How Earth sheds heat into space

Earth
A composite image of the Western hemisphere of the Earth. Credit: NASA

Just as an oven gives off more heat to the surrounding kitchen as its internal temperature rises, the Earth sheds more heat into space as its surface warms up. Since the 1950s, scientists have observed a surprisingly straightforward, linear relationship between the Earth's surface temperature and its outgoing heat.

But the Earth is an incredibly messy system, with many complicated, interacting parts that can affect this process. Scientists have thus found it difficult to explain why this relationship between surface temperature and outgoing is so simple and linear. Finding an explanation could help climate scientists model the effects of climate change.

Now scientists from MIT's Department of Earth, Atmospheric and Planetary Sciences (EAPS) have found the answer, along with a prediction for when this linear relationship will break down.

They observed that Earth emits heat to space from the planet's surface as well as from the atmosphere. As both heat up, say by the addition of carbon dioxide, the air holds more , which in turn acts to trap more heat in the atmosphere. This strengthening of Earth's greenhouse effect is known as water vapor feedback. Crucially, the team found that the water vapor feedback is just sufficient to cancel out the rate at which the warmer atmosphere emits more heat into space.

Their findings, which appear today in the Proceedings of the National Academy of Sciences, may also help to explain how extreme, hothouse climates in Earth's ancient past unfolded. The paper's co-authors are EAPS postdoc Daniel Koll and Tim Cronin, the Kerr-McGee Career Development Assistant Professor in EAPS.

A window for heat

In their search for an explanation, the team built a radiation code—essentially, a model of the Earth and how it emits heat, or , into space. The code simulates the Earth as a vertical column, starting from the ground, up through the atmosphere, and finally into space. Koll can input a surface temperature into the column, and the code calculates the amount of radiation that escapes through the entire column and into space.

The team can then turn the temperature knob up and down to see how different surface temperatures would affect the outgoing heat. When they plotted their data, they observed a straight line—a linear relationship between surface temperature and outgoing heat, in line with many previous works, and over a range of 60 kelvins, or 108 degrees Fahrenheit.

"So the radiation code gave us what Earth actually does," Koll says. "Then I started digging into this code, which is a lump of physics smashed together, to see which of these physics is actually responsible for this relationship."

To do this, the team programmed into their code various effects in the atmosphere, such as convection, and humidity, or water vapor, and turned these knobs up and down to see how they in turn would affect the Earth's outgoing infrared radiation.

"We needed to break up the whole spectrum of infrared radiation into about 350,000 spectral intervals, because not all infrared is equal," Koll says.

He explains that, while water vapor does absorb heat, or infrared radiation, it doesn't absorb it indiscriminately, but at wavelengths that are incredibly specific, so much so that the team had to split the infrared spectrum into 350,000 wavelengths just to see exactly which wavelengths were absorbed by water vapor.

In the end, the researchers observed that as the Earth's surface temperature gets hotter, it essentially wants to shed more heat into space. But at the same time, water vapor builds up, and acts to absorb and trap heat at certain wavelengths, creating a greenhouse effect that prevents a fraction of heat from escaping.

"It's like there's a window, through which a river of radiation can flow to space," Koll says. "The river flows faster and faster as you make things hotter, but the window gets smaller, because the greenhouse effect is trapping a lot of that radiation and preventing it from escaping."

Koll says this greenhouse effect explains why the heat that does escape into space is directly related to the surface , as the increase in heat emitted by the atmosphere is cancelled out by the increased absorption from water vapor.

Tipping towards Venus

The team found this linear relationship breaks down when Earth's global average go much beyond 300 K, or 80 F. In such a scenario, it would be much more difficult for the Earth to shed heat at roughly the same rate as its warms. For now, that number is hovering around 285 K, or 53 F.

"It means we're still good now, but if the Earth becomes much hotter, then we could be in for a nonlinear world, where stuff could get much more complicated," Koll says.

To give an idea of what such a nonlinear world might look like, he invokes Venus—a planet that many scientists believe started out as a world similar to Earth, though much closer to the sun.

"Some time in the past, we think its atmosphere had a lot of water vapor, and the would've become so strong that this window region closed off, and nothing could get out anymore, and then you get runaway heating," Koll says.

"In which case the whole planet gets so hot that oceans start to boil off, nasty things start to happen, and you transform from an Earth-like world to what Venus is today."

For Earth, Koll calculates that such a runaway effect wouldn't kick in until global average temperatures reach about 340 K, or 152 F. Global warming alone is insufficient to cause such warming, but other climatic changes, such as Earth's warming over billions of years due to the sun's natural evolution, could push Earth towards this limit, "at which point, we would turn into Venus."

Koll says the team's results may help to improve climate model predictions. They also may be useful in understanding how ancient hot climates on Earth unfolded.

"If you were living on Earth 60 million years ago, it was a much hotter, wacky world, with no ice at the pole caps, and palm trees and crocodiles in what's now Wyoming," Koll says. "One of the things we show is, once you push to really hot climates like that, which we know happened in the past, things get much more complicated."


Explore further

Scientists pinpoint the key mechanism for amplification of global warming

More information: Daniel D. B. Koll el al., "Earth's outgoing longwave radiation linear due to H2O greenhouse effect," PNAS (2018). www.pnas.org/cgi/doi/10.1073/pnas.1809868115
Citation: How Earth sheds heat into space (2018, September 24) retrieved 20 October 2019 from https://phys.org/news/2018-09-earth-space.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
192 shares

Feedback to editors

User comments

Sep 24, 2018
Except the out-going radiation to space has not increased one iota since we had had satellites up there measuring it.

Sep 24, 2018
Heat is a changing E field that aggravates charge centers. Since all charge centers feel the field, they all respond. As atmosphere is constantly being bombarded with Plane Waves and charge centers; then, because we've added more centers into our air, it will get hotter. When it gets hot enough to release these centers, we become a comet orbiting the sun, i.e. How heat is shared into the space from which it comes!

Sep 24, 2018
Except the out-going radiation to space has not increased one iota since we had had satellites up there measuring it.


Is an "iota" an SI unit of power or one you made up?

Sep 24, 2018
Except the out-going radiation to space has not increased one iota since we had had satellites up there measuring it.


Is an "iota" an SI unit of power or one you made up?

That implies the Earths reflective properties don't change with satellites and the Earth's Luminescence is constant. Think this is accurate?

Sep 24, 2018
ATTACH a L shaped PIPE to a SMALL Volcano and See what happens. The Vertical Pipe of L should face towards the Sky. (To do it, we do need a Vertical Tunnel to go down on the side of the Volcano first).
If it succeeds, we will have FREE Thermal Energy in the future.
Widen the bottom of the tunnel to attach horizontal pipes.

Sep 24, 2018
ATTACH a L shaped PIPE to a SMALL Volcano and See what happens. The Vertical Pipe of L should face towards the Sky. (To do it, we do need a Vertical Tunnel to go down on the side of the Volcano first).
If it succeeds, we will have FREE Thermal Energy in the future.
Widen the bottom of the tunnel to attach horizontal pipes.

USE ROBOTS, since it could be dangerous to do it.

Sep 24, 2018
ATTACH a L shaped PIPE to a SMALL Volcano and See what happens. The Vertical Pipe of L should face towards the Sky. (To do it, we do need a Vertical Tunnel to go down on the side of the Volcano first).
If it succeeds, we will have FREE Thermal Energy in the future.
Widen the bottom of the tunnel to attach horizontal pipes.

USE ROBOTS, since it could be dangerous to do it.

Whatever the specs are, don't trust those that built The Twin Towers! Check ya metal. A lot of stuff just melts, juz sa'ing

Sep 24, 2018
It would seem that the extinction theory from global warming just got a lot more plausible. So all the sudden heat does accumulate much quicker with water vapor being the trapping element. Yikes.

Sep 24, 2018
Please learn what the word 'range' means. They weren't specifically referring to the range 0 K to 60 K.

Sep 24, 2018
@barkan, I corrected it. Just refresh. I did see the word 'range' after I submitted.

Sep 24, 2018
Sheesh! I thought that climate prediction had moved on beyond 1-d models. This model is, in effect modelling only the column of air above one point on the Earth's surface. The problem with such models is that the lock the air in place, and there is no way for circulation patterns to move warm air past cold air or vice-versa. This means that radiation is the only way for heat to move--convection is ruled out.

Also what make this article even sillier, is the discussion of an average temperature of 152 F. With a single point model, it might be possible to get to 152 F in Death Valley or other hotspots, not to mention erupting volcanoes. But if it were a real global average temperature, there would be areas much colder (the poles) and hotter--the equatorial oceans boiling away.

Sep 24, 2018
Except the out-going radiation to space has not increased one iota since we had had satellites up there measuring it.

And why should it increase? The radiation out should more or less equal the solar radiation coming in*. Note that this study only studies longwave radiation and does not appear to include cloud cover or surface albedo affects, especially from ice, which reflect a large amount of shortwave radiation. Of course this news release was released prior to the actual publication of the paper, so this is partly conjecture.

* not counting energy absorbed during phase changes (ice -> water -> vapor), energy produced during combustion of fossil hydrocarbons, etc..

Sep 24, 2018
Sheesh! I thought that climate prediction had moved on beyond 1-d models.
Global Climate Models have to take a lot of shortcuts to reduce the problem to a manageable size. Models like this help make sure that the assumptions used in GCMs are correct.
This model is, in effect modelling only the column of air above one point on the Earth's surface....--convection is ruled out.
"The team can then turn the temperature knob up and down to see how different surface temperatures would affect the outgoing heat... the team programmed into their code various effects in the atmosphere, such as convection, and humidity, or water vapor, and turned these knobs up and down to see how they in turn would affect the Earth's outgoing infrared radiation." Did you actually read the article, eachus?

Sep 25, 2018
I have as much faith in climate models as I do in voodoo, but it's an interesting finding. It does fit in with observations that earth's climate has feedback mechanisms that tend to attenuate rather than amplify warming.

Global warming alone is insufficient to cause such warming

If true, that should put the final in the coffin of global warming alarmism, but one should never underestimate the capacity for hysteria of the science-challenged.

My prediction? Alarmists will dismiss this as another "outlier". Because 97 percent consensus, or something.

Sep 25, 2018
I have as much faith in climate models as I do in voodoo, but it's an interesting finding. It does fit in with observations that earth's climate has feedback mechanisms that tend to attenuate rather than amplify warming.

No, it doesn't. Objects should radiate energy proportional to their temperature to the fourth power (Stefan–Boltzmann law), but the warming Earth throws on an extra water vapor blanket to SLOW the radiation output so that it varies only linearly with (surface) temperature. It is therefore exacerbating the warming, not attenuating it.
Global warming alone is insufficient to cause such warming

If true, that should put the final in the coffin of global warming alarmism

The "insufficient" statement was in reference to an average temperature of 152 F, which no proponent of AGW has suggested as a possibility. So aksdad has made a strawman argument which can be safely ignored.

Sep 25, 2018
b, I wish I had your optimism! However, thee ugly reality is once the denier shills such as ad start agitpropping their falsehoods? They never give up repeating themselves, hoping repetition of lies, will wear down resistance to their fraudulent claims.

Sep 25, 2018
Easier to simply die.

Sep 25, 2018
Global Climate Models have to take a lot of shortcuts to reduce the problem to a manageable size. Models like this help make sure that the assumptions used in GCMs are correct.

Let me do that for you. There are two primary forcing effects on global temperature, GHG, including water, and explosive volcanic eruptions. Ash, and smoke contribute, but the major effect is global cooling due to sulphur dioxide reaching the stratosphere. This spreads worldwide in about a year, and causes global cooling. Look up the eruption of Mt. Tambora in 1815, and you will realize that all the global warming alarmists have it backwards. Cooling from the VEI 8 Toba eruption about 75 thousand years ago almost wiped out the human race. Some other species were not so lucky. Over a billion year span these two effects must cancel out on average. Any correct (but useless) climate model will tell you it will keep getting warmer until most people freeze to death (or starve). Wash, rinse, repeat.

Sep 25, 2018
@barakan says;
Earth throws on an extra water vapor blanket to SLOW the radiation output so that it varies only linearly with (surface) temperature. It is therefore exacerbating the warming, not attenuating it.


That is exactly the meat of this article. This is just another big piece of meat that describes the dire situation that global warming has created for our planet. This is so extreme of a problem that I'm stunned at how many denier types we run into here. I can always say that 10 years ago we were looking at H2O evaporation from the oceans as causing a feedback loop that would add on to, or basically pile-on to, the problem of CO2 global warming. It's unfortunate that this has fallen into a political split among people that are going to suffer.

I don't think the deniers recognize how dire the situation is for the future of the human race and the rest of the planet that we master from global warming.

Sep 25, 2018
@eachus; It's CO2 you big dummy that's the cause of global warming. All of the others or just add ons to what the end result is.

Sep 26, 2018
I DON'T THINK the deniers recognize how dire the situation is for the future of the human race and the rest of the planet that we master from global warming.

howhot3..aka...howShat da Turd brays again.
This jackass believes CO2 means dire consequences for humans. Yet, he rode into NYC, spewing CO2 all the way, just to snort the methane from his False "Profit", Al Gore.
This Chicken shit jackass is correct when he claims -- "I DON'T THINK.."

Sep 26, 2018
@eachus; It's CO2 you big dummy that's the cause of global warming. All of the others or just add ons to what the end result is.

howhot3: GHG stands for greenhouse gases. Water vapor and CO2 are the two biggest on Earth, but there are also methane and other hydrocarbons. There are areas like deserts and near the poles where CO2 is the primary GHG. Water vapor is by far the most complex, it can turn into clouds, rain or ice crystals so just the percentage of H2O doesn't tell you much.

The point you, and most other AGW advocates miss is that GHG gradually warm the earth, explosive volcanic eruptions can wipe out a century or more of global warming in a day. This graph https://upload.wi...cord.png helpfully marks the drop from the Mount Pinatubo eruption in 1991. It was one of about half-a-dozen VEI 6 eruptions in the past century. VEI 6: -0.4 C, VEI 7: -2..-3 C, VEI 8: ???

Sep 26, 2018
You are overstating the case. Your own graph shows that Pinatubo wasn't able to wipe out a century of warming, in fact it wasn't able to wipe out the amount of warming that started in 1985, only 6 years prior to the eruption. Your graph shows the Pinatubo effect only lasting a couple of years. And your graphs show a handful of other dips in the annual average that aren't correlated with large volcanic eruptions.

Sep 26, 2018
ATTACH a L shaped PIPE to a SMALL Volcano and See what happens. The Vertical Pipe of L should face towards the Sky. (To do it, we do need a Vertical Tunnel to go down on the side of the Volcano first).
If it succeeds, we will have FREE Thermal Energy in the future.
Widen the bottom of the tunnel to attach horizontal pipes.

USE ROBOTS, since it could be dangerous to do it.

https://www.techn...st-bets/

Oct 15, 2018
You are overstating the case. Your own graph shows that Pinatubo wasn't able to wipe out a century of warming, in fact it wasn't able to wipe out the amount of warming that started in 1985, only 6 years prior to the eruption.

There are ocean oscillations in both the Atlantic and Pacific that have to be accounted for, so you probably heard about the twenty year "pause" in global warming around the turn of the century. But all that is detail. There is a scale for explosive volcanoes. A VEI 6 eruption like Pinatubo, is about ten times more powerful than a VEI 5, like Mt. St. Helens. There are, on average several VEI 6 eruptions per century. There are several VEI 7 eruptions per millenium. (How many? The count keeps increasing, one every century or three is about right.) The last was Mt. Tambora, in 1815. 1816 was called the year without summer, and global crop failures resulted in mass starvation and disease. The most recent VEI 8 (Toba) almost wiped out the human race.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more