carbon dioxide and the rice video

I’m curious what it is you teach, exactly?

Just to add to this for completeness, the first-order approximation for CO2 radiative forcing is given here. The approximation says that the net change in radiative forcing to the planet, in watts per square meter, is 5.35 times the natural log of the ratio of any given CO2 level to a reference level. We can sanity check this by computing

5.35 ln(400/285)

where 285 ppm is the approximate pre-industrial CO2 level, and we get 1.81 W/m[sup]2[/sup]. This compares very well with the much more precisely calculated and modeled IPCC estimates which have a median value of 1.82 W/m[sup]2[/sup].

It should also be noted that this is net CO2 forcing and doesn’t include other GHGs, nor does it include feedbacks. One of the most important feedbacks is the increase in atmospheric water vapor with rising global average temperature, which acts as a powerful amplifier to the net forcing. So does the darkening of the Arctic surface as less ice and more water (and land) increases sunlight absorption.

They don’t, and no one knows why!

That’s not correct, at least for the Miocene.

I teach high school science.

No, he’s basically correct in his assertion regardless. The problem is that it’s rather silly to use a word like “only” in a context like “only going back hundreds of thousands of years, perhaps a million years” and then concluding that “… you can’t say that CO2 levels are abnormal.” Because going back that far, you’re dealing with an entirely different ecosystem – you may as well think of it as an alien planet. This is going back to the mid-Pleistocene. Our present ecosystem is not just entirely different, it’s also exquisitely finely balanced and sensitive to disruption, with tremendous inter-dependencies that are only vaguely understood, and with troubling and increasing loss of essential biodiversity, to the point that it’s been credibly speculated that climate change is driving us to an ecological if not climatic tipping point and potentially a sixth mass extinction.

The only meaningful measure of relative CO2 levels is the range within which they have varied during the roughly 100ky glaciation cycles of the past million years or so, depending exactly where you want to draw the demarcation point for the beginning of the modern glaciation cycles. This is the earth in which we live, and all the flora and fauna that live with us and on which we intimately depend. And in this era, CO2 levels have varied between a low of about 180 ppm to a high of between 280 and no more than 300 ppm. 400 ppm is unprecedented since the mid-Pleistocene, when nothing even close to humans existed. And further, it’s not going to stop at anywhere near 400 before we can finally get control of it. This is not a small matter. Dredging up ancient tectonic-scale geological history is completely irrelevant to the existential problems we face.

Yeah … you tell them kids their futures are messed up BAD … they’re going to be cooking and there’s going to be nothing but death and destruction and they might as well quit school now and enjoy themselves before the burning eternity of HELL falls upon their fates …

Just going to be cooking … parboiled …

Deniers often use the unexplained and huge climate changes of the past as reason to be unconcerned about present-day changes, but the opposite lesson seems more appropriate. The huge changes in the past show how fragile and potentially unstable climate can be, controlled as it is by some positive feedback loops, e.g. cold → ice formation → even colder from increased albedo.

An Australian perspective, because Roberts is (for our sins) one of us. I would not encourage the OP to resort to ad hominen attacks in class, but some background might be useful.

Roberts is a former coalminer. He has a history of associating with sovereign citizen ideas (Malcolm-Ieuan:Roberts), although he denies current affiliation. He has been a ACG denialists since he saw Gore’s movie. Wiki here.

He was elected to the Australian Senate in 2016 with the One Nation Party. This is a fringe political party created essentially by a politician named Pauline Hanson, and it taps into Alt-Right ideas with which Americans will be familiar. She applauds POTUS in his endeavours, etc. Her party was in the wilderness for a long time, but got some seats around the country in the 2016 election, partly on the back of the international rise in right wing discontent that propelled POTUS to office.

To put some perspective on Roberts’s views, he went on a political TV show here called Q&A and tried to debate climate change with Professor Brian Cox. Here is the debate. Goes for about 20 minutes.

Here is a scathing review of Roberts’s performance from the Sydney Morning Herald (serious national newspaper) about it.

The review might require some local knowledge to fully understand. Gough Whitlam was a former Prime Minister who had a certain grandeur of style, even while he was a Labor man. Norman Gunston was an early proponent of that style of comedy in which the comedian pretends to be a naif while interviewing the great and powerful, a schtick epitomised in the modern era by Sacha Baron Cohen in his various incarnations.

One particualr line from the review I liked was a description of Roberts performing with “all the confidence of a taxi-driver telling Roger Federer what is wrong with his backhand”.

I disagree. Humans transported that far back would feel very much at home. But the subsidiary point is that the atmosphere changes, regardless of humans.

Ah … that’s the big question … yes, the atmosphere changes without human help … but does that also mean humans can’t change the atmosphere … and if they can, then by how much and how quickly?

How much and how quickly the climate changes depends entirely how we classify climate … polar deserts have always been polar deserts and always will be … it’s the nature of heat transport, and that’s not changing …

Only if they are accustomed to being chased by sabertoothed cats on their way to work.:wink:

We have no record of the global atmosphere changing as fast as it currently is in geological history (possibly excluding an asteroid strike). Even other rapid changes have been orders of magnitude slower than the current one, and they often had catastrophic effects. It’s the unprecedented rapidity of the current changes that’s the problem, since adaptation and migration are too slow to keep up with them.

As I’ve said before, the problem is global warming, not global warmth. If the climate consistently stayed warm for a long period of time, that might well be good. But the rapid transition from what we have now to that is the problem.

Here is something else to point out: if the level of CO[sub]2[/sub] were 0 ppm, the Earth would turn into an ice ball. So while it may be “just” a trace gas, the temperature of the Earth is very sensitive to the ppm of CO[sub]2[/sub] in the air.