Greenhouse effect and greenhouse gases | High school biology | Khan Academy

The greenhouse effect, driven by gases like carbon dioxide, methane, and water vapor, is essential for maintaining Earth's habitable temperatures. However, excessive concentrations of these gases—particularly due to human activities—can lead to global warming and climate change.

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[dylantjaviation]

great! learning more things everyday not just me playing video games all day

[BertWald-wppz]

The other half of the explanation of Greenhouse gasses deals with the way the earth absorbs light reaching the surface and re-emits this as a black body in the form of long wave radiation which is what the CO2 is absorbing then re-transmitting. What often gets omitted from explanations is the absorption spectrum of CO2 which is relatively narrow plus at a certain point it becomes saturated because it has absorbed as much as it can. This can be measured. Then there is the issue of treating the earth’s surface as a black body because this is a function of temperature difference between emitter and surroundings which is not always positive - think of the sea. It also is affected by the colour. Add to this that the theory is based on a vacuum and there are a load of new questions that need to be addressed in even a simple explanation such as this so as to avoid the error of assuming all questions have been answered. Weather systems including evaporative heat loss and wind are also driven by energy from the sun though exactly how much energy is tied up in this does not appear in the explanation. Cloud reflectivity is considered but difficult to model. To cause a serious problem positive feedback is required due to increased humidity but this is also only crudely modelled. So far I have not found the answers. It does however go some way to explaining why to the average person the climate models appear poor predictors and justified retrospectively.

[douglasengle]

My Falls Church VA USA high school George C. Marshall science in the late 1970s told that earth's greenhouse effect was the model of a system always in saturation from the strong greenhouse gas water vapor that adds 10°F (5.55°C) to the earth's average temperature and takes place within 20 meters of the surface, typically the earth. After 20 meters from the radiating surface all the greenhouse radiant energy has been completely absorbed by greenhouse gases. Its further heat transfer is by convection i.e. gas molecules bumping into each other. At 1% average tropospheric water vapor over 99% of earth's greenhouse effect is from water vapor. This is a short and definitive description of the greenhouse effect.

Once a system is in saturation it can no longer be made to have further effect by increasing its active elements. The greenhouse effect is frequently studied in high school as demonstration of the physical property of a system always in saturation. The noncondensing greenhouse gases can not change the overall greenhouse effect. They could be theoretically removed or increased many times and the overall greenhouse effect would remain the same. The greenhouse effect is frequently used as the model of system always in saturation from water vapor even though water vapor varies hugely across the earth's surface. The variance is made up by the statement within 20 meters of the surface. In many situations all the greenhouse radiant energy is completely absorbed by greenhouse gases in a distance less the 20 meters from the radiating surface.

The United Nation's IPCC science report in its back pages acknowledges that it is NOT in-fact discussing greenhouse gases in a manor constructive to the discussion of global warming by a legal statement of data transparency that it took its greenhouse gas samples at 20, 000 meters altitude and only that one altitude. There is no greenhouse radiant energy more than 20 meters from the radiating surface, typically the earth. That IPCC data transparency statement of 20, 000 meter altitude gas sampling is acknowledging it is not dealing with active greenhouse gases of earth greenhouse effect in a manor constructive to the discussion of global warming. This is the same marketing practice that takes place when a beverage is labeled "All Natural Fruit Flavors" and then in the ingredients it tells the truth "contains no actual fruit juices"

Global warming has been paused at about 1°C since the early 1990s. Global warming was reported at 1.1°C in 1991 and 1.06°C in 2022.

The physics mechanics of the greenhouse effect is that a certain band width of the far inferred radiation from surface interacts loosely with the lumpy electrostatic fields of greenhouse gas molecules typified by gas molecules of largely differing sized atoms such as H2O water vapor and CH4 methane. CO2 carbon dioxide is almost inert as a greenhouse gas. The diatomic gas molecules O2 and N2 have no interaction with greenhouse radiant energy. Once the greenhouse radiant energy has been absorbed by greenhouse gas they do not reradiate the energy as their main heat transfer. Heat transfer is by convection i.e. gas molecules bumping into each other. It is a one way energy transfer in the electromagnetic spectrum used by the greenhouse effect.

[Ask_]

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[joeyk]

Why doesn't the CO2, for instance, block incoming radiation from the sun at the same rate it blocks it from the earth? Why is it not a net zero effect?

[samlair]

If not for gases like carbon dioxide, the Earth’s biosphere would be perpetually frozen solid because infrared radiant energy is absorbed only by greenhouse gas molecules (not by nitrogen or oxygen). The absorption of this energy causes the greenhouse gas molecules to vigorously vibrate and bump into and impart kinetic energy to surrounding air molecules. The total atmospheric field of kinetic and radiant energy is what registers as temperature.

Note: Though it’s often pointed out that nitrogen and oxygen comprise 99% of the atmosphere, it’s seldom mentioned that they are unable to absorb infrared energy. Their contribution to atmospheric temperature is their ability to transfer the kinetic energy that they receive from vibrating greenhouse gases.

[miked]

I enjoyed your presentation. thank you for sharing it.

Have you considered that in the presence of the atmosphere the Earth's Surface is not radiating more than trace amounts of infared?

This would be wonderful news for mankind as it would mean that CO2 has no IR to absorb and thus is not a danger to the plant.

Basic physics suggests the Earth's energy (99%) is dissipated thru conduction and confection to the top of the atmosphere where it will then radiate harmlessly to space.

[DesigningInFigma]

I finally have a clear understanding! Thank you!

[SwaSwaPlayz]

Thank you so much! Loved the explanation!

[gufpott]

The idea of a GHE might have merit, but the idea of an Enhanced GHE (sensitivity to CO2) doesn't. For the extra absorption of IR in the atmosphere to have a warming effect on the surface, the warming aloft has to exceed the temperature rise at the surface. Nothing could have a radiative warming effect unless the radiator rise in temperature exceeds the temperature rise of the IR absorber. All (yes ALL) of the climate models predict this particular pattern of warming, and it became known as the "tropospheric hotspot" . Only thing left to do was to observe it to confirm this exists in the REAL atmosphere (not the MODELLED atmosphere). But it isn't observed. They first tested this 15-20 years ago and reported the failure in the literature. More observations have not changed this observation. There isn't an Enhanced Greenhouse Effect or sensitivity to CO2 in the REAL atmosphere. That's an observation and it is decisive. The physics behind all the MMGW theory doesn't work in the real world.

[kimlibera]

Let me offer a critique. First, 800, 000 years is a blip in geochronology. The video that focuses on just this one period neglects all the other geochronological periods including the first & the other 5 ice ages. Also I would not begin the video focusing on the composition of the atmosphere starting with greenhouse gases because that neglects the 2 major gases. Thus it can give the impression that our atmosphere is dominated by co2 & h2o.

[kayjay]

The largest source of greenhouse gas is The Congress of The United States.😢I am a citizen of the United States😢.

[karlostj]

1. Of all the radiation energy absorbed by the ground and the seas, how much is re-radiated as "blackbody" (aka, temperature-caused) radiation? NO ANSWER
2. Of the "greenhouse" gases in the atmosphere - notably H2O, CO2, and CH4 - how much of the "blackbody" radiation is absorbed by each (aka, what is their "absorption spectrum")? NO ANSWER
3. Of the "greenhouse" gases in the atmosphere and their absorption of "blackbody" radiation, how much of that radiation is re-radiated (aka, what is their "emission specrtum")? NO ANSWER
4. If CO2 absorbs less "blackbody" radiation than H2O (and CO2 absorbs FAR LESS BBR than does H2O), how can CO2 be responsible for "global warming" of the atmosphere? NO ANSWER

This is yet another gaslighting video, making fact-free and science-free statements. It'd be great if "Khan Academy" provided the CV of this narrator, who doesn't seem to understand anything about basic sciences such as physics or thermodynamics. Which makes the narrator yet another soapbox snake-oil preacher.

[Xhoppr]

When man was emitting close to 0 greenhouse gasses, the concentration of greenhouse gasses was still high. Sure the concentration went higher once man starting emitting greenhouse gasses according to the graph, but the 800k years graph shows the same spikes prior to man.

[petermukooza]

so simply put - I can have any amount of greenhouses, all I have to do is put holes in them?

[AdeToz]

This video is incredibly misleading and myopic is scope. The narration states that the temperature of earth is driven radiative forces. What he doesn't say is that the overwhelming driver of temperature in the troposphere are convective forces which are essentially driven by the atmospheric pressure and are not controlled by the nature of the gases in the troposphere. This one single fact is why the greenhouse model is a myth. I expect more from Khan Academy.

[TurboSol]

Important topic but earth will be fine, it's gone through periods of CO2 ppm in the thousands and life flourished like never before (around the time of the Cambrian explosion). The doomsday predictions are just fantasy but just because earth will be fine it doesn't mean it won't cause us humans problems.

[josiahwetter]

Hi do they know the green house has levels from four million years ago without the technology to monitor back then?

[Scott]

Nice cartoon. Can you show us the GHE being physically measured in reality?

[troydixon]

Does Oxygen not radiate? It seems to me that more compounded particles in the atmosphere would deduct heat from electro radiation to psychical surfaces by radiating the particles and processing them back into physical vegetation objects and the oceans. Like a cloud would block the sun from the mercury and the human. How does the energy from a gas compound heat anything? Gas particles don't store any energy compared to the physical. All the particle does is move around and process back into the planet. I mean, when it gets warmer the vegetation grows faster. Every lawn mower man knows this. I don't see how it has any affect on the physical temperature. You lose energy when you shiver. As for rising sea levels, what about the procession wobble (chandler effect)? We see cyclical storms (intensity and frequency level patterns) of 10, 30 and 100 years. If you look at all the records we have. We don't have them all. How do you gather infra red on the dark side of the planet? How are there ancient trees all over the Earth? How is carbon dating not considering other potential variables as well? You can't get a statistic from a limited data set anyway. The bell curve only works with a sample from complete data set. Even then it's plus or minus 4, right? What ever that means. I think the less cultivation the worse the storm potential is. The more trees and vegetation with an increase in Oxygen, which has more electrons than the carbon element, the more kinetic energy there is in the atmosphere the stronger the winds can get. I think human cultivation and vegetation management stabilizes the planet's weather. But then you got too many bats and covid. I think Carbon sinks and Oxygen is suspended for biological life. I think if all the humans and animals died it would be a massive violent storm. Makes sense to the color spectrum, the sky is blue, the carbon is green.