CH 7 FEEDBACKS

Carbon cycle feedback -many potential feedbacks between climate and the carbon cycle -warming the atmosphere increases the temp of the surface ocean, which tends to drive CO2 to degas from the ocean to the atmosphere. The ultimate trigger of the glacial-interglacial cycles is thought to be variations in the Earth's orbit, but the climate swings would have been much smaller if the carbon cycle had not somehow shifted, pulling CO2 out of the atmosphere as the ice sheets started to grow in a positive feedback climate -the land's surface stores a lot of carbon. If the Amazon or Indonesian rain forests were to burn, for example, they could release a significant amount of carbon as CO2 to the atmosphere. Other sources of carbon that might feed back to climate change include peats, organic carbon in permafrost soils, and methane hydrates in the ocean. The methane cycle could also feed back to climate if there are climate-driven changes in wetlands, for example, or changes in the radical oxidation chemistry of the atmosphere.

Explain el Nino.

-In the el Nino phase of the oscillation, the slope in the ocean temperature boundary and the winds in the atmosphere collapse (West and east exposed to warm water, while cold water is at the bottom). -The cold water near Peru gets covered with warm water during El Nino. The winds along the equatorial falter because the sea surface temperature different that drove them has disappeared. -The coupled atmosphere/ocean system flips back and forth between these 2 states, el nina and el nino, every 4-7 years, affect weather patterns around the rest of the world.

Explain the Stefan-Boltzmann Feedback.

-NEGATIVE FEEDBACK When temperature of the Earth increases, Earth will emit more IR radiation to space. (This is because the outgoing energy flux depends on the temperature according to the Stefan-Boltzmann rule. The hotter the object, the more radiation it emits). When an object emits radiation, the tendency will be for the object to cool b/c it has emitted energy. So temperature will decrease. Stefan-Boltzmann Feedback The energy budget of the Earth, balancing IR against sunlight energy flux (& additional longwave fluxes) is controlled by a NEGATIVE feedback mechanism. -the outgoing energy flux depends on the temperature according to the Stefan-Boltzmann equation. If you were to suddenly deposit a whole lot of extra energy on the planet, the feedback would pull the temperature back down. This is a negative feedback because the feedback pulls in the opposite sense from the perturbation. (When an object emits radiation, the tendency will be for the object to cool because it has emitted energy)

-The effect of clouds in the visible light energy budget is to send energy back to space, increasing Earth's albedo and cooling the planet. -Light can be scattered when the electric field of the incoming visible light causes the electric field in the particle to oscillate. The oscillating electric field in the particle then emits visible light, the same frequency as the light that came in. The difference to Earth's energy budget between absorbed and scattered sunlight is that when light is scattered back to space, its energy is never converted to heat, so it never enters into the planet's heat energy budget. -The fraction on incoming sunlight that is scattered versus that absorbed by a cloud varies a lot between different types of clouds. You cannot see through low clouds, meaning that they are optically thick, capturing or scattering most of the visible light that tries to get through. Cirrus clouds contain less water per volume than lower altitude clouds typically hold. They're so thin you can often see blue sky right through them. Cirrus clouds therefore have a weaker cooling impact on the visible light budget than low clouds do.

-The effect of clouds in the visible light energy budget is to send energy back to space, increasing Earth's albedo and cooling the planet. -The fraction on incoming sunlight that is scattered versus that absorbed by a cloud varies a lot between different types of clouds. You cannot see through low clouds, meaning that they are optically thick, capturing or scattering most of the visible light that tries to get through. Cirrus clouds contain less water per volume than lower altitude clouds typically hold. They're so thin you can often see blue sky right through them. Cirrus clouds therefore have a weaker cooling impact on the visible light budget than low clouds do.

What is a feedback?

-a loop of cause and effect -positive feedback amplifies an initial change -negative feedback stabilizes the system

How does the runaway greenhouse effect stop?

-if the vapor concentration in the air reaches saturation with liquid water or ice, so that any further evaporation would just lead to rainfall or snow -the amplifying loop of cause and effect stops if the vapor pressure and temperature hit the liquid or ice stability fields

What are the effects of high clouds (cirrus)

-infrared effect: strong warming influence because high altitude cloud top -visible light effect: weak cooling influence because they're optically thin -overall effect: warming

What are the effects of low clouds (stratus/cumulus)

-infrared effect: weaker warming influence cloud tops are lower -visible light effect: stronger cooling influence because they're optically thicker -overall effect: cooling

Explain the hydrological cycle.

-the NEGATIVE FEEDBACK that controls the atmospheric water vapor, given an atmospheric temperature -increase in water vapor concentration, more rain evaporates. This will later condense as rain, so water vapor concentration will decrease.

What affects the scattering efficiency of clouds?

-the cloud droplet size -the smaller the drop, the better for scattering The size of cloud droplets can be affected by cloud condensation nuclei, seeds that help droplets forms. The strongest human footprint in the clouds comes from coal-fired power plants releasing sulfur. Sulfur is emitted in flue gas SO2 and it oxidizes in a week or so to sulfuric acid, which condenses into small droplets called sulfate aerosols. These are so small that they scatter a lot of the light that encounters them. The aerosols act as cloud condensation nuclei because the strong acid tends to pull water out of the air. So the cloud will have more water droplets, each of which is very small. Most of the near surface atmosphere has enough natural condensation nuclei that the issue is not whether to form a droplet or not when the air gets supersaturated. But adding more condensation nuclei will encourage the water to form a greater number of smaller-sized droplets. The climate impact of changing the cloud droplet size arises because smaller droplets scatter light more efficiently than larger droplets do. This is called the sulfate aerosol indirect effect. The climate impact of indirect aerosol effect is very uncertain, but it is probably even larger than the direct effect of scattering light by aerosols themselves. Clouds that form in the dirty air tend to be better scatterers with a higher albedo, cooling the planet.

What are some terrestrial biosphere feedbacks?

-the terrestrial biosphere has the potential to feed back to climate if changes in vegetation alter the albedo of the land surface. Expansion of the northern forests into areas previously covered by tundra, for example, could make the land darker, tending to warming things up further. -the land surface affects the albedo, and it stores carbon -trees also impact the hydrological cycle by extracting ground water and evaporating it from their leaves, a process called transpiration. Rain forests in particular are thought to to perpetuate their own existence by extracting ground water and evaporating it to the air, recycling it to rain again again, rather than allowing it to escape in river flow to the ocean. -in a drought, vegetation dies and soils dry out, losing the ability to retain water, thereby perpetuating the water shortage in a positive feedback. It takes an extra boost of water supply to get out of a drought, overcoming this vegetation feedback.

A negative feedback is a stabilizer. It pulls in the opposite sense from the perturbation.

A positive feedback is an amplifier. There's a positive feedback in the climate system known as the ice albedo feedback, which operates on the state variable of temperature. An input perturbation, such as a rise in greenhouse gases, drives the temperature up a bit. Ice melts, reducing the albedo (the reflectivitty of the Earth), allowing the dark ground to absorb more sunlight than the ice would have, warming things up more. This is called a positive feedback because the direction of the feedback loop agree with each other. A positive feedback can work in the opposite direction as well, taking a cold time and make it even colder. A positive feedback loop amplifies an excursion in either direction.

A positive feedback makes the temperature change larger than it would have been without the feedback, amplifying the temperature change. A negative feedback counteracts some of the external forcing, tending to stabilize the state variable.

Another potential feedback from the ocean to climate is called the meridional overturning circulation in the North Atlantic Ocean. Warmer water is carried to the North Atlantic in the Gulf Stream. As the water cools, its density increases and it sinks into the abyss, making room at the surface for more water water to carry more heat from the tropics.

At high temperatures and low pressure, you expect to find only vapor. Vapor likes it hot. Cool it down and increase the pressure, and liquid will condense and when it gets colder, ice will form. At the triple point, a specific pressure and temperature condition, you get all 3 phases coexisting together, a glass of boiling ice water. -To understand the water-vapor feedback, imagine what would happen if you suddenly introduced water to a planet that originally had none. This starting position is all the way on the bottom of the figure, where the pressure of water vapor in the air is low. From here, what will happen is that water will evaporate and the vapor pressure in the atmosphere will rise. Water vapor is a greenhouse gas, so as the water vapor content of the atmosphere increase, the temperature warms. Therefore as the condition of the planet moves upward on the figure, to higher water vapor pressure, it veers to the right, which is higher temp.

At the center of a feedback is a state variable. The state variable in many climate feedback loops is the avg temp of the Earth

Clouds are loose cannons in climate models. They are the largest source of uncertainty in climate models. Most of the uncertainty in the climate sensitivity of the Earth (temp change that would result from doubling CO2 concentrations) arises because of a positive feedback involving clouds, amplifying the effect of the CO2 change. There are no models that exhibit a negative feedback from clouds.

Clouds are pretty good blackbodies, absorbing and potentially emitting just about any frequency of IR. This makes them different from greenhouse gases, which are choosy about what frequencies of IR radiation they interact with. Clouds are blackbodies because they're made of liquid droplets or ice crystal solids. In general, liquids and solids at the Earth's surface tend to be black in the IR.

Clouds interfere with both the visible light and IR energy fluxes in the Earth's radiation balance. -in the IR, clouds act as blackbodies, warming the planet -the effect on the visible light energy budget is to reflect light to space, cooling the planet. -the overall impact of a cloud depends on which of these 2 effects is stronger, which in turn depends on what type of cloud it is.

Clouds that form in the dirty air tend to be better scatterers with a higher albedo, cooling the planet.

Contrails are another example of cloud seeding by humans. They form when a jet airplane passes through clean air that's somewhat supersaturated with water vapor. The exhaust contains cloud condensation nuclei that quickly absorb water from the air to form droplets. Contrail particles spread out and eventually become indistinguishable from natural cirrus particles. This makes it difficult to know how much impact aircraft have on the cloudiness of the upper atmosphere. Contrails tend to warm the plant, just like natural high clouds.

Different types of cloud droplets scatter light in different directions. Most of the light scattered by a spherical liquid droplets continue in a more or less forward direction, which, if the incoming direction is downward, would mean to continue downward toward Earth. Ice crystals are better at actually reversing the direction of light, sending it back up into space.

Explain la Nina.

During la Nina, the boundary between warm/cold water in the ocean slopes up from west to east, exposing cold water to the atmosphere in the east near Peru (and warm water in the west). The cold water drives a strong wind from East to west that tends to sustain the slop in the ocean temperature boundary. In the la Nina state, there is cold water at the sea surface in the eastern part of the Pacific ocean near Peru. The contrast in sea surface temperature between the eastern and western equatorial Pacific drives a wind along the equator that blows from East to West. The warm water, floating on the colder water with a boundary called a thermocline, piles up in the West. The titled thermocline keeps the surface waters cold near Peru, which drives winds, which keep the thermocline tilted and the cold water at the surface.

During la Nina, the boundary between warm/cold water in the ocean slopes up from west to east, exposing cold water to the atmosphere in the east near Peru (and warm water in the west). The cold water drives a strong wind from East to west that tends to sustain the slop in the ocean temperature boundary. In the la Nina state, there is cold water at the sea surface in the eastern part of the Pacific ocean near Peru. The contrast in sea surface temperature between the eastern and western equatorial Pacific drives a wind along the equator that blows from East to West. The warm water, floating on the colder water with a boundary called a thermocline, piles up in the West. The titled thermocline keeps the surface waters cold near Peru, which drives winds, which keep the thermocline tilted and the cold water at the surface. -In the el Nino phase of the oscillation, the slope in the ocean temperature boundary and the winds in the atmosphere collapse (West and east exposed to warm water, while cold water is at the bottom). -The cold water near Peru gets covered with warm water during El Nino. The winds along the equatorial falter because the sea surface temperature different that drove them has disappeared. -The coupled atmosphere/ocean system flips back and forth between these 2 states, el nina and el nino, every 4-7 years, affect weather patterns around the rest of the world.

Earth has retained its water as a result of the temperature structure of the atmosphere. It gets colder aloft until you reach the tropospause. The tropospause acts as a cold trap for water water vapor, making sure that most of it rains or snows out before the air rises too close to space. The oceans have been protected by a thin layer of cold air. EARTH'S CLIMATE USES THE HIGH LATITUES AS COOLING FINS TO AVOID THE RUNWAY GREENHOUSE EFFECT -Theoretically, if the Sun were to get hotter, of if CO concentrations were high enough, the Earth would move to the right on the figure, sufficiently far that it could escape the liquid water stability field and hence run away. But there's not enough fossil fuel carbon on Earth to do this. If the equator were isolated from the poles, blocked from any heat transport and forced to balance its energy fluxes using outgoing IR only, the tropics would be a runaway greenhouse.

an oscillation of the structure of the atmosphere and ocean, centering in the equatorial Pacific but with climate impacts around the world

El Nino

Evaporation of all of a planet's water is a one-way street because if water vapor reaches the upper atmosphere, its chemical parts will get blown apart by the intense UV light. The hydrogen atoms, once they're disconnected from oxygen, are small enough and light enough that they are able to escape to space. The water is lost for good. This is the presumed fate of Venus's water. A RUNWAY GREENHOUSE EFFECT MEANS THE END OF A PLANET'S WATER

What are the 3 main types of clouds?

High altitude clouds: -cirrus clouds -wispy and thin -strong warming influence because of high-altitude cloud top -weak cooling influence because they're optically thing -so the have an overall warming effect 2 types of Low altitude clouds -cumulus clouds (towers) -stratus clouds (layered) -weaker warming influence because cloud tops are lower -stronger cooling influence because they're optically thicker -so they have an overall cooling effect

High clouds warm, low clouds cool.

Ice albedo feedback. An example of a positive feedback. Some external perturbation increases the temperature. The increase in temp causes ice to melt, allowing the land to absorb more of the incoming solar radiation (by decreasing the albedo), The melting ice drives temperature up further.

In general the world dries out during el Nino.

The humidity of the atmosphere depends on what?

In general, the humidity of the atmosphere depends on the patterns of circulation and access to evaporating water. -One mechanism controlling the distribution of atmospheric water vapor is the HADLEY CIRCULATION. Warm air at the equator rises convectively. Water condenses as the air rises and cools. The rising column of air generally has a lot of water vapor in it. Then the air spreads out at high latitudes and begins to subside in the subtropics, about 30 latitude north and south. This is the air that has been through the wringer, the cold tropospause, and there is not much water vapor left in it. The great deserts of the world are located under these dry air subsidence regions. The air flows back equator-ward along the surface, picking up water vapor as it goes. In general, the humidity of the atmosphere depends on the patterns of circulation and access to evaporating water.

It's possible for the water-vapor feedback to feed into itself, running around the loop of cause and effect in what's known as a runaway greenhouse effect. A runway greenhouse effect stops if the vapor concentration in the air reaches saturation with liquid water or ice, so that any further evaporation would just lead to rainfall or snow

Oceans interact with climate in many ways -In the el Nino phase of the oscillation, the slope in the ocean temperature boundary and the winds in the atmosphere collapse (West and east exposed to warm water, while cold water is at the bottom). -The cold water near Peru gets covered with warm water during El Nino. The winds along the equatorial falter because the sea surface temperature different that drove them has disappeared. -The coupled atmosphere/ocean system flips back and forth between these 2 states, el nina and el nino, every 4-7 years, affect weather patterns around the rest of the world.

Oceans interact with climate in many ways During la Nina, the boundary between warm/cold water in the ocean slopes up from west to east, exposing cold water to the atmosphere in the east near Peru (and warm water in the west). The cold water drives a strong wind from East to west that tends to sustain the slop in the ocean temperature boundary. In the la Nina state, there is cold water at the sea surface in the eastern part of the Pacific ocean near Peru. The contrast in sea surface temperature between the eastern and western equatorial Pacific drives a wind along the equator that blows from East to West. The warm water, floating on the colder water with a boundary called a thermocline, piles up in the West. The titled thermocline keeps the surface waters cold near Peru, which drives winds, which keep the thermocline tilted and the cold water at the surface.

Explain how oceans interact with climate.

Oceans interact with climate in many ways. One example is a periodic flip flop between 2 states of the ocean called el Nino and la Nina -on the atmospheric side, there's a corresponding cycle in the atmospheric pressure difference across the Pacific called the Southern oscillation. Emphasizing that this is a coupled atmosphere/ocean phenomenon, the el Nino cycle has been abbreviated ENSO (el nino southern oscillation). The state of the ENSO cycle affects patterns of climate all around the world. -in general the world dries out during el Nino. In the la Nina state, there is cold water at the sea surface in the eastern part of the Pacific ocean near Peru. The contrast in sea surface temperature between the eastern and western equatorial Pacific drives a wind along the equator that blows from East to West. The warm water, floating on the colder water with a boundary called a thermocline, piles up in the West. The titled thermocline keeps the surface waters cold near Peru, which drives winds, which keep the thermocline tilted and the cold water at the surface. During la Nina, the boundary between warm/cold water in the ocean slopes up from west to east, exposing cold water to the atmosphere in the east near Peru (and warm water in the west). The cold water drives a strong wind from East to west that tends to sustain the slop in the ocean temperature boundary. The cold water near Peru gets covered with warm water during El Nino. The winds along the equatorial falter because the sea surface temperature different that drove them has disappeared. In the el Nino phase of the oscillation, the slope in the ocean temperature boundary and the winds in the atmosphere collapse (West and east exposed to warm water, while cold water is at the bottom). Although both of these states seem self-stabilizing (the winds and thermocline tilt arrayed in a positive feedback), the atmosphere/ocean system flips back and forth between the 2 climate states, about 1 cycle every 4-7 yrs.

Oceans interact with climate in many ways. One example is a periodic flip flop between 2 states of the ocean called el Nino and la Nina -on the atmospheric side, there's a corresponding cycle in the atmospheric pressure difference across the Pacific called the Southern oscillation. Emphasizing that this is a coupled atmosphere/ocean phenomenon, the el Nino cycle has been abbreviated ENSO (el nino southern oscillation). The state of the ENSO cycle affects patterns of climate all around the world. -in general the world dries out during el Nino. In the la Nina state, there is cold water at the sea surface in the eastern part of the Pacific ocean near Peru. The contrast in sea surface temperature between the eastern and western equatorial Pacific drives a wind along the equator that blows from East to West. The warm water, floating on the colder water with a boundary called a thermocline, piles up in the West. The titled thermocline keeps the surface waters cold near Peru, which drives winds, which keep the thermocline tilted and the cold water at the surface. During la Nina, the boundary between warm/cold water in the ocean slopes up from west to east, exposing cold water to the atmosphere in the east near Peru (and warm water in the west). The cold water drives a strong wind from East to west that tends to sustain the slop in the ocean temperature boundary. The cold water near Peru gets covered with warm water during El Nino. The winds along the equatorial falter because the sea surface temperature different that drove them has disappeared. In the el Nino phase of the oscillation, the slope in the ocean temperature boundary and the winds in the atmosphere collapse (West and east exposed to warm water, while cold water is at the bottom). Although both of these states seem self-stabilizing (the winds and thermocline tilt arrayed in a positive feedback), the atmosphere/ocean system flips back and forth between the 2 climate states, about 1 cycle every 4-7 yrs. Another potential feedback from the ocean to climate is called the meridional overturning circulation in the North Atlantic Ocean. Warmer water is carried to the North Atlantic in the Gulf Stream. As the water cools, its density increases and it sinks into the abyss, making room at the surface for more water water to carry more heat from the tropics.

On the real Earth, mercifully, the relative humidity is not everywhere 100%. One mechanism controlling the distribution of atmospheric water vapor is the HADLEY CIRCULATION. Warm air at the equator rises convectively. Water condenses as the air rises and cools. The rising column of air generally has a lot of water vapor in it. Then the air spreads out at high latitudes and begins to subside in the subtropics, about 30 latitude north and south. This is the air that has been through the wringer, the cold tropospause, and there is not much water vapor left in it. The great deserts of the world are located under these dry air subsidence regions. The air flows back equator-ward along the surface, picking up water vapor as it goes. In general, the humidity of the atmosphere depends on the patterns of circulation and access to evaporating water.

Describe the HADLEY CIRCULATION.

One mechanism controlling the distribution of atmospheric water vapor is the HADLEY CIRCULATION. Warm air at the equator rises convectively. Water condenses as the air rises and cools. The rising column of air generally has a lot of water vapor in it. Then the air spreads out at high latitudes and begins to subside in the subtropics, about 30 latitude north and south. This is the air that has been through the wringer, the cold tropospause, and there is not much water vapor left in it. The great deserts of the world are located under these dry air subsidence regions. The air flows back equator-ward along the surface, picking up water vapor as it goes. In general, the humidity of the atmosphere depends on the patterns of circulation and access to evaporating water.

Explain the water vapor feedback.

POSITIVE FEEDBACK an initial warming allows more water to evaporate into the atmosphere, so water vapor concentration increases. (Because warmer air holds more water vapor than cooler air, warming allows more water to evaporate before it rains). Water vapor is a greenhouse gas, so increasing its concentration leads to further warming -the water vapor feedback significantly amplifies the temperature effect of rising CO2 in our climate

Describe the ice albedo feedback.

POSITIVE FEEDBACK warming leads to melting of ice, which decreases the albedo, leading to further warming.

Phase diagrams show what phases of water you'll find as a function of temperature and pressure. Phases of water are solid, liquid, gas. A phase diagram for water demonstrates that the water-vapor feedback on Earth and Mars is limited, where as Venus is free to have a runway greenhouse effect.

Positive feedbacks act as amplifiers of variability, whereas negative feedbacks act as stabilizers. -The ice albedo feedback amplifies the warming in high latitudes by a factor of 3 or 4. -The water vapor feedback doubles or triples the expected warming owing to rising CO2 concentrations. -Clouds have a potentially huge impact on climate. Clouds are expected to exert an AMPLIFYING feedback to climate warming, although the strength of this feedback is uncertain. Clouds are the largest source of uncertainty in model estimates of climate sensitivity.

Putting together the IR and visible parts of the energy budget, high clouds warm the Earth and low clouds cool it. The greenhouse effect wins for high clouds and the albedo effect wins for low clouds. Overall, the cooling effect of the low clouds dominate, leading to an net cooling of Earth's climate. When climate models are subjected to higher atmospheric CO2, their clouds tend to respond by amplifying the warming from the CO2 in a positive feedback. No models predict a negative feedback from clouds, but the strength of the feedback is very uncertain, and is the main source of uncertainty in model calculation of the climate sensitivity of the Earth. High clouds warm, low clouds cool.

Reconstructions of the climate and oceanography of the North Atlantic region from the last ice age point to an instability in the meridional overturning circulation. The climate records from ice cores in Greenland show huge temperature swings called Dansgarrd-Oeschger events, changes of 10C within just a few years. Oceanographic reconstructions from sediment cores show that the depth of the meridonial overturning circulation in the North Atlantic changes in synchrony with these temp swings. One large climate shift, called the 8.2 K event, 8200 yrs ago, has been correlated with the catastrophic release of a Great Lake's worth of fresh water into the North Atlantic, as an ice dam holding the lake finally let water past. -Sudden changes in the overturning circulation in the North Atlantic have driven abrupt global climate changes in the past. In the future, this circulation might be impacted by warming or by melting Greenland's ice.

Stefan-Boltzmann Feedback The energy budget of the Earth, balancing IR against sunlight energy flux (& additional longwave fluxes) is controlled by a NEGATIVE feedback mechanism. -the outgoing energy flux depends on the temperature according to the Stefan-Boltzmann equation. If you were to suddenly deposit a whole lot of extra energy on the planet, the feedback would pull the temperature back down. This is a negative feedback because the feedback pulls in the opposite sense from the perturbation. (When an object emits radiation, the tendency will be for the object to cool because it has emitted energy)

Terrestrial Biosphere Feedbacks -the terrestrial biosphere has the potential to feed back to climate if changes in vegetation alter the albedo of the land surface. Expansion of the northern forests into areas previously covered by tundra, for example, could make the land darker, tending to warming things up further. -the land surface affects the albedo, and it stores carbon -trees also impact the hydrological cycle by extracting ground water and evaporating it from their leaves, a process called transpiration. Rain forests in particular are thought to to perpetuate their own existence by extracting ground water and evaporating it to the air, recycling it to rain again again, rather than allowing it to escape in river flow to the ocean. -in a drought, vegetation dies and soils dry out, losing the ability to retain water, thereby perpetuating the water shortage in a positive feedback. It takes an extra boost of water supply to get out of a drought, overcoming this vegetation feedback.

The amplifying loop of cause and effect stops for the water-vapor feedback is the vapor pressure and temperature hit the liquid or ice stability fields.

The amplifying loop of cause and effect stops for the water-vapor feedback is the vapor pressure and temperature hit the liquid or ice stability fields. -The middle of the three curves in the figure labeled Earth moves up and to the right until it intersects the stability field of water. At this point, the atmosphere is holding as much was vapor as it can. Any further evaporation just makes it rain. The curve on the left represents Mars. Here the water-vapor feedback path intersects the stability field of ice. The only planet in the diagram with a runaway greenhouse effect is Venus. Water on Venus would evaporate, increasing the temperature as before. The difference is that the path that Venus follows never intersects the stability fields of either liquid or solid water. Venus originally had as much water as Earth but that the high solar heat flux associated with orbiting so close to the sun drove the water to evaporate into the atmosphere, rather than condense into oceans as it has on Earth.

The effect of a cloud on the IR energy budget depends on the temperature at the top of the cloud, where IR radiation heading upward escapes the cloud and heads to space. High clouds emit IR radiation at cold temps, blocking the bright IR from the warm ground. Clouds with low tops have a smaller effect on the outgoing IR light. The effect of clouds on IR light is to warm the Earth and that high clouds warm the Earth more than low clouds do.

What is the effect of clouds on IR light?

The effect of clouds on IR light is to warm the Earth and that high clouds warm the Earth more than low clouds do. -High clouds have a stronger warming influence because of high-altitude cloud top -low clouds have a weaker warming influence because cloud tops are lower. The infrared effect of clouds warms the Earth depending on the altitude (temperature) of the cloud tops. High clouds have high altitude (lower temps). So they emit IR radiation at cold temps, blocking the bright IR from the warm ground. Clouds with low tops have smaller a smaller effect on the outgoing IR light

The ice albedo feedback is most important in the high latitudes because that's where the ice is. The warming response of climate models to extra CO2 is 2-4 times stronger in high latitudes than on the global average. This is also observed in the warming pattern of the last few decades, with a caveat. Warming is stronger in the Arctic than the global average, drive in part because the sea ice in the Arctic is melting rapidly. At the other pole, the interior of Antarctica is actually cooling, which may be a special case, the result of the Antactic ozone hole and its impact on a spinning column of air called the polar vortex. Sea ice around Antarctica is also holding relatively steady, not melting like in the Arctic. But the Antarctic Peninsula as warmed more than any place else on Earth, and this is where most of the exploding ice shelves are from.

The infrared effect of clouds warms the Earth depending on the altitude (temperature) of the cloud tops. High clouds warm, low clouds cool

The infrared effect of clouds warms the Earth depending on the altitude (temperature) of the cloud tops.High clouds warm, low clouds cool

The meridional overturning circulation in the North Atlantic may be sensitive to future changes in climate and fresh water discharge. If the Greenland ice sheets were to melt within a century, it would release enough fresh water to slow the overturning circulation. Climate models also predict a slow down in the circulation with very high levels of CO2. If the overturning circulation slows, it could lead to cooling in the high northern latitudes, driven by the loss of heat coming up from the tropics in the poleward surface current. The climate models generally find that by the time the overturning circulation slows down in a model run, the warming from the CO2 is much stronger than the local cooling from the collapse of the circulation. This makes the "Day After Tomorrow" scenario, of a sudden collapse into a new ice age, seem unlikely. However, climate models tend to under predict the severity and spatial footprint of past abrupt climate changes driven by instability of the meridional overturning circulation. So the impact of a shutdown in the future could also be stronger than the models predict.

The presence of absence of sea ice can also have a huge impact on local temps because air temperatures over open water are moderated by the heat sink of the water column. As the air draws heat from the water, turbulent mixing and convection in the water will quickly refresh the surface water from below. As a result, the air over water does not get much colder than freezing OC, but air over ice or land can be much colder. If a landmass is frozen into a vast expanse of sea ice, it will have a climate more typical of the interior of a continent. This sea ice temperature feedback helps explain the abrupt climate models recorded in the Greenland ice cores

The scattering efficiency of clouds varies a lot with meteorological conditions and it is also affected by human pollution. The important factor is the cloud droplet size. -Scattering would be most efficient if the droplets were about the same size as the wavelength of the light. But cloud droplets are almost all much larger than the wavelength of visible light, so the smaller the drop, the better for scattering.

The size of cloud droplets can be affected by cloud condensation nuclei, seeds that help droplets forms. There are natural cloud condensation nuclei from sea salt, dust, pollen, smoke and sulfur compounds emitted by phytoplankton. The strongest human footprint in the clouds comes from coal-fired power plants releasing sulfur. Sulfur is emitted in flue gas SO2 and it oxidizes in a week or so to sulfuric acid, which condenses into small droplets called sulfate aerosols. These are so small that they scatter a lot of the light that encounters them. The aerosols act as cloud condensation nuclei because the strong acid tends to pull water out of the air. So the cloud will have more droplets, each of which is very small. Most of the near surface atmosphere has enough natural condensation nuclei that the issue is not whether to form a droplet or not when the air gets supersaturated. But adding more condensation nuclei will encourage the water to form a greater number of smaller-sized droplets. The climate impact of changing the cloud droplet size arises because smaller droplets scatter light more efficiently than larger droplets do. This is called the sulfate aerosol indirect effect. The climate impact of indirect aerosol effect is very uncertain, but it is probably even larger than the direct effect of scattering light by aerosols themselves. Clouds that form in the dirty air tend to be better scatterers with a higher albedo, cooling the planet.

The strength of the water-vapor feedback depends on what happens in the upper atmosphere, where water vapor is most important as a greenhouse gas.

The water vapor feedback amplifies the temperature change that you would get from increasing CO2 on a dry planet.

There's a possibility that with global warming the Pacific may tend to favor the El Nino state, the climate impacts of which could be considered a feedback. However, the extent and strength of this potential feedback are impossible to forecast reliably. A warmer world might have a permanent El Nino or maybe not.

Water tends to evaporate when the air is warm and condenses as rain or snow in cold air. Water vapor amplifies the warming effects from changes in other greenhouse gases. This water-vapor feedback more or less doubles the temp change we would expect from rising CO2 concentrations without the feedback, in a dry world, for instance.

What is the runaway greenhouse effect?

an extreme water vapor feedback that results in boiling dry the oceans. This happened on Venus but is not expected to happen on Earth

Water vapor is also involved in a positive feedback loop acting on global temperature. Because warmer air holds more water vapor than cooler air, warming allows more water to evaporate before it rains. Water vapor is a greenhouse gas, so its increase tends to warm the planet still further. The water vapor feedback is a positive cycle, powerful enough to more or less double the climate impact of rising CO2 concentrations. Water vapor traps more than CO2 does, but it uses its power to amplify climate changes driven by CO2.

Water vapor is most important as a greenhouse gas at high altitude, where the air is cold. Relative humidity in the coldest air can be lower than at the surface, as dry as 10% relative humidity in the subsiding areas. Climate models tend to predict that the relative humidity of the atmosphere should stay about the same as the temperature rises. Because the saturation vapor pressure increases with temperature, the absolute humidity (number of molecules of water per molecule of air) rises with temperature. So the water vapor feedback still operates, even though the air is not everywhere saturated

Water vapor is responsible for more greenhouse heat trapping on Earth than CO2 is. But no one seems concerned about global warming from running a lawn sprinkler. This is because there's a NEGATIVE feedback loop that controls the amount of water vapor in the atmosphere at any given temperature, having to do with rainfall and evaporation. If there's too much water vapor in the air, it will condense out as rain. In the other direction, if the air is extremely dry, any available liquid water will tend to evaporate into it. So the lawn sprinkler isn't going to lead to any global warming because any water forced to evaporate into the atmosphere today will just rain out the next week.

particles in the atmosphere around which water droplets can form. If condensation nuclei are scarce, the clouds will have fewer droplets, each of which is larger. Sulfate aerosols act as a cloud condensation nuclei, leading to what is known as the indirect effect of sulfate aerosols

cloud condensation nuclei

condensation trails left by aircraft flying in the upper troposphere visible as lines in the sky. After a few days, these may be indistinguishable from cirrus clouds.

contrails

What are the 2 ways in which the ocean can interact with climate?

el nino/la nina & meridional overturning circulation

What is cloud condensation nuclei?

particles in the atmosphere around which water droplets can form. If condensation nuclei are scarce, the clouds will have fewer droplets, each of which is larger. Sulfate aerosols act as a cloud condensation nuclei, leading to what is known as the indirect effect of sulfate aerosols

an extreme water vapor feedback that results in boiling dry the oceans. This happened on Venus but is not expected to happen on Earth

runaway greenhouse effect

reflection of light by cloud droplets. This differs from absorption in that the energy of the light is not absorbed and the frequency of the light is unchanged

scattering

when sulfur is released to the atmosphere from combustion, it forms tiny particles of sulfuric acid. These scatter light and act as cloud condensation nuclei.

sulfate aerosols

What are sulfate aerosols?

when sulfur is released to the atmosphere from combustion, it forms tiny particles of sulfuric acid. These scatter light and act as cloud condensation nuclei.

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