U.S. Drought Monitor

The University of Nebraska-Lincoln has a nice image that sums up the current drought quite nicely:

You can browser their Drought Monitor site for more information.

Changes in sea level

One of the downsides to having a PhD is that my relatives have no idea what it is I do. For some it seems that having a PhD means that I am a "scientist" with expertise in anything that could be lumped under the term science. My degree is actually in computer science and then I specialized in a narrow subset of that field. From there I went into industry to work on projects that are only vaguely related to my dissertation. My general point though is that I don't have any particular expertise in other scientific fields. I do have an interest and read some books intended for laymen, but that doesn't mean I'm an expert on those topics.

A number of my relatives have recently taken an interest in global warming and wanted my opinion on the matter because I was the "scientist" in the room. My general answer is to just point to the scientific consensus and state that I provisionally accept it without being aware of all of the details. The EPA provides a summary of evidence for climate change and in particular a page describing the current state of knowledge. This put me at odds with them suggesting that global warming is some sort of conspiracy and that there is no real evidence. I couldn't really tell whether they disagree that the earth is warming or whether they just disagree that human activity is causing or at least contributing to it. The only thing that really seemed consistent in their arguments was the certainty that they were right and that nothing needed to be done to rectify the situation. Of course, I lost the debate because my typical retort was "I don't know." I haven't spent much time looking into global warming so I'm not that well versed on the evidence to support it.

Anyway, there were a number of questions that came up and for my own curiosity I wanted to know the answer. For this particular post, the question I want to look at is: what do we know about changes in the sea level? This question comes up in the context of global warming because melting ice sheets lead to an increase in sea level. My relatives were interested in the doom and gloom reports, but the numbers that caught my eye were the rate of increase since the 1960s:

Global average sea level rose at an average rate of around 1.8 mm per year over 1961 to 2003 and at an average rate of about 3.1 mm per year from 1993 to 2003.

That is a pretty accurate measurement. Go to the ocean and look at the waves and tides. How would you accurately measure the average sea level? Now consider less obvious sources of problems such as evaporation and how much water gets stuck on land vs returned to the oceans from year to year. These days we use measurements from satellites to help improve the accuracy, but what is the tried and true technique for measuring the sea level?

The answer is the tide gauge. Tide gauges are cool because of the simplicity of the basic mechanism. It is essentially a big pipe with a hole below the sea level to allow water in. The pipe protects the water inside from all of the normal disturbances on the surface such as waves. As the name suggests it will still vary with the tides, but it allows fairly accurate measurement of the high and low tides. If you record this for a long enough time you could work out the average sea level for the location of the gauge as well as how this has changed over time. Place enough of these devices around the world and keep track of the measurements and you can figure out the average global sea level and if there are any discrepancies across the world.

The next obvious question is: with such a simple device how much tide history do we have? Humans have had the technology to make such a device for a long time, especially if you allow for manual measurement instead of various automated schemes that seem to have been developed in the mid to late 1800s with Kelvin's tide gauge. The Permanent Service for Mean Sea Level (PSMSL) has a page listing various long term records with the oldest being from Amsterdam starting in the year 1700. They also provide the data with sea level values relative to the NAP (a fixed reference level frequently used in Europe):

From this data set there is a clear rise in mean sea level starting in the 1800s. The PSMSL site also lists data from Stockholm over the period 1774 to 1984. Does it show the same trend? At first glance the answer is no:

What is going on? How could this record be so different? The explanation I found was from a paper Swedish Sea Level Series - A Climate Indicator and the reason is because the land is rising. Specifically this is known as post-glacial rebound (although glacial isostatic adjustment seems to be the preferred term now) and the land is slowly rising after being depressed by the weight of huge ice sheets that covered the region in a previous ice age. To figure out what the sea level has done we need to remove the trend caused by the rising land. Post-glacial rebound can vary from place to place, e.g., see the paper Measuring Postglacial Rebound with GPS and Absolute Gravity that looks at four sites in North America. That doesn't help me for determining the rate for Stockholm Sweden though. I couldn't find a good data set for showing what the rate of the land rise is, and the sources I read suggest it varies over time. The Swedish Sea Level Series paper mentioned earlier shows a trend, but it isn't clear to me what source they used for the rate. Various sources I have seen suggest the rate is less than 1cm per year now, one example is the description of the lake Mälaren. If I assume a rate of 5mm per year and generate a trend the output looks close to what the Swedish report is showing:


There is also a data provided for Liverpool. For this data set there are two versions: an annual MHW and adjusted MHW. For those that are not aware, MHW is the mean high water measurement. The adjustment is supposed to be described in the associated paper, but I could not find a version of the paper for free online so I don't know exactly what was done. I included both in the graph:



Both the annual and adjusted MHW show that the MHW level is rising. The adjusted value at a slower rate than the raw annual reading, in particular for older measurements. A 2008 paper uses these sources to show a trend in mean sea level from 1700 to 2000. The general trend is that mean sea level has been increasing for the last 200 years.

So what does this tell us? The three data sets being checked here are all from Europe and it is pretty clear that the sea level in that region has been rising for the last 200 years. It would be interesting to see what the longer term sea level has looked like. In particular, are there any long term cyclical trends that take place over thousands of years. Such data may exist, I looked at a handful of the top sources that came up when searching for information and as stated in the opening I am not an expert in this field. There are some interesting complications such as the post-glacial rebounding that can make it difficult to discern what is really happening. I should also point out that I did not look at the evidence for what was causing the rise in sea level. Of course, the general explanation is melting ice sheets as well as just the expansion of water due to warmer oceans. At some point I'll have to look at the evidence for the actual temperature changes, but most importantly (to me at least), it looks like climate change will be an interesting topic to explore.

Polls and Research on Public Acceptance of Evolution

It was brought to my attention that my post on the acceptance of evolution by state was cited in an ASA article Polls and Research on Public Acceptance of Evolution. The article provides a summary of around 50 sites discussing the public acceptance of evolution. The ASA, American Scientific Affiliation, is an organization of Christian scientists so I would guess they have some bias towards creationism. That said, this is the first time I have heard of the ASA and their article seems to provide a fair summary of the findings presented.

What is Life?

ASU Origins Project ASU Gammage Auditorium Feb. 12, 2011

Richard Dawkins, J. Craig Venter, Nobel laureates Sidney Altman and Leland Hartwell, Chris McKay, Paul Davies, Lawrence Krauss, and The Science Network’s Roger Bingham discuss the origins of life, the possibility of finding life elsewhere, and the latest development in synthetic biology.

How Cats Lap

It's a bit humbling how little we know about common activities. A recent article in Science talks about how cats drink. This is a topic I have never given much thought, but it seems like something that would have been studied and understood a long time ago. It turns out it has been an open question for some time. A 1940's short film called Quicker'n a Wink captured a cat drinking using one of the earliest high speed cameras. Luckily the video is now on YouTube:



Before reading the paper or seeing the video included above, I tried to think about how lapping would work. I guessed that a cat would curve the tongue and make a cup to carry the water into the mouth. It turns out this is how dogs drink as shown in the video below:



Cats use a different technique. Like dogs they curve the tongue back, but cats barely touch the surface of the water with their tongue and then quickly withdraw the tongue letting the inertia create a stream of water into the mouth. For more information see:

• Supplementary videos for the paper
• Ed Yong's take
• Jerry Coyne's take

The Poetry of Science: Richard Dawkins and Neil deGrasse Tyson

Family Planning

It was a popular week for family planning. First there was a TED talk by Mechai Viravaidya discussing the work he has done in Thailand to encourage family planning, in particular, the use of condoms. How Mr. Condom made Thailand a better place:

It is too bad the religious nuts in the U.S. aren't swayed by evidence showing that abstinence education does not work. Then I came across an article in Science, Has China Outgrown The One-Child Policy?, about the effects of the one-child policy on the Chinese population. One issue is a rapidly aging population:

The country has benefited from a "demographic dividend"—a surfeit of young workers born during a 1960s baby boom—that will dry up as China gets old before it gets rich. From 2010 to 2020, the number of Chinese aged 20 to 24 will drop by a whopping 45%, from 125 million to 68 million.

If you look at an age pyramid for China you can see that the population is starting to contract:

I'm not sure what caused the sharp reduction of individuals in their twenties compared to teens and those in their thirties. Here is a similar pyramid for to the United States:

The pyramid for Afghanistan shows a more typical pyramid shape:

However, if you look carefully at the age pyramid for China there is another problem. There are considerably more males than females:

China's ratio of male to female births—now 119 boys born for every 100 girls—has been "really intensified by the family-planning policy," says Shuzhuo Li, a demographer at Xi'an Jiaotong University. The gender imbalance is projected to yield 30 million more men than women by 2030, heightening the risk of social instability.

The skew seems to be the result of cultural preferences for a male child leading to practices such as sex-selective abortions. These problems are further compounded by the complexity of the laws:

That decentralized structure, which still stands, has yielded a clunky policy that is comparable in complexity to the U.S. tax code, says Wang. To discourage sex-selective abortion, many provinces allow rural parents whose first child is a girl to try again for a boy, an exception sometimes called the "1.5-child policy." All told, there are 22 exceptions qualifying a couple for more children, ranging from one partner being disabled to one being a miner.

Another similarity to the U.S. tax industry is the huge bureaucracy that has been built up around the policy:

As of 2005, the family-planning bureaucracy had swollen to 509,000 employees, along with 6 million workers who help with implementation. Those stakeholders are "risk-averse," says Wang. "They pay no cost for doing nothing."

It'll be interesting to see how China reacts to these problems in the coming decades.

Acceptance of Evolution by State

There is a well known chart showing the public acceptance of evolution in 34 countries. The United States was second to last. Thus far, I have been unable to find a similar chart showing a breakdown of the acceptance of evolution by state. Looking around though I did find a freely available data set that has the raw information. The Pew Forum's U.S. Religious Landscape Survey has the question:

Q.10c Evolution is the best explanation for the origins of human life on earth

RESPONSE CATEGORIES:

1. Completely agree
2. Mostly agree
3. Mostly disagree
4. Completely disagree
5. Don't know/Refused (VOL.)