Could Climate Change And Deforestation Spark Amazon Dieback?

Could Climate Change And Deforestation Spark Amazon Dieback? Amazon wildfires in Rondonia, Brazil, 24 August 2019. Credit: EFE News Agency / Alamy Stock Photo.

Last summer, the Amazon rainforest was in the news again for all the wrong reasons. Deforestation rates are on the rise under the leadership of Brazilian President Jair Bolsonaro and 2019 brought the highest number of forest fires in almost a decade.

For the global climate, this is a cause for concern. The Amazon plays a vital role in the climate system, recycling water to help sustain rainfall in the region and drive atmospheric circulations in the tropics. In addition, destroying the forest would have a major impact on atmospheric CO2.

Tipping points

This article is part of a week-long special series on “tipping points”, where a changing climate could push parts of the Earth system into abrupt or irreversible change

It is estimated that the remaining intact Amazon rainforest currently absorbs 5-10% of human CO2 emissions, helping to slow climate change. Deforestation removes this sink of carbon and replaces it with a source, which would make the already challenging Paris climate targets impossible.

There are many legitimate reasons to argue for greater protection of the Amazon rainforest. But even if the rate of direct human-deforestation slows again, could the forest disappear because of climate change?

Climate change-induced Amazon forest dieback

The recent Amazon fires have sparked claims that burning of the rainforest will have a significant impact on the amount of oxygen in the air that we breathe.

This is one aspect of Amazon destruction that we need not worry about. The Amazon rainforest contains about 15% of the total carbon stored worldwide in vegetation. If that 70bn tonnes of carbon was released, it would combine with oxygen in the air and be released largely as CO2. But because oxygen makes up as much as 21% of our atmosphere, this would only reduce the oxygen concentration by less than 0.01%.

However, there are much more pressing reasons to be worried about the destruction of the Amazon rainforest – not least that it has been touted as a possible climate tipping point.

Glossary: Carbon vs. CO2: The terms “carbon” and “CO2" are often used interchangeably, but there is an important difference. Carbon is an element, while CO2 is a compound containing one carbon atom with two oxygen atoms.

This is due in part to the climate model simulations carried-out by my research group at the Met Office Hadley Centre for Climate Prediction and Research in the late 1990s and early 2000s. We included a representation of how vegetation types might shift in response to climate change and how this could feedback to affect the rate of climate change.

Alarmingly, our first coupled model projections saw the predicted Amazon forest “dieback” under climate change – even though we had not included direct human-caused deforestation and fires in our simulations.

This modelling outcome was stark, but it turned out to be the result of a subtle interplay of different feedback mechanisms.

First and foremost, our Amazon rainforest died because the climate model predicted severe warming and drying under a “business as usual” emissions scenario called “IS92a”. That reduced the extent of the forest that can be sustained in a changing climate. With less forest there was less efficient recycling of the diminishing rainfall in the region, which led to further warming and drying, and further reduction in forest area.

But it was not as simple as that. As the climate change was being driven largely by increases in CO2, there were also counteracting direct effects of CO2 on the forests.

Higher levels of CO2 in the atmosphere have a “fertilisation” effect on plants and trees, boosting photosynthesis and promoting growth. Under elevated CO2, plants also tend to use water more efficiently, such that they need less water for a given amount of photosynthesis.

Could Climate Change And Deforestation Spark Amazon Dieback?

Where there is adequate soil water and nutrients, this effect manifests itself as increased carbon uptake by a forest. However, where there is a limited supply of water, the increased efficiency will manifest itself as reduced evapotranspiration from trees. This provides protection from reductions in rainfall, but at the cost of causing further increases in local surface temperature as a result of reduced evaporative cooling.

In our model, the evolution of the Amazon rainforest was at the mercy of this competition between the largely negative impacts of climate change and the largely positive impacts of increasing CO2.

Our model suggested that the CO2 effects had dominated over the 20th century – leading to a carbon sink in the intact rainforest. However, the model had the negative climate effects eventually winning out – resulting in an abrupt dieback of the Amazon rainforest from about 2040 onwards, when global warming had reached about 3C in this projection.

You can see this in the chart below, which shows how our model projected vegetation in the Amazon could change as the climate warmed through to 2100. It shows an Amazon dominated by trees (solid line) for decades, but then the fraction of the region that is covered by trees drops off dramatically through the middle of the 21st century. It is then replaced with grasses (dashed lines) and bare soil (dashed and dotted line).

Could Climate Change And Deforestation Spark Amazon Dieback? Modelled evolution of Amazonian vegetation under the IS92a business-as-usual emissions scenario. Reprinted by permission from Springer. Cox et al. (2004) Amazonian forest dieback under climate-carbon cycle projections for the 21st century, Theoretical and Applied Climatology

Good and bad news

Our findings were stark. However, recent research hints that Amazon forest may be more resilient to climate change. A lot of relevant research has flowed under the bridge since we published that dieback scenario in 2000 – some good news and some bad news for the forest.

First, the good news. It now seems that climate change is unlikely to be as damaging to the Amazon rainforest as we originally feared. In 2013, we discovered that the year-to-year variation in the annual increase in atmospheric CO2 allows us to estimate the sensitivity of tropical carbon sinks to climate change.

Global CO2 concentration has been increasing year-on-year due to increasing CO2 emissions from human activities, most notably fossil fuel burning, deforestation and cement production. But if you take out that long-term trend you find a variation in the CO2 growth-rate that correlates well with the climate variations in the tropics associated with the El Niño-Southern Oscillation. This signal, therefore, shows us something about how sensitive tropical land carbon is to climate variations.

We can use an ensemble of climate-carbon cycle models to relate this short-term sensitivity to the longer-term sensitivity of tropical ecosystems to climate change – to create a so-called “emergent constraint”. The across-model relationship allows us to convert an observation of the variation in the CO2-growth-rate in the real world, into an improved estimate of the sensitivity of tropical land carbon to future climate change.

The resulting emergent constraint on the sensitivity of tropical land carbon to global warming indicates a negative impact, with warming alone leading to carbon loss of about 50bn tonnes of carbon per degree of global warming in the tropics. However, the magnitude of the effect is about a third as large as seen in our original Amazon dieback projection.

But there is also some less optimistic news. It now also seems that the CO2-fertilisation effect is unlikely to be as large as many early models assumed. This is because first and second generation climate-carbon cycle models did not include nutrient limitations on forest growth.

In the real world, the growth of vegetation is often limited not just by water and CO2, but by nutrients. In most regions the key limiting nutrient is nitrogen, but in tropical forests phosphorus or other micronutrients limit tree growth. These nutrient limitations will cap the CO2 fertilisation of plant growth, most likely below that seen in early climate-carbon cycle models.

This would leave tropical forest more vulnerable to the negative impacts of climate change than our original dieback scenario, even though those climate effects may themselves be less negative than originally feared.

So what’s the overall prognosis for climate change driven Amazon dieback?

The latest Earth system models show limited evidence of Amazon forest dieback in the absence of direct human deforestation. A handful of models show reductions in Amazonian forest cover due to climate change, but most models show increasing forest cover due to CO2 fertilisation.

None of these models include phosphorus limitations or forest fires, though, so the jury is still out. However, personally, I am less concerned about climate-change driven Amazon dieback than I was when we published our study in 2000.

Greater reason to be concerned about direct human deforestation

Rather ironically, this makes me more concerned about increasing rates of deliberate deforestation in Amazonia. It might even be argued that there is less value in conserving a forest if that forest will subsequently be damaged by climate change. On the contrary, greater resilience of the Amazon rainforest to climate change provides additional reasons to save it for the future.

Could Climate Change And Deforestation Spark Amazon Dieback?View across canopy of Amazon rainforest with mist at dawn. Credit: David Tipling Photo Library / Alamy Stock Photo.

The Amazon rainforest sustains its own climate by recycling water to the atmosphere, which maintains rainfall and reduces the length of dry seasons. Deforestation undermines those regulatory mechanisms and may, ultimately, lead to a tipping point.

This, in combination with the dry season becoming long enough to permit regular natural fires, could see the forest transition to a permanent savannah. This would be characterised by a mixed tree and grassland system with an open canopy that allows the soil to become much hotter and drier, as well as store much less carbon.

Therefore, the twin pressures of deforestation and climate change on the Amazon rainforest remain a great concern. We are unlikely to know the vulnerability of the rainforest to climate change with any confidence until it is too late. However, we are sure that human-caused deforestation reduces the resilience of the forest to climate change and other stressors.

Many had thought the problem of Amazonian deforestation was on the path to being solved. The rate of deforestation dropped from a peak in 2004 of 28,000 square kilometres (km2) – equivalent to removing an area of forest almost the size of Belgium each year – to less than a fifth of that rate by 2014.

But that is all in the past now. With deforestation on the up and global warming continuing, there are, once again, multiple threats to the longevity of the Amazon rainforest.

About The Author

Prof Peter Cox, professor of climate system dynamics at the University of Exeter and a lead author on the “global carbon and other biogeochemical cycles and feedbacks” chapter of the forthcoming sixth assessment report (AR6) of the Intergovernmental Panel on Climate Change (IPCC).

This article originally appeared on Carbon Brief

Related Books

Climate Change: What Everyone Needs to Know

by Joseph Romm
0190866101The essential primer on what will be the defining issue of our time, Climate Change: What Everyone Needs to Know® is a clear-eyed overview of the science, conflicts, and implications of our warming planet. From Joseph Romm, Chief Science Advisor for National Geographic's Years of Living Dangerously series and one of Rolling Stone's "100 people who are changing America," Climate Change offers user-friendly, scientifically rigorous answers to the most difficult (and commonly politicized) questions surrounding what climatologist Lonnie Thompson has deemed "a clear and present danger to civilization.". Available On Amazon

Climate Change: The Science of Global Warming and Our Energy Future second edition Edition

by Jason Smerdon
0231172834This second edition of Climate Change is an accessible and comprehensive guide to the science behind global warming. Exquisitely illustrated, the text is geared toward students at a variety of levels. Edmond A. Mathez and Jason E. Smerdon provide a broad, informative introduction to the science that underlies our understanding of the climate system and the effects of human activity on the warming of our planet.Mathez and Smerdon describe the roles that the atmosphere and ocean play in our climate, introduce the concept of radiation balance, and explain climate changes that occurred in the past. They also detail the human activities that influence the climate, such as greenhouse gas and aerosol emissions and deforestation, as well as the effects of natural phenomena.  Available On Amazon

The Science of Climate Change: A Hands-On Course

by Blair Lee, Alina Bachmann
194747300XThe Science of Climate Change: A Hands-On Course uses text and eighteen hands-on activities to explain and teach the science of global warming and climate change, how humans are responsible, and what can be done to slow or stop the rate of global warming and climate change. This book is a complete, comprehensive guide to an essential environmental topic. Subjects covered in this book include: how molecules transfer energy from the sun to warm the atmosphere, greenhouse gases, the greenhouse effect, global warming, the Industrial Revolution, the combustion reaction, feedback loops, the relationship between weather and climate, climate change, carbon sinks, extinction, carbon footprint, recycling, and alternative energy. Available On Amazon

From The Publisher:
Purchases on Amazon go to defray the cost of bringing you InnerSelf.comelf.com, MightyNatural.com, and ClimateImpactNews.com at no cost and without advertisers that track your browsing habits. Even if you click on a link but don't buy these selected products, anything else you buy in that same visit on Amazon pays us a small commission. There is no additional cost to you, so please contribute to the effort. You can also use this link to use to Amazon at any time so you can help support our efforts.

 

enafarzh-CNzh-TWdanltlfifrdeiwhihuiditjakomsnofaplptruesswsvthtrukurvi

follow InnerSelf on

facebook icontwitter iconyoutube iconinstagram iconpintrest iconrss icon

 Get The Latest By Email

Weekly Magazine Daily Inspiration

LATEST VIDEOS

can we cool the planet 7 22
Can We Cool The Planet?
by Robert Jennings, InnerSelf.com
Climate change has emerged as one of the most pressing challenges of our time. Over the past century, human activities…
i5w7rk3a
The Devastating Impact of 3C Global Warming
by Robert Jennings, InnerSelf.com
Global warming is a pressing issue that poses severe threats to our planet and all its inhabitants. In recent years,…
The Great Climate Migration Has Begun
The Great Climate Migration Has Begun
by Super User
The climate crisis is forcing thousands around the world to flee as their homes become increasingly uninhabitable.
The Last Ice Age Tells Us Why We Need To Care About A 2℃ Change In Temperature
The Last Ice Age Tells Us Why We Need To Care About A 2℃ Change In Temperature
by Alan N Williams, et al
The latest report from the Intergovernmental Panel on Climate Change (IPCC) states that without a substantial decrease…
The Caspian Sea Is Set To Fall By 9 Metres Or More This Century
The Caspian Sea Is Set To Fall By 9 Metres Or More This Century
by Frank Wesselingh and Matteo Lattuada
Imagine you are on the coast, looking out to sea. In front of you lies 100 metres of barren sand that looks like a…
Five Climate Disbeliefs: A Crash Course In Climate Misinformation
The Five Climate Disbeliefs: A Crash Course In Climate Misinformation
by John Cook
This video is a crash course in climate misinformation, summarizing the key arguments used to cast doubt on the reality…
The Arctic Hasn't Been This Warm For 3 Million Years and That Means Big Changes For The Planet
The Arctic Hasn't Been This Warm For 3 Million Years and That Means Big Changes For The Planet
by Julie Brigham-Grette and Steve Petsch
Every year, sea ice cover in the Arctic Ocean shrinks to a low point in mid-September. This year it measures just 1.44…
What Is A Hurricane Storm Surge and Why Is It So Dangerous?
What Is A Hurricane Storm Surge and Why Is It So Dangerous?
by Anthony C. Didlake Jr
As Hurricane Sally headed for the northern Gulf Coast on Tuesday, September 15, 2020, forecasters warned of a…

LATEST ARTICLES

global boiling is here 7 29
U.N. Warns: The Era of Global Boiling Has Arrived
by Robert Jennings, InnerSelf.com
The world faces an unprecedented climate crisis as temperatures soar and heat records are shattered across the globe.
amoc map 7 26
The Unseen Tipping Point: Understanding the Potential Impact of an AMOC Shutdown
by Robert Jennings, InnerSelf.com
The Unseen Tipping Point: Understanding the Potential Impact of an AMOC Shutdown Have you ever heard of the Atlantic…
can we cool the planet 7 22
Can We Cool The Planet?
by Robert Jennings, InnerSelf.com
Climate change has emerged as one of the most pressing challenges of our time. Over the past century, human activities…
global hungry 7 22
The Rising Tide of Global Hunger: Pandemic, Climate & Conflict Fuel Food Insecurity
by Robert Jennings, InnerSelf.com
In recent years, the world has witnessed a distressing surge in global hunger, painting a bleak picture of food…
keeping cool 7 20
Beat the Heat: Your Guide to Staying Safe in Extreme Temperatures
by Robert Jennings, InnerSelf.com
As the temperatures rise during the summer months, it's important to be aware of the risks associated with extreme heat.
i5w7rk3a
The Devastating Impact of 3C Global Warming
by Robert Jennings, InnerSelf.com
Global warming is a pressing issue that poses severe threats to our planet and all its inhabitants. In recent years,…
how hot is too hot 7 19
How Hot is Too Hot? The Risks of Extreme Heat on the Human Body
by W. Larry Kenney, Penn State et al
The answer goes beyond the temperature you see on the thermometer. It’s also about humidity. Our research is designed…
european heatwave 7 18
European Heatwave: What’s Causing It And Is Climate Change To Blame?
by Emma Hill and Ben Vivian, Coventry University
Europe is currently in the midst of a heatwave. Italy, in particular, is expected to face blistering heat, with…

Imagine you are on the coast, looking out to sea. In front of you lies 100 metres of barren sand that looks like a beach at low tide with gentle waves beyond. And yet there are no tides.

Permanent flooding has become commonplace on this low-lying peninsula, nestled behind North Carolina’s Outer Banks. The trees growing in the water are small and stunted. Many are dead

Environmental campaigners in Alaska and across the country are cautiously celebrating the Biden administration's Tuesday decision to suspend some fossil fuel drilling leases that were sold in the...

Researchers have identified more than 1,700 large sources of methane in an oil field that spans Texas and New Mexico, with about half of them likely being malfunctioning equipment.

The Reuters Hot List of “the world’s top climate scientists” is causing a buzz in the climate change community. Reuters ranked these 1,000 scientists

Sea level rise isn’t the only way climate change will devastate the coast. Our research, published today, found it is also making waves more powerful, particularly in the Southern Hemisphere.


 Get The Latest By Email

Weekly Magazine Daily Inspiration

New Attitudes - New Possibilities

InnerSelf.comClimateImpactNews.com | InnerPower.net
MightyNatural.com | WholisticPolitics.com | InnerSelf Market
Copyright ©1985 - 2021 InnerSelf Publications. All Rights Reserved.