Re: [geo] paper on optimizing latitudinal distribution of sulfate aerosols to maximize climate metrics

[John Nissen]

Thanks Ken and George for this important paper. It raises a number of issues to my mind, some of which we've been already discussing. 1.  Cooling the Arctic David Keith was saying that the trouble with aerosols at high latitude to cool the Arctic was that the aerosols would quickly spread to lower latitudes.  Is that so?  Note that Nathan Myhrvold, in the CNN interview about his hosepipe invention [1], says that a side-effect of aerosols to cool the Arctic would be to halt global warming, if I remember correctly.  He also said he'd used conventional models, that other people used, to make his predictions. 2.  Mixed method Doesn't the difficulty in optimising for several things at once call for a combination of geoengineering techniques, including the cloud brightening?  Would it be possible for you to team up with say Stephen Salter and John Latham to work out what could be done with a mixed method approach? 3.  Countering heat flux The observed warming of the Arctic must involve extra heat flux.  We still do not have a figure for this do we?  But we do have some figures of sea ice volume decrease per year from PIOMAS.  How much heat does this equate to, in terms of say Watts per square metre averaged over the Arctic and over the year? 4.  Heating of deeper waters - vertical mixing Albert Kallio has pointed out that deep waters tend not to freeze over so much in winter [2].  This implies that much of the extra heat flux must go into heating water to significant depth.  Do we have any quantitative estimates of this effect?  Can anything be done to reduce vertical mixing? Cheers, John [1] http://freakonomics.blogs.nytimes.com/2009/12/21/nathan-myhrvold-on-geoengineering-and-penguin-poo/ [2] Albert's email on Cryosphere Today, posted earlier today.  Quote: I stick to my position that 2.6% increase in the area of ocean sea ice cover, 1/40th increase in the 2007 melt record is not enough to justify optimism and we need geoengineering and also to think about if we could prevent the increased vertical mixing of the Arctic Ocean that transfers heat due to themal intertia of water lying beneath the floating sea ice on just next to the North Pole. Any suggestions to stop the increase in winds, or to cover the widening leads between ice floes? --- Ken Caldeira wrote: Hi, we have a new paper out in Environmental Research Letters, titled "Geoengineering as an optimization problem". To me, the most interesting thing in this paper is Figure 2 which indicates that, at least in this climate model, the climate response to a linear combination of aerosol distributions is very similar to a linear combination of the climate response to each aerosol distribution taken singly. (Of course, this model does not include the large ice sheets and changes in ocean circulation and consideration of these factors could affect these results.) We find that in this model (NCAR CAM3.1), distributions of aerosols that are parabolic in latitude can diminish 94% of the rms change in zonal mean land temperature or 74% of the rms change in zonal mean land precipitation minus evaporation (runoff). See also:  http://environmentalresearchweb.org/cws/article/news/43750 Sep 16, 2010 Geoengineering the tailor-made way So far, researchers investigating geoengineering have typically decided on a regime of aerosol injection and modelled how it will affect climate. Now scientists have turned this approach on its head by setting climate goals first before finding out the injection pattern that best creates them. "We started out asking if it would be possible to predict the aerosol distribution pattern that would come closest to minimizing climate change," George Ban-Weiss of the Carnegie Institution for Science, US, told environmentalresearchweb. "To do this we used an approach often used in engineering called optimization. Since some people have begun to talk about engineering the climate as a possible last-resort fix for climate change, we wanted to see if results from a global climate model were predictable enough for this engineering approach to work." Ban-Weiss and colleague Ken Caldeira found that the optimization approach did indeed work. But, as ever, there's a snag. Creating temperature conditions most like today's calls for a higher concentration of sulphate aerosols over the poles than at the equator. Minimizing disruption to the water cycle, on the other hand, requires a much more uniform sulphate distribution. "Temperatures and the hydrological cycle cannot be minimized simultaneously, a consequence of the fact that the hydrological cycle is more sensitive to changes in sunlight than are surface temperatures," explained Ban-Weiss. "One implication is that when attempting to minimize changes in surface air temperature, the surface of Earth becomes overly dry in many latitude bands in the model. If the goal is to minimize changes in the hydrological cycle, many latitude bands have residual warming." The team carried out five simulations using a global climate model; each employed a different distribution of aerosol by latitude, with a total aerosol loading of 10 megatonnes. "The results from these so-called 'basis function' simulations were used as 'training' information for our optimization model," said Ban-Weiss. "We found that predictions of zonal average surface temperatures and water runoff from the optimization model were very similar to that from the global climate model." Ban-Weiss and Caldeira are keen to stress that their study only uses one climate model and does not include all processes that are important in reality, such as socio-political consequences, changes in stratospheric ozone, ocean circulation alterations, aerosol transport and microphysics. "Our results are illustrative and do not provide a sound basis for making policy decisions," said Ban-Weiss. "We also point out that geoengineering options can never reverse all of the consequences of greenhouse-gas emissions. For example, it doesn't reverse ocean acidification. And it obviously has associated risk. So geoengineering is not an alternative to greenhouse-gas emissions reductions." Next the researchers would like to look at the effects of geoengineering at smaller scales than latitude bands, for example attempting to minimize climate change at all grid cells in the model. "This could be important because there could be longitudinal shifts in climate (in the east-west direction) that do not show up in our latitude averages," said Ban-Weiss. "In addition we could use other metrics of climate change besides surface temperature and runoff – some examples could include minimizing changes in polar sea ice or monsoonal cycles." According to Ban-Weiss, the linearity of the climate response to various aerosol forcings also suggests a way of addressing paleo-climate studies. "If we can understand the response to changing solar insolation, carbon dioxide levels, vegetation type, continental position, ice sheet volume, and so on – each individually – and then estimate the climate consequences of a combination of those effects through linear super-position, it means that we do not need to get the entire story to have at least a partial understanding of paleo-climate dynamics," he said. The researchers reported their work in ERL. About the author Liz Kalaugher is editor of environmentalresearchweb. The reference is: George A Ban-Weiss and Ken Caldeira. Geoengineering as an optimization problem, Environ. Res. Lett. 5 (2010) 034009 (9pp) doi:10.1088/1748-9326/5/3/034009 ___________________________________________________ Ken Caldeira Carnegie Institution Dept of Global Ecology 260 Panama Street, Stanford, CA 94305 USA +1 650 704 7212 kcalde...@carnegie.stanford.edu http://dge.stanford.edu/labs/caldeiralab  @kencaldeira -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to geoengineering@googlegroups.com. To unsubscribe from this group, send email to geoengineering+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to geoengineer...@googlegroups.com. To unsubscribe from this group, send email to geoengineering+unsubscr...@googlegroups.com. 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