Is 350 the right target for atmospheric CO2?

For those who really grok the precautionary principle, aiming for a lower, and therefore inherently safer, maximum atmospheric carbon-dioxide concentration is the logical choice. Civilization arose over the last 10,000 years in a world in which CO2 represented just 280 of every million atoms we and every other respiring organism inhaled. Given the uncertainty over what level of the trace gas leads to dramatic changes in the climate -- we know there's a relationship but haven't been able to nail down the tipping point -- the closer to pre-industrial levels the better.

But there's a problem.

That problem is we've already crossed the 350 ppm threshold that some climatologists say is the highest safe level. Such speculation, put forward by NASA's James Hansen and a growing number of others, is based on paleoclimatic data that links the freezing and thawing of the planet's ice caps with such a number, give or take 100 ppm. When CO2 levels fall below that range, the ice caps grow, and so the inference is that letting them rise above that range will cause them to melt.

There isn't anything like a universal scientific consensus on whether 350 or something higher, around 450, make more sense as a global target. One of the problems is that "safe" is a tricky term to define. Just how much risk are we willing to live with? Everyone has different estimates of just what the probability is that we can hold global average temperatures to no more than 2 °C above pre-industrial levels for a given concentration of CO2.

Terms like "Herculean" are typically attached to the goal of keeping CO2 levels below 450 before we have gotten off the business-the-usual train. Reducing them from today's 387 to 350 seems like a fantasy, no?

Not to activists like Bill McKibben, who was behind yesterday's global 350 Action Day, in which lots of concerned citizens arranged themselves in those three numerals for the benefit of aerial cameras. His logic, as relayed to the New York Times Andy Revkin goes like this:

"Three-fifty is the number that says wartime footing, let's see how fast we can possibly move, and let's hope against hope that it's fast enough."

But it isn't just passionate activists who believe that 350 is doable. There's Tufts University economist Frank Ackerman, for one. At Yale's 360 magazine he argues that most economics studies of the cost of climate change mitigation show it's entirely within the real of practicality to cut emissions of fossil fuels dramatically without causing another global financial meltdown.

At first glance, there is a bewildering range of estimates of the costs of climate protection. Look more closely, however, and there are just a few projections of economic disaster, out in right field by themselves. Other estimates range from modest costs to small net economic gains.

The outliers are the handful of private consultant studies funded by partisan lobbying groups such as the U.S. Chamber of Commerce and the National Association of Manufacturers.


These projections of economic ruin have not been reproduced by any major academic or non-profit research group. Many economic models find that the modest steps called for in recent U.S. proposals would have very small costs and virtually undetectable effects on total employment

And of four studies that looked specifically at getting emissions down enough to manage a reduction to the magic number:

One group starts from the (realistic) assumption of high unemployment, and finds that long-run employment and economic growth would be increased by a program of public investment in green technology and emissions reduction that leads to 350 ppm. The other three groups adopt the common assumption that short-run unemployment can be ignored in long-run models. They generally find that the needed emissions reductions will cost an average of 1 to 3 percent of world economic output, for some years to come.

There are some other challenges associated with focusing exclusively on 350 ppm. For one thing, just as important as the target is the speed with which we get there. We can only afford to pour so much more carbon into the biosphere (see the trillionth tonne thing), so we can't afford to wait very long to stop cutting emissions. The longer we wait, the steeper the slope of the graph that charts the reductions necessary to keep the cumulative carbon emissions below the critical value.

It may very well be that 350 is the best long-term target. But no one, or at least, no one worth blogging about, is demanding we bring down emissions to 350 ppm directly from current levels. It is widely recognized that our best efforts will probably see CO2 levels top 400 ppm before they can begin falling. Short-term targets are at least as important. And it can be argued that a simple "350-or-bust" message (which I just made up) could do more harm if it doesn't acknowledge that there's no easy way to get there within a century. Even Hansen says he isn't expecting action on a shorter schedule.

And if we need a short-term CO2 target, we need short-term emissions reductions goals. Ambitious ones, too, on the order of 40% cuts by 2020 in the developed world. Sounds like a lot, but the alternative is to give up or pretend that the world's climatologists are wrong.

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At this point I think 350 is not a real target. I don't think anybody really wants it that much.

Demonstrators just want to demonstrate and politicians just want to maintain power and everyone wants cheap energy now.

The world wants 350 like I want a flying car. Nice dream but I'm not going to actually pursue it.

Goal that makes sense: Limit the human population to 3,500 billion people, with zero population growth.

I don't know if 350 carbon limit makes sense or not. I know for sure that if we had been able to heed the warning of Ehrlich and others and had free access to education about family planning, cheap available birth control -- people might have freely chosen (no coercion) to limit family size. All of our environmental problems would be much easier to solve if the Earth had fewer people.

As long as population keeps growing, nothing else we do matters. Might as well just pray, and we all know how well that works.

By stilldreaming (not verified) on 26 Oct 2009 #permalink

3.5 Billion? how about 1 B?
Birth control in the world food supply?

Population change is too slow. We wouldn't see significant changes in consumption of fossil fuels for decades. It's 20-year-olds who buy SUVs, not newborns.

And if we -do- get clean energy sources, there'll be a lot less need to reduce population. It's set to stabilize at c. 10 billion anyway. With technological progress, I see no reason 10 bil isn't sustainable. (The -average- person is better fed now than any other time in human history. Yes, there is a *lot* of hunger in Africa and South Asia; but that was the general state of the peasantry - that is, the bulk of the population! - in even the -richest- nations for most of human history!)

Malthusianism always fails if technology progresses. And decreasing populations cause huge social problems (insane tax burdens on the few remaining workers to support the vast number of retirees, lack of 'new blood' in intellectual and technical fields, etc. etc.)

By intercostalwaterway (not verified) on 26 Oct 2009 #permalink

We already are in a state of biological overshoot, since it is the availability of cheap fossil energy than has powered industrial growth and the agricultural revolution, particularly the "green" revolution of the mid-20th century. Meanwhile other resources continue to be degraded and depleted, such as petroleum, topsoil, fresh water, fisheries, metals for industry (even for "alternative" energy industries), and so on. The planet, therefore, is actually far over-populated, much like an invasive species overconsumes its resource base. The result is dieoff. Technology is hardly the answer, as demostrated clearly by Albert Bartlett. That is not to suggest that any individual, country, or culture is to blame. That's just the way it is. That's what organisms do when given the possibility of earning energy subsidies and I guess its reassuring to know that we behave no differently than any other organism on the planet.

Coal also should be placed into the category of depleting resources. Total energy yield from coal already is post-peak, in part because the high grade anthracites now are virtually gone. Several recent studies, summarized in Richard Heinberg's "Blackout," also suggest the quantity of recoverable reserves are overestimated. Consequently, David Rutledge of Caltech has shown that the IPCC model scenarios for CO2 concentrations are vastly overestimated for just these reasons and ultimately may struggle to exceed 450 ppm. Still a dangerous proposition.

In my opinion, the most likely future involves energy scarcity, whether or not this is a voluntary action.

A note on civilization and climate. Civilization, as we think of it, emerged comparatively recently following the independent origins of the domestication of plants and animals, and the subsequent emergence of sedentary village life, in several parts of the world. Antrhopologists have long dispelled the notion the the origins of agriculture represent a stage in human "progress." In any case, humans were around, successfully, long before the current interglacial. During the past two million years, continental glacial conditions have prevailed far more than interglacial conditions. Ultimately, the modern pulse of CO2 will be scrubbed from the atmosphere (time frame within the hundreds or thousands of years), and the Quaternary will continue on its merry way. But to prescribe an "ideal" level of CO2 concentration that would preserve optimum conditions and land area for agriculture would suggest a level of human intervention equivalent to modifying the Earth's orbit every several thousand years, even as the Earth continues its long-term cooling trend beginning around 55 million years ago, or so.

By Eric the Leaf (not verified) on 26 Oct 2009 #permalink

Nuclear, biofuels (though not corn ethanol!), and solar (especially space-based solar) could provide successfully far more energy than we currently use. And new energy sources will certainly be invented (Polywell fusion, maybe?) No resource except water is currently close to depletion, and with clean energy, we can desalinate seawater.

Use of coal in the current climate situation is absolutely inexcusable.

Every other prediction of population-caused problems, from Malthus on, has been incorrect. I see no reason to believe the current ones are any more accurate. In the 60s versions, we were all supposed to be starving at 6-7 billion. We're there, and world hunger is less prevalent than it was in the 60s.

Environmental preservation is absolutely necessary, but it has to progress on a basis of what is actually best both for biodiversity and the long-term good of human civilization, not on platitudes of "nuclear power and population is bad". The environmental movement's ties to left-leaning/liberal politics are hurting it. (Not anything left-specific: it would have been just as much a problem if the environmental movement had allied originally with the political right. Science-based things like environmentalism just suffer when they become too much politically-run and too little science-run.)

By intercostalwaterway (not verified) on 26 Oct 2009 #permalink

Goal that makes sense: Limit the human population to 3,500 billion people, with zero population growth.

Presuming you meant 3.5 billion, not 3.5 trillion... The next question is which 3.5 billion? If we're going to rebalance our ecological impact by reducing the population, who do we start with?

intercoastal, while it is true that a lot of predictions about population-related disasters were wrong, the problem is that we came up with other ways to make population a problem. And there isn't always a technological solution.

Northern Nevada had more people in it in 1890 than it does now. Why? No water. Water is finite. Put enough farmers someplace and you run out, it's that simple. Reduce the number of farmers and it becomes more feasible, unless you mine out all the water, which is why Route 50 is the loneliest road in America.

Rwanda: an entire social system was based on giving land to people in the next generation (you divided the land among descendants). What happened when they ran out of land to give? The social system broke down right quick (and left an opening for genocidal maniacs to take over).

Ireland: large population base pre-potato famine, because a brand new crop (potatoes) could support loads more people per acre than wheat. (You can grow enough for a pretty large family on much less land). The problem? Blight. Oops. Now, had there been fewer people to begin with, there might have been time to switch to wheat production as there would have been land available and you could have grown enough to feed people. But the per-person plots were so small that it wasn't an option and the bigger landowners weren't willing to sell food to people with no money. The result was one of history's most effective depopulations.

The Mayans. Copan was once one of the largest cities in the world. But corn cultivation only works for a certain period of time and there is simply no technological magic bullet -- even if they had had modern fertilizers -- to replenish soil. Well, Copan was empty within a generation.

You can expand energy and water use to a certain point -- but after that the amount of energy required to extract a given amount -- for instance, the amount of energy you need to extract oil -- rises to the point where it costs you more to get a given number of joules. In theory you could filter seawater to get oil form the old spills, but that obviously wouldn't work because by the time you got a gram of petroleum you'd have filtered the whole Caribbean or something.

We could probably maintain the entire population of the world right now at a standard of living approaching Europe in the early 70s or the Soviet Union more recently. (Don't knock on the latter, I was there and can tell you it wasn't that bad, the stories of lines for toilet paper are myths -- it was much more complicated than that). I am speaking, of course, in terms of energy use -- obviously we wouldn't go back to driving Ladas. That is a big step up for a whole lot of people.

There are some things for which, however, there is no technological fix. Phosphates, for instance. There is no substituting these, not at all. And the supply is limited. Morocco is going to be the most important country in the world soon. And reclaiming them is almost impossible to do in the way that is likely necessary. Yet modern agriculture depends on that. (In the old days before intensive farming there was enough from local bird guano et al, but nowadays the inputs are awfully large).

That's why changes in behavior are so important. There are plenty of examples of people outstripping resources. The difference then was people had a place to go. Now they don't.

Population growth does tend to slow down as people industrialize, true enough. But before that happens there tends to be a spike -- it takes a generation or so for the habits of agriculture disappear and people do not de-acquire children.

While that happens, you have to increase the efficiency with which people use resources.

intercostalwaterway, do you have even the smallest CLUE how much biodiversity has been lost since the 60s in the continuing expansion of human population?

When you've figured this out, get back to me.

By Luna_the_cat (not verified) on 27 Oct 2009 #permalink

Wow! That Marine Biology degree is CERTAINLY coming in handy here. The 350PPM mark is NOT arbitrary or based on paleoclimate data- it is a reflection of the energy imbalance caused by greenhouse gasses. Climate forcings are driving the imbalance typically referred to in W/m2- Watts per square meter. Above 350ppm and the energy imbalance increases- already demonstrated empirically. We are now .9W/m2 out of balance and it's getting worse.

"But no one, or at least, no one worth blogging about, is demanding we bring down emissions to 350 ppm"

Aargh. Et tu James?

People will not get a proper grasp of the problem as long as writers on the subject keep making the mistake of confusing emissions and concentrations. Understanding the relationship between these quantities is crucial before you start to think seriously about the mitigation problem. I presume in your case it was just a typo, but please, please fix it!

What is the carrying capacity of Earth? Does that question even have an answer? I'd argue not - except within the context of a particular technological base. Earth's carrying capacity for hunter-gatherers is probably in the tens of millions; for pre-modern agriculturalists, probably somewhere in the hundreds of millions; for modern industrialized civilization, somewhere in the billions; for 2500-AD civilization, how can we predict? Would a hunter-gatherer of 30,000 BC in his tribe of perhaps 100-150 people be able to predict our cities of 10 million+? He would say 'You can't feed that many people!'. And he'd be right: within his own technological limitations.

@Jesse: BTW, my username is 'intercostalwaterway'; it's a pun, though admittedly a stupid/geeky one.

Re Nevada: It lost people because "The Silver State"'s silver boom ended and people realized 'hey, I'd rather be living somewhere with a nicer climate than this continent's worst desert. And frankly, I can't think of any place that *doesn't* have a nicer climate than here...'. Facing this mass exodus the Nevada government went 'oh $@#!, soon we won't have any taxpayers! Hey, I know - let's legalize gambling, prostitution, and easy divorce [which was a big deal in the 1890s], and people will come live here!' And it worked ... sort of, for Las Vegas anyway; Nevada has *some* people left!

Re Rwanda: I'm not saying *places* aren't overpopulated; but *Earth* isn't, not if managed properly. A lot of blame for that can be placed on Rwanda's social/economic system (as your own comment suggests). Anyway, Earth's human population, even in this age of globalization, is *not* one ecological unit. The fact that Nation A is overpopulated does not itself imply that Nation B is, nor that Earth is, any more than 'American cockroaches' as a species are considered to be in danger of extinction if 'the cockroach population in city X' is dying out.

Ireland, the Mayans: these (especially Ireland) are examples of 'crappy economic/social/ecological decisions have consequences', not of overpopulation. Relying on a monoculture for your food source is *always* a really bad idea on the order of playing with unexploded nuclear ordnance; sadly, our own industrial agriculture has tendencies in this direction.

The Mayans were not a technologically advancing society, not once they got to the 'Classic Maya' phase of their civilization, and thus don't affect my argument. I'm not saying 'overpopulation is a myth and Malthusian collapses have never happened', I'm saying 'in a society which continues to develop technologically and respond to challenges effectively, Malthusian collapses will not happen'. That's a very different statement.

We need to be off oil anyway. Earth has (to use a technical term) craploads of uranium, thousands of years' worth at the very least just in the reasonably-usable ores, and we'll have nuclear fusion long before we run through all that. And the Sun gives us 1366 Watts/square meter every day, all day, just there for the taking - all we have to do is harvest it.

"We could probably maintain the entire population of the world right now at a standard of living approaching Europe in the early 70s or the Soviet Union more recently." Yes, we could - with current infrastructure. I'm arguing that with currently-possible-but-not-paid-for-yet infrastructure, like truly large-scale nuclear and solar power generation, ocean desalination, etc. - we can give everybody a much better standard of living with less harm to biodiversity and the environment.

Honest question: why can't phosphates be synthesized? Phosphorus isn't all that rare.

Also, I'd take issue with the assumption that there isn't anywhere else to go. Even ruling out for the sake of argument large-scale migrations/colonizations off-Earth, as it's hard to imagine them moving *that* many people, we can get *resources* from off-Earth. Business deals for space-based solar power are in progress *right now*. Asteroids can be mined for metals if we ever run low on Earth. (It takes less delta-V - which is what really matters, not distance, which is just a matter of time - to get to and from a near-Earth asteroid than to get to and from the Moon.)

What are the main (direct) causes of ecological damage?
-Pollution/climate change. Getting off fossil fuels will fix the latter, and a very significant portion of the former. Saner agricultural methods (as opposed to the 'slop it on, chemicals are cheap' mindset) will fix most of the rest of the former.
-Habitat destruction. Superficially this is caused by population, but there are other solutions. Specifically the one now being thought about, and beginning to be adopted, in Tokyo etc. - build your 'urban sprawl' *vertically* not *horizontally*.

Other big causes of habitat destruction? Slash-and-burn rainforest agriculture. Only real solution: make them wealthier so they can buy food from places with decent farmland rather than trying to grow it in cruddy rainforest soil. Easier said than done. Mountaintop removal for coal mining. Absolutely inexcusable in the current situation (or any situation, actually), and the ne plus ultra of the 'it's cheap and easy, who cares about the long term cost' school of thought which is the real source of 90% of ecological problems.
-Overhunting. Not really a problem in the developed world anymore, we learned our lesson from the Passenger Pigeon and a few others, but still a very significant problem in poorer areas - the 'bushmeat' trade is one of the major threats to chimps. Solution: don't force these people to choose between starving or eating an endangered, often Ebola-virus-ridden ape. Basically, more wealth, therefore requiring more industry, and more energy use. Again clean energy is needed, or it'll just make climate change worse.

Big question: why do I argue about this? Even if a big population is sustainable, wouldn't a smaller one be easier to sustain? Two reasons, actually.

One, there's often an uncomfortable streak of almost defeatist thought in the 'the only solution is smaller population' school of thought - an implication that human civilization is *always and necessarily* harmful to nature, and that harm is more or less in proportion to the number of humans. I think this is a line of thought which is ultimately unproductive. We need to guard against the idea that our really important ecological choice is how many children to have. Humanity is part of the Earth's biosphere too, we're not some pest or introduced species that needs to be chipped away at and reduced in numbers. We belong here too, we have at least as much right to live and procreate as any other lifeform. We are not House Sparrows or Starlings, we can *control* our own impact in ways subtler than the crude method of limiting our numbers. More importantly, *it is our lifestyle that matters more than our number of children*. If we make it through this climate crisis intact as a civilization - then *the very same technologies and social attitudes that allowed us to do that* are the ones we'd need to support a far larger population. If we don't - well, there won't be a big enough population to *be* a problem...

Secondly, there are severe - extremely severe - social risks to lowering population. In a developed country with a social safety net, the problems are, somewhat paradoxically, worse. The long-lived retirees become numerous; and so, the few remaining workers will by necessity have to be hideously taxed to support the retirement of the vastly numerous retirees. (Any attempt to cut retirement benefits or social security will of course fail, since so many voters will be retirees or close to that age!) I simply see no way (short of truly immense immigration, but a) that is probably impractical and b) that's not really "lowering population" anyway - and if people had fewer kids worldwide, there'd be no place for the immigrants to come from!) for the 'high taxes/high government benefits' societies to come through OK. 'Low taxes/low benefits' societies like the US might be somewhat OK... but we still have Social Security, and Medicare...

Also, there's good historical examples (late Rome, Sparta...) to show that a lowered birthrate is closely tied to a lack of innovation, a decline in the arts and sciences, and general decline in other ways. 'Science progresses one funeral at a time' as Planck said; innovation is disproportionately produced by the young, not by those already set in their ways.

I just think that it will be easier to manipulate the physical resources (energy, minerals, food supplies) with technology than to manipulate human nature. One has a proven track record (a higher percentage of the world's people are well-fed now than ever before. Yes, there are many hungry people, but in many eras the peasantry - the majority of the population - were *all* staving off the wolf at the door one meal at a time. We have many nations now in which missed meals are an oddity rather than a fact of life, where the middle-class majority finds real poverty and hunger hard to even understand.); the other haa a 100% failure record.

By intercostalwaterway (not verified) on 29 Oct 2009 #permalink

Earth has (to use a technical term) craploads of uranium, thousands of years' worth at the very least just in the reasonably-usable ores

Really? Last time I read something about it, we had 60 years' worth left at the current rate of consumption.

By David MarjanoviÄ (not verified) on 30 Oct 2009 #permalink

David MarjanoviÄ "Really? Last time I read something about it, we had 60 years' worth left at the current rate of consumption."
Uranium resources vary hugely based on your assumptions. If you assume we can do fuel reprocessing or breeder reactors or remove the uranium in seawater then you can go thousands of years. I wouldn't bet the farm on the high estimates, but 60 years is a pretty low estimate.

"We need to guard against the idea that our really important ecological choice is how many children to have."
I fully agree with this. The extreme environmentalist message that humans are the problem is incredibly destructive because it convinces huge numbers of humans to oppose environmental planning. By our biological heritage, humans are never going to just stop population growth because somebody told us it was bad. So either we find ways to convince people to behave in ways that sustainably supports 7 to 10 billion people on the planet (which is technically workable but right now humans just don't choose to behave in those ways) or the population has to decrease (which isn't going to happen in the next 70 years without a lot of suffering and environmental destruction). It seems to me that intercostalwaterway is right that the only realistic thing to do is to try to convince people to live sustainably. And that is much easier to do if we drop the anti-human message.