Filed under: Global change
There’s a fascinating paper by Corinne Le Quéré and many other hands out in Nature Geoscience on what’s up with sources and sinks of carbon dioxide. The authors claim that the sinks are getting weaker, and that a greater proportion of the carbon dioxide emitted is staying in the atmosphere, which is a pretty big thing. They are not absolutely sure of this, and when they spoke to the press earlier this week they recognised that another recent analysis by Wolfganag Knorr suggested the sinks were sucking up just as great a proportion as they ever did. The datasets are not great, which is one reason for the uncertainty; another, as I understand it (haven’t dug into the matter) turns on how you filter out variability when looking for the trend. This matters not least because variability may be driving some of the trend: El Ninos, for example, decrease the tropical land sink because they dry places out, and if El Nino frequency is part of the long-term climate signal then removing them from the data means removing some of the trend too. Anyway, the paper doesn’t say for sure that the sinks are beginning to slow down, but the authors do find it likely-in-the-ipcc-sense, which means they assess the probability as 2 to 1 odds on or better. (Update: John Timmer at Ars Technica has more on the differences between the papers.)
SMAP also looks pretty cool
Now there’s some fascinating stuff in this, which I may come back to, but there’s also cause for deep frustration. A real sense of what the sinks are doing would be hugely helped by having better measurements of carbon dioxide, both from global monitoring networks and from satellites. But that just doesn’t seem to be a priority. Global ground based monitoring of carbon dioxide capable of showing regional effects is still underfunded — this summer in Boulder Pieter Tans was telling me that there was a lot more that could be done for relatively little money. And satellite measurements took a terrible blow when the Orbiting Carbon Observatory, OCO, didn’t make it to orbit in February. OCO could have been rebuilt and relaunched quickly: the team was all still there,the designs were good, it was as shovel-ready a piece of spending as you could wish for. But it wasn’t funded as such, and doesn’t seem to have any new money associated with it. So as I understand it the money to refly OCO will have to be gouged out of NASA’s existing earth science budget (8% of its total budget, because it’s not like the earth is a sexy supernova or galaxy or anything like that). I have to assume that that means it will fly later than it could have (and cost more); that probably means delays for SMAP, the soil moisture mission currently due to launch in 2013. SMAP would provide unparalleled data on one of the key parts of the planet — the part just beneath our feet that contains the root zones of plants and the water that those roots require.
Not to be treating such missions as a global priority strikes me as simply crazy. Now I know that there is an argument that the need for new climate science is overstated — that we know the outlook is bad, and that there is no science that is going to change the degree of action or inaction that that badness is held to merit. I understand that stressing a need for more data and science might be seen as offering reasons for delay. But the OCO and SMAP data really matter. They matter to understanding the processes going on — where the carbon is coming from and going to, how ecosystems are being effected, and so on. In SMAP’s case they even have operational implications — better soil moisture data means better forecasting. But despite the fact that great things turn on these issues, they don’t get the money. And their ground-based correlates, which offer even more bang for the buck, get penny pinched too.
Scientific monitoring isn’t going to save the world — but it will tell us what is going on as we try to adapt and to prioritise mitigations. Which means we should be taking it seriously.
Refs:
“Trends in the sources and sinks of carbon dioxide” Corinne Le Quéré, Michael R. Raupach, Josep G. Canadell, Gregg Marland et al. Nature Geoscience (2009) | doi:10.1038/ngeo689
“Is the airborne fraction of anthropogenic CO2 emissions increasing?” Wolfgang Knorr Geophys. Res. Lett., 36, L21710, (2009) | doi:10.1029/2009GL040613
Yes, it's melting
Having been a little disobliging about Pen Hadow, an explorer, in a previous post about “Heroes of the Environment” I now feel moved to return, briefly, to the subject. This morning the BBC is putting data gathered during Hadow’s recent Arctic adventure — a trek with two companions, called the Catlin Arctic Survey, that was meant to get to the North Pole but didn’t — into its main radio news bulletins at the moment. As Professor Peter Wadhams of Cambridge puts it in the BBC’s online version of the story and many other places:
The Catlin Arctic Survey data supports the new consensus view – based on seasonal variation of ice extent and thickness, changes in temperatures, winds and especially ice composition – that the Arctic will be ice-free in summer within about 20 years, and that much of the decrease will be happening within 10 years.
Which seems fine: but not news. What we have here is a consensus for which, because it is a consensus, we must assume there is already a lot of evidence, being backed up by some incremental unpublished data (pdf of science findings) that will later be presented at the Copenhagen meeting and submitted to Cold Regions Science and Technology, a journal I am pretty sure that the BBC does not often use as a source. What Wadhams says seems true and sensible, but reporting stuff that is widely accepted as news doesn’t.
To be fair, the BBC further reports that
Pen Hadow admitted that the expedition had not led to “a giant leap forward in understanding” but had been useful as an incremental step in the science of answering the key questions about the Arctic.
but it doesn’t go on to say why it reports this incremental step. The answer, obviously, is that it thinks the public likes explorers, and will find science done by explorers interesting, even if the equipment broke down and the observations are not yet of any proven value; it also probably thinks that raising awareness about global warming is a good thing. Personally I find people who “explore” a planet that has already been pretty thoroughly explored and do so in deliberately over-challenging and attention-seeking ways (Hadow first came to fame walking to the North Pole on his own without resupply) a little off-putting, even, in my more misanthropic moods, distasteful, though on the only time I met one he seemed a nice enough chap (that said, we were both talking to Edwina Curry, so contrast may have had something to do with it). If such people want to try to contribute to science and advertise a reinsurance company as they do so, fair enough (though the apparent shennanigans with data on their website suggest that this most recent undertaking was not utterly rigorous in its approach). But following HRH the Prince of Wales, who says this is a “remarkably important project”, in treating this data gathering as news seems to be a pretty straightforward mistake, even before you get on to the mistakes in headlining that “news”, such as “North Pole ice cap gone in 10 years“.
The generally grumpy tone of this post, and the unaccustomed act of linking to Watts, brings to mind a point a friend recently made to me — that I am more critical of climate-change claims that tilt beyond science into propaganda in private than I am in public. I think that to the extent this is true it is only because most of what I do in public isn’t about that sort of thing; I don’t spend much time attacking climate sceptics in public, either, and that certainly shouldn’t be seen as suggesting support. But while I am tapping away I will take this opportunity to say that I think people who talk about a climate sensitivity of more than 4ºC as remotely likely need to explain why they think this when others such as James Annan have argued well against it*. And I think when people talk about multi-metre sea-level rises, as Jonathan Porritt did on Radio 4 recently (“I have increasingly less time for those whose nimby-ist sentiments persuade them that somehow the best route to defending their cherished landscapes is by letting it be drowned by a huge amount later on in life. Which particular bit of the landscape do you want to defend James if what we’re threatened by is a seven metre rise in sea levels? ” — rtf transcript), they need to make clear that they are talking about the situation that’s not “later on in life” for anyone who doesn’t expect to live for a few centuries.
*hint: explanations that include phrases such as “I don’t use the classical Charney measure of sensitivity because I think one also has to take into account biosphere and other long-term feedbacks to which it pays no heed” seem to me to be headed in a plausible direction; I may also show sympathy to “unlikely events in the long tail dominate the risk assessment”, though rather less so…
Not terribly relevant image from A Davies/Greenpeace, used under a Creative Commons licence
Filed under: Geoengineering, Global change, Interventions in the carbon/climate crisis, Trees
Spot the dune...
An interesting paper in Climatic Change: Irrigated afforestation of the Sahara and Australian Outback to end global warming by Leonard Ornstein, Igor Aleinov and David Rind Doi: 10.1007/s10584-009-9626-y. (Mason Inman has a nice write up with some background and comment over at ScienceNow; [update] and corresponding author Len Ornstetin chronicles the idea’s rocky research road on his own site). The central idea is that with enough irrigation you can turn big deserts into big forests: forests big enough to suck up a large part of total carbon dioxide emissions for decades or even centuries. I think that you can take this notion as a serious plan, a thought experiment, a jeu d’esprit, a warning or a jumping off point, depending on predisposition. Aspects of all that in what follows.
Here are the basic numbers: The Sahara is about a billion hectares in area, on which you could fit a trillion eucalyptus trees. Those trees, if working flat out, could each put on twenty kilos of biomass a year. If roughly half that biomass is carbon, that would mean a net annual sink on the order of ten billion tonnes of carbon. That’s about the amount that humans currently emit.
To create such a forest in a century, you would have to plant as many hectares of trees every year as are currently lost to deforestation worldwide. And, even harder, you’d have to provide them with what they need to order to grow. You need a great many things to turn a desert into a forest — soil nutrients, microbiota, possibly pioneer plants, a compelling reason for doing the work, and so on — but the biggest hurdle, pretty obviously, is water. Eucalyptus, the authors say, needs about a metre of rainfall a year. For a billion hectares, that’s 10 trillion tonnes of water. The authors assume, reasonably for all that I know, that if you have smart irrigation getting the water to just where it is needed you can get away with half that amount. Even so, even the vast aquifers beneath the Sahara don’t contain the amount of water required, so it will have to come from desalination plants on the and be pumped it up to where it is needed (the average elevation of the Sahara is about 450m). The size of this undertaking — more than 50 new Niles, flowing in reverse — may explain why the authors feel they need to use that fine old-school term “terraforming” for their undertaking. The power requirement, if I’m reading their figures right (4.04kWh/m^3 fresh water delivered), is a bit to the north of 2.2 terawatts, about 40% of it for desalination by reverse osmosis and about 60% for pumping.
The world’s electricity generators currently provide about 18,000 TWh of energy, which averages out at 2TW of constant supply. So in energy terms the desalination and pumping needed for the Sahara forest would use a bit more electricity than the world currently generates for every other purpose. This unavoidably sounds nutty. But that is at least in part because of the nuttiness of the situation, rather than its proposed solution — the nutty situation in which we burn fossil carbon at tens or hundreds of thousands of times the rate at which it is sequestered over geological time. If humanity insists on putting so much carbon dioxide into the air every year that it would take a brand new forest the size of the Sahara to suck it all up, then that’s where the madness starts. That creating such a forest would have to be a large undertaking — large in terms of the whole world economy — is just a consequence of the initial folly.
And in practice the investment would be smaller. A nice thing about forests is that they can go some way to creating their own weather, and the authors have looked at this effect with some climate modelling work. If a forest with irrigation dampened soil is imposed on the Sahara, rain begins to fall, in some places as much as a metre of it every year. This rainfall doesn’t obviate the need for irrigation, because it is strongly seasonal — basically an extension of the West African monsoon of April to November. But it might significantly reduce the irrigation requirements. Maybe you could get away with just a terawatt…
The Sahel, to the south of the Sahara, also gets damper in those enhanced and extended monsoon rains, which is definitely a plus, I’d guess, and the African Easterly Jet, a feature which is driven in large part by the temperature contrast between the desert and surrounding land, seems to more or less vanish. Since a large number of Atlantic hurricanes get their starts as kinks in the AEJ, that might be a pretty significant change, too. Beyond that, the rest of the world seems pretty much unaffected. In particular, the authors say that their models show no additional warming that might be laid at the door of the change of albedo which comes with replacing light desert with darker trees. (I think this fits with the 2007 Bala et al paper in PNAS, which suggested that warming associated with afforestation would be due to changes in boreal, rather than tropical, forest cover).
The Bodélé depression (pic by Charlie Bristow)
There is, however, a fly in the ointment. The Bodélé depression in Northern Chad is only a small part of the Sahara, but it is the world’s greatest source of mineral dust, with the winds drawing some 700,000 tonnes a day off the surface. According to Koren et al in ERL, 2007 40 million tonnes of dust a year travels from the Bodélé to the Amazon rain forest, half the total annual mineral inputs into the forest basin (the dust fertilises the mid Atlantic, too, and it may play a role in abating hurricanes too — Jim Giles wrote a lovely piece on this for Nature some time back). There’s a real chance that this dust is crucial to maintaining the soil fertility of the forest, and even if the Bodélé itself were left unirrigated and unforested, the increase in precipitation all round it, and the wetter atmosphere downwind of it, would probably shut it down as a dust producer. If growing a forest in the Sahara hurts the one we already have in the Amazon it obviously becomes a less attractive proposition (though if we are going to lose the Amazon forest anyway, things might look different…). That said, if you are pumping trillions of tonnes of water across continental scales, thenpaying to air dump a few tens of millions of tonnes of fine-particle mineral fertiliser upwind of where you want it is hardly going to break the bank.
Something the authors don’t look into is that the higher the CO2 level in the atmosphere gets, the easier this all becomes. Higher carbon dioxide levels make plants more water efficient, all other things being equal. All other things are not, necessarily, equal — higher CO2 also makes things hotter, which plants don’t much care for. In a world with some solar radiation management, though (such as aerosols in the stratosphere) all things might indeed be kept equal, or at least temperature might be. Martin Claussen has been working for some time on the idea that the Sahara is a “tipping element” in the climate regime, one that can be pushed from a dry state to a wetter one relatively easily. In a more carbon rich but not-too-hot world the circumstances might be right for it to tip the other way, and it might take rather less than a 50-Nile terraforming project to nudge it over.
In the final analysis, I don’t think I take this paper very seriously as a practical proposition. Doubling global electricity generation for a single project seems far fetched. For such a thing to be put anywhere near the top of one’s list of African infrastructure investments would require that a great many other large and important development initiatives (provision of power, water, roads, cold chains, vastly improved agronomical advice, etc to the vast majority of the population, for starters) would already have had to have been put in place. But it’s kind of nice to imagine a world in which we were wealthy and together enough to have actually taken the pressing need for those changes to heart, and were thus in a position to consider greening a great desert too.
Bahrain's Tree of Life -- a limited pilot project?
And regardless of practicalities I think there’s real value in taking the analysis further. A big idea like this throws off many fascinating questions that force you to look at the earth, and what we know about it, in new ways (or old ways but with a new twist):
What polycultures would you build the new forest with? (all-eucalyptus-all-the-time is fine for first calculations, but doesn’t sound like anyone’s idea of a proper landscape. Baobabs? Laurels? And what fauna might be good, or bad?)
What genetic engineering — reduced flammability, higher albedo leaves, more refractory soil carbon, who knows what else — might help?
How much bioenergy with carbon capture could be built into the scheme, perhaps initially to power some of the inland the pumping stations?
Can biochar help? (and a million other soil-creation questions)
What are the best silvicultural ways to make the new woodlands pay, as that is something people by and large like their environments to do, and can there be room for some agriculture too?
How could local people best be convinced this was a good idea? And what are the property title reforms that would be prerequisite?
If the AEJ stops, do hurricanes stop too? Or does some other mechanism initiate them, maybe somewhere else? And does the dust really have an effect?
When the Sahara was wetter and less dusty in the past, did the Amazon actually suffer from lack of nutrients? (I think there is actually some research already out there on that — but can’t offhand think where)
How can the transformation be made stunningly beautiful?
What regions and landforms do you want to keep as monuments/heritage sites/national or world parks? There would undoubtedly be a real aesthetic/biodiversity loss in the removal of the desert, not to mention risks to some utterly wonderful buildings.
How to stop the Fremen becoming soft and decadent now that Arrakis has become a land of milk and honey?
and so on.
In particular, it would be nice to see some analysis of halfway houses; where in the Sahel and points north might merely huge, as opposed to planet-sized, afforestation be attempted, and what would be the costs and benefits? It is possible to transform land on very large scales, if not quite this large: 40m hectares of the Brazilian cerrado have been brought into agricultural production over the past fifty years. Can afforestation/silvicultural interventions on such scales ever make sense? And where else might be suitable for such things?
And on the topic of where else: My apologies to any Australian readers for not going into the paper’s analysis of foresting the Outback in addition, or as an alternative, to the Sahara. Basically the arguments are largely the same but the costs and effects are a bit smaller. There’s also a risk of interfering with El Nino that would definitely merit further attention. If anyone wants to blog more on that aspect of the subject send me a link and I’ll post it up here.
Image credits: Eucalyptus trees at the top from Big Lands Brazil, who would like to sell you some…; Bodele from Charlie Bristow, reused with permission; Tree of life from Flickr user Solvo under Creative Commons license
This week’s Nature has a review article in it I have been waiting for for some time, and which I suspect may become something of a classic:
Marten Scheffer et al, Early-warning signals for critical transitions Nature 461, 53-59 (3 September 2009) | doi:10.1038/nature08227. Here’s the abstract
Complex dynamical systems, ranging from ecosystems to financial markets and the climate, can have tipping points at which a sudden shift to a contrasting dynamical regime may occur. Although predicting such critical points before they are reached is extremely difficult, work in different scientific fields is now suggesting the existence of generic early-warning signals that may indicate for a wide class of systems if a critical threshold is approaching.
One of the problems with tipping points in complex systems is that straightforward analysis is incredibly unlikely to be precise and accurate about the tipping point’s threshold. A model may happily tell you that a system has a tipping point, bit it will not tell you where it is. In climate terms, you can be sure that there is a point at which the Greenland ice sheet will collapse, but you don’t know how far we are from it. This article reviews work which suggests a way round this. The system itself may tell you when it is getting close to a tipping point through subtle changes in the way its behaviour varies over time — in particular changes associated with “critical slowing”. What follows is my interpretation of the paper, which seems impressively approachable for a piece of mathematics, but which I may nevertheless be getting wrong; any real mathematicians in the audience should feel free to chip in in the comments.
A key symptom of critical slowing are that the system becomes lower to restore itself to its usual state after being perturbed. This means that if the system is fluctuating, its present state will become more closely determined by previous states — its “memory” will increase. In mathematical terms, this is an increase in autocorrelation. At the same time, and seemingly contradictorily, its variance may also increase because it becomes less able to recover from external shocks; that effect appears not to be as well grounded as the autocorrelation, but it does turn up in a lot of models.
As well as slowing down in this way the system will also start to get assymetric, because fluctuations that push it towards the tipping point and those that push it away will not be responded to in quite the same ways. It may also start to “flicker” as it moves back and forth across the boundary between two states before plumping firmly for one or the other. There are also ways of looking at differences over time, which I can’t really sum up: instead I’ll quote an example from the paper dealing with desertification:
Models of desert vegetation show that as a critical transition to a barren state is neared, the vegetation becomes characterized by regular patterns because of a symmetry-breaking instability. These patterns change in a predictable way as the critical transition to the barren state is approached, implying that this may be interpreted as early-warning signal for a catastrophic bifurcation [that being is one of the types of tipping point under discussion]
More on the desert stuff in this fascinating Science paper from 5 years back, one of the authors of which, Max Rietkerk, is also an author on the Nature paper.
How does this work in practice? Here’s an example using data from a 2008 PNAS paper by Dakos et al, on which many of the review’s authors worked.
The top plot is showing calcium carbonate percentages in a deep sea sediment core as a marker for the influence of the carbon cycle on the climate, as discussed in this 2005 Nature paper. The bottom plot is the measure of autocorrelation. As you can see, the time series goes from being not autocorrelated at all to being highly autocorrelated, and then bang. Similar autocorrelations can be seen in front of seven other abrupt climate shifts the PNAS authors looked at. The review looks at similar patterns in the onset of asthma attacks, ecological events, epileptic seizures and sudden stockmarket surges, and as the authors conclude
Flickering may occur before epileptic seizures, the end of a glacial period and in lakes before they shift to a turbid state; self-organized patterns can signal an imminent transition in desert vegetation and in asthma; increased autocorrelation may indicate critical slowing down before all kinds of climatic transitions and in ecosystems; and increased variance of fluctuation may be a leading indicator of an epileptic seizure or instability in an exploited fish stock.
So these processes really do seem to have a lot in common, much of which is related to the mathematical treatments reviewed in the paper. This is not to say everything is settled:
More work is needed to find out how robust these signals are in situations in which spatial complexity, chaos and stochastic perturbations govern the dynamics. Also, detection of the patterns in real data is challenging and may lead to false positive results as well as false negatives.
There are a lot of complexities here to do with how you filter the data, what data you choose, whether all the bifurcations that cause critical slowing are really catastrophic tipping points, and more. There are probably people who think it is all hogwash (and people should feel free to point me towards them). But I must say that after reading the review and feeling I have come a little way towards understanding what is going on, I look forward over the next years to people with climate models that show tipping-point behaviour getting stuck into this sort of analysis looking for precurssors. (Here’s a topical question: what does an autocorelation on the year-by-year arctic sea ice minimum show?) The idea that such mathematical work will ever reach a level where you would feel justified in saying “the Greenland ice tipping point is ten years away” may be far fetched. But you don’t know til you try.
Image copyright Nature Publishing Group
Filed under: Geoengineering, Global change, Interventions in the carbon/climate crisis, Published stuff
The last of my filling-in-for-Olivia columns at the NYT is now up, a quick run through some points from the later parts of Eating the Sun and subsequent stuff. It’s a carbon-climate crisis, energy is about flows not stocks, many wedges needed, yadda yadda yadda:
Given that humans are changing the atmosphere at an unprecedented rate, what responses should we expect from the biosphere? And is there anything that we can do to make those responses work to human benefit? For those in a hurry, the answers in brief: a) complicated ones; b) yes, at least a bit.
Filed under: Earth history, Geoengineering, Global change, Interventions in the carbon/climate crisis, Plant physiology
Here’s the video of a conversation I had with Jim at the Nature offices a few weeks ago. Also available in its full glory at the Nature site. And indeed apparently at The Guardian too. I’d post excerpts from a transcript if I had the time, or a transcript…
It appears that the action on Wednesday afternoon was where I was not: in the session on tipping points. Chris Jones of the Met Office’s Hadley Centre presented some studies of the Amazon (abstract in pdf) that have caused a big media stir. The studies suggest that a) there is a threshold level of warming beyond which much of the Amazon forest is committed to die back (probably being replaced by savanna) and b) that for significant parts of the forest that threshold is alarmingly low. Indeed it is quite possibly either unavoidable in the near future or already dwindling in the rear-view mirror. As I understand it from people who saw the presentation, models in which all the warming already in the pipeline (ie with no further emissions) is realised leave the forests pretty much committed to some dieback, and modest further warming seals the deal. I wasn’t able to check that with Jones himself, but it seems to fit with what he and his colleagues write:
We present results to show a possible climate threshold beyond which some dieback is committed and this commitment rises dramatically for global temperature rise above 2 degrees C, a threshold often used by policy makers in their definition of dangerous climate change. Any subsequent recovery is on such a long timescale as to make the dieback effectively irreversible on any pragmatic level.
Here’s the coverage from the Times and here’s some from The Guardian. Worth noting that it’s a single study, that there are error bars to consider and that people have in the past suggested that the Amazon is often more vulnerable in the Hadley Centre model than in most others. But still very worrying; all the more so if it were to be spun as a counsel of despair on efforts to stop deforestation on the basis that there’s no point preserving a forest that’s already doomed.
I’ll see if I can find Chris Jones, or some Brazilians, or both to talk about this with on Thursday.
Cross posted at Climate Feedback
Andrew Revkin has an interesting post on dot.earth. It’s common to talk (as I sort-of did back here) as if cheap energy solves, if not everything, all the big stuff. But might it just bring more problems in its wake — perhaps by pushing the human population so high that much of the rest of the natural world is pushed out, or perhaps through some other dire and unforeseen consequence? Andy:
On a finite planet, where would limitless energy, combined with humanity’s infinite aspirations, take us? This leads to a question that’s been touched on here periodically. Does a shift in values and aspirations have to accompany the technological leaps that will assuredly be made in the coming decades?
There have been heaps of warnings for a very long time about unintended consequences from a rush to new technologies. (If you haven’t read Bill Joy’s 2000 essay for Wired, “Why the Future Doesn’t Need Us,” I encourage you to do so — possibly with a stiff drink nearby.)
…
Jesse Ausubel of Rockefeller University has often asserted that technological advances will inevitably lead to more space for nature, allowing forests to expand, fisheries to rebuild and the last refuges for wild things to persist. But others warn that creeping deterioration of the world’s biological patrimony is happening in parallel with our creeping disinterest in the diversity of life and ecosystems. As Edward O. Wilson explained here in laying out “Wilson’s Law,” if we focus too much on the physical infrastructure that sustains us, without sustaining the planet’s variegated veneer of life, we’re in deep trouble.
It probably won’t surprise readers that with various caveats I am more of the Ausubel opinion. I don’t think that higher standards of living necessarily correlate with worse environmental outcomes. And I don’t think energy breakthroughs will have the same sort of demographic effect that fossil fuelled modernioty has But I am aware that it is an inductive argument. The history of the past few centuries suggests that the phenomenon of the demographic transition is real: from a situation where birth rates and death rates are both high, you move to a situation where death rates drop (leading to an expansion of the population) that is followed after a lag by a period where birth rates drop, too, and the population thus stabilises.
The demographic transition, from Keith Montgomery's online essay
It seems likely to me that in the near term world population is going to play out this way, and that after nearly three doublings in the past few centuries we have less than a single doubling left to go. I don’t think a massive influx of clean energy will change that and lead to the sort of growth seen during the fossil-fuel era again. The precise height of the plateau, though, remains unknown, and important: things are probably a lot easier with a world of nine billion than of twelve billion.
And that which might lie in wait further on down the x axis should also give us some pause. It’s a bit end-of-history to think that humanity goes through millennia of premodernity, a couple of centuries of transition and population growth and then millennia of postindustrial population stasis, end of. This seems to be demographics a la Christopher Robin: “Now we are six we’re as clever as clever, and we think we’ll stay six for ever and ever”.
Not that any of this matters, people will say, if the planet’s carrying capacity is surpassed over the long term. But how many people the world can support depends on how they live and what technologies they live with: applying a simplistic ecological notion of carrying capacity that doesn’t take differential attitudes and technologies into account makes littlesense. Humans need to understand the environment and the ecosystem services it offers a lot better, but not so that they can discover some set-in-stone carrying capacity and adapt to it. They need to do it to understand how to engineer and sustain a carrying capacity that suits, within the limits of what is possible.
Which brings us to “Wilson’s law” , which Andy has quoted E O Wilson as defining thus:
If you save the living environment, the biodiversity that we have left, you will also automatically save the physical environment, too. If you only save the physical environment, you will ultimately lose both.
I can’t make up my mind whether this is trivial or obtuse, and I haven’t seen the argument that Wilson makes to back it up. The first part seems true by inspection, in that saving “the living environment” would necessarily entail massive action on the physical-environment side (curbing climate change). The second part sounds like something that Wilson would like to be true and that might be true but that can’t be proved true. A priori it seems unlikely that the current living environment is uniquely capable of providing non-substitutable ecosystem services without which the physical environment collapses, taking humanity with it. Other biospheres — perhaps differently or more simply arranged — might do as well. They might have less resilience, but a lack of resilience isn’t the same as certain doom, especially when there is active observation and course correction going on.
Filed under: Geoengineering, Global change, Interventions in the carbon/climate crisis
A very useful paper (abstract|pdf|discussion space) comes out today in Atmospheric Chemistry and Physics by Tim Lenton and his student Naomi Vaughan. Tim told me when I was reporting the Andy Ridgwell paper on leaf albedo (Nature story|blog entry) that he’d become pretty interested in evaluating geoengineering schemes, and was setting up a group at the University of East Anglia to assess them. This paper presumably represents the first fruits of that interest, providing a ranking of most of the geoengineering schemes proposed in the literature in terms of the amount of radiative forcing they can provide.
Radiative forcing is, more or less, the difference in terms of energy per square metre that’s associated with any given action that changes the climate; it’s a pretty routine way of expressing things in IPCC-land. The IPCC puts the radiative forcing associated with the greenhouse gas industrial and industrialising societies pumped into the atmosphere from 1800 to 2005 at about 1.6W/m², and the forcing for a doubling of CO2 at about 3.7W/m².
Lenton and Vaughan first divide geoengineering proposals into two sorts: shortwave and longwave. Shortwave schemes seek to reduce the amount of energy that gets into the earth system by reflecting away incoming sunlight. Longwave schemes seek to increase the amount of energy leaving the earth system by making the atmosphere more transparent to outgoing infrared radiation — that is, by reducing the greenhouse effect. Then they assess the two with some very simple modelling (well, for the longwave there are some wrinkles, but it’s all in principle pretty simple). They don’t claim that the figures they come up with are the best available in any particular case, just that they are all derived the same way, and so allow fairly straightforward comparisons. By standardising the techniques they also show up a few errors in previous analyses: for example, if you increase the total amount of light reflected back into space by clouds, you reduce the amount reflected by the surface, simply because less light gets there in the first place.
The first and most striking conclusion is that if you want to have a big effect, go shortwave. Sulphate aerosols in the stratosphere (which were the main topic of this piece and these Climate Feedback posts) and mirrors/refractors in space (also in that piece, and in this paper by Roger Angel) both have the potential to provide as much by way of negative forcing as a doubling of CO2 provides by way of positive forcing. Not surprising; if you’re not constrained by money or by concerns about environmental side effects, you can put mirrors in the sky and particles in the stratosphere until it’s darkness at noon.
When you leave these global technologies behind, the other shortwave interventions rank, unsurprisingly, more or less according to the area they affect. Increasing the brightness of marine stratocumulus clouds, as proposed by John Latham, would affect about 17% of the earth’s surface, and the Lenton-Vaughan analysis suggests that the whitening effect would have to be considerably more marked than previous work has assumed; but if that brightening could be achieved then a negative forcing that averages more than 3W/m² should be possible. Covering non-sandy deserts with aluminium and polyethylene (not an idea I had come across before, and a pretty silly one as far as I can see: more here if you want it) makes 2% of the surface a lot brighter, and gets you an average 1.7W/m² of negative forcing, obviously very unevenly spread. Increasing the brightness of the planet’s grassland as Robert Hamwey has discussed (pdf) gets you 0.64W/m², and the Ridgwell et al idea of planting brighter crops gets you 0.44W/m² at best, croplands being smaller than grasslands. Lightening everywhere that people actually live (another idea from the Hamwey paper) gets you 0.19W/m²; increasing the area of plankton blooms that seed the creation of clouds in parts of the southern ocean gives you just 0.016W/m² (and that may be an overestimate) and restricting yourself to just creating shinier cities gives you no more than 0.01W/m².
What of the longwave? In principle, capturing carbon dioxide from the air (pdf of the Keith et al paper) and burying it in the ground could give you whatever radiative forcing you wanted; the limits to such a scheme are entirely economic, rather than being imposed on the earth system. All the other schemes, though, which involve making changes in the natural carbon cycle, are quite constrained, with none able to counter a doubling of carbon dioxide, even given the most extreme assumptions.
The biggest effect comes from really aggressive planting of forests, as described in an essay (pdf) by Peter Read on his global gardening plans. This involves growing enough plant material in the next 50 years to more than completely make up for all the arbon dioxide lost through deforestation and land use change over the past few centuries, which is really remarkably ambitious, especially if people are still going to have some space to grow food. By 2050 this strategy gets you an effective 0.49W/m² of negative forcing thanks to 88 gigatonnes of carbon dioxide being stored away. A variant of the idea in which you grow the biomass and burn it in power stations fitted out for carbon capture and storage does even better: 0.69W/m² by 2050 and almost 2W/m² by 2100 (For the longwave calculations, the radiative forcing depends on how long the programme has been going on. It also depends on what assumptions you make about how effective carbon-emissions control is; Lenton and Vaughan calculate all the forcings in terms of what extra relief the carbon-dioxide drawdown provides in a world that is already making serious cuts in emissions).
A lower tech idea that Read is fond of, as for that matter am I, is turning biomass into biochar and ploughing it into the ground. Jim Lovelock, Lenton’s mentor and friend, was extolling this as a possible way of making things better in New Scientist last week, speaking to the in-this-case-aptly-named Gaia Vince. This may make sense for all sorts of reasons, and the fact that making the charcoal also provides you with fuel (see Johannes Lehmann’s commentary in Nature a few years ago) is obviously a plus, but even a really aggressive campaign along these lines gives ou a negative forcing of only 0.40W/m² by 2100.
After that come a bunch of ocean fertilization schemes, using phosphorous, nitrogen and iron, all of which offer something in the region of 0.1-0.2W/m². A system of pumping nutrient-rich water up to the ocean surface sketched out by Lovelock and Chris Rapley (earlier blog entry) delivers a truly meagre 0.003W/m² by 2100.
None of this, as Lenton and Vaughan are at pains to make clear, counts as an endorsement; all the schemes have side effects and risks, as well as in some cases (ahoy there, vast fleet of space parasols) quite remarkable costs. But looking at the options this way does allow a sense of what might be possible, and a way of seeing what might be done in a mix and match sort of way. And the fact that the paper is published in the discussion section of ACPD means that the various researchers whose work is discussed will have a chance to answer back, correct any poor assumptions, and carry the debate forward.
Cross-posted to Climate Feedback
Image from flickr user gianky, under a creative commons licence.
Filed under: Earth history, Global change, Nature writing, Published stuff
It takes nothing from the beauty and power of the image, though, to point out that it was the photographer, far more than its subject, who was isolated, and that the fragility is an illusion. The planet Earth is a remarkably robust thing, and this strength flows from its ancient and intimate connection to the cosmos beyond. To see the photo this way does not undermine its environmental relevance — but it does recast it.
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To substitute these flows for the fossil fuels poised to despoil our planet and also run out on us — worst of both worlds — is an epic task. But the message that frames all the other messages of “Earthrise” is that we can rise to epic tasks. Look where the photo was taken. “If we can put a man on the Moon …” quickly became shorthand for society’s failure to achieve goals that seemed far simpler. But still: we put a man on the Moon, and that does say something. Efforts on a similar scale aimed at harvesting the energy flowing about us are entirely appropriate, and could make things a great deal better. We cannot solve all problems; some climate change is inevitable. But catastrophe is not.
“Earthrise” showed us where we are, what we can do and what we share. It showed us who we are, together; the people of a tough, long-lasting world, shot through with the light of a continuous creation.
Happy Holidays
