[THS] Playing Russian roulette with a large portion of the Amazon
The Harder Stuff in news and commentary
ths at psalience.org
Thu Jun 2 15:30:19 CEST 2011
Dr Simon Lewis: we're playing Russian roulette with a large portion of the Amazon
27th May, 2011
The world's largest rainforest is under combined threat from deforestation and
human-caused climate change. In an interview with the Ecologist, tropical forest
expert Dr Simon Lewis explains what is happening
Tom Levitt: Can you explain how the Amazon could start adding more emissions to
the atmosphere than it soaks up?
Dr Simon Lewis: The remaining intact Amazon rainforest isnt currently at equilibrium,
as on average, in a normal year, these forests are getting bigger. That is, carbon
dioxide is being removed from the atmosphere and the carbon incorporated into the
trees. The rate is about 1.5 billion metric tonnes of carbon dioxide per year.
Therefore, these forests are providing an important free service to humanity,
reducing the rate and magnitude of climate change. The exact reasons for this
increase in carbon storage are debated, but the leading candidate is the amount of
carbon dioxide in the atmosphere itself, which is fertilising these forest trees. In a
drought that is severe enough to kill many trees, the dead trees start to rot, returning
the carbon to the atmosphere as carbon dioxide.
These emissions offset some of the usual carbon uptake. So, if the climate changes in
the Amazon to a regime with more severe and frequent droughts, then the dead
trees may be numerous enough to cancel-out all the usual carbon uptake, and
perhaps even add carbon dioxide to the atmosphere. This could happen if the
Amazon starts to suffer from three or more severe droughts per decade. Worse still,
this could set into motion a positive feedback mechanism, by which the droughts
could lead to greater emissions of carbon dioxide, further exacerbating the problem,
which could lead to the loss of rainforest in some areas of the Amazon. Our current
emission pathways are essentially playing Russian roulette with a substantial portion
of the worlds largest rainforest.
TL: What is the biggest cause of deforestation in the Amazon?
SL: It is difficult to define single causes of deforestation, and care must be taken to
note not only the proximate drivers, for example, forest removal for soya bean
production, but also the ultimate drivers of such decisions, for example, economic
drivers like the price of agricultural commodities, and policy choices, such as
government infrastructure projects that open areas to become within reach of
national and international markets. The key proximate driver of deforestation in the
Amazon is agricultural expansion for cattle and soya itself allied to road-building.
However, over the past 6 years the deforestation rate in the Amazon has decreased
substantially (by about 50 per cent in Brazil), driven by law enforcement, the
intensification of agricultural production on land that has already been deforested
and campaigns by NGOs to stop companies expanding production into rainforest
TL: Could the Amazon, on its own, cause runaway climate change?
SL: If the forests of the Amazon were all removed, then the repercussions would be
felt worldwide in terms of the disruption of usual climatic regimes. In terms of climate
change, this would perhaps add 100-200 billion tonnes of carbon to the atmosphere.
We humans currently emit about 10 billion tonnes, so we would add 10-20 years
worth of todays level of emissions. This hypotheically shows that it will be the direct
emissions of fossil fuels that will most strongly determine the rate, magnitude and
impacts of climate change this century and beyond. Furthermore, given that the
rainforest has persisted in some form in what is now the Amazon region for at least
55 million years, the rainforest will probably persist under projected climate change if
greenhouse gas emissions are reduced. The key problem is the climate change-direct
human impact interaction, which is novel in the history of the Amazon forest as
humans only arrived there about 12,000 years ago.
TL: Can you explain what you mean by the climate change-human impact
SL: It can take several forms. Firstly, droughts allow more forest to be burnt and then
cleared, as it is possible for more land to be burnt when it is dry. Secondly, people
use fire as a land management tool, but in severe droughts fires can get out of
control and encroach forests. Thirdly, degraded forests, like logged-over or fire-
impacted forest, can dry-out more easily, which make them more susceptible to fires.
Fourthly, large-scale deforestation can reduce local rainfall, which could exacerbate
future droughts if deforestation continues. This complex set of interactions could see
much larger impacts on the forest compared to analysing any one trend, like climate
change or deforestation rates, in isolation.
TL: Out of the Amazon rainforest, Arctic and Antarctic ice-caps and Tundra
permafrost - which is closest to its 'tipping point'?
SL: The Arctic sea-ice will certainly disappear, as the trend is already clear and
physical mechanism air temperature warming will continue. So in terms of an
irreversible shift in the average state, then the sea-ice is the place to watch. For both
the Amazon and the Tundra the situation is much more complex, as they both
include lots of living organisms, which adapt to changing conditions. For example,
trees might die due to droughts, but more drought-tolerant species will likely take
their place, so living tipping points are much more difficult to predict than those
more purely physical parts of the Earth system.
TL: What about rainfall? If the Amazon starts to die back will rainfall in neighbouring
countries and further afield also be affected?
SL: There is no good evidence so far that the Amazon is drying out. With a warming
climate we expect more rainfall, as warmer air can hold more moisture, and there
would also be more evaporation. The recent Amazon droughts were due to a change
in the distribution of rain across the year, not the total amount. The problem was that
the driest part of the year got drier. However, the Amazon forest does re-cycle
rainfall, so very large-scale deforestation could cause reduced rainfall over the
TL: Previous research that used NASA satellite data said the droughts had little
negative impact on the Amazon and that the forest was resilient to the droughts.
How did you research come to different conclusions?
SL: There has been some debate amongst scientists about what satellites that
measure forest greenness see regarding droughts in the Amazon, and what that
greenness measure actually means. The assumption is that more greenness means
more forest growth, but it could mean a loss of canopy leaves (exposing those below)
or a flush of new leaves. Some scientists suggested that the Amazon got greener
during the 2005 Amazon drought, but others argued that this was largely an artefact
due to the corruption of the signal due to the amount of burning in the Amazon
during the drought: with appropriate filtering of the data another group of scientists
showed that there was no green-up. For the 2010 drought new results show that the
forest did not green up in, indeed the canopy went brown over large areas in this
more severe drought. The most likely explanation is that the forests start the drought
with clear skies and therefore lots of sun and plenty of water in the soils and do grow
well but in an extended drought tree growth slows and eventually stops as water
runs out. Ground measurements shows that growth is not largely affected over an
entire year, but mortality increases strongly with drought intensity. Therefore caution
is required regarding this type of satellite data, as it may not be detecting the most
important ecological process.
TL: Do you believe more evidence about an Amazon die-back, could be enough to
push momentum towards a global deal and emission cuts?
SL: No. The lack of a global deal on carbon emission and the failure to cut global
emissions is due to long-term nature of the problem, the fact that it makes no sense
for any one country to make concessions unless most others do, the centrality of fossil
fuels to almost all aspects of modern life, and the immensely powerful vested
interests in government and industry against taking meaningful action. In essence,
countries and fossil fuel companies will not agree to what they view as trillions of
dollars sitting under the ground, and leaving it there in perpetuity. They want the
money now regardless of the longer-term impacts.
TL: Are their any geoengineering solutions that could be applied to negate any die-
back of the Amazon rainforest?
SL: There are currently no geoengineering proposals that are sufficiently researched
to assess whether they are a good idea or not, and on which ecosystems they may
have positive or negative impacts. However, one lesson from recent research is that
given that carbon dioxide gives some protection to plants from the impacts of
drought (as plants increase the efficiency with which they utlise water when growing
under higher carbon dioxide conditions), but other greenhouse gases do not provide
this protective effect, which suggests that we should make stronger efforts to quickly
and substantially reduce non-CO2 greenhouse gas emissions, such as methane,
nitrous oxide, and black carbon.
TL: You yourself have been at the centre of media mis-reporting on climate change -
are the media now getting it right? Or is the scientific evidence being lost in
controversy and political arguments?
SL: No they arent getting coverage right. Unfortunately the media are mostly
ignoring the science, or selecting stories to fit their editorial prejudices on climate
change. For example, scientific papers that may appear to underplay the severity of
climate change will be reported in the Telegraph and Times, in the UK, and Wall
Street Journal in the US, but these newspapers largely do not cover those stories that
report the more alarming new results. Similarly, those newspapers with editorial lines
that climate change should be taken seriously have better coverage, but do choose
differing stories to cover. So the stories themselves may be reasonable, but the
selection is highly skewed towards confirming already entrenched positions.
Is the Amazon heading towards a 'tipping point' as a carbon sink?
27th May, 2011
The world's largest rainforest is ravaged by deforestation and two recent droughts. If they continue, says one expert, the Amazon risks entering a period where it can no longer be relied upon to absorb more greenhouse gas emissions than it produces
The Amazon rainforest is facing the combined threat of increasingly severe droughts and continuing deforestation that could wipe out large areas of the forest, warned a respected forest scientist this week.
In a groundbreaking study published in the journal Science earlier this year, Dr Simon Lewis, of Leeds University, found the 2010 drought in the Amazon was more widespread than the 2005 one, previously thought of as a once-in-a-century event.
In an interview with the Ecologist he now says if greenhouse gases are the cause of the severe droughts and such droughts are repeated three or more times a decade it could set in motion a vicious cycle by which droughts would lead to higher emissions of carbon dioxide from rotting trees and, in turn, potentially more frequent and severe droughts.
* Read the interview in full
'If the climate changes in the Amazon to a regime with more severe and frequent droughts, then the dead trees may be numerous enough to cancel-out all the usual carbon uptake, and perhaps even add carbon dioxide to the atmosphere...our current emission pathways are, to be blunt, playing Russian roulette with a substantial portion of the worlds largest rainforest,' he says.
Dr Lewis says much of the forest has survived past climatic changes over millions of years, but what is different now is the interaction of other human interventions, such as deforestation, which together poses an even greater threat to the Amazon rainforest.
For example, he explained, droughts allow more forest to be burnt and cleared, while logged forest dry-out more easily making them more susceptible to fires. To make matters worse, large-scale deforestation can reduce local rainfall and potentially exacerbate future droughts.
Despite the fears over large-scale losses to the Amazon rainforest and the demise of its role as a major carbon sink, Dr Lewis says it was not possible to predict the loss of large areas of rainforest, unlike, say, the disappearance of the Arctic sea-ice.
'The Arctic sea-ice will certainly disappear, as the trend it already clear and physical mechanism air temperature warming will continue. So in terms of an irreversible shift in the average state, then the sea-ice is the place to watch.
'For both the Amazon and the Tundra the situation is much more complex, as they both include lots of living organisms, which adapt to changing conditions. For example, trees might die due to droughts, but more drought-tolerant species will likely take their place, so living tipping points are much more difficult to predict than those more purely physical parts of the Earth system,' he says.
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