For the "why geoengineering could prove to be vital" department...

[David Lewis]

Jim Hansen is circulating a note calling attention to the Hansen, et.al. "near final" paper (entitled Climate Sensitivity, Sea Level, and Atmospheric CO2)  presently available on arXiv.org, i.e. here.

The concluding sentence of the abstract reads:  "Burning all fossil fuels, we conclude, would make much of the planet uninhabitable by humans, thus calling into question strategies that emphasize adaptation to climate change."

Over to those putting forward or supporting the McBurger hypothesis... 

(The "McBurger Hypothesis" holds that climate change may only become an issue of secondary importance to those who matter, even if all fossil fuels are burned, because it is thought possible or even likely that the American middle class will continue to find ways to remain riveted to their video game screens while surviving on orders of Chicken McBurgers or whatever else is delivered to their climate change proof homes and civilization....)

[Ken Caldeira]

I am of the opinion that while climate change may pose an existential threat to those already facing existential threats (i.e., the poor, the marginalized, etc) it is far less clear how large a threat climate change poses to those who live in gated communities.

I was quoted in the New Yorker recently (behind a pay wall, but slightly misquoted here): http://stevemasover.blogspot.com/2012/06/human-are-like-rats-and-cockroaches.html

"I have two perspectives on what this might mean," he said. "One says: humans are like rats or cockroaches. We are already living from the equator to the Arctic Circle. The weather has already become .7 degrees warmer, and barely anyone has noticed or cares. And, yes, the coral reefs might become extinct, and people from the Seychelles might go hungry. But they have gone hungry in the past, and nobody cared. So basically we will live in our gated communities, and we will have our TV shows and Chicken McNuggets, and we will be O.K. The people who would suffer are the people who always suffer.

"There is another way to look at this, though," he said. "And that is to compare it to the subprime-mortgage crisis, where you saw that a few million bad mortgages led to a five-per-cent drop in gross domestic product throughout the world. Something that was a relatively small knock to the financial system led to a global crisis. And that could certainly be the case with climate change."

http://www.newyorker.com/reporting/2012/05/14/120514fa_fact_specter

I think the uninhabitable claim of Hansen is a bit excessive.  While such a world might not be very pleasant, I don't see it as threatening fundamental habitability.

In the attached Scientific American article, I wrote:

We are re-creating the world of the

dinosaurs 5,000 times faster [than it was created in the Cretaceous].

What will thrive in this hothouse? Some

organisms, such as rats and cockroaches,

are invasive generalists, which can take advantage

of disrupted environments. Other

organisms, such as corals and many tropical

forest species, have evolved to thrive in

a narrow range of conditions. Invasive species

will likely transform such ecosystems

as a result of global warming. Climate

change may usher in a world of weeds.

Human civilization is also at risk. Consider

the Mayans. Even before Europeans

arrived, the Mayan civilization had begun

to collapse thanks to relatively minor climate

changes. The Mayans had not developed

enough resilience to weather small

reductions in rainfall, and the Mayans

are not alone as examples of civilizations

that failed to adapt to climate changes.

Crises provoked by climate change are

likely to be regional. If the rich get richer

and the poor get poorer, could this set in

motion mass migrations that challenge

political and economic stability? Some of

the same countries that are most likely

to suffer from the changes wrought by

global warming

also boast nuclear weapons.

Could climate change exacerbate existing

tensions and provoke nuclear or

other apocalyptic conflict? The social response

to climate change could produce

bigger problems for humanity than the

climate change itself.

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[Andrew Lockley]

For gated communities and chicken mcnuggets to exist, we need semiconductor factories, international shipping, agribusiness, chemical plants, business air travel, governments, nuclear arms control, the oil industry,  police, etc., etc., etc.

I see no reason to assume that most of the above will still exist if we get 6-10C warmer.

Maybe they'll be a small vestigal community of neo-cavemen manually forming chicken entrails into nuggets behind a rusting gate, but I doubt that's what Ken meant.

If we're collectively stupid enough to use the atmosphere like a cesspool, then it's geoengineering or bust.

A

[Fred Zimmerman]

Huber & Sherwood (PNAS 2010) establishes a hard biological limit to habitability under warming.

http://www.pnas.org/content/early/2010/04/26/0913352107.abstract

An adaptability limit to climate change due to heat stress

Steven C. Sherwooda,1 and Matthew Huberb

Author Affiliations

Abstract

Despite the uncertainty in future climate-change impacts, it is often assumed that humans would be able to adapt to any possible warming. Here we argue that heat stress imposes a robust upper limit to such adaptation. Peak heat stress, quantified by the wet-bulb temperature TW, is surprisingly similar across diverse climates today. TW never exceeds 31 °C. Any exceedence of 35 °C for extended periods should induce hyperthermia in humans and other mammals, as dissipation of metabolic heat becomes impossible. While this never happens now, it would begin to occur with global-mean warming of about 7 °C, calling the habitability of some regions into question. With 11–12 °C warming, such regions would spread to encompass the majority of the human population as currently distributed. Eventual warmings of 12 °C are possible from fossil fuel burning. One implication is that recent estimates of the costs of unmitigated climate change are too low unless the range of possible warming can somehow be narrowed. Heat stress also may help explain trends in the mammalian fossil record.

---

Fred Zimmerman

Geoengineering IT!   

Bringing together the worlds of geoengineering and information technology

GE NewsFilter: http://geoengineeringIT.net:8080 

[Russell Seitz]

" Even before Europeans arrived, the Mayan civilization had begun to collapse thanks to relatively minor climate changes. "

The classic Maya civilization collapsed late in the 8th century, and all its great urban ceters were abandoned by the end of the first millennium. More inreresting is the role of climate change and migration  in the dissapearance of the Olmec civilization that went before, taking much of mesoamerica's neolithic trade network with it- 

http://www.nytimes.com/2002/05/22/world/in-guatemala-a-rhode-island-size-jade-lode.html?pagewanted=all&src=pm

[eugg...@comcast.net]

And some parts of the world; northern Canada, Alaska  Northern Europe for example, may prefer some warming and will prosper.

---

From: "Russell Seitz" <russel...@gmail.com>
To: geoengi...@googlegroups.com
Cc: jrando...@gmail.com, kcal...@carnegiescience.edu
Sent: Wednesday, April 17, 2013 10:50:12 PM
Subject: Re: [geo] For the "why geoengineering could prove to be vital" department...