Letters

From Mark Whitehead

It appears that being a chemist has more associated hazards than previously realised. The arrest and subsequent release of Magdi al-Nashar raises some important questions. Members may remember that Mr al-Nashar had a passing acquaintance with some of the presumed London Underground bombers. He is also a biochemist. Shortly before the tube bombings, Mr al-Nashar flew to Egypt, where he has family ties. 

Not unusually, the yellow press immediately vilified him as the ’bombmaker’. He was detained by the Egyptian police, but has been released and completely exonerated of any involvement with this horrendous act of terrorism. 

It seems he was guilty of two ’crimes’; being a Muslim, and having a knowledge of chemistry. Now, I cannot claim any allegiance with his faith, but I am a chemist. Does that mean that I am already half-way to suspicion? 

Perhaps we should, as a society, explain to the general public that the manufacture of acetone peroxide trimer is well within the capabilities of any half-decent A level chemist with more respect for his skills than his life. Any synthetic organic chemist, I am sure, could manufacture this substance on a semi-industrial scale without much difficulty or any particularly unusual risk. 

We need to redouble our efforts to educate the public and cast aside the idea that there is something mysterious about chemistry. Synthesis instructions for acetone peroxide, freely available on the internet, are no more complex than a recipe for fairy cakes. 

M S Whitehead MRSC
Melton Mowbray, UK

From Jack Barrett

Peter Dryburgh (Chemistry World, July 2005, p29) is correct in his failure to find articles that verify the connection between global warming and human activity. Rich Chandler (Chemistry World, August 2005, p29) and the Intergovernmental Panel on Climate Change (IPCC) agree with the ’consensus amongst climatologists’ that if the carbon dioxide partial pressure doubles, the Earth’s surface temperature will increase considerably. Consensus is not verification. Global climate may be changing; the question is what are the causes; natural or human made?

Enhancement of global warming by extra carbon dioxide in the atmosphere is to be expected. The sun warms the Earth’s surface. The energy is transferred to the atmosphere and beyond by conduction, convection, water evaporation and the absorption of terrestrial infrared radiation by the greenhouse gases. The warmed gases emit infrared radiation in all directions, the downward radiation further warming the Earth’s surface - the greenhouse effect. 

John Young (Chemistry World, August 2005, p29) expresses doubts about carbon dioxide being a greenhouse gas. About five per cent of terrestrial radiation escapes through the infrared ’window’ where very few components of the atmosphere absorb. Of the rest, which is absorbed by the current atmosphere, water vapour is responsible for absorbing about 63 per cent and carbon dioxide absorbs 27 per cent, the other 10 per cent being absorbed mainly by methane and dinitrogen monoxide. The absorption and consequent downward emission causes the Earth’s surface to be about 34?C warmer than it would be with a radiatively inert atmosphere. 

The question that remains to be answered is what would be the increase in global temperature if the carbon dioxide partial pressure were to double from its pre-industrial value of 285ppm and is the increase cause for alarm? 

Models of the atmosphere based on the energy budget, embracing the known physical processes, indicate that the temperature would rise by about 1?C. The range of more sophisticated models used by the IPCC, all using the same physics, give results that vary between 0.8?C and 3.0?C (IPCC third assessment report: climate change 2001). 

In spite of the consensus on the future climate much research funding is being consumed, hopefully to reduce the uncertainties in the predictions. Rich is still burning fossil fuel and it does not matter from whom he buys it. Whatever climate the future brings we should all be using our finite natural resources as prudently as possible.

J Barrett CChem MRSC
Kingston-upon-Thames, UK

From Les Hearn

In his letter about the greenhouse effect (Chemistry World, August 2005, p29), John Young has put his finger on the conceptual difficulty with this analogy. He is right that carbon dioxide in the atmosphere absorbs infrared light of wavelengths 4.3mm and 15 mm, whether it is falling on the Earth or leaving it. The net warming effect in the atmosphere arises because the inward and outward fluxes at these wavelengths are not equal. The inward radiation originates from the Sun, surface temperature some 6000K, with a peak at about 0.5 mm, in the visible range. Proportionately, very little energy is carried by the 4.3 m m and 15 mm wavelengths.  

The Earth absorbs at all wavelengths, becoming warmer. It then re-radiates the absorbed energy, a steady state being reached at about 300K, on average. Because the Earth’s temperature is much lower than the Sun’s, the peak in its radiation spectrum is at about 10 mm, well into the infrared range and quite close to the wavelengths absorbed by carbon dioxide. Proportionately, more energy is carried by these wavelengths and so increased carbon dioxide levels will lead to increased atmospheric temperatures and so on. Beyond the fact that greenhouses are warmer, I don’t see much similarity with global warming either.

L Hearn MRSC 
London, UK 

From Tony Milward

The recent plethora of letters in Chemistry World on climate change and the related issue of future energy sources were, as one would expect, mainly well informed. However, there were one or two surprising and worrying exceptions when one considers that as chemists our discipline provides the tools for the science of detecting past and present climate changes and possible means of circumnavigating such changes. An article in Chemistry World to bring some of us up to speed in this important aspect of earth science would therefore be very useful.

I can sympathise with Norman Groocock (Chemistry World, August 2005, p29) in his response to the conflicting predictions that on the one hand we are moving from a warm interglacial into another glacial period, whereas the present concerns are of global warming and rising sea levels. However, this apparent contradiction is not so surprising when one takes into consideration the importance of oceanic currents in transferring heat. These currents are driven by differences in water density largely due to differences in salinity. Consequently, if the northern ice melts as a result of global warming this would significantly reduce the density of sea water at the northern end of the Atlantic conveyor current and prevent it from sinking and circulating thereby switching off the supply of heat so essential to our present equable climate. Thus we could experience a rapid (by geological standards) warming period followed by an equally rapid chilling. 

The point that needs to be emphasised is that as an already over prolific species very reliant on stable climatic conditions we should not be embarking on a global experiment of changing any of the parameters on which stability may depend. The undeniable increase in atmospheric carbon dioxide levels and global mean temperature since man’s clearing of the forest and the industrial revolution is one such change which we have already unwittingly made.

It therefore seems prudent to reduce, or at least prevent, further increases in carbon dioxide. This cannot be achieved by alternative ’clean’ sources and as Derrick Stevens pointed out (Chemistry World,  August 2005, p28) hydrogen is not a universal answer to the problem since it is energy dependent for its production and storage. Most of the other alternative energy sources, such as solar, wind and wave power, are weather dependent and intermittent. There is therefore an urgent need as the editorial (Chemistry World, June 2005, p2) pointed out, to reconsider nuclear fission power stations and also to put a lot more effort into nuclear fusion research.

The last time the earth experienced high carbon dioxide levels, admittedly three or more times the present concentrations - although at the present rate of increase it will not take long to reach this - was during the Cretaceous period and it took about 80 million years for temperatures to come down to something like present day levels.

A F Milward CChem MRSC
Exeter, UK

From Colin Cook

Global warming works because the radiation that penetrates the Earth’s atmosphere comprises a broad spectrum of wavelengths, and these are partially absorbed by the atmosphere and partially by the ground or oceans. This results in the warming of both, which then radiate their heat away as infrared rays (IR), and it is these that are absorbed by the atmosphere instead of freely returning to space. So the more IR-absorbing molecular species present in the atmosphere (and this includes water and methane), the warmer the atmosphere becomes, and its heat is re-radiated back towards the ground to warm the whole planet.

We can get an idea of the sensitivity of the atmosphere to small amounts of absorbing species if we imagine the Earth as a perfect sphere, and all the atmosphere liquified on the surface as an ocean. This ocean would be only about 11 metres deep. The ’greenhouse’ molecular species are analogues of dyes, except that dyes absorb in the visible spectrum instead of the IR. It is not difficult to imagine how a handful of dye could colour the water in a three metre deep swimming pool, and likewise CO₂  and CH₄ need only be in small concentrations to ’colour’ the 11 metres of air, except that for the species to have a warming effect they have to blank off the infrared ’glow’ from the warm surface rather than absorb the incoming solar heat.

While we are on the subject, there is surely only a limited mass of CO₂ in the atmosphere and oceans, and once this is fixed as biomass (ie forests), it is no longer available to cause global warming. All the arguments about forests producing more CO₂ (and CH₄) than they absorb are surely spurious if there are more of them in the future than there are now, aren’t they? Considering just the total mass of carbon, surely the answer to global warming is to initially plant more trees, and then wait until vast areas like Siberia become warm enough to support coniferous forests, when nature should correct the balance.

C J Cook CChem MRSC
Basildon, UK

From Neville Hartley

Whenever one reads articles scorning legitimate, healthy debate by exaggeration (eg, comparison with Flat Earth Society), one can be pretty sure that there are very good grounds for scepticism.

Rich Chandler (Chemistry World, August 2005, p29) is scathing about sceptics of man-made global warming whilst offering no reasoned arguments - statements such as ’consensus amongst climatologists is so overwhelming there is not a debate to be had’ are only worthy of the popular press and have no place in a scientific argument.

Atmospheric chemistry is exceedingly complex and very difficult to model at high dilutions using a planet-sized test tube - a study of published literature will demonstrate a bewildering number of possible reaction paths and variables. Whilst the evidence for current planetary warming is indeed convincing, the real questions for a chemist (as opposed to a climatologist) are: how much has the atmospheric concentration of carbon dioxide increased due to purely human activities, and, is there a theoretical model that can causally relate this increase to a specific rise in temperature?

Like Peter Dryburgh (Chemistry World, July 2005, p29) I have seen no such evidence and would like to see a reliable model explaining how an increase from 280ppm to 360ppm of a gas which is not at the top of the global warming efficacy league can be responsible for the observed temperature increase.

The need for robust scientific debate is as real as ever and must never be shut out by pre-emptive statements.

T N Hartley CChem MRSC
by email

From Nick Clatworthy

I am not surprised Peter Dryburgh (Chemistry World, July, 2005, p29) has seen no articles verifying the connection between global warming and human activity; neither have I. Suggesting, yes but not verifying. Rich Chandler’s (Chemistry World, August 2005, p29) dogmatic and anti-scientific reply requires an answer.

The latter is wrong to say that there is no debate over the science as the science is not complete yet. Future work on climate change and events may reverse current thinking or more likely modify it.

If Rich Chandler is in denial about the value of future research into the connection between human activity and global warming he is, apparently, of the opinion that Chemistry World should not give space for his views. There is a need for debate and Rich Chandler’s intolerance is out of place.

N Clatworthy CChem MRSC
Whitstable, UK

From Nick Gudde

Derrick Stevens’ request for calculations on the energy efficiency of hydrogen-fuelled vehicles (Chemistry World, August 2005, p28) has already been granted. Comprehensive studies by the EU’s Joint Research Centre/Institute for Environmental Sustainability (JRC-IES) or by the Argonne National Labs in the US are available online. These examine the energy efficiency and greenhouse gas emissions of all the steps from initial production of a fossil resource (natural gas or oil well), through shipping by tanker or pipeline, conversion of the resource into a usable transport fuel (eg refining to diesel or petrol; manufacture of hydrogen or methanol etc) and distribution of the fuel itself. 

These are known generically as ’well-to-tank’ assessments. The reports also give the complementary assessment of the efficiency of the powertrain (internal combustion engine, fuel cell.). The ’well-to-tank’ and ’tank-to-wheels’ are then combined to give the overall ’well-to-wheels’ impact of each resource, fuel, powertrain combination. As well as addressing fossil energy, some of the studies also examine renewables such as vegetable oil products (eg biodiesel), fermentation products (eg ethanol from maize, sugar beet or sugar cane) and advanced biofuels made by gasification of woody biomass. A few even delve into nuclear and photovoltaic electricity.

The IES concludes that natural gas (or coal) is currently the only viable large-scale source of hydrogen. These resources would however increase well-to-wheels greenhouse gases relative to conventional fuels (although use of hydrogen in fuel cells may give a moderate reduction) It suggests that biofuels from arable crops (or hydrogen from non-fossil sources such as biomass, wind, nuclear) give more significant reductions in greenhouse gas emissions. It is however illuminating to look at the costs of such CO₂mitigation compared with other options (eg biomass for power generation; energy efficiency improvements.)

There is also some wider-ranging material on the future of transport in the Mobility 2030 report by the World Business Council for Sustainable Development.

N J Gudde CChem FRSC 
Surrey, UK

From Colin Britton

I am writing regarding the article Saving a steam ship (p46-49) in the July issue of Chemistry World.

In the review of the month in the same issue (p4) it was written ’And the unlikely heroes of this rescue operation? A bunch of chemists’ Why unlikely, I ask? For your readers’ information, the complement of those working to prevent corrosion represent chemists (around 40per cent), material specialists (around 40per cent) with the balance representing a bunch of other scientific disciplines and even biologists! 

This is due to the fact there is no basic degree in corrosion.There is however an option to take a one year MSc in corrosion science at Umist.

I have in the past few years presented talks on corrosion to schools ( both primary and secondary level) expanding the general science examples of corrosion in the GCSE curriculum and giving examples where chemistry can control corrosion and save our infrastructure. The children’s enthusiasm shows no bounds. 

By the way, the article was great!

C F Britton MRSC
Kimbolton, UK

From Barry Culpin

Brian Malpass should be careful with his anagrams (Chemistry World, August 2005, p72). ’Mad on Chemistry’ might be an anagram of thermodynamics but so is ’No Dam Chemistry’.

B Culpin MRSC
Chorley, UK