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Researchers Evaluate Climate Cooling Potential of Different Geoengineering Schemes

27 January 2009

Schematic overview of the climate geoengineering proposals considered. From Vaughan and Lenton (2009). Click to enlarge.

Researchers at the University of East Anglia (UEA) have carried out the first comprehensive assessment of the relative merits of different geoengineering schemes in terms of the climate cooling potential. Their paper appears in the journal Atmospheric Chemistry and Physics Discussions.

Climate geoengineering proposals seek to combat the effects of climate change—in particular to counteract the effects of increased CO2 in the atmosphere. There are two basic approaches proposed: reducing the atmospheric absorption of incoming solar (shortwave) radiation, or removing CO2 from the atmosphere and transferring it to long-lived reservoirs, thereby increasing outgoing longwave radiation.

“The realization that existing efforts to mitigate the effects of human-induced climate change are proving wholly ineffectual has fuelled a resurgence of interest in geo-engineering.”
—Prof. Tim Lenton

A number of schemes have been suggested including nutrient fertilization of the oceans, cloud seeding, sunshades in space, stratospheric aerosol injections, and ocean pipes.

The critical metric for a geoengineering scheme is its effectiveness in cooling the climate; Tim Lenton and Nem Vaughan at UEA quantified that effectiveness in terms of radiative forcing potential.

Among their findings:

  • Enhancing carbon sinks could bring CO2 back to its pre-industrial level, but not before 2100—and only when combined with strong mitigation of CO2 emissions. Carbon cycle geoengineering carries less risk associated with failure.

  • Stratospheric aerosol injections and sunshades in space have by far the greatest potential to cool the climate back to pre-industrial temperatures by 2050. However, they also carry the most risk because they would have to be continually replenished and if deployment was suddenly stopped, extremely rapid warming could ensue.

  • Existing activities that add phosphorous to the ocean may have greater long-term carbon sequestration potential than deliberately adding iron or nitrogen.

  • On land, sequestering carbon in new forests and as bio-char (charcoal added back to the soil) have greater short-term cooling potential than ocean fertilization as well as benefits for soil fertility.

  • Air capture and storage shows the greatest potential, potentially combined with afforestation/reforestation and bio-char production.

  • Increasing the reflectivity of urban areas could reduce urban heat islands but will have minimal global effect.

  • Other globally ineffective schemes include ocean pipes and stimulating biologically-driven increases in cloud reflectivity.

  • The beneficial effects of some geo-engineering schemes have been exaggerated in the past and significant errors made in previous calculations.

Without mitigation, anthropogenic climate forcing could reach ~7W m-2 on the century timescale and remain greater than ~7W m-2 on the millennial scale. Even in a strong mitigation scenario, anthropogenic forcing will remain >1W m-2 for the rest of the millennium, exceeding 3W m-2 on the century timescale.

Climate geoengineering is best considered as a potential complement to the mitigation of CO2 emissions, rather than as an alternative to it. Strong mitigation could achieve the equivalent of up to -4W m-2 radiative forcing on the century timescale, relative to a worst case scenario for rising CO2. However, to tackle the remaining 3W m-2, which are likely even in a best case scenario of strongly mitigated CO2, a number of geoengineering options show promise.

...If our estimates are even remotely accurate, recent interest in ocean carbon cycle geoengineering seems a little misplaced, because even the more promising options are only worth considering as a millennial timescale activity. Perhaps the most surprising result is that activities that are already underway, particularly inadvertent phosphorus addition to coastal and shelf seas, may have greater long-term carbon sequestration potential than the much-studied iron fertilization. Some other suggestions that have received considerable media attention, in particular “ocean pipes” appear to be ineffective. The real value of such suggestions has been to redirect attention to the whole topic area. We hope that the present contribution provides a useful quantitative first step that can inform the prioritization of further research into various climate geoengineering options, and provide a common framework for the evaluation of new proposals.

—Lenton and Vaughan (2009)


January 27, 2009 in Climate Change, Climate Change Adaptation, Geoengineering | Permalink | Comments (19) | TrackBack (0)


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If I realy wanted to cool down the planet fast id just do the following.

Take a large set of pipelines from the ocean to the top of very tall mountains.

Pipe warm surface water up the mountain and shoot it out to form snow releasing all the heat into the air way up there where it can more readily go back into space.

Let the brine travel back down a set of concrete "rivers" to the ocean.

Now when the snow melts you have dams along the way to catch about 70% of the energy you used to put the water up there.

Now just plant 1 million windmills to power the sucker.

Now you have all the power you want all the fresh water you want and cool the planet all at the same time.


I'm not very knowledgeable on this subject so I apologize ahead of time. But what happens if we just phase out the internal combustion engine and go all-electric or fuel cell? Seems to me the biggest global greenhouse gas culprit is the gasoline/diesel engine.

But what happens if we just phase out the internal combustion engine and go all-electric or fuel cell?

Nothing. Earth has been on a cooling trend over the past eight years. That is with internal combustion engines increasing in use. The Earth warms and cools in cycles based on Sun activity. Please see Ohio covered by glaciers tens of thousands of years ago for evidence of Global Warming pre-SUV. Don't let the Globalwarmists newfangled religion warp your thinking.

We need to focus on energy independence and cutting back on pollution. Throwing away trillions of dollars on an already discredited Global Warming scheme should be a crime.

I don't think is very hewlpful.
They seem to arbitrarily discard some solutions and extol others.
Also they say "basic approaches proposed: reducing the atmospheric absorption of incoming solar (shortwave) radiation, . ..."
So, let it through to the ground?
Did they mean "reducing the atmospheric transmission (increasing reflection)of incoming solar (shortwave) radiation?"

Cheapest and quickest option - white paint.

"already discredited Global Warming scheme"...

And who, praytell, has decided that? There are a few natural phenomenon that very clearly support GW.

Granted, the jury is still out. But it certainly is not 'discredited' (well, except in the minds of the people who already had their minds made up).

One recommendation I had seen was to bury trees in deep oxygen poor mines.

Can't we just bury the AGW deniers in deep, oxygen poor, mines?

What would it cost to make crampons and fitting from stainless to handle the salt.
Surely freshen the water first, algae, potable , irrigation.

agreed - but I think transport (and ice) only accounts for 15%

ai vin,
Shouldnt we be concerned about smell from the Avon pit?

>>Earth has been on a cooling trend over the past eight years.
Reference please.

>>The Earth warms and cools in cycles based on Sun activity.
Reference please. Don't tell me to Google "maunder"

Gee, Mark, influence of solar and cosmic ray activity over numerous parameters of climate is common knowledge. If you want references, there are hundreds of published articles referenced here:

Cooling trend over last 10-8-6 years (pick your own starting point, result would be the same) is also common knowledge to anyone interested in the subject. Both satellite measurements and both ground stations measurement systems point out to cooling trend, with three sources pretty close and GISS (compounded by Hansen) showing slightly weaker cooling trend. For graphs and comparison take a look, for example, here:

You AGW deniers could be setting yourselves up for a big fall. Let's say you're right and Earth has been on a cooling trend over the past eight years. Well if the Earth warms and cools in cycles based on the Sun's activity then the cooling trend could end and reverse itself when the Sun's activity cycles back, right?

And the thing you're not facing is the fact of how hot it is; 2008 [a cold year] was still the 10th hottest on record. If the record goes back 150 how many of these cycles did we go through and why were all 10 of the hottest years only in the last 15?

A few things about the temperature record: "The reliable instrumental record only goes back 150 years in the CRU analysis, 125 in the NASA analysis. This is a simple fact that we are stuck with. 2005 was the warmest year recorded in that period according to NASA, a very close second according to CRU. Because of this limit, it is not enough to say today that these are the warmest years since 150 years ago, rather one should say 'at least': 1998 and 2005 are the warmest two years in at least the last 150."

"But there is another direct measurement record available that can tell us things about temperature over the last 500 years, and that is borehole measurements. Basically, this involves drilling a deep hole and measuring the temperature of the earth at various depths. This gives us information about century scale temperature trends as warmer or cooler pulses from long term surface changes propagate down through the crust. Using this method we can see that temperatures have not been consistently this high as far back as this method allows us to look. This way of inferring surface temperatures does smooth out yearly fluctuations and even short term trends, so we can not know anything directly about individual years. But given the observable range of inter-annual variations recorded over the last century, it is quite reasonable to rule out single years or even decades being far enough above the baseline to rival today.

Thus, using this record, we can extend our timeframe and reasonably conclude that it is warmer now than any time in at least the last 500 years."

How many of these cycles did we go through in the last 500years?

"It is possible to make reconstructions of temperature much further back, using what are called proxy data. These include things like tree rings, ocean sediment, coral growth, layers in stalagmites and others. The reconstructions available are all slightly different and provide sometimes more and sometimes less global versus regional coverage over the last one or two thousand years. Note: this covers the period often referred to as the Medieval Warm Period. As noted, all these reconstructions are different, but: they all show some similar patterns of temperature change over the last several centuries. Most striking is the fact that each record reveals that the 20th century is the warmest of the entire record, and that warming was most dramatic after 1920
Thus we can reasonably say it is warmer now than any other time in at least the last one thousand years."

How many of these cycles did we go through in the last 1000years?

"The only other candidate for a higher temperature period going back through the entire Holocene (~10,000bp to now) is called the Holocene Climatic Optimum some 6000 years ago. It is not known exactly what the temperatures were then, the farther back in time we try to look, the greater the uncertainties there are to deal with. Even so, the Holocene Climatic Optimum has long been cautiously thought to be almost as warm or even warmer than now. That conclusion is starting to look less likely as it has been determined that the anomalous warmth of that time was actually confined to the northern hemisphere and occurred only in the summer months.

Robert Rohde's website, Global Warming Art has a nice graph- -of many reconstructions of Holocene temperature, regional and global, all super-imposed with an average of all of them combined, shown below. This represents the best estimate available of global temperatures in the Holocene.

Thus one can reasonably believe that it is warmer now than at any other time in at least the last 10,000 years."

How many of these cycles did we go through in the last 10,000years?

"Before the current interglacial the planet was in the grip of a much colder glacial period with ice sheets well down into the continental US. This period only just ended some 11,000 years ago. The record of glacial-interglacial cycles can be read in Antarctic ice core analysis and it shows these cycles over many 100Kyr periods. The IPCC offers a good version of this graph-
Thus we can say that if our reading of the Holocene is correct, it is warmer now than at any other time in over the last 100,000 years."

How many of these cycles did we go through in the last 100,000years?

Thanks for the links to I'll have a look through those, although I have to chuckle. I've spent quite some time on that website sifting through their reports, doing what they don't want you to do, and actually checking their references back to the original sources ... quite illuminating!!!!

Oh, now Mark_BC... if you start going back and seeing what the people who actually did the research wrote, how will you every learn anything about anything? Just because someone else deployed the instruments, collected the data, made the models, tested the assumptions doesn't mean that the editors at CO2Science don't do a better job of drawing conclusions...

Ai Win:

Proxy reconstruction of past temperatures is very tricky business. Most comprehensive and notoriously wetted evaluation (IMO) was done by Craig Loehle:

Presence of Medieval Warm Period, Little Ice Age, and Modern warm period are very clearly visible on combination of 18 world-wide reconstructions. Author cautiously point out that it appears that MWP was slightly warmer than current warm period, but it is inconclusive due to insufficient data.

Global warming in a short simple analogy starting with a fact: CO2 traps heat. Adding CO2 to the atmosphere is like putting a lid on a pot of water on a cooktop. It may be impossible to predict where every vapor bubble will form and rise and where every water droplet will condense and fall, but it is a physical certainty that the pot will get hotter and boil faster.

Since about 2000 the additional heat trapped by excess CO2 has been going into the deep ocean and warming the water there. As we have few instruments there, this causes an in-obvious form of global warming. Once the deep ocean has absorbed enough heat, circulation patterns will change, most of the heat will again go into the atmosphere, and obvious (that is, atmospheric) global warming will resume with a vengeance.

Global warming deniers are invited to demonstrate the strength of their convictions by buying ocean front property.

“The Gores in late 2005 bought a condo at San Francisco's St. Regis…” at Fishermen Warf.

The Gores have money, they can live wherever they want to and move whenever they need to and are probably well insured against any losses.

But the millions of poor people crowded into low coastal land around the world? - Not so lucky.

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