 Thanks, Jen. Well, welcome again to a climate episode of the Science Circle. I seem to be developing a habit of coming back here. I wanted to talk a little bit today about natural cycles and where they fit in and where they don't fit in. And basically, currently, they don't fit in. But we'll see a little more why I go through this. One of the statements that I frequently encounter goes along the line of earth has always had climate cycles and change. And when people say that, the implication is generally, well, any climate change that occurs is just some natural happenstance. That's like saying, because you have vanilla, you can't have chocolate. The natural climate change and anthropogenic, meaning human cause climate change can both occur. Currently, it's the human cause climate change that's driving things. One of the important cycles is what's called the slow carbon cycle. And it's composed of volcanic emissions of CO2 or emissions from a mid-sea vault. So, again, it's volcanic activity. Over time, rainwater containing CO2 weathers rocks. And that weathering rocks, weathering silicate rocks, actually, brings the cations down into the ocean. It's some of the smaller sea life uses that to form calcium carbonate shells. And if you notice, the carbonate is in there. So, what we've done is removed carbon from the atmosphere-ocean system. When those perimeter die, they sink to the ocean floor. Over time, the shells are compressed to form limestone. And then ultimately, and we're talking time scales of 100 to 300 million years, that limestone is subducted along with whatever plate it's on into the mantle. I've added the comments that a colder ocean can dissolve more CO2. And ice sheets over land can slow down weathering. Basically, if you cover up the rocks, they're not accessible to the rain, which will remove part of the surface. And feel free to ask questions. I'll repeat them as I see them on the screen. I try to answer that. Basically, we've always lived in a greenhouse gas-affected world. If there were no greenhouse gases, then the atmosphere wouldn't interact at all with infrared radiation from the surface. And the temperature that would balance what the surface is currently absorbing is about minus 18 degrees centigrade. Water vapor is actually the strongest greenhouse gas, stronger than CO2 and methane. But the amount of water vapor in the atmosphere is controlled by the concentrations of carbon dioxide and methane. But you would call non-precipitating greenhouse gases. In 2010, LASA said, I'll perform dissimulation, which they zeroed out non-water greenhouse gases. The results are pretty dramatic. After 50 years, the global temperature stands at minus 21 degrees C. That's a global annual average. A decrease of 4.8 degrees C. Actually, that may be one year decrease. Atmospheric water vapor is at 10% of the control climate. Global cloud cover increases from its 58% control value to more than 75%. And the global sea ice fraction goes from 4.6% to 46.7%. Causing the planetary albedo of the Earth to also increase from approximately 29% to 41.8%. This has the effect of reducing the absorbed solar energy to further exacerbate the global cooling. At the current albedo, the radiative balance would be at minus 18 degrees C. So the increased albedo of the Earth cools at another 21 degrees C. That we live in a world with an average surface temperature of plus 15 degrees centigrade can be attributed to natural levels of non-precipitating greenhouse gases. And there's no physical reason to expect that the warming effect will disappear as we increase the concentrations of carbon dioxide. And the reference for the simulation of removing the greenhouse gases is here at the bottom by Lasus et al. Emission of infrared radiation to space occurs in the upper troposphere. And the troposphere is the part below the tropopies. So when we increase greenhouse gases, we make the atmosphere more opaque to infrared radiation. It's emitted to space from somewhat higher. And as you can see here, as you go higher in the troposphere, you go colder. So the emission of infrared radiation is strongly dependent on temperature. When you go colder, you emit less radiation. And if you were in radiative balance before with what the planet was absorbing, you're now emitting less than you're absorbing. And that could be defined as heating. It might be melting ice. It might be heating the deep ocean. But the Earth is taking on energy. To obtain balance, you have to make the new altitude, effective altitude, the same temperature as the prior altitude was. So now you need this to be that warm. And because the whole troposphere is connected by convection, you basically have to move the whole temperature profile to the right, to warmer temperatures. And that's the essence of global warming right there. If the atmosphere were isothermal, meaning all one temperature, you wouldn't have global warming from greenhouse gases. The temperature rises in the stratosphere. You're above the convective zone now. And you're into the ozone layer, which absorbs UV radiation protecting the surface of the Earth. And that absorbed radiation causes the stratosphere to heat. Now one of the interesting things with greenhouse gas warming of the troposphere is less radiation is upwelling from the troposphere into the stratosphere. And so while the troposphere heats, the stratosphere cools somewhat. Good question. Is that making sense to everyone so far? What do we have more questions? Yes, Mike. The collisions redistribute the energy is heat. The collisions also keep CO2 other than right near a source or a sink. Homogeneity is up to about 80 kilometers, which is called the homozone. And convection basically sets the temperature profile in a troposphere. Now the nitrogen and oxygen, although they're not greenhouse gases, do affect the greenhouse gas warming by broadening the lines, absorption lines due to collisions. So there is an effect from the other gases and the total pressure. There's always comments that, well, maybe it's just the sun warming the planet. Looking at this reconstruction of total solar irradiance from 1980 to nearly the present, you see the 11-year sunspot cycle or 11-year solar cycle. But there's no real trend. So the sun is not changing in a way that would be causing climate change, global warming. People have reconstructed back 400 years with much the same result based on correlation between total solar irradiance and sunspots. So basically any change at the present time is not substantially due to the or significantly due to the sun. Yes, Vic. The sun started out weaker, what they call the young sun paradox, and could very well be increasing slowly in magnitude, but like the 0.1% due to the solar cycle that Sisiji just mentioned. The Earth's orbit is not a constant. We think we just go around the sun, go around the sun. We don't really think in our time scale about the orbit of the Earth actually changes. It's perturbed mainly by Jupiter and Saturn over thousands of years. Over time, the Earth's eccentricity changes. That's high eccentricity means it's less round, low eccentricity means it's nearly round. If the eccentricity goes into sync with the precession, for instance, if the northern hemisphere summer is at the far point in a highly eccentric orbit, then you're going to get less radiation in the north hemisphere at about 60 to 65 degrees during the summer and that may be insufficient to melt the previous winter snow. If that continues each year, building up more snow over enough years, you get ice sheets. Shiloh, you had a question? Look at this top graph, which is the orbital eccentricity. Zero is about, current time is about here. In about 2,500 years we'll be reaching an eccentricity minimum, meaning the orbit will be very close to round. With a low eccentricity, you're not going to get extremes of cold or heat. The orbital basically damns out any orbital effect underneath a reconstruction and prediction of solar energy at 65 degrees north. That's an interesting effect because orbital forcing takes extremes and we aren't going to see any extremes for 50,000 years. In the paper I was reading by Berger Edel, the comment was that the last interglation that was similar to what we're in now was 400,000 years ago, not the more recent interglacials. What remains when we eliminate immediate solar variation and orbital forcing is forcing by carbon dioxide that the very rapid human cause increase in atmospheric CO2 concentration, which is a rate far faster than natural changes. CO2 makes the atmosphere more opaque, the infrared radiation. A more opaque atmosphere, meaning radiation to spaces from a higher altitude in the troposphere, it's the reverse of a satellite looking down to an inky atmosphere and basically asking how far can you see down. This is the atmosphere looking upward to space and saying at what atmosphere can I effectively see space. The higher altitude because we are still in the troposphere is colder, meaning less energy is radiated. That's your greenhouse effect right there and the surface and high altitude temperatures are tied together by convection. If you warm the upper atmosphere where you're radiating to come back into balance, you're also warming the surface and with natural CO2, this is where we've always lived, that the average temperature of the Earth has been about plus 15 degrees C and the radiative balance temperature is about minus 18 degrees C. So the natural greenhouse gases have basically kept us from freezing. Balance is regained when the whole vertical temperature profile moves to higher temperatures. So that's what I have in slides and I'm open to taking questions, comments and noting any commas. S is a G. The idea of polluting the air with reflective dust has actually been done naturally. I think that the last major event was the explosion and eruption of Pinatubo in 1991, June 1991 in the Philippines, which blew sulfate into the stratosphere with a half-life of about 13 months and increased the reflectivity of the atmosphere and a cooling, which was a natural experiment in looking at the effects of heating and cooling on cloud cover and also just the effect of a cooling that is different than the radiative heating. And thank you all for coming. It's been my pleasure.