Actually, it's 500ppm when we should entertain thoughts about possibly being concerned.

"No longer: for the first time in recorded history, CO2 concentrations remained above 400 ppm for the entire month—meaning they’re unlikely to ever fall below this symbolic milestone again. "

Nonsense. In the past Earth's atmospheric CO2 concentration has ranged as high as 10x the amount today and to less than half what it is today. That means CO2 levels can fluctuate up or down. There is no reason to think that the 400 ppm we are seeing today is "..unlikely to ever fall...".

If the sentence had read "...they’re unlikely to ever fall below this symbolic milestone again in the lifetime of everyone alive", you'd be on more solid ground.

@2:

I felt like that was implied - by the time CO2 levels fall back down below 400 ppm, there most likely won't be anyone around to take the measurement.

@3 That is also nonsense. We are in for problems to be sure, some likely to be quite difficult - especially geo-political ones- but there is no reason at all to think the warming will wipe us out.

@4:

Perhaps not completely, but given that roughly half the world's population now lives within a few tens of miles of the oceans, and given the anticipated rise in sea levels and global temperatures over the next half-century or so, the massive, wholesale disruptions to civilization caused by Climate Change are going to have catastrophic effects on population, economies, governments - pretty much everything we characterize as human civilization. And the CO2 levels are going to continue to climb in the meantime, which means atmospheric and environmental degradation will simply accelerate. At current rates of increase it might literally be a couple thousand years before the rate of increase starts slowing, let alone dropping. By then we could be back to a state roughly akin to the Middle Ages, eking out lives of short, brutal desperation on what remains of the local flora and fauna, but with lots of scrap metal around to melt down into swords and plows.

@2 and @4, It's happened before, but it's happening NOW at a rate that makes it difficult for nature and human civilization to adapt.

@1, it's not JUST about whether the air is poisonous to breath, dum-dum.

@5 Yeah, if worst case scenarios come to pass then there is likely to be large scale disruptions of coastal populations. More worrisome is that current rain fall patterns are likely to change (some places will get wetter, some drier). In places of the world already under water stress a loss in annual rainfall has the potential to be devastating and could induce large scale migrations. And we all know how welcoming humans are to refugees; there is the possibility of real conflict in some regions.

Many non-human species will suffer too, though many will not and some will benefit. The problem for both us and wildlife is the speed at which this is happening. We may not be able to adapt quickly enough to survive (for certain animals and plants - the human species is in no danger) or to cope with disruption.

Thanks for the discussion, all.

@2, fair point. On geologic time scales, it's likely to dip below 400 ppm again one way or other. On the sort of time scale relevant to extant human civilizations, it's unlikely to.

If we're going to continue to sit on our ass DOING NOTHING, BECAUSE GREED, and allowing those psychopathic CEOs to continue killing the planet - thinking they can use their wealth to survive the Climargeddon or escape to Mars once Earth is unlivable - then I hope we humans all get wiped out fast, so some of the other species can survive. And I hope the next alpha species will treat our beautiful planet, and all the live forms it support, better than we have.

@10:

It's rather unlikely Musk or Bezos will "survive the Climargeddon", but their children or grandchildren might, if they succeed. They're thinking long-term survival and have decided getting off this mud ball and learning to live on some other mud ball might be a potential way of achieving that. Not to say we shouldn't also expend every effort to make things better here, but so far as the species is concerned, it's probably best to not put all our eggs (and sperm) into one planetary basket.

@8, you're right. Sorry.

You Leftists bed wetters like to pretend you're hip with Science! and Evolution! but when they do their thing you squeal like piglets…

Climate changes.
It always has, it always will.
Because Science!
Part of Climate change is that some species are advantaged, others disadvantaged.
Frankly,
your hysterical Chicken Little Bitchin is really dragging down the adaptability composite score for our species.
More planning to adapt to Climate Change.
Less hysterical shrieking about 'OMG Climate Change!!'

Especially Social Collapse is going to Rock Your Worlds way sooner than climate change.
Relax and Enjoy.

Especially since…..

@13: Would you be cool with someone setting you on fire?
I mean, what are you whining about, you big baby? Your body temperature changes. It always has, and it always will.

(Remember, climatology is on the list too.)

@13:

The entire reason we're in this mess is because we are the ones making the climate adapt to us, and not the other way around.

Perhaps when trump loses in Nov. the air will become less polluted with the poison that comes out of his mouth.

@10: Psst, it's not the "psychopathic CEOs" that are the problem. They are A problem, but it's the general populace that is causing THE problem. The people that refuse to get out of their cars and/or giving up their (free) parking spaces, the people that refuse to allow anything to reduce their housing prices, the people that refuse to change their behavior by consuming less and instead buy more and more useless plastic shit. Instead of looking for a scapegoat, try looking in the mirror.

We could've gotten off oil in the 70s, but no - everyone wanted their little slice of The American Dream. A house with a 2 car garage in the suburbs, burning fossil fuels to keep it hot in the winter and cold in the summer. Miles and miles from work, school, and the supermarket, guaranteeing that tons of oil will be wasted with every trip. Meat at every meal, because we're Americans and that's what America is. Downright throwing a temper tantrum any time someone tries to change things in any way that might make you even the slightest bit uncomfortable.

Not to pick on you in particular (I don't know you), but the majority of Americans out there are the problem. And they've provided a splendid example to people in other countries.