However, Hansen himself has been waging a campaign that is far more radical.

In his now seminal article Target Atmospheric CO : Where Should Humanity Aim?, he calls for 350ppm as the goal.

This means we must not only 'reduce' emissions, no, that would be too weak an offer. We must actively remove CO2 from the atmosphere. Else we face collapse.

In short, this means we have to invest in four priority areas outlined by Hansen:

1. phasing out all coal, and implementing CCS
   
2. coupling bioenergy production to CCS, which results in negative emissions energy (actively takes CO2 out of the atmosphere; no other form of renewable energy is capable of this; wind, solar, etc... are all carbon-positive and contribute CO2 over their lifecycle; only carbon-negative bioenergy can remove atmospheric CO2)
   
3. investing in reforestation in the subtropics
   
4. investing in biochar and soil carbon sequestration, and in a transition from slash-and-burn to slash-and-char

In short, I wish Grist were more ambitious. Instead of focusing on a catastrophic 450ppm scenario - which is the certain pathway to catastrophy - it should follow Hansen in his plea for a 350ppm target.

For example, the internet has simplified my life, I can enjoy online banking and buy stuff online. But the backbone is a highly complex technology.  Simplification does not always mean more efficiency or it doesn't mean that what's simple on the surface is so on the backbone.

Take the 'cradle-to-cradle' design paradigm. It can take on extremely refined, smart and highly complex forms, but it is certainly more sustainable than the simplified tricks of the current petrochemical industry.

Simplicity should not equal an aversion to science or technology or to progress.

Likewise, "more natural" can mean anything. What does it mean to you? To me it can mean making use of nature in very smart ways - but to make use of nature's resources in any case. There is no 'pristine' nature anywhere (terra preta would show this nicely: large tracts of the 'pristine' Amazon rainforest are actually man-made). Nature has been denaturalised long ago. The result of a new smart reliance on nature could be very different from the quite natural lifestyle we live today. It could, on the contrary, be very un-natural and highly complex. Nobody knows.

There's an interesting philosopher in Europe (Slavoj Zizek) who has some lectures on why we need to "denaturalise" ourselves in order to live sustainably and to "save the environment" (which actually means "saving the human race", because nature doesn't give a damn about what we do; we don't have to protect nature, we have to protect ourselves).

His ideas go against most of what you will hear basal environmentalists say.

The calls for a move 'back to nature' and for 'reterritorialisations' of all kinds ('re-localisation', 'autarky', 're-gression') are very dangerous. There's no escape from globalisation and deterritorialisation, we must just use it to our advantage (like Deleuze would say: in order to beat deterritorialisations, you have to deterritorialise even more and faster...). It might be much smarter to jump forward and alienate ourselves far more from nature, because that would allow us to develop hyper-technologies that make the human race much more performant in its environmental caretakership.

Check it out:

Slavoj Žižek - Ecology: A New Opium for the Masses (1/10) (starts at minute 9.30, plz skip the boring Lacanian woman at the start; or start with part II).

Note, for those who don't know Zizek: he hisses a bit and is hyper-neurotic (being a psychoanalist), but aside from this, he's currently probably Europe's most influential thinker. A Lacanian neo-stalinist.

But I suspect by your post that you're not at all interested in what simple and natural means.  Your priorities are very anthropocentric and you show no concern for the natural world, except as it can be exploited by humans.

And BTW, I watched an hour long interview with Zizek and was not at all impressed.  His thinking is very myopic and anthropocentric, as are those of all leftists, and he understands nothing of the natural world.

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What is Earth Expansion?

There simply aren't enough caves to turn 6.4 billion people back into cavemen.

But perhaps you are advocating the mass-slaughter of people so that the limited number of caves is no longer an obstacle to the realisation of your naive dream?

My alternative would be a radical denaturalisation of mankind. Build hyper-efficient high-rise cities that are self-sufficient in food and energy and that have an ultra-low impact on their surroundings; make all productive activities part of a cradle-to-cradle cycle. And leave nature to fend for itself.

Just imagine 6.4 billion people returning to villages or bands of hunters-gatherers. That would be environmentally catastrophic. It would mean the death of all forests and its wild animals. It would mean the wholesale destruction of all more or less conserved ecosystems. It would cause mass social warfare.

Instead of my view being "simplistic" as you call it, it is a view that is shaped by a strong reverence for the natural world, which you obviously lack.

First and foremost, I guess you haven't seen any of my posts on the subject, but overpopulation is one of the twin root causes of all serious environmental harm, the other being overconsumption.  However, I've never advocated killing anyone.  The way to address this problem is through birth control, specifically a one-child-family policy like that of China, which has worked so well that the average number of children per family there is now 1.4 in urban areas, where most of the people are.  Abortion and birth control methods should be completely unrestricted and free on demand, and both carrots and sticks need to be used for the one-child-family policy.  That's the way you reduce human population, not by killing people.

Second, of course I don't advocate people becoming hunter-gatherers at this point in human history, mainly for the reasons you identified.  Humans have been causing serious ecological harm to the Earth for 10-12,000 years, so these problems are not going to be completely corrected anytime soon.  But the goals worked toward, whether those goals are set in the near or far future, determine present actions.  Returning to a far more natural way of living must be our ultimate goal, albeit one that transcends the hunter-gatherer lifestyle that humans have known to this point.  What humans should NOT be doing is seeking more, and more advanced, technologies, because that puts us on a path to ever greater destruction of the natural world.

Third, while your idea of all humans living in an extremely dense skyscraper environment and leaving nature alone is a quite tempting one, there are two major problems with it.

First, humans society would be far from leaving nature alone, because the immense waste created by and consumption of natural resources needed in order to sustain your type of community would wreak havoc on the natural world.  These communities would also be ecological dead zones just because of the ridiculously dense human population.  So while I'd support your idea as one that prevents humans from further harming the natural world, it unfortunately would not come close to accomplishing that goal.

Second, this would be a very unpleasant way to live, despite its purported advantages for the natural environment.  I live in San Francisco, where I find the extreme density of humans to be despicable.  The constant industrial noise and feeling of living like a rat in a cage packed with other rats is overwhelming.  (The only reason I live here is because we have a rent controlled apartment and can't afford to move.  Otherwise, I'd be in Berkeley, a much more sane city re human density.)  You're always talking about what's practical; well, this idea clearly isn't, as if even a city boy like me doesn't want to live in such a dense environment, most others won't either.