Publié le April 28, 2021
Why do we talk about “runaway” climate change so much? Or the “point of no return”? And “absolute” climate emergency? Where does this idea that “we must not exceed 2°C” come from?
Climate disruption is in no way a linear problem. Some of the consequences of global warming themselves become additional causes of climate disruption. “Vicious circles” of a sort. Scientists call them “positive feedback loops”. But beware, “positive” doesn’t mean that they are positive for the climate. Quite the contrary. It means that they enhance the initial perturbation. Some loops have an amplifying effect and some represent a grave danger: “climate bombs” that could potentially render the climate completely out of control in an irreversible way.
Let’s take a look at six: the albedo effect, ocean currents, forest degradation, water vapor, melting permafrost and methane hydrate release.
Albedo is the measure of a surface’s reflective power. Every surface or object reflects back into space a fraction of the light it receives. It absorbs the rest, raising its own temperature.
The albedo is the proportion of solar energy that is reflected in relation to what is absorbed.
Albedo is different depending on a surface’s color and composition. The lighter the color, the higher the albedo. As snow, clouds and ice are white, they reflect a lot of solar radiation.
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When ice melts as a result of global warming, frozen and snow-covered surfaces decrease in volume. These surfaces are white and reflect the solar radiation due to the albedo effect.
Today, the albedo effect reflects around 30% of the sun’s energy back into space. As white and iced surfaces diminish and even disappear, they are replaced by dark surfaces - such as oceans and land masses, lowering the albedo effect considerably. This increases the temperature of land, oceans and the atmosphere due to higher absorption of the sun’s rays and thermal energy.
Hence the vicious circle: lowering the albedo effect increases the average temperature, causing the ice to melt, which lowers the albedo effect even further. A perfect positive feedback loop.
When the ice shelves and glaciers melt due to global warming, they release a large quantity of fresh water. Fresh water is not as dense as salt water, which means that it remains in the ocean’s surface water longer because it sinks more slowly. This weakens what are known as "downwelling” currents which flow from the ocean’s surface to its depths.
The ocean stores CO2 differently on the surface and in deep water. The deep ocean is the main carbon sink, where it stores 30 to 40 times more CO2 than on the ocean’s surface.
With the weakening of the downward currents, the deep ocean becomes less accessible as a carbon sink. The ocean's surface can’t send its surplus of dissolved CO2 any lower. The surface becomes saturated with CO2 and in turn, it becomes a less effective carbon sink. Instead of dissolving the CO2 it can start to reject it into the atmosphere through evaporation. As a result, the carbon sinks become a source of GHG emission. All that because of the altered marine currents.
Releasing GHG rather than absorbing it exacerbates the greenhouse effect. This leads to more global warming, more glacier melt and increased alteration of ocean currents. That’s the positive feedback loop.
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As we have seen in the carbon cycle, forests form a large carbon sink. As living matter, flora is made up of carbon. With photosynthesis, it absorbs atmospheric CO2 and transforms it into oxygen.
Conversely, when a forest dies or where there is deforestation, the decomposition of plants drives up CO2 emissions. Likewise, when forests are ravaged by fire, combustion releases all the stored, stable CO2 into the atmosphere.
With climate disruption we are witnessing:
Between the Australian bush fires burning throughout the summer of 2019, and President Bolsonaro’s efforts to deforest the Amazon as quickly as possible, this is not a hypothetical situation, but a positive feedback loop that’s well underway.
+1°C is bad enough already
In 2019, in the Amazon, fires and deforestation destroyed more than 10,000km2 of forest - about the size of Lebanon.
In Australia, the huge 2019-20 bush fires burned more than 20% of the country’s forests and killed more than one billion animals.
Remember the water cycle: with the rise in air temperature, the atmosphere has an increased capacity to store water vapor. This intensifies extreme weather events, but that's not all.
Atmospheric water vapor increases the greenhouse effect. With a growing concentration of water vapor in the atmosphere, global warming is accelerated. And like every positive feedback loop, global warming increases the atmosphere’s storage capacity for water vapor which amplifies the phenomenon, and feeds into this vicious circle.
Permafrost is permanently frozen ground where its temperature has not exceeded 0°C degrees for at least two consecutive years.
Permafrost can be found on around 20% of the planet's surface, particularly in Greenland, Alaska, Canada and Russia. It can even be found in the French Alps.
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The major problem with permafrost is that it contains elements that have been locked into the ice for thousands of years. And we can’t really let these elements out into the atmosphere. Why not?
Picture this: permafrost is like a huge freezer. If you leave the door open, your pizza will defrost, your ice-cream will melt and germs will feed off these organic elements. In the same way, permafrost releases organic matter. Depending on germ activity, this produces either CO2 when oxygen is present or methane when there is no oxygen. These GHGs join the atmosphere and accelerate warming.
The GHG potential from permafrost is colossal: we are talking about 1,500 GtC. That’s double the amount of GHGs already present in the atmosphere. This would triple the concentration. Just imagine the additional greenhouse effect that would be generated. In this sense, the thawing of a large part of the permafrost represents one of the two possibly irreversible “climate bombs”.
An additional, not insignificant, effect is that the permafrost has locked in diseases that disappeared hundreds and thousands of years ago. Thawing permafrost could free them and create major health crises.
+1°C is bad enough already
In 2016, anthrax, a disease which had disappeared from the region over 75 years ago, killed several people and 2,300 reindeer in Siberia. When the permafrost thawed, bacteria from a frozen and anthrax-infected reindeer was released. Today we know how to treat anthrax with antibiotics. This won’t necessarily be true for all other viruses and bacteria that are unfamiliar or untreatable. Epidemics and pandemics far worse than Covid 19 are another risk of climate disruption.
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Methane represents another potential “climate bomb”.
Here we’re talking about methane molecules trapped in the ice. There are large quantities:
For now, methane storage in these reservoirs is stable. It is difficult to estimate the precise quantities, but we are talking around 10,000 GtC. That’s 7 times more than all the GHGs contained in the permafrost, and 21 times more than all the GHGs present in the atmosphere.
Unfortunately, if temperatures exceed the infamous 2°C, these molecules could become unstable. In fact, with the melting permafrost and warming oceans, methane will be increasingly in contact with higher temperatures. And the probability of these molecules becoming unstable is significant at 2°C and above. In that case, the molecules could dissociate and methane would escape directly into the atmosphere. Given that we’re talking about a gigantic volume of methane, it’s easy to understand the disastrous consequences for global warming and life on Earth.
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