Introduction to AGW

HBS Guy

Head Honcho
Staff member
AGW has enormous impact on plants and critters, surface and marine. It is therefore extremely relevant to this board.

Temp_change_last_8000yrs_inck_Milankovitch_Cycle_001.jpeg

I find this an extremely interesting graph for many reasons:

The orange curve is the Milankovitch cycle, insolation (sunlight reaching the surface) north of 60°N latitude. When it is low the NH gets very cold and major ice ages form. This has happened at 100,000 year intervals for the last 800,000 years. It is due to regular changes in the orbit of our planet and the inclination of the axis of rotation, precession of Equinoxes etc.

At about 4500 years ago the Milankovitch Cycle started declining and is getting close to bottom. We see temperatures start to decline, but they start to decline slower and slower over time. Hmmm what could the reason be?

As the chart shows: intensive agriculture started in 5500. This means deforestation, more animals to pull ploughs and carts, more cities–agriculture is not carried out by nomads.

As cities and intensive agriculture continued and the human population grew more and with it the number of draft, dairy and meat animals more and more CO2 was generated. Eventually the Industrial Revolution took off and is still spreading and the globe has warmed 1.1°C since 1905.

I will do some research into the decline in insect populations and why they are declining. AGW will be part of it I am sure.
 

HBS Guy

Head Honcho
Staff member
Despite forcings from the Milankovitch Cycle the Arctic is not getting colder—Arctic ice has been disappearing all through the satellite period 1979–. The last two melt seasons have seen massive amounts of Arctic Sea Ice melt in place or melting after being exported from the Arctic Ocean down the Framm Strait (between Greenland and the Svalbard archipelago.)

Scientists examining climate forcings find that CO2 by far has the biggest influence.

In the Arctic there is another positive feedback: albedo is decreasing.

A world completely covered with ice—which has happened twice, both times ended by CO2 from volcanic eruptions causing warming—has a high albedo. A world, or an object, that is all black has a very low albedo. High albedo surfaces reflect a lot of radiant energy away, low albedo surfaces, like exposed Arctic Ocean, absorb sunlight and are warmed by it. This sees more bottom of the ice melting in what should be the freezing season. Salty warm water is heavier than colder but fresh, not salty, water. Hence a lot of the huge amount of heat absorbed by the Arctic Ocean this NH summer is still there 30 Sep 2020, until conditions change.

So no ice age major or minor is happening any time soon. Warming is what is happening, more and more heat accumulating especially in the oceans.

CO2 is accumulating in the oceans too*, making them more acidic due to the increase in H+ and HCO3+ ions. This is causing problems for small fauna in the oceans, zooplankton. Terrestrial heat dries out vegetation causing any fires started by dry lightning to burn much more fiercely, killing huge numbers of animals and destroying property and killing people.

*Some say the oceans are outgassing CO2, that heat causes the growth in CO2, not burning fossil fuels. A preposterous notion probably floated by FF interests. Oceans do lose their ability to absorb gases as they warm. But the oceans are so vast and the specific heat of water is so high that the nearly 50% increase in partial pressure of CO2 vastly outweighs the effect of the tiny temperature increase on solubility. The oceans absorb over half of the manmade CO2 absorbed by carbon sinks.
 

HBS Guy

Head Honcho
Staff member
In 1859, Tyndall showed that gases including carbon dioxide and water vapour can absorb heat. ... He realised that any change in the amount of water vapour or carbon dioxide in the atmosphere could change the climate. His work therefore set a foundation for our understanding of climate change and meteorology.

https://theconversation.com/john-tyndall-the-forgotten-co-founder-of-climate-sci...

There is one difference between CO2 and water vapor: water vapor condenses and falls out as rain, hail or snow, CO2 at our temperatures does not (not even on the top of the Antarctic Plateau because the partial pressure is too low: any CO2 that may freeze there sublimates back to gaseous CO2 quickly.)

CO2 is the driver of global warming, water vapor is a feedback: More CO2 more warming the more warming the more water evaporates from the oceans and the more water vapor the more warming.

Our planet is a globe in a vacuum that is hit everyday by radiation including UV, visible light and a small amount of near infrared. This warms our globe causing IR to be radiated by it which acts to cool the climate. Want to know more? Read up on black bodies and the Stefan-Boltzmann law governing how much radiation is emitted from a surface:

https://www.britannica.com/science/Stefan-Boltzmann-law

If this infrared radiation reaches space then the planet is cooled. Look at our Moon, located in the same area of space as us, it has huge temperature swings between light and dark—no atmosphere with greenhouse gases in it to moderate temperature loss.
 

HBS Guy

Head Honcho
Staff member
So a photon of IR (radiation in the far infrared part of the spectrum of electromagnetic radiation) is emitted from the surface. There are billions of CO2 molecules in every cubic centimetre of the atmosphere near the surface known as the lower troposphere. One of these molecules will absorb the IR photon within a few metres of the surface.

That molecule of CO2 is “excited” or has an increase in its energy level. The two oxygen atoms vibrate around the carbon atom. Within an incredibly short time the CO2 molecule collides with thousands of nitrogen and oxygen molecules, transferring its extra energy to these molecules that do not absorb IR themselves.

As we increase atmospheric CO2 we are decreasing the amount of IR reaching space which means we are decreasing the ability of the surface + lower troposphere to cool. There is no doubt about that:

Spectrum_looking_down_001.png

BTW, atmospheric CO2 and its greenhouse effect is not saturated. As CO2 concentrations increase the spectrum lines where CO2 absorbs IR widen.

There is also a more important effect:

What happens to infrared radiation emitted by the Earth’s surface? As it moves up layer by layer through the atmosphere, some is stopped in each layer. To be specific: a molecule of carbon dioxide, water vapor or some other greenhouse gas absorbs a bit of energy from the radiation. The molecule . . .transfer the energy into velocity in collisions with other air molecules, so that the layer of air where it sits gets warmer. The layer of air radiates some of the energy it has absorbed back toward the ground, and some upwards to higher layers. As you go higher, the atmosphere gets thinner and colder. Eventually the energy reaches a layer so thin that radiation can escape into space.

What happens if we add more carbon dioxide? In the layers so high and thin that much of the heat radiation from lower down slips through, adding more greenhouse gas molecules means the layer will absorb more of the rays. So the place from which most of the heat energy finally leaves the Earth will shift to higher layers. Those are colder layers, so they do not radiate heat as well. The planet as a whole is now taking in more energy than it radiates (which is in fact our current situation). As the higher levels radiate some of the excess downwards, all the lower levels down to the surface warm up. The imbalance must continue until the high levels get hot enough to radiate as much energy back out as the planet is receiving.

Any saturation at lower levels would not change this, since it is the layers from which radiation does escape that determine the planet’s heat balance. The basic logic was neatly explained by John Tyndall back in 1862: "As a dam built across a river causes a local deepening of the stream, so our atmosphere, thrown as a barrier across the terrestrial [infrared] rays, produces a local heightening of the temperature at the Earth’s surface."

Any saturation at lower levels would not change this, since it is the layers from which radiation does escape that determine the planet’s heat balance. The basic logic was neatly explained by John Tyndall back in 1862: "As a dam built across a river causes a local deepening of the stream, so our atmosphere, thrown as a barrier across the terrestrial [infrared] rays, produces a local heightening of the temperature at the Earth’s surface."

I suggest everyone interested (for or against) AGW read the above article in full.
 

HBS Guy

Head Honcho
Staff member
I think all here know we have warmed and that the warming is anthHistorical_solar_activity_reconstruction.jpegropogenic in origin.

We also know that there is no GSM now or soon:
 
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HBS Guy

Head Honcho
Staff member
I wrote this intro at OzPol to discuss how AGW affects critters—the subject of my MRB there. One effect Seth might know of is the boost to pine bark beetle populations.
 
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