Stop the tide
Among the ideas Stephen Battersby discussed for limiting sea level rise was the option of flooding inland basins (18 September, p 40). Yet he neglected to mention the only one big enough to make any difference.
Most of the lowlands around the Caspian Sea are desert, up to 27 metres below sea level. To flood it we need only deepen the old channel linking it to the Black Sea.
Although this would mean drowning towns, oilfields and farmland, not to mention the cities of Baku and Astrakhan, there may be compensating benefits from a larger Caspian. It might moderate temperatures and increase rainfall throughout central Asia, expanding fisheries and sea trade.
Admittedly, it may be hard to get the five affected countries bordering the Caspian to agree.
From Frank Fahy
The references to King Canute on your cover and contents page in relation to the article on sea level rise are somewhat misleading, but ominously relevant.
It is believed that Canute (or Cnut), a modest man in spite of reigning over England, Denmark, Norway and part of Sweden, sat on the bank of the Thames at Thorney Island in London and commanded the tide to retreat, to convince his nobles, who annoyed him with their flattery, that there were limitations to his power.
Let’s hope that future generations will find the ingenuity, resources and the will to do better than His Majesty.
King’s Somborne, Hampshire, UK
Presenting statistics
Linda Geddes states that the first time DNA evidence was challenged in a UK court was during the trial of Sean Hoey for the 1998 bombing in Omagh, Northern Ireland (21 August, p 8). While it is true that until then DNA evidence had not been substantially challenged on the basis of its scientific reliability, the way it was presented in court had previously been challenged successfully several times.
In the case of , for example, DNA evidence was challenged on the grounds of the “prosecutor’s fallacy”. This way of presenting evidence mistakenly implies that the probability that the accused is innocent must be small when their DNA has been found to match a sample at the crime scene, as the probability of a randomly chosen person’s DNA matching that from the crime scene is also small.
Forensic scientists and statisticians have expended much energy in developing the best way to calculate the statistics relating to DNA evidence. It is equally important that we understand how these statistics should be best presented in court.
Complex inheritance
Evelyn Fox Keller expresses dismay at the persistent rejection of the answer “neither nature nor nurture, but both” to the perennial debate setting one against the other (18 September, p 28).
This ambiguity is unpalatable to many people because they want an answer that they can do something with. If we know whether genius or criminality is a result of a gene or an upbringing, then we can act accordingly.
It is unfortunate that the public have been trained by simple models, such as the inheritance of eye colour, to believe that the underlying genetic mechanisms are simple. Despite the impression given by animations of DNA helices and printouts of sequences from the Human Genome Project, it is not easy to tell whether something is genetic.
The continuation of the nature vs nurture debate is an implicit call for a simple answer one way or the other. Until our portrayal of genetics progresses beyond simple clockwork models, people will not accept the answer that it is all very complicated.
Food-chain reactions
It was interesting to read that cane toads have not had a devastating impact on Australian wildlife as was initially feared (11 September, p 18). However, there is an impact in south-east Queensland that was not mentioned.
At night the toads hop onto city roads to soak up the warmth coming off the asphalt, and end up getting squashed by traffic. Crows feast on their bodies, having learned to avoid eating their poison glands, and crow numbers have been increasing as a result. The storm bird, a cuckoo that lays eggs in crows’ nests, has also experienced a growth in numbers, although this could be due to the effect of Brisbane’s warming weather on their migration pattern. In summer, Brisbane now resounds with the crows’ cawing and the storm birds’ shrieks.
The increase in the crow population wouldn’t be so bad if they ate only toads. But they eat flesh of any kind, driving other birds from their nests to get at the chicks. Has anyone studied this?
Straight sets
In Richard Elwes’s otherwise excellent article on the arithmetical implications of the concept of infinity (14 August, p 34), it is suggested that a finitist theory of arithmetic 鈥� one in which there is no infinity 鈥� will be truncated, or limited to only finite mathematics. The finitary approach, usually associated with the intuitionist logic of L. E. J. Brouwer and others, stems from a deep unease about treating infinities as real. Yet one is still allowed to consider sets like the natural numbers as potentially infinite.
This leads to an approach to set theory 鈥� the branch of mathematics that deals with collections of objects 鈥� that considers external relations like “subset of” to be fundamental. Sets are then generalised to objects and the subset relation replaced with a generic operator that maps one set to another. The result is category theory and its significant subclass, topos theory, which is, roughly, a unification of logic and geometry. Rather than being truncated, this is a different and in some ways deeper approach to arithmetic, and the only thing ruled out is transfinite nonsense, as the intuitionists regard it.
Oestrogen overload
Andy Coghlan discusses the rise in the number of white girls in the US reaching puberty at the age of 7, suggesting oestrogen-like chemicals or obesity as causes (14 August, p 16). Indeed, when I moved to Maryland, as the mother of girls aged 10 and 8, I was shocked to meet a 9-year-old who was fully developed.
The early puberty in the US might not be the result of exposure to chemicals that mimic oestrogen, but to oestrogen itself. Unlike in Australia, where the use of hormones in farming is prohibited, calves and piglets in the US are ear-tagged with oestrogen pellets. Oestrogen causes weight gain, and so obesity might be a symptom rather than a cause of the problem.
For my own part, when I returned to Australia I suffered incredible mood swings and other symptoms of oestrogen withdrawal. The amount of oestrogen in the US food chain bears studying.
Oil perspective
Mick Hamer’s article on the danger of oil pollution from sunken ships (4 September, p 34) and the uncharacteristically histrionic editorial on the same subject (p 5) seriously overstate the potential for disaster.
Over the past two decades my company has used imaging radar satellites to map oil on the sea surface for 70 million square kilometres of ocean. Illegal dumping of oil from ships is obvious in most shipping lanes, especially in unpoliced seas, such as the South China Sea.
However, we have found that the biggest source of oil in the sea is natural seepage. We estimate that during the 87 days of the Deepwater Horizon oil spill, which leaked up to 5 million barrels of oil into the Gulf of Mexico, an additional 3 million barrels leaked naturally. This natural seepage has been going on for thousands of years.
To check every oil slick occurrence against known wrecks we use NASA’s Global Maritime Wreck Database. Of 87,000 mapped oil slicks, we found that only 0.4 per cent were located near shipwrecks. Of these, only five could not be attributed to surface shipping, industry installations or natural seepage. If wrecks do leak, the volumes and flow rates are insignificant compared with that from natural seepage or deliberate pollution from ships.
Happy winner
One explanation for the finding that an income of $75,000 is sufficient for maximum day-to-day happiness, while overall life satisfaction continues to grow with increasing income above that level (11 September, p 16), may lie in the tendency to equate monetary reward with success and social recognition.
I suggest that a scientist or writer who has been awarded a top accolade in their field, such as a Nobel prize, might experience a level of overall life satisfaction typical of someone on a much higher income.
Unspotted animals
I tried to spot the animals hidden in the picture accompanying your article on a new technology used to camouflage images, but I was foiled (17 July, p 17). If this technique is indeed going to be used online to make Captcha images to distinguish real people from software bots, then a lot of people are going to end up even more frustrated by computer systems than they already are.
Glass-flowing
A recent debate on your pages about whether one can observe the flow of glass, given time (12 June, p 27, and 24 April, p 25) put me in mind of a falsehood I was told as a child. I heard that if a long piece of glass is supported at its ends and weighted in the middle, it will permanently sag. I tried to observe this, using three house bricks as the supports and weight. I have used many glass shelves since, and it would have been inconvenient if they had not stayed straight. As it is, chipboard shelves have to be turned over occasionally if heavily loaded.
For the record
鈥� Due to an editing error, we incorrectly stated that the power consumption of a cold-chain refrigerator is less than a clock radio (18 September, p 24).