[dividido]

This is something taught about in most introductory earth science classes in college and is pretty interesting. Recently, I've seen it referenced as a means to debunk global warming as the historical evidence of the fluctuation of temperature throughout history and natural global warming. However, it doesn't account for anthropogenic changes in CO2 output, albedo changes as ice masses melt, and of course cow farts.

[tasty_freeze]

Seconded -- I know little about climate science, but I have faith that the people who have PhDs in in and have dedicated their working lives to learning more are aware of Milankovitch cycles. Yet over and over some other internet dummy who is no more educated on the subject than me will dismiss the IPCC report and triumphantly say something like, "AGW is a hoax. The climate changes cyclically because of Milankovitch cycles", as if climate scientists had never heard of it or hadn't factored that into their models already.

Another good one is when they will trot out some statistic, say, 30M years ago the CO2 levels were at 4000ppm and we are doing just fine. What they seem to fail to recognize is that the only reason they have that knowledge is due to climate researchers. Somehow the deniers will accept climate research if they think it supports their position, but then will decry the researches as ignorant, as if the climatologists weren't aware of the very facts they have amassed.

[chrisweekly]

Speaking of PhD's, a little more than 20 years ago I was an undergrad at the University of Virginia (the top-ranked public university at the time, top-20 overall in the US). I took a class on atmospheric environment, and the instructor was (he claimed, and I had no reason to doubt) the first and only person in the US with a PhD in the subject. I remember being a bit disenchanted with his take on anthropogenic global warming; he seemed to take it as a given that the students all believed AGW to be a real and serious problem, and all semester long espoused a very fossil-fuel-industry-friendly perspective. I was unhappy to learn that funding for his position came in large part directly from said industry. (What's that quote about people having trouble understanding something if their livelihood depends on not understanding it?)

[krona]

False equivalence? Research about things which happened in the past are empirical, and it matters little who discovered them. Predictions about future events are not empirical, since they have not happened.

[Fellshard]

Extrapolations from data measured in the present to assume the state of the past is not empirical in the same way as actively measuring the state of the past empirically.

[danioli]

It's not that I'm sceptical of climate science, it's just that the discussion is now... entrenched. The random person will not debate the wisdom of human-induced changes to the weather, but also will probably not understand the Milankovitch cycles, or know the ocean water levels rise and fall on geological timescales by about 130 meters?, that we know this because (IIRC) of Wallace (I think, in tandem with Darwin?) who also noted that the divergence between different variants of the same species across the islands of an an archipelago varied more with the depth of the water between islands, than with just the distance. What about the PET (Paleocene-Eocene transition)? I'm sure that climate scientists are doing their jobs, but that doesn't mean that there aren't many (including "activists") who are willing to debate the matter without this key. Why doesn't this ever come up? (both the cycles, and the lack of depth in the discussions) If it's as dire as some seem to imply, we should all switch to nuclear right now. And personally, I am even more sceptical when I hear talk of climate justice, but that is an entirely different issue.

[tasty_freeze]

If I said human activity doesn't affect the stock market -- it just operates on cycles. It goes up for awhile, then it goes down for awhile, you'd rightfully laugh at me. But that is exactly what you are doing about AGW.

Yes, the climate has changed in the past. But that doesn't mean the driver of those historical changes is driving the current change. People have always died, but that doesn't mean we shouldn't require safety devices in automobiles. Second, "cycles" is just way too blithe of a summary, as if there was a clockwork mechanism driving things. The gaps between the ups and downs is irregular.

> Why doesn't this [Milankovich cycles] ever come up?

I'm 100.00% sure climatologists are well aware of it and it has been modeled and found unable to explain the trends we are seeing.

[Kadin]

> If it's as dire as some seem to imply, we should all switch to nuclear right now.

We probably should, or take other similar-scale approaches (multiple, as it wouldn't do to put all our eggs in one basket).

The lack of response shouldn't be taken as any indication that the problem isn't dire. That would be placing a truly ridiculous amount of faith in human civilization to tackle collective-action problems, which there is little evidence we are especially good at doing.

In fact, what you see in the world is exactly consistent with an extremely dire problem and a very insufficient response.

Why the response to such a dire problem is so lukewarm is left as an exercise for the reader.

[ZeroGravitas]

I think it's notable that he's saying "I don't believe in this, but I'd belive it if you did X" where X has been considered and dismissed by most relevant experts (nuclear is simply too slow to build and and too expensive to fix the problem) exactly like these cycles have been discounted as an explanation of global warming.

So if someone keeps bringing these things up, then it's likely they're acting in bad faith or they've been duped by someone else doing likewise.

Enthusiastic nuclear support while downplaying other sensible solutions (carbon fees, renewables, insulation and efficiency) is basically the socially acceptable face of climate change denial at this point.

[Arn_Thor]

I'd hazard to guess that Milankovitch cycles come up seldom because they're pretty widely recognized as not being a determining factor in the climate change we see. For an in-depth explanation of how the phenomenon relates to climate change see this well-sourced video: https://youtu.be/zQ3PzYU1N7A

[akvadrako]

They are relevant. Most of the previous interglacials during this ice age were about 10ka. How come this one continues and how long do we expect it to last? To know this one uses Milankovitch cycles.

There is quite some debate over the issue, but we probably have 5-30ka left of warm weather.

[andygates]

> Why doesn't this ever come up?

Because it's not responsible: it's currently a tiny downward trend that is only noticeable over millennia.

Science doesn't bring up every damn thing every damn time, because life is too short. People questioning this haven't even done high-school level reading. They're not adding to the sum of human knowledge, they're just flapping their jaws.

[anewguy9000]

The average IQ is 100. Do you know what someone with an IQ of 100 is capable of? Just about anything except science. The random person has no idea what they know or why and how they know it.

http://www.iqcomparisonsite.com/occupations.aspx

[coldtea]

>However, it doesn't account for anthropogenic changes in CO2 output, albedo changes as ice masses melt, and of course cow farts.

The latter is probably for the best, as is one of the most tedious and long fetched pro anthropogenic climate change argument (and at best a tiny contribution). We could talk about the meat industry in toto instead which is 10x worse than cow flatulence.

[bartimus]

I wouldn't reference it to debunk global warming. I believe humanity has made a contribution.

But is it a problem?

It's also scientific fact that ice ages happen. If the climate cycle has entered a cooling period. Wouldn't it be beneficial if we can prevent or soften it?

What exactly is the ideal gas composition for earth considering carbon based life forms?

[dTal]

"carbon based life forms" is a rather broad umbrella, that includes anaerobic bacteria. I don't think you want to be using that as a criterion.

Perhaps we can agree on "the best composition for humans"? In which case I humbly submit the answer is "the one we (and every animal we care about) evolved with".

[bartimus]

Fair enough. So looking at the hundred millions of years of our evolution. What I've been able to gather is that apparently we've had CO2 levels far beyond 1000ppm (0.1%). It's actually been relatively low in "recent times". Plant life pretty much thrives on CO2. Plant life has also been responsible for burying our needed carbon underground.

Is science asking this question? And does science offer a clear answer here?

[ahje]

Are you suggesting that multiple teams of skilled scientists from various parts of the world all forgot to account for historical CO2 levels when they created their models? Really?

CO2 levels has been higher than current levels before, like back in the Triassic. Incidentally, very few humans would like to live in such a climate. It's also worth mentioning that the Triassic was preceeded by one of the worst extinction events that ever affected the planet. An extinction event caused by very high temperatures and increases in CO2 levels.

Sure, life will survive. Probably humans as a species too. The planet won't be the same as now though.

[bartimus]

No not at all. I'm saying the alarming message gets vague beyond "humanity has made a contribution to global warming".

I try to research the available science but have trouble finding clear answers. The most accurate data seems to comes from the ice samples. But that only dates back 800.000 years.

You mention the Triassic period. Co2 levels were 2000ppm during that time. That sounds like a dramatic increase (from 0.04% to 0.2%). But then I also read we already often experience such levels at home or at work. For office workspace 1000ppm is considered acceptable and official limits are set at 5000ppm (as 8-hour TWA). I also read plants will grow ~5 times as fast. More faster reforestation?

We know there will be a change. But how accurately are we able to predict what that change will look like? Is there a strong consensus about it?

[ahje]

CO2 makes water acidic. Acidic water screws with a lot of aquatic organisms. Aquatic organisms create a large amount of the planet's oxygen. Considering the marine ecosystem is extremely sensitive, well, I can see how high CO2 could be a problem even if we humans can still breathe just fine.

[andygates]

We've got enough CO2 in the atmosphere right now to offset the next ice age millennia from now.

Offsetting something that will happen as far in the future as all of recorded history sounds a lot like looking at the horizon and ignoring the pitfall at your feet.