency. Back in March of this year
a research paper was published in a journal called Frontiers in Forests and Global Change.
The paper's objective was to accurately assess the extent to which the Amazon basin
is now acting either as a carbon sink or a carbon source as a result of sustained human activities
in the region over recent decades. It referenced well over a hundred previous research papers
each focused on a specific aspect of the intricate interconnections and dynamics of
the amazon ecosystem and its interaction with the local and global atmosphere.
Until recently climate research in the Amazon has been overwhelmingly focused only on the cycling of
carbon dioxide and its implications for the global climate. What hasn't been so well considered
are the climate impacts of other non-co2 variables including methane, nitrous oxide,
black carbon particles, evapotranspiration, and albedo. All these things respond dynamically
to local events like fire, land use change, infrastructure development, and storms, and
to global events like warming, drying and even to some extent to El Ninos, which from time to time
warm the tropical Atlantic. Net carbon dioxide exchange between the Amazon and the atmosphere is
a balance of CO2 intake by weathering and primary production - which is basically photosynthesis as
plants and trees grow - and CO2 output as a result of respiration, decomposition of plant residues
in soil and water, and the burning of biomass. A 2012 study estimated that the Amazon at that time
held between 150 and 200 billion tons of carbon. Between 1990 and 2007 the best research suggests
that the Amazon was sequestering about half a billion tonnes of carbon from atmospheric CO2
every year. Since then land conversion, drought and sustained forest degradation
have reduced the amount of above-ground biomass by a third. The consequence of that is that between
2010 and 2017 the soils of the Amazon basin have been transformed from a net carbon store to a net
emitter of at least 200 million tons of carbon per year. The complex river systems of the Amazon
are the lifeblood of the region's ecosystem and biodiversity they transport essential nutrients
and drain carbon and sediment out to the Atlantic ocean, which acts as a massive carbon sink. The
sediment settles onto the ocean floor and the carbon gets used in the process of photosynthesis
in aquatic life like phytoplankton that eventually dies and also settles on the bottom. It used to be
assumed that the vast majority of organic matter from trees and vegetation got swept out of the
Amazon and permanently stored in the oceans via this system, but more recent studies have shown
that the increase in the levels of this waste material could be fuelling as much as 50 percent
of the CO2 outgassing from the rivers before they reach the coast. There are
now more than 190 dams on the river network as well, with another 246 hydroelectric reservoirs
planned or currently under construction. The dam's wreck migration routes for many species,
change the temperature of the rivers, reduce water quality, and alter the frequency and timing of
essential flooding across wetlands and freshwater ecosystems. As the sediment moves downstream,
some of the carbon content is deposited in floodplain lakes. Dams are disrupting that
movement as well, decreasing river productivity and harming fisheries. Hydroelectric plants
are touted as a low carbon alternative to fossil fuels, but in fact research suggests
that their net climate impact may be greater than the power plants they replace.
Older studies of Amazonian rivers and wetlands suggest they were a source of about 470 million
tons of carbon released into the atmosphere every year. Those studies have now been expanded
to include streams, small rivers, lakes, flood plains in different tributaries, and the lower
section of the Amazon river. And that expanded assessment has increased estimates of carbon
dioxide emissions from the Amazon water system four-fold to 1.8 billion tons of CO2 per year.
Tropical forests are a globally important source of nitrous oxide. Although it's not a carbon-based
molecule it is nevertheless an impactful greenhouse gas that's 265 times more potent
than CO2. Climate studies from all of the tropical regions suggest that there are ebbs
and flows of nitrous oxide depending on what's happening in a local area. As we humans have
burnt more and more forest land to clear space for agriculture and mining that burning biomass has
released very large quantities of nitrous oxide. Reservoir construction in the Amazon may also be
increasing nitrous oxide emissions by as much as eighty percent. According to one research paper
the limited research that's been carried out so far indicates that the Amazon basin now emits
1.9 million tons of this greenhouse gas each year, and because of its potency that's equivalent to
nearly half a billion tons of carbon dioxide. Methane doesn't last as long in the atmosphere as
carbon dioxide. It's relatively quickly broken down by what are known as hydroxyl radicals.
But while it's up there it's a far more potent greenhouse gas, more than 80 times more impactful
over a 20-year period and about 28 times more over the course of a century. Soils and sediments can
both produce and consume methane. Well-drained upland soils in the Amazon currently take in
between one and three million tons each year, but waterlogged soils, sediments and vegetation
release significant amounts of methane. It's also a product of activity by indigenous plants
and by native animals and insects. The rapidly increasing quantity of livestock now being reared
on vast tracts of deforested Amazon land is also massively adding to that methane output.
Even more land is being cleared for agriculture like soybean production for animal feed,
and of course for the logging industry. Both those activities tend to compact the soil which
decreases its ability to store methane. Cattle ranching and soybean planting are especially
interconnected self-reinforcing industries. Once the ranchers have secured and exploited a frontier
of newly cleared pastureland they sell that land to the soy producers for a nice tidy profit and
then move on to slash and burn another zone and establish a new frontier deeper into the basin.
And so the demise of forestry land is continued on and on through these commercial arrangements. And
as a macabre additional kicker the smouldering fires from all that deforestation produce
large quantities of carbon monoxide, and carbon monoxide is very good at removing
those hydroxyl radicals that break down methane in the atmosphere. The result of that is that
the average lifetime of atmospheric methane is extended. Then there's the flooding that happens
as a direct result of all the dam construction we just talked about. That flooding decreases oxygen
levels in the local aquatic ecosystem, which means more organic matter decomposes without
oxygen. The product of that anoxic process is yet more methane. Studies show that the effect is 10
times stronger in the tropical regions than it is in dams built in temperate parts of the world.
Once the paper's researchers had extrapolated all the available field study results
they found that the Amazon now emits about 43 million tons of methane every year which
is about eight percent of the global total and the equivalent of between one and four billion
tons of co2 depending on what time scale you measure its atmospheric presence over.
Black carbon is mainly produced by the incomplete combustion of fossil fuels biofuels and biomass.
There's no fixed global warming potential number relative to carbon dioxide, so it's difficult to
be precise about its atmospheric influence, but research does show that 40 percent of global
open fire emissions come from forest burning in the tropics. And carbon emissions of about a
third of a million tons come from black carbon in Latin America. About 140 000 tons of that
is due to forest degradation and deforestation across South America. Despite the fact that
the Amazon is undoubtedly a large contributor to this figure, management and minimization of black
carbon is not included in Brazil's nationally determined contributions towards the Paris
agreement. Nor does that look likely to change at the COP 26 conference in November this year. The
indirect impacts of black carbon particulates on things like cloud formation, which in turn
affects atmospheric warming, get worse as more biomass is burnt down. At low rates of burning,
black carbon in the atmosphere actually has a modest dimming and cooling effect.
But that switches to a strong warming influence as the atmospheric concentrations increase. And as
a little extra gut punch, black carbon emissions have also been found to be speeding up the melting
of glaciers in the Andes by an estimated three percent. That number will certainly
increase as widespread drought intensified burning increases black carbon emissions in the future.
Evapotranspiration is a critical driver of local and regional climate in the amazon.
It provides surface cooling and water recycling and it controls vegetation patterns throughout
the basin. Regional changes in rainfall patterns closely mirror changes in local hydrological
cycles that have happened as a result of land use change. Generally speaking, the more we humans
remove vegetation from the area the more we reduce evapotranspiration. That intensifies surface water
runoff which dries the soils and alters moisture transport dynamics in a way that increases
local temperatures. That effect is particularly pronounced during the dry season. Transpiration is
thought to be an important factor in triggering and sustaining the onset of the wet season,
so a reduction means longer dry seasons, which leads to reduced growth in the secondary forests,
which are in turn more vulnerable to drought stress and at greater risk from fire.
Research has shown that even modest deforestation driven reductions in rainfall
can dry the atmosphere enough to put a region into decline. That results in even more reduction in
rainfall which combines with intense warming to accelerate forest dieback still further. Analysis
of atmospheric water fluxes in the Amazon suggests this self-amplification effect might reduce forest
cover by somewhere between 10 and 13 percent - more than enough to offset the cooling effect
of increased albedo that land clearance might bring about. In the first year of the Bolsonaro
administration nearly 10 000 square kilometers of the Amazon was deforested. That was a 30% increase
over the previous year. Indigenous land rights are being compromised and monitoring and enforcement
agencies are being scaled back or wound down completely, giving more or less free rein
to the land grabbers. Between 2005 and 2015 legal and illegal mining resulted in about 12 000 square
kilometers of unauthorized deforestation beyond mining operation lease boundaries. That's almost
10% of the total Amazonian forest losses during that period. Registered mining interests now
account for more than a million square kilometres of Amazonia, including indigenous land and some
strictly protected areas. The paper concludes that despite uncertainty in their responses to change,
current warming from non-CO2 variables - especially methane and nitrous oxide - largely
offsets, and most likely exceeds, the carbon sink provided by atmospheric CO2 drawdown. The research
also finds that most human impacts are increasing the surface temperature in the rainforest.
The authors argue that simply focusing just on carbon uptake and storage is way too simplistic
and misses a wide range of crucial biogeochemistry of the climate in a rapidly changing amazon basin.
I must admit this was quite a difficult video to compile and produce. Not just difficult from a
technical editorial point of view, but also on a more visceral level in discovering yet more
evidence of the profligate and reckless violence that human beings are capable of inflicting upon
our own and only life support system. I hope it's given you some food for thought,
and I hope it's provided you with some impetus to do whatever you can wherever you are either
by looking at your own lifestyle and purchasing choices or through collective action to put
pressure on elected representatives to influence the direction and urgency of climate mitigation.
Thanks for watching and I'll see you soon