Rising atmospheric carbon dioxide might cause so much heating that some countries will respond by releasing sulfate aerosols to reflect sunlight and cool the planet. If that happens the question arises: Will the net effect of less sunlight (which would reduce energy flowing to plants) be outweighed by the plant-boosting effects of lower temperatures and higher CO2? Some climate scientists did modeling that suggests globally crop yields would rise overall but fall in some areas.
Although scientists know that climate change in recent decades has negatively impacted crop yields in many regions, the study by Pongratz and colleagues is the first to examine the potential effect of geoengineering on food security. Pongratz's team, which included Carnegie's Ken Caldeira and Long Cao, as well as Stanford University's David Lobell, used models to assess the impact of sunshade geoengineering on crop yields.
Using two different climate models, they simulated climates with carbon dioxide levels similar to what exists today. A second set of simulations doubled carbon-dioxide levels – levels that could be reached in several decades if current trends in fossil-fuel burning continue unabated. A third set of simulations posited doubled carbon dioxide, but with a layer of sulfate aerosols in the stratosphere deflecting about 2% of incoming sunlight away from the Earth. The simulated climate changes were then applied to crop models that are commonly used to project future yields.
The team found that, in the model, sunshade geoengineering leads to increased crop yields in most regions, both compared with current conditions and with the future projection of doubled carbon dioxide on its own. This is because deflecting sunlight back to space reduces temperatures, but not CO2. "In many regions, future climate change is predicted to put crops under temperature stress, reducing yields. This stress is alleviated by geoengineering," Pongratz said. "At the same time, the beneficial effects that a higher CO2 concentration has on plant productivity remain active."
Of course this work was done with a model that is much simpler than the real planet. Future improvements in model quality could yield different results. Still, an interesting result.
The researchers point out that sulfate aerosols would not reverse the ocean acidification caused by more CO2 dissolving into the oceans. Speaking of ocean acidification, rising atmospheric CO2 will increase the acidification of the oceans so much that the coral reefs would drastically shrink in extent.
"In some regions, the man-made rate of change in ocean acidity since the Industrial Revolution is hundred times greater than the natural rate of change between the Last Glacial Maximum and pre-industrial times," emphasizes Friedrich. "When Earth started to warm 17,000 years ago, terminating the last glacial period, atmospheric CO2 levels rose from 190 parts per million (ppm) to 280 ppm over 6,000 years. Marine ecosystems had ample time to adjust. Now, for a similar rise in CO2 concentration to the present level of 392 ppm, the adjustment time is reduced to only 100 – 200 years."
On a global scale, coral reefs are currently found in places where open-ocean aragonite saturation reaches levels of 3.5 or higher. Such conditions exist today in about 50% of the ocean – mostly in the tropics. By end of the 21st century this fraction is projected to be less than 5%. The Hawaiian Islands, which sit just on the northern edge of the tropics, will be one of the first to feel the impact.
If necessary we could use a variety of climate engineering techniques to prevent the melting of Antarctica and Greenland. But I've yet to come across a proposal for how to prevent a shift in ocean acidity as atmospheric CO2 continues to rise.
| Share | | Randall Parker, 2012 January 24 10:42 PM Climate Engineering |
Hello Randall. If possible, please add RSS feeds for comments in each post so we can follow the conversation. Thanks.
Corals first appear in the fossil record around 500 mya. The GEOCARB III reconstruction of atmospheric CO2 back then is 3000 ppm at the bottom of the error bar. Corals can easily stand far more CO2 than the current atmospheric levels.
I don't think those 500 million year old corals are the same ones we have today. I think they may have been corals that were adapted to conditions that existed 500 million years ago, although they may have been just as sensitive to changes in acidity as corals are today.
Why not dump rust into the open ocean to create large phytoplankton blooms? These are already the #1 converters of CO2 on Earth and the introduction of iron oxide into the oceans has already been shown capable of increasing their numbers and cooling the Earth's temperature...radically.
Randall, there is a geoengineering suggestion that deals with increasing ocean acidity. Basically it consists of scraping a large part of South Australia into the oceans, but first heating it to turn the limestone into calcium oxide or quicklime. There are some problems with this idea. Firstly, it's not clear that it would actually work as advertised and secondly the scale of the project is enormous, requiring more mining than currently exists on the planet and vast amounts of energy. It would be far cheaper to simply reduce CO2 emissions instead, but that seems to be the case for just about every geoengineering scheme I hear about.
Jason, seeding the oceans with iron has been tried and is not very cost effective as not much of the CO2 absorbed is sequestered long term. But if the technique is improved so it becomes competitive with other options it might be used in the future.
How could it not be cost effective? Due to the high cost of old rusty garbage?
From what I've heard, when diatoms die they take most of the carbon with them to the bottom of the ocean. Perhaps I'm mistaken, but even if the efficiency is low, I cannot possibly see how it would prove cost ineffective...particularly when the other options are shaving off South Australia or destroying to world's industrial base.
Large blooms of diatoms tend to attact filter-feeders. Increasing the population of zooplankton and fish isn't a bad thing, but if your goal is to remove carbon from the surface waters and move it to the ocean floor it's counterproductive.
Jason, I don't think we face an option between seeding the oceans, scraping off South Australia, or destroying the world's industrial base. For example, we could scrape off parts of Western Australia instead. Or instead of destroying the world's industrial base, we could instead use it to manufacture low emission generating capacity and electric vehicles. Since the existing fossil fuel based infrastructure will eventually need to be replaced anyway, the cost of gradually replacing it is quite low. And the benefits of less pollution and a more stable climate are well worth it.
"Since the existing fossil fuel based infrastructure will eventually need to be replaced anyway, the cost of gradually replacing it is quite low. And the benefits of less pollution and a more stable climate are well worth it."
Kyoto as is would indeed destroy the world's industrial base. As far as "gradually" goes, clearly once solar power can REALLY compete, and be installed EVERYWHERE, the problem is all but solved.
What we need, supposing global warming is indeed a real threat, are interim solutions. Given the current economic situation, that can be something like Kyoto, or major expensive engineering solutions. It seems to me that iron fertilization is both cheap and potentially viable in the near to medium term.
As far as the argument that iron seeding does not trap carbon long term insofar as it is eaten, that's only proven true in certain conditions, and moreover the same could be said of forests, etc. The carbon they trap is only for a decade or so. Diatoms can trap much more and for longer.
I was wondering why all the factories in my town had been utterly destroyed. It must have been Kyoto. And here I was thinking it had been Godzilla. It took five years though. You'd think a Japanese treaty would be more punctual, wouldn't you?
And here I thought I was talking to someone with a desire to make sense. My apologies.
Did their calculations assume that farmers kept growing the same crops, or adapted to the new conditions? Crops are grown at present over a wide range of climates--and one effect of global warming would be to increase the amount of land in Canada, Siberia, etc. that was warm enough for agriculture.
Just because they're warm enough doesn't mean they'll have the other required attributes. I understand that the soils under most of that Canadian forest which the "global warming is a GOOD thing" camp thinks ought to be cropland are very thin. And if rainfall doesn't coöperate, you get something warm enough but too dry. And what if it's too variable? Frosts in late June, or frequent drought years; what then?
If you bet on northern Canada turning into Iowa but it becomes more like north Nevada, you're screwed (meaning dead).
Kyoto wouldn't be an issue if we just grew nuclear power. Even biofuels work beautifully with it; there are a number of processes for breaking down cellulose into sugars which only need process heat in the sub-300°C range, which happens to be what water-cooled reactors produce. Imagine a host of reactors cranking out peak watts by day and turning garbage and crop stalks into fuels by night; that would have a big impact on both carbon emissions and petroleum demand right there. Add a vehicle electrification campaign and you'd see a lot more carbon disappear.
You could justify much of this with the benefits from waste destruction/conversion (no need to dispose of something that ceases to exist qua waste), reduced pollution and reduced imports of petroleum. You'd also mine and ship less coal and dispose of less ash. This is win/win/win as I see it (Peabody Energy would not agree, and railroad interests might not either).
Sorry Jason, when you came out with, 'Kyoto as is would indeed destroy the world's industrial base.' I thought we were in a contest to see who could make the most outlandish statement. After all, we did have an industrial base back when our emissions were equal to the Kyoto treaty's target and we also have ways of obtaining energy other than fossil fuels.
An invasion by the lizard people of the Pleiades star cluster would indeed destroy the world's industrial base. So I've got you all beat on outlandishness (even though the invasion by the lizard people really would be a disaster). By contrast, I expect Peak Oil will only shrink the world's industrial base. Kyoto: Obviously countries will stop short of inflicting on themselves such severe reductions in fossil fuels usage that they return to farming economies after mass starvation.
"After all, we did have an industrial base back when our emissions were equal to the Kyoto treaty's target"
Yes and we also had BOTH a lower population and standard of living. So what exactly are you suggesting? Give more money to Solyndra and everything will be rainbows?
As far as my "outlandish" suspicions concerning Kyoto...why don't you try selling it to China or India? They're not as blinkered to reality, nor so pampered by a first-world lifestyle that they've lost track of how wealth is actually created.
With people like you it's obvious that the "solution" to global warming is your real interest, rather than the "problem" itself. This is why cheap and potentially effective solutions like iron fertilization cannot—must not—be taken seriously.
Jason, on the first of July Australia's carbon price will be $23 per tonne of CO2. Like many socialist nations, Australia has introduced a market based mechanism for reducing emissions. So, if you can sequester CO2 for less than $23 per tonne using iron fertilization, please go ahead and do so and you can strike it rich. Personally, being a slow and blinkered thinker, I can't see any methods for removing CO2 from the atmosphere and sequestering it for less than around $33 a tonne or more. But I hope you can show me how wrong I am.
What about those of us whose solution is things like nuclear power, Jason?
Iron fertilization has been tried. It is not the quick fix you seem to think it is. There is no solution that doesn't involve a major reduction in carbon emitted; you're not going to triple or even double carbon absorbed.