Climate models' value
Lenny Smith wisely counsels against the incautious use of the results of climate models (6 December 2008, p 42), but in doing so he risks denying decision-makers access to the best available climate science.
In recent years “ensembles” of many climate models have been run in order to explore the uncertainties inherent in each one. The UK scenarios that Smith refers to in your interview will be based on an ensemble of over 300 runs of global climate models. This approach does not quantify all of the uncertainty inherent in climate modelling, but it does provide a means of averaging out some of the “noise”.
The use of a weather generator in the forthcoming UK Climate Projections has been a source of persistent confusion. Weather generators are intended to provide scenarios for engineers and planners that are statistically consistent with changes projected by climate models. They are obviously not forecasts, and in our experience users of weather generators do not misinterpret them as such.
We agree with Smith that great care is needed when summarising the outputs of several climate models as probability distributions. We know that the probability distributions that are extracted from ensemble experiments are themselves uncertain 鈥� especially in the “tails” at the extremes of the distribution, which are often particularly important for decision-makers.
This does not, however, imply that decision-makers should ignore the best available information, which sometimes seems to be what Smith is suggesting. It does mean that they should seek adaptation options that are as far as possible robust to uncertainty.
Tax carbon at source
Michael Le Page, in his open letter to Barack Obama (6 December 2008, p 20), would have done better to build on his excellent critique of the Kyoto protocol’s bureaucracy and “leakage” problems.
Part of the difficulty with Kyoto is that carbon caps are applied at the point of emission to the atmosphere. The alternative of capping the extraction of carbon from the geosphere would necessitate far fewer control points. Of course there would be objections. OPEC countries would have to measure oil production accurately, and some oil states may not be keen on revealing their true sales totals.
I would be interested to see some debate here on the relative merits of emissions caps and caps on carbon mining.
Thinking matter
Peter Millican discusses the history of controversy over “thinking matter” (29 November 2008, p 23), but the real trouble with the mind-body problem centres on the word “materialism”. This word is itself a relic of dualism: it suggests that there are two rival stuffs 鈥� mind and matter 鈥� competing to be seen as basic to the world. It tells us to choose one of these and reduce the other to it.
There are not two such separate stuffs. There is just a complex world containing complex creatures, about whom many sorts of question arise. Each question must be answered in its own terms.
When Einstein has just solved a difficult problem, his reasoning cannot be explained by giving even the most accurate account of the actions of his neurons. To suggest that their actions were its real cause would mean that they did the work on their own and told him about it afterwards. Anyone who has tried leaving such work to their neurons will agree that this story is improbable.
Of course he needed the neurons. But what did the work was the whole person, using the conscious effort which alone was able to produce it. Explaining it simply means tracing the thoughts relevant to that effort.
Unluckily, many scientists seem to regard materialism as a sacred ideal which tells us always to find a more “real” physical cause behind our thoughts. But actually our thoughts are quite as real as our coffee cups, and “matter” is every bit as obscure a concept as “mind”.
Heavy drinking water
The suggestion that drinking heavy water might counter ageing (29 November 2008, p 36) reminds me of the late 1950s when, as a fresh graduate, I joined a team of nuclear physicists at a UK research establishment that I had better not name.
My older colleagues had both formidable intellect and a mischievous sense of humour. One of them was known on at least one occasion to have brewed and drunk a cup of tea using heavy water.
This did him no harm at the time, and he did live to an age substantially greater than that expected by those who considered his daily consumption of beer and cigarettes to be life-shortening.
From John Morton
It cannot be right, in principle, that “deuterium atoms bound to carbon in amino acids are ‘non-exchangeable’ and so don’t leak into body water”. All the amino acids in proteins are periodically released by the continual breakdown and re-synthesis of proteins.
The amino acids will enter the cellular pool: some will be deaminated, releasing ammonia, and the rest of the molecule (the “carbon skeleton”) will be used to provide energy and will be ultimately converted to carbon dioxide and water. So the deuterium will find its way into the cell water.
But how much? An adult human with a daily dietary protein intake of 70 grams degrades and synthesises about 250 g of protein every day 鈥� more than 2 per cent of their total body protein.
When dietary intake is low, the recycling efficiency is about 90 per cent. So if each amino acid molecule carried one deuterium atom, 25 g of amino acids lost per day would produce about 4 g of deuterated water: just 0.01 per cent of your total body water. So the chance of getting up to the toxic 20 to 35 per cent content is minimal, given that the half life for body water is just over a week.
What this calculation does show is that even if you restricted dietary protein intake to encourage recycling, and if you could deuterate all the protein in your body, it would all probably be gone within a year.
Pontypridd, Glamorgan, UK
Safer sex for whom?
It is indeed a shame that the potentially lifesaving pre-exposure prophylaxis (PrEP) for HIV will certainly be heavily criticised by those who are against “carefree sex” (22 November 2008, p 41 and p 5). Detractors will no doubt include those who are also against vaccinating girls against cervical cancer, just because in order to get it you have to have had sex at some point.
Those who criticise the use of the PrEP pill on such grounds, and those in favour of abstinence-until-marriage campaigns, should consider the fact that in Africa and other parts of the world huge numbers of married women are contracting HIV. This is in large part due to their low social and economic status, allowing them little power to insist that their husband wears a condom even if they know or suspect he is HIV-positive, and even if they know he visits local prostitutes. Unmarried women also often face violence and force if they ask for condom use or refuse sex.
This pill, if provided cheaply, could be a lifeline to millions of women, their children, and men. It is an opportunity that must be embraced.
From Marsha Rosengarten,
Though you covered many of the key issues raised with the promise of HIV pre-exposure prophylaxis (PrEP), enthusiasm for the possibility of reducing new infections appears to have glossed over the .
The most appealing feature of PrEP is that it offers women who are unable to institute the use of condoms a form of possible protection. But on the basis of experience with the contraceptive pill, we can anticipate that PrEP will affect gender relations: while it will enhance some women’s capacity to protect themselves, it may place more onus for HIV prevention on them.
Implementation of PrEP could merely replace some of the risk of HIV infection in otherwise healthy women with the risk of side effects from the drug 鈥� including risk in pregnancy.
PrEP presents us with a quandary, one that will require advanced techniques for managing the coming together of a complex mix of biomedical and social factors.
London, UK
Principles first
Mark Buchanan’s report of the claim by Mitchell Feigenbaum and Vittorio Gorini that the celebrated space-time anomalies of Special Relativity “emerge… from basic, purely mathematical considerations” shows how once-discredited “a priori” reasoning is becoming somewhat acceptable in science again (1 November 2008, p 28).
The philosopher Gottfried Leibnitz took a broadly “rationalist” position, which essentially claims that certain truths about the universe can be deduced by reasoning alone. Isaac Newton, who also invented calculus at the same time, claimed to take an empiricist position: “I do not make hypotheses,” he famously wrote in 1713 concerning the nature of gravity.
During the 20th century, largely because of the crushing weight of the positivist position in philosophy, a priori reasoning became thoroughly unrespectable in science. The work by Feigenbaum and Gorini and colleagues is a real body blow to that positivist scientific correctness.
Testing the obvious
Your correspondent Tony Kline implies that any human who has walked in the woods with a hungry Labrador that has dragged them towards a previously discovered food source will find the hypothesis that the animal has foresight obvious. He also says that “comparative psychologists should get out more and keep their eyes and minds open” (22 November 2008, p 25).
This is an insult to the scientific process. Just because something is “obvious” doesn’t mean that it shouldn’t be tested. It was once “obvious” that the Earth was flat, 5000 years old and at the centre of the universe. It took scientists with a lot of guts to stand up and challenge those ideas.
For the record
鈥� We reported that the Wilkins Ice Shelf in Antarctica was “about the size of Scotland” (6 December 2008, p 7). In fact, the ice sheet used to cover about 16,000 square kilometres, and Scotland is actually almost five times that area.
鈥� To refer, as we did, to a photovoltaic panel “rated to give 1 kilowatt per square metre in peak conditions… in the UK” (6 December 2008, p 30) was a tad over-optimistic. More realistically, it would take around 10 square metres of PV panel to generate 1 kilowatt.
鈥� The half a million people expected to buy genetic tests in 2008 (22 November 2008, p 7) is the American Society of Human Genetics’ , not the US alone.
How nanotubes were discovered
Your recent article on tunnelling nanotubes (15 November 2008, p 43) begins: “Had Amin Rustom not messed up, he would not have stumbled upon one of the biggest discoveries in biology of recent times.” Well, perhaps I can give my account of events.
Everything started when I ordered a fluorescent membrane dye. Having some cells left, the day it arrived, I tried to figure out appropriate concentrations and excitation wavelengths. Although the provided protocol demanded several washing steps, I decided to skip them. Some would say intuition, others laziness 鈥� presumably both are true.
After a while, and completely unexpectedly, thin membrane strands became visible, spanned between individual cells. I will never forget spending hours in front of our microscope, buried in a gloomy cellar room, observing the peculiar structures, which sometimes started to vibrate and break. The highly ordered appearance was mind-blowing, unlike to anything I had seen.
I called Hans-Hermann Gerdes 鈥� my former supervisor 鈥� upstairs in his office to show him what, I thought, could represent some kind of intercellular channel. He was as excited as I was. We both agreed to start pilot experiments to see, whether it was worth investigating further.
It soon became apparent that the structures were indeed extremely sensitive and difficult to handle. When I decided to switch projects, my colleagues said that I was crazy. We set out to prove that these structures were hollow tubes through which things could pass from cell to cell. However, our initial trials failed. There was nothing comparable available in the literature and nothing seemed to pass along the channels.
The project was on its way to drowning and I was meekly on my way to switching research topics again, filing this phenomenon as an interesting side observation, when 鈥� again by chance 鈥� I leafed through a copy of Nature that was on the desk in our seminar room, and stumbled across an article by Anders Karlsson and colleagues, describing in-vitro generated membrane tubes between liposomes. This instantly triggered the idea of active organelle transfer between cells. We followed up the notion and managed to demonstrate the intercellular transfer of endosomal structures. From that moment on, things joined together like jigsaw pieces.
Now, almost five years after publishing and nine years after the initial observation, I have to admit that I have ambivalent feelings. I have achieved delayed gratification with recent studies confirming, bit by bit, our initial ideas, such as the transfer of pathogens. On the other hand, it is still… let us say “challenging” to convince some other scientists.
The discovery of tunnelling nanotubes means we may have to rethink models of intercellular communication and how multicellular life forms evolved. But that will be another story.
Ploughing in carbon
In acting against climate change, we are not limited to high-tech initiatives. Simpler solutions can take carbon dioxide out of the atmosphere. In Australia, a pilot scheme exists to pay farmers to capture and store carbon in their farm soils, yielding the farmer around A$20 (US$14) per hectare per year above normal farm income: see .
Replacing carbon also brings back higher moisture retention and greater fertility to soils 鈥� just what is required in this increasingly hungry world. It would take, the leader of the scheme says, around 2 per cent of Australian agricultural soils to be part of the scheme to capture all of the nation’s CO2 emissions, allowing more time for the nation to make the transition to greener ways. It would require, he says, only a further 5 per cent of Aussie agricultural soils to be involved to reabsorb all the carbon exported in fossil fuels each year.
Automobile engines
John LeBrun makes some good points about the advantages of diesel engines (6 December 2008, p 22), but there is more to be said.
Diesels have a great advantage in city traffic because they burn very little fuel when idling, while gas engines burn about as much at idle as they do while driving at city speeds.
Because the fuel consumption of spark-ignition engines varies by displacement, cars with gas engines should be taxed by engine displacement. Because more cylinders mean more friction, all cars should be taxed by the number of cylinders. Because a three-cylinder piston engine balances better than either a two or a four, taxes could accept the three cylinder as basic and add a surcharge for each additional cylinder.
And for the future, I’ve always wondered why diesel engineers don’t build double or triple expansion engines. We know that steam engines were not practical for ships until the double expansion engine was developed, and the same principle should work for diesels.
Cancer treatments
Your articles about new cancer treatments were interesting (25 October 2008, p 26). However, when my wife was diagnosed with breast cancer a year ago the treatment was based on slash-and-burn approaches that have been around for years. On offer were: amputation and pre-emptive amputation 鈥� the cancer was in one breast, but “just to be sure” pre-emptive amputation of the other was recommended; chemotherapy, which makes people very sick; and radiation therapy.
It takes one to two years to recover from these treatments. Recorded cancer survival rates are getting better, but whether this is based on better treatments or just on earlier diagnosis it is very much the question. It is unbelievable, given those wonderful new specific treatments and all the money put in research, that in practice treatment mainly relies on the earliest crude treatments developed.