The Earth has plenty of negative and positive feedback loops. A positive
feedback loop is when a situation causes something to happen in another system
that increases the first effect, which I turn impacts the second, which causes
the first effect to get bigger and so on. A negative feedback loop has the
opposite effect. The something has an effect on a second system which then has
an effect on the first system, which is now smaller and it in turn has a
smaller effect the second, which causes the first to be smaller and so on.
There that was confusing; how about some examples? Luckily the Earth has quite a few of these systems.
The Mountain Pine Beetle in Northern Canada: Normally this little critter lives in trees in northern Canada, on the slopes of British Colombia's mountains. The life cycle of this critter is kept in check by cold temperatures which kill off most of the larvae over wintering in the trees, very cold weather. The climate has been getting warmer, which reduces the number of larvae killed each winter. The larvae infest more trees and kill the trees. The trees die and the sun reaches the ground evaporating all the water and heating the ground and air. This increases climate change, minor changes first, but the more larvae that survive affect more trees the next year. The tinder dry dead trees are more likely to burn and the needle litter on the forest floor is much drier and when forest fires occur they are larger and burn more forest increasing climate change, killing less larvae which kill even more trees. At times in the northern boreal forests the mature flying beetle blots out the sky as it moves across the northern forests, no longer confined to the slopes of mountains in northern British Columbia.
They get more complex than that and more simple too, here is a simple one: As climate gets warmer in the north the permafrost in the north melts more. Permafrost is when the ground freezes and never thaws in the short summer. In the muskeg, any northern areas that are made of watery, boggy moss. It is a saturated mess of dead, decaying moss soaked in water that descends deep into the earth, most of which is permanently frozen. Anyone who has spent time in a marsh or swamp knows that it smells bad; vegetation that decays in water produces methane gas instead of carbon dioxide. Methane gas is a much more powerful greenhouse gas than carbon dioxide; water vapor is also a much more powerful greenhouse gas than carbon dioxide. The positive feedback loop is that as temperatures in the north rise, more water in the ground evaporates, releasing the methane into the atmosphere and melting the permafrost allowing more muskeg to decay, increasing methane production. The release of powerful greenhouse gasses, water vapor and methane gas accelerates climate change which increases the temperature of the north, which melts more permafrost and increases greenhouse gas production.
A more complex positive feedback loop can contain a negative feedback loop: Climate change in the tropics heats the air which does a number of things. The first process is that it evaporates more water from the ground and the water. The second is that warm air can hold more water than cold air. As the air warms more water can be stored in the air, it is an exponential rate of increase, so any increase of temperature means a lot more water being absorbed by the air. Everyone knows that warm air rises, that is why hot air balloons work, but moist air rises faster than dry air, which is counter intuitive. Water is heavier than air right? Air is made of oxygen and nitrogen, which have an atomic mass of 16 and 14 respectively, but they occur paired as N2 and O2, so masses of 32 and 28. Water vapor (H2O) has and atomic mass of 18, so moist air rises. As the air rises, the air cools and as it cools it becomes saturated and condenses out as cloud material, suspended water droplets or much higher suspended ice particles.
Clouds are white, at least from the top, and reflect light from the sun, less light reaches the ground so less heating occurs. That is a negative feedback loop and it does indeed work, but it is a weak feedback loop. The amount of extra cloud cover is marginal, a few percent, so the reduction is also marginal, but on the other hand, climate change is dependent on slight overbalances exaggerated by positive feedback loops, so it might be significant.
But, the problem with that idea is that when the water condenses into the air as clouds, it releases a fantastic amount of heat dealt with in a previous post. In pre-climate change Earth, most of the energy would have bled off into space, but an increase in carbon dioxide reflected more or the energy back to earth, increasing the temperature of the planet and increasing the amount of water vapor in the atmosphere. Greenhouse gasses are always clear to visible light, like glass in a greenhouse, but opaque to heat energy also like glass in a greenhouse, so more of the heat radiation is contained. The extra latent heat excites that air molecules causing the particles to move more, it also means more evaporation, more convection in the clouds, and more suspended water in the clouds and more water vapor reflecting more energy back to earth. A truly powerful positive feedback loop system.
There are a lot of positive feedback and negative feedback loops in the Earth's climate. Tropical rainforests transpire a lot of water, which goes back into the air which falls as rain and is in turn transpired. It has been found that as the rainforests are harvested; the area receives less rain than when there were more trees. Less rain harms the trees, decreasing rainfall as the trees die or dries out reducing the rain more. This is a negative feedback loop.
There that was confusing; how about some examples? Luckily the Earth has quite a few of these systems.
The Mountain Pine Beetle in Northern Canada: Normally this little critter lives in trees in northern Canada, on the slopes of British Colombia's mountains. The life cycle of this critter is kept in check by cold temperatures which kill off most of the larvae over wintering in the trees, very cold weather. The climate has been getting warmer, which reduces the number of larvae killed each winter. The larvae infest more trees and kill the trees. The trees die and the sun reaches the ground evaporating all the water and heating the ground and air. This increases climate change, minor changes first, but the more larvae that survive affect more trees the next year. The tinder dry dead trees are more likely to burn and the needle litter on the forest floor is much drier and when forest fires occur they are larger and burn more forest increasing climate change, killing less larvae which kill even more trees. At times in the northern boreal forests the mature flying beetle blots out the sky as it moves across the northern forests, no longer confined to the slopes of mountains in northern British Columbia.
They get more complex than that and more simple too, here is a simple one: As climate gets warmer in the north the permafrost in the north melts more. Permafrost is when the ground freezes and never thaws in the short summer. In the muskeg, any northern areas that are made of watery, boggy moss. It is a saturated mess of dead, decaying moss soaked in water that descends deep into the earth, most of which is permanently frozen. Anyone who has spent time in a marsh or swamp knows that it smells bad; vegetation that decays in water produces methane gas instead of carbon dioxide. Methane gas is a much more powerful greenhouse gas than carbon dioxide; water vapor is also a much more powerful greenhouse gas than carbon dioxide. The positive feedback loop is that as temperatures in the north rise, more water in the ground evaporates, releasing the methane into the atmosphere and melting the permafrost allowing more muskeg to decay, increasing methane production. The release of powerful greenhouse gasses, water vapor and methane gas accelerates climate change which increases the temperature of the north, which melts more permafrost and increases greenhouse gas production.
A more complex positive feedback loop can contain a negative feedback loop: Climate change in the tropics heats the air which does a number of things. The first process is that it evaporates more water from the ground and the water. The second is that warm air can hold more water than cold air. As the air warms more water can be stored in the air, it is an exponential rate of increase, so any increase of temperature means a lot more water being absorbed by the air. Everyone knows that warm air rises, that is why hot air balloons work, but moist air rises faster than dry air, which is counter intuitive. Water is heavier than air right? Air is made of oxygen and nitrogen, which have an atomic mass of 16 and 14 respectively, but they occur paired as N2 and O2, so masses of 32 and 28. Water vapor (H2O) has and atomic mass of 18, so moist air rises. As the air rises, the air cools and as it cools it becomes saturated and condenses out as cloud material, suspended water droplets or much higher suspended ice particles.
Clouds are white, at least from the top, and reflect light from the sun, less light reaches the ground so less heating occurs. That is a negative feedback loop and it does indeed work, but it is a weak feedback loop. The amount of extra cloud cover is marginal, a few percent, so the reduction is also marginal, but on the other hand, climate change is dependent on slight overbalances exaggerated by positive feedback loops, so it might be significant.
But, the problem with that idea is that when the water condenses into the air as clouds, it releases a fantastic amount of heat dealt with in a previous post. In pre-climate change Earth, most of the energy would have bled off into space, but an increase in carbon dioxide reflected more or the energy back to earth, increasing the temperature of the planet and increasing the amount of water vapor in the atmosphere. Greenhouse gasses are always clear to visible light, like glass in a greenhouse, but opaque to heat energy also like glass in a greenhouse, so more of the heat radiation is contained. The extra latent heat excites that air molecules causing the particles to move more, it also means more evaporation, more convection in the clouds, and more suspended water in the clouds and more water vapor reflecting more energy back to earth. A truly powerful positive feedback loop system.
There are a lot of positive feedback and negative feedback loops in the Earth's climate. Tropical rainforests transpire a lot of water, which goes back into the air which falls as rain and is in turn transpired. It has been found that as the rainforests are harvested; the area receives less rain than when there were more trees. Less rain harms the trees, decreasing rainfall as the trees die or dries out reducing the rain more. This is a negative feedback loop.
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