I've had a look at the Nature paper you reference. It is not persuasive. Look at their Figure 4a, and try to ignore their fitted curves. What do you see?

I see highly variable data, which is clearly auto-correlated. And indeed the paper discusses how ENSO and NAO are correlated with the measurements, which is a reason to expect strong autocorrelations. As far as I can see, none of their error bars or significance tests account for autocorrelation. So you should ignore them.

Just eyeballing the data points does not give any clear impression of a decline over time. Consider the four regions with the most early data. Arctic has values around 1930 comparable to the most recent, and no clear indication of a trend, either long term, or in recent decades. North Atlantic has early values around 1910 that are lower than recent values, and again no sign of a trend. North Pacific seems trendless as well, with any slight indication of a downward trend not significant in view of the autocorrelation. Only Equatorial Pacific could be seen as showing a declining trend, but it is also the most variable, with some very high points (as well as lower points), with the high points all before 1960. One might wonder whether the high points represent measurement anomalies.

The thing I have trouble understanding is this....

How can the same people be worried about human extinction as a result of environmental collapse, also think we might be able to develop a sustainable colony on Mars.

I agree that climate change is a huge problem and could result in horrific loss of life and a world wide traumatic event like we have never seen before. But there is no way that global warming will make this planet LESS hospitable than Mars could be possibly be in the next 200 years.

I think the technologies developed to make a mars habitat possible we end up also being useful for making some parts of a future earth habitable. That's a coincidence I hope doesn't come true.

Personally, I think every billion destined for mars exploration is money not being spend on addressing the more pressing crisis: What about the health of our current planet. Mars can wait, so to speak, for us to ensure our survival here on earth. A mars colony probably wouldn't survive a collapse of earth-based civilization.

> How can the same people be worried about human extinction as a result of environmental collapse, also think we might be able to develop a sustainable colony on Mars.

We would control the size and direction of growth on a colony. As it stands the tradoffs we make with regard to earth's climate affect 7.5+Bn people. A colony can be planned/optimized before we get there. We don't need to terraform the entirety of mars to get a small colony. If you want to have mars rival earth, then we can start talking about the scales of comparison you're making.

You're quite right. Let's see some habitable biodomes out in the Sahara, a much more tractable environment than Mars. But nobody seems to be pursuing this technology at scale, preferring to focus on the rockets.

Agreed. I suggest all scientists/engineers working on Mars or Lunar habitability, office exclusively in Antarctica.... once they get their offices up and running and self-sustaining, I'll pay more attention to them.

I don't believe we will be able to develop a sustainable colony on Mars, at least not with present technology. Every attempt we have made to build a self-sustaining ecosystem, such as Biosphere 2, has failed.

Eerily when Biosphere 2 collapsed the insects died first, which is exactly what we are observing now globally.

Unrelated: But Biosphere 2 has a nice Facebook page, and they are worth following for their live events.

https://www.facebook.com/pg/Biosphere2/

I love seeing experiments with vertical farming.

>There is also plenty of cause for concern about human extinction

Do you seriously mean literal extinction, as in, not one single human being left alive? That seems really implausible to me. Of course, it's academic in some sense--if all but 100 humans die out, then certainly that's the end of civilization as we know it. But that's not the same as bona fide extinction!

Relevant scene from Dr. Strangelove: https://www.youtube.com/watch?v=jf9iTZ433zs

I mean literal extinction in the long-term. The current mass extinction we are in most closely resembles the Permian-Triassic extinction which was caused by a runaway greenhouse effect acidifying the oceans and warming the atmosphere: https://en.wikipedia.org/wiki/Permian–Triassic_extinction_ev.... It wiped out 96% of known species at the time: https://phys.org/news/2018-09-end-permian-extinction-earth-s...

I don't know if you realize this or not, but humans are capable of living in entirely self-contained biodomes, outer space, and deep under the ocean for months at a time. Humans have invented nuclear energy, a nearly infinite energy source, along with countless other forms of electrical energy. Humans have perfected the science of agriculture and can even grow plants underground and even grow tropical plants in Canada. This is hyperbole. If you had to put the odds at humans going extinct, you'd have to place the odds at something like 1 in a trillion chance, short of an interstellar disaster or nuclear war.

I realize it- months don't really matter when we're talking about the survival of the human race. We have never produced a self-sustaining closed system. The space station, Biosphere 2, and not any of the other closed environments we have ever created managed to stay closed and succeed without outside intervention. We have invented nuclear energy, and then have chosen to not utilize it at scale. The other forms of electrical energy we have created are exactly the problem- we have now realized we were doomed the moment we built the first coal power stations and created this faustian bargain with our environment. We can grow tropical plants in Canada at a huge expense of energy and utilizing fertilizers produced by fossil fuels. This carbon-rich energy let us balloon our population so that now we can't just turn it off- we are stuck. It isn't hyperbole- the soil, the insects, and the marine life that sustain us are disappearing and we have no technology to survive without them.

If that were true, why wouldn't we be doing it now? You could feed the world from the Sahara.

The fact is that ecosystem management is incredibly important technology, absolutely required for things like Mars missions, planetary terraforming, and Not Killing Earth - and we do not have it yet.

Obviously there's more efficient farmland elsewhere that works better than the Sahara. Why would we do it now when we feed 7 billion people under the current system?

Define long-term. You could just as well say the universe will eventually collapse in on itself and that will cause extinction in the long-term. None of the species during the Permian-Triassic extinction knew about things like nuclear power plants etc.

Using Mark Lynas' book Six Degrees and the representative concentration pathways from the IPCC report long term for me is a century. The earliest we would see 5 degrees of warming would be around 2100 under RCP 8.5, the business-as-usual pathway. At that amount of warming we can expect a Cretaceous-like climate where methane eruptions destroy infrastructure in the northern hemisphere, super hurricanes flood the coasts, and hydrogen sulfide from the dead oceans suffocate terrestrial life. Of course, we likely are no longer on the business-as-usual pathway, we are taking some limited steps to mitigate climate change so I would say more likely long-term means 100-500 years, unless we significantly make changes to put us closer to the RCP 6.0 or RCP 4.5 pathways which are merely disastrous instead of fatal.

> There is also plenty of cause for concern about human extinction- between the insect die off and the marine die off it is unclear how we will be able to produce food going forward.

Has there been a noticeable reduction in human food supply with the reported 50% reduction of insect and plankton populations?

Not yet, like many effects of ecological collapse there is a lag time. As much as 50-90% of our calories come from angiosperms which are dependent on insects: https://www.livescience.com/52752-what-if-all-insects-died.h... and insects help us produce new top soil, of which we have lost half in the last 150 years: https://www.worldwildlife.org/threats/soil-erosion-and-degra...

The combination of soil loss, pollinator loss, and decomposer loss helping us produce new soil will be a double-whammy for our agriculture. Thus far I would assume the reason why we have gotten away with growing plenty of (increasingly less nutritious) food is because of the wasteful practices that are killing the insects and depleting our soil, so we are on borrowed time.

Here's an article from 1981 fearing the impending effect on soil loss in the U.S. due to expanded global exports of wheat, corn, and soy. https://www.csmonitor.com/1981/0603/060350.html

Nearly 40 years later...doomsday has yet to arrive.

Interesting article. More like here's an article noticing that its happening, covers some of the reasons why (like fertiliser enabling the end of traditional crop rotation), and it deserves place in planning and ideally mitigating. No suggestions soil will be gone by 2020, or even 2100 or 2200.

the bigger claim, if one looks beyond the near decades, is to consider the state of the nation's agricultural resources ... our oil is clearly running out, and so is the most precious of our resources -- topsoil

Is about as "fearing" of the "impending" "doomsday" as it gets.