Earth heading towards irreversible 'hothouse' state: Study
Our planet is at the risk of entering an irreversible 'hothouse' condition - where the global temperatures will rise by four to five degrees and sea levels may surge by up to 60 metres higher than today - even if targets under the Paris climate deal are met, a study warns.
According to the researchers, keeping global warming to within 1.5-2 degrees Celsius may be more difficult than previously assessed. Human emissions of greenhouse gas are not the sole determinant of temperature on Earth. The study suggests that human-induced global warming of two degrees Celsius may trigger other Earth system processes, often called "feedbacks," that can drive further warming - even if we stop emitting greenhouse gases.
The study considers ten natural feedback processes, some of which are "tipping elements" that lead to abrupt change if a critical threshold is crossed. These feedbacks could turn from being a "friend" that stores carbon to a "foe" that emits it uncontrollably in a warmer world.
These feedbacks include permafrost thaw, loss of methane hydrates from the ocean floor, weakening land and ocean carbon sinks, increasing bacterial respiration in the oceans, Amazon rainforest dieback, boreal forest dieback, reduction of northern hemisphere snow cover, loss of Arctic summer sea ice, and reduction of Antarctic sea ice and polar ice sheets.
These tipping elements can potentially act like a row of dominoes. Once one is pushed over, it pushes Earth towards another. It may be very difficult or impossible to stop the whole row of dominoes from tumbling over.
Maximising the chances of avoiding a "Hothouse Earth" requires not only reduction of carbon dioxide and other greenhouse gas emissions but also enhancement and creation of new biological carbon stores through improved forest, agricultural and soil management, and technologies that remove carbon dioxide from the atmosphere and store it underground, researchers said.
Scientists noted that the Earth has never in its history had a quasi-stable state that is around 2C warmer than the preindustrial and suggest that there is substantial risk that the system, itself, will 'want' to continue warming because of other processes—even if we stop emissions. Earth will itself become a primary source of greenhouse gas emissions. It can come to a point where nothing humans can do will help mitigate the changes. They would then be unable to live near the equator, and would be forced to migrate to the poles to survive.
Even if the world ceased all carbon emissions by 2050, that’s still not enough to stop the feedback loop from cascading into the nightmare scenario outlined in the study. “If the 2 degree threshold is crossed, the resulting trajectory would pose severe risks for health, economies, political stability, and ultimately, the habitability of the planet for humans.
Today, we emit 40 billion tons of carbon dioxide a year from burning fossil fuels. But roughly half of those emissions are taken up and stored by the oceans, trees and soil. Scientists fear that if we reach a certain temperature threshold, some of these natural processes will reverse and the planet will become a self-heater. That means, forests, soil and water will release the carbon they're storing.
Nature has feedback mechanisms, such as a rainforest's capability to create its own humidity and rain, that keep ecosystems in equilibrium. If the rainforest is subject to increasing warming and deforestation, however, the mechanism slowly gets weaker.
When it crosses a tipping point, the feedback mechanism changes direction, and the rainforest morphs from a moisture engine into a self-dryer. Eventually, the rainforest turns into a savanna and, in the process, releases carbon. This, in turn, can become part of a cascade that would influence other processes around the world.
While the biggest impacts of all this may not be felt for hundreds of years, once it starts, we won't really be able to do anything about it - so experts say it's important we take steps now to stop the 'Hothouse Earth' situation from happening.
The IPCC said in one of the reports because of model and other uncertainties we cannot preclude the possibility that the enhanced greenhouse effect has contributed substantially to past wanning - not even that the greenhouse gas induced warming has been greater than that observed, but is partly offset by natural variability and/or other anthropogenic effects.
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Planetary geologists think there is good evidence that Venus was the victim of a runaway greenhouse effect which turned the planet into the boiling hell we see today.
But that raises an important question: is it possible that we could trigger a runaway greenhouse effect ourselves by adding carbon dioxide to the atmosphere?A similar catastrophe is almost certain to strike Earth in about 2 billion years, as the Sun increases in luminosity.
According to the climate scientist James Hansen, that’s a distinct possibility. A couple of years ago, he wrote: “If we burn all reserves of oil, gas, and coal, there’s a substantial chance that we will initiate the runaway greenhouse. If we also burn the tar sands and tar shale, I believe the Venus syndrome is a dead certainty.”
The fear is that adding carbon dioxide to the atmosphere is warming the planet and increasing evaporation from the oceans. The extra water vapour, itself a greenhouse gas, causes more warming and more evaporation in a vicious cycle of temperature increases that eventually result in the ocean boiling away.
Our planet is at the risk of entering an irreversible 'hothouse' condition - where the global temperatures will rise by four to five degrees and sea levels may surge by up to 60 metres higher than today - even if targets under the Paris climate deal are met, a study warns.
According to the researchers, keeping global warming to within 1.5-2 degrees Celsius may be more difficult than previously assessed. Human emissions of greenhouse gas are not the sole determinant of temperature on Earth. The study suggests that human-induced global warming of two degrees Celsius may trigger other Earth system processes, often called "feedbacks," that can drive further warming - even if we stop emitting greenhouse gases.
The study considers ten natural feedback processes, some of which are "tipping elements" that lead to abrupt change if a critical threshold is crossed. These feedbacks could turn from being a "friend" that stores carbon to a "foe" that emits it uncontrollably in a warmer world.
These feedbacks include permafrost thaw, loss of methane hydrates from the ocean floor, weakening land and ocean carbon sinks, increasing bacterial respiration in the oceans, Amazon rainforest dieback, boreal forest dieback, reduction of northern hemisphere snow cover, loss of Arctic summer sea ice, and reduction of Antarctic sea ice and polar ice sheets.
These tipping elements can potentially act like a row of dominoes. Once one is pushed over, it pushes Earth towards another. It may be very difficult or impossible to stop the whole row of dominoes from tumbling over.
Maximising the chances of avoiding a "Hothouse Earth" requires not only reduction of carbon dioxide and other greenhouse gas emissions but also enhancement and creation of new biological carbon stores through improved forest, agricultural and soil management, and technologies that remove carbon dioxide from the atmosphere and store it underground, researchers said.
Scientists noted that the Earth has never in its history had a quasi-stable state that is around 2C warmer than the preindustrial and suggest that there is substantial risk that the system, itself, will 'want' to continue warming because of other processes—even if we stop emissions. Earth will itself become a primary source of greenhouse gas emissions. It can come to a point where nothing humans can do will help mitigate the changes. They would then be unable to live near the equator, and would be forced to migrate to the poles to survive.
Even if the world ceased all carbon emissions by 2050, that’s still not enough to stop the feedback loop from cascading into the nightmare scenario outlined in the study. “If the 2 degree threshold is crossed, the resulting trajectory would pose severe risks for health, economies, political stability, and ultimately, the habitability of the planet for humans.
Today, we emit 40 billion tons of carbon dioxide a year from burning fossil fuels. But roughly half of those emissions are taken up and stored by the oceans, trees and soil. Scientists fear that if we reach a certain temperature threshold, some of these natural processes will reverse and the planet will become a self-heater. That means, forests, soil and water will release the carbon they're storing.
Nature has feedback mechanisms, such as a rainforest's capability to create its own humidity and rain, that keep ecosystems in equilibrium. If the rainforest is subject to increasing warming and deforestation, however, the mechanism slowly gets weaker.
When it crosses a tipping point, the feedback mechanism changes direction, and the rainforest morphs from a moisture engine into a self-dryer. Eventually, the rainforest turns into a savanna and, in the process, releases carbon. This, in turn, can become part of a cascade that would influence other processes around the world.
While the biggest impacts of all this may not be felt for hundreds of years, once it starts, we won't really be able to do anything about it - so experts say it's important we take steps now to stop the 'Hothouse Earth' situation from happening.
The IPCC said in one of the reports because of model and other uncertainties we cannot preclude the possibility that the enhanced greenhouse effect has contributed substantially to past wanning - not even that the greenhouse gas induced warming has been greater than that observed, but is partly offset by natural variability and/or other anthropogenic effects.
++++++++++++++++++
Planetary geologists think there is good evidence that Venus was the victim of a runaway greenhouse effect which turned the planet into the boiling hell we see today.
But that raises an important question: is it possible that we could trigger a runaway greenhouse effect ourselves by adding carbon dioxide to the atmosphere?A similar catastrophe is almost certain to strike Earth in about 2 billion years, as the Sun increases in luminosity.
According to the climate scientist James Hansen, that’s a distinct possibility. A couple of years ago, he wrote: “If we burn all reserves of oil, gas, and coal, there’s a substantial chance that we will initiate the runaway greenhouse. If we also burn the tar sands and tar shale, I believe the Venus syndrome is a dead certainty.”
The fear is that adding carbon dioxide to the atmosphere is warming the planet and increasing evaporation from the oceans. The extra water vapour, itself a greenhouse gas, causes more warming and more evaporation in a vicious cycle of temperature increases that eventually result in the ocean boiling away.
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