Bodélé: "More or Less" a major dust source

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Recently I am help doing a study on dust transport and deposition
concerning central and northern Libya. [A geochemical study](http://dx.doi.org/10.1016/j.atmosenv.2006.02.020) by my mentors suggest
that some of the dust in Hun and Sebha, even some in the coastal
areas, may be from the Bodélé, which is the largest source of dust in
Libya. [This preprint article on
PNAS](http://dx.doi.org/10.1073/pnas.0711850106), therefore, is of
special interest to me.

However, if the authors of the paper are right about the transport
mode of dust from Bodélé, our story may prove wrong. The authors
claim that the prevailing direction of the dust transport from this
area is towards the west in winter, which is also the maximum of dust
output in a year in the area. But our study area shows a constrasting
trend: lowest dust deposition both by ground data and remote sensing,
in winter, and it is to the north of Bodélé. The summer
transportation, if any, may contribute very little to our study area,
limited both by transport and production.

The MODIS brightness temperature difference (BTD) data is being
derived, which can provide us a picture of dust plumes for major dust
events. We are also looking at the geochemical properties and
meteorological data around the area. Combining these data, hopefully,
can provide more information on the transport mode in our study.

In the PNAS paper, the authors point out that the Bodélé area may be a
"tipping element" in the context of climate change, due to its
dominant position in the output of dust and its location. Some
climate models suggest that the area may become wetter, yet the wind
will be strengthened. As a result, it is really difficult to tell how
the dust output will be influenced by climate change at the moment.
Will we have more or less dust from Bodélé? This will be an
interesting problem, as dust from this area interacts with many
large-scale systems. It is a wonder, considering that the Bodélé
Depression is so small. The difficulty is that we only have inaccurate
model and incomplete data for this area, and for the North Africa.
New remote sensing technology such as
[SEVIRI](http://www.esa.int/esapub/bulletin/bullet111/chapter4_bul111.pdf)
(imagine quasi-MODIS resolution images every 15 minutes, very cool) may partly solve
the problem, but more geochemical and meteorological data are
essential to answer the complex dust question.

Washington, R., Bouet, C., Cautenet, G., Mackenzie, E., Ashpole, I., Engelstaedter, S., Lizcano, G., Henderson, G., Schepanski, K., & Tegen, I. (2009). Tipping Elements in Earth Systems Special Feature: Dust as a tipping element: The Bodele Depression, Chad Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0711850106

OHARA, S., CLARKE, M., & ELATRASH, M. (2006). Field measurements of desert dust deposition in Libya Atmospheric Environment, 40 (21), 3881-3897 DOI: 10.1016/j.atmosenv.2006.02.020

Some like it hot ... or variable

I have the impression that someone on researchblogging.org has already used a similar title to describe the link between rising temperature and vectors of contagious diseases. But [this article](http://dx.doi.org/10.1073/pnas.0903423106) has pointed out another layer of complexity existing in the temperature-disease connection. Turns out that malaria does not necessarily need hot weather, a reasonably warm mean temperature with high diurnal temperature range (DTR) will do.

The malaria parasites will need to develop to a certain stage before it can actually infect people. And this takes time. Researchers already know that the length of the period depends on the environmental temperature, and accordingly they predict that the risk of malaria epidemics will increase, as the mean temperatures in many areas rise. It takes less time for the parasite to develop, and the carrier -- mosquitoes -- has more time to bite and infect people before it dies. If the period of development is so long that it almost equals or even exceeds the mosquito's life expectancy, very little harm is done.

The authors of the PNAS paper find that the period of development depends not only on daily mean temperature, but also on the temperature range through the day. In areas with relatively low temperature, given the same mean temperature, malaria parasites in areas with higher temperature variation in a day need significantly shorter time to develop. Similarly, high DTR in areas with high temperature may slow down the development. Thus the authors say the picture of malaria and similar epidemic in a global climate change context may be more complex than we previously think.

The immediate lesson is that we may have overestimated the additional risk in some tropical areas, and underestimated that in some temperate regions. But exactly what are these areas asks for studies at local scale.

Paaijmans, K., Read, A., & Thomas, M. (2009). Understanding the link between malaria risk and climate Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0903423106

Ocean acidification below the surface

The climate change deniers say that climate change and relevant concerns are a fad. Well they must be wrong. From my personal experience I was reminded of [the climate change scenario](http://www.jstor.org/action/doAdvancedSearch?q0=global+warming&f0=all&c0=AND&q1=&f1=all&c1=AND&q2=&f2=all&c2=AND&q3=&f3=all&wc=on&sd=1980&ed=1989&la=&jo=&Search=Search) in 1980s -- right, before I went out of the kindergarten -- and that was like 20 years ago. And scientists today are using data that are accumulated continuously in the past 20 years to study the impact of climate change.

One instance is this [preprint](http://www.pnas.org/content/early/2009/07/24/0906044106.abstract) published on the PNAS website. The authors creatively used the fixed-temperature pH data, avoiding problems like the change of H₂CO₃ equilibria with temperature, and making the seasonal trend pronounced. It is pointed out that there is a trend of decreasing pH at sea surface, and more importantly, the seasonal pattern of water change between surface and sub-surface zones of the ocean may be a profound factor in a more complicated ocean acidification picture.

There are drivers at different scales at play here, causing diurnal, seasonal and annual variabilities of the ocean acidity. The authors mentioned a strong pH negative anomaly in 1998, which causes me to think whether there could be some cross-scale interactions, such as El Nino, also at play.

Another thought that occurred to me is that the dissolved organic carbon may be a slow variable in the ocean system. Of course I am not an oceanographer and this is just a wild guess. But if there is any oceanographer reading, would you care to explain the circulation of inorganic carbon in the ocean? We all know the acidity in the ocean is slowly increasing, but if there is an accumulation process of inorganic carbon that we do not know, one day it is going to give us a bigger surprise given adequate temperature and mixing conditions.

John E. Dore, Roger Lukas, Daniel W. Sadler, Matthew J. Church, & David M. Karl (2009). Physical and biogeochemical modulation of ocean acidification in the central North Pacific Proceedings of the National Academy of Sciences of the United States of America DOI: 10.1073/pnas.0906044106

怎样识别气候变化（及其它常识的）否定论者

先定义一下，这里的否定论者不是拿出实实在在的证据以科学的方法证明或证伪观点的人，而是编造理论并以为只要通过想象就能让事实站在ta们一边的人。

《卫报》的环境板块今天刊载了 [denialism blog](http://scienceblogs.com/denialism/) 作者的一篇文章，汇总了气候变化否定论者的[五大常用伎俩](http://www.guardian.co.uk/environment/blog/2009/mar/10/climate-change-denier)。

其一是将气候变化归因于政府的阴谋。但是几乎所有的阴谋论都会走向一个困境，即提出的问题比解决的问题还要多，最终也不能自圆其说。人人都喜欢都市传说和阴谋论，但如果要把它们用来解释光天化日之下的现象，最好还是先掂量掂量我们手里的奥卡姆剃刀。

其二是选择性地使用证据。畅销书作家，不论其观点是对是错，都喜欢使用这一招。但畅销书作者至少有的还能拿出统计数据，否定论者们最喜欢的却是用特例来推翻建立在大量实例和统计以及严密的理论计算上的观点，比如前几天 Fox News 不无揶揄地报道在华盛顿特区针对新电厂进行的游行[遭遇了大雪](http://www.foxnews.com/politics/2009/03/02/shiver-global-warming-protest-frozen-massive-snowfall/)，但它想用美国东海岸的[典型气候](http://www.weather.com/outlook/travel/vacationplanner/climatology/daily/USDC0001?climoMonth=3&from=vac_monavg)说明什么呢？要知道伊索老人家早就指出用[特例](http://ebooks.adelaide.edu.au/a/aesop/a3t/a3t_3.html#240)而非统计规律指导行动是靠不住的。

其三是利用“专家”。有些专家是在别的场合说的话被断章取义，还有的是一贯的否定论者。我个人最近的发现则是气候变化的否定论者和“智能设计”论者有一定程度的[交集](http://theevolutioncrisis.org.uk/testimony2.php)。

其四是吹毛求疵。否定论者们试图将科学解读为完美的、绝对的知识体系，ta们不断要求更完整的证据，时间段更长的记录，或者要求完美无缺的模型。即使你按ta们的要求给出了更多的数据，否定论者们也只会提出更多的要求，而不会改变哪怕一点点否定的态度。还是不要这么跟ta们玩下去了，科学家们到底无法用整个地球来做实验说明气候变化正在发生（即使有这么一个实验，否定论者们也会要求在火星上“获得可重复的实验结果”的！）。

其五是不讲逻辑。这一类策略从指责艾尔戈尔的耗电量到捏造[“夹缝中的上帝”](http://en.wikipedia.org/wiki/God_of_the_gaps)，可谓五花八门。但所有这类争论都有一个共同点：看起来很讲道理，其实跟气候变化这个主题都没关系。

需要指出的是这五大伎俩从有科学和争议以来就一直在被各种否定论者使用，从当年否认吸烟有害健康的烟草公司到现在否认进化论的神棍都有意无意地在使用这些手段。豆瓣上的[一个讨论串](http://www.douban.com/online/10088828/discussion/12544512/)集了这五种伎俩之大成。有一位 Mac 同学的应对方式我觉得很好，就是另开新帖阐述观点。denialism blog 的作者认为跟否定论者争吵没有什么用处，这点我也同意。然而不论是豆瓣，还是 Guardian 的网站上，都有一群不明真相的群众，何况在如此重大的危机面前采取鸵鸟策略是[人之常情](http://blog.talkingphilosophy.com/?p=803)——怎么办？我在做的工作跟气候问题沾一点边，我以为我有这个义务传播一点信息，让更多的人看到气候变化问题的严重性和解决的可行性。虽然我可能只有一丁点的发言权，但我也想把它利用好，不要让主流观点反而陷入了（反向的）[沉默的螺旋](http://en.wikipedia.org/wiki/Spiral_of_silence)。[1. 这个说法来自于对“沉默的螺旋”观点的一个质疑，认为事实上人们乐于表达与主流意见不同的观点，只要背后有个人或者群体的支持。见 ERIC。]

Yet another use of ice record

Today's ScienceDaily [reported](http://www.sciencedaily.com/releases/2008/12/081231131813.htm) a new possibility of ice core sample analysis, this time using bacteria frozen in the ice.

It was found that in ice core sample collected from Mountain Geladaindong, the abundance of bacteria is in accordance with $$\delta ^{18}\text{O}$$, which can serve as an indicator of temperature. It is already known that higher $$\delta ^{18}\text{O}$$ level implies higher temperature, now it seems bacteria abundance also increases with $$\delta ^{18}\text{O}$$, therefore it is possible to use bacteria numbers as an indicator of historical temperature change.

However, $$\delta ^{18}\text{O}$$ can also serve as an indicator of precipitation, with higher level in low-precipitation years. It has also been noted that in the ice core higher bacteria level concurs with higher amount of dust. So here's my speculation: it may well be that in dry years the dust activity is more pronounced, leading to more dust and bacteria precipitate on the glacier. In that case, bacteria itself is not a useful indicator of either temperature nor precipitation.

It is also interesting to note that the lowest bacteria level was found in 1938 and the highest in 1997. According to [Desert Research Institute](http://www.wrcc.dri.edu/enso/ensodef.html), 1938 was a strong La Niña year, while 1997 was a strong El Niño year. So there is possibility that the effect of El Niño/La Niña may have so strong signals that the actual trend due to climate change is harder to observe. Moreover, if the bacteria abundance is proved more correlated to El Niño/La Niña, it suggests the increased possibility that bacteria level is linked with precipitation rather than temperature, as [earlier research](http://ecosystems.wcp.muohio.edu/studentresearch/climatechange03/elnino/Ice%20core%20records.pdf) argued that precipitation is more correlated to El Niño than $$\delta ^{18}\text{O}$$ does.

On the other hand, if this method is proved feasible, it would mean that scientists have get hold of another relatively cheap way of deriving historical climate data, and do not have to deal with expensive isotope analysis. Similar method may also be used in lake sediment or peat analysis. But to validate this method, "we need more data".

科学地表达科学

这期的 Science 杂志在 Policy Forum 栏目刊载了一篇文章，报道了在 MIT 进行的一次实验：

[caption id="" align="alignleft" width="235" caption="测试中使用的材料。上半部分取自 IPCC 的决策者报告（SPM），下半部分是测试题目。来源：J. D. Sterman. Economics: Risk communication on climate: Mental models and mass balance. Science, 322(5901):532–533, 2008. "][/caption]

实验对象都是 MIT 的高材生，给他们的材料上给出了 IPCC 一份给决策者看的报告[1. 这并不是去年出版的最新报告，不过新报告也有此文中讨论的同样问题。]中的一个大气二氧化碳含量趋于稳定的图景。测试要求实验对象们首先根据目前的二氧化碳自然去除水平（图中的黑点）估计未来的自然去除水平，然后画出实现 IPCC 二氧化碳稳定图景所需的未来二氧化碳排放量的走势。

在往下看之前，你不妨也做一下这道题。你画的图是什么样的？

MIT 的学生们的测试结果让人失望。84%的答案都忽视了这个简单的问题：就像要让澡盆里的水面保持稳定，进水量和出水量必须一致一样，二氧化碳含量的稳定要求排放量与自然去除量相等。被测试者典型的答案是二氧化碳的排放量趋于稳定，但仍然是去除量的2倍左右。这种情况下，二氧化碳的含量只会越来越高。

文章的作者据此提出，在这个问题当中，人们固有的思维模式影响了他们的判断。人们倾向于认为只要排放量不再增大，总量也不会再增大。而且这次犯这种错误的学生中有约3/5还是理工科的学生，大部分都已经有硕士及以上的学位。

而这个问题，只要 IPCC 的报告中能够用澡盆或者其它的物质平衡现象打个比方，就完全可以避免。

我自己则怀疑造成这种现象的至少一部分原因是题目文字的表述。题目原文是“given the scenario above”，对于一直在中文语境中接受考试的我来说，其提示作用并不是那么强烈，我的理解是画出未来可能的排放量。在没有其它信息的情况下，我自然很可能认为未来的排放量会维持现状，因此得出那样的答案也就不奇怪了。如果改成“in order to achieve the scenario above”，做对答案的人会多一点吗？

所以我用中文转述这个问题的时候有意改变了措辞。你做对了吗？

[caption id="" align="alignleft" width="411" caption="测试中大部分对象给出的答案。粉红线为学生的答案，金色线为实现 IPCC 图景需要的排放量轨迹。来源：J. D. Sterman. Economics: Risk communication on climate: Mental models and mass balance. Science, 322(5901):532–533, 2008. "][/caption]

不管 MIT 的高材生们因为什么原因被这道题阴了，它确实暴露出将科研成果传达给公众和决策者时的一个问题。IPCC 的报告和其它报道类似问题的学术刊物中，使用的表达手段还是科学家之间讨论这些问题所用的语言。连 MIT 的理工科学生都不能完全理解的，要让决策者和老百姓理解就更困难了。

在无法理解科学家所说的那些“事实”“预测”的情况下，大部分人选择照常营业等待科学家解决问题，或者干脆否认气候问题的存在，也就是完全可以理解的反应了。

于是文章的原作者提出不应该继续让决策过程继续基于错误的思想模式，要做到这一点，科学家和科技通信作者需要更好地了解普通人的心理和认知模式，用心理学和社会学的科学方法进行思想的交流，同时不再用大量专业的科学数据来进行灌输和恐吓。关于气候变化的思想工作，科学证据是充分的，真正的困难在于如何用正确的方式传播，同时保证其对民众的心理起到正确的作用。对于气候变化这样一个复杂的综合性问题，沟通科学家和其他人的想法还真是个难题。

图片来源：J. D. Sterman. Economics: Risk communication on climate: Mental models and mass balance. Science, 322(5901):532–533, 2008.

Effects directly attributed to climate change

Attributing physical and biological impacts to anthropogenic climate change

This is the first time observed changes in physical and biological characters of natural systems are explicitly linked to anthropogenic climate change.  The method used seems to be data mining and statistics.