Sir — Stephen Budiansky in hisCorrespondence1 “How affluence could be good for the environment” calculatesthat, thanks to increased crop yields, the‘ecological footprint’ of North Americansis much smaller than that calculated by the World Wide Fund for Nature. Hetouches on the inclusion of per capitagreenhouse-gas emissions, but heoverlooks the impact of intensive cropproduction on emissions of the non-CO2

greenhouse gases methane (CH4) andnitrous oxide (N2O).

Agricultural soils and livestock farmingalready emit around 7 million tonnes ofnitrogen as N2O to the atmosphere eachyear2; worldwide nitrogen-fertilizerapplications at the rate Budiansky suggests as typical for the United States(115 kg ha11) would lead to furtherincreases. Similarly, agriculture around theworld constitutes a source of more than100 million tonnes of methane each year— more intensive farming is likely toincrease this methane source, while at the

same time increased global nitrogenapplication and deposition may greatlyreduce the soil methane sink (about 30 TgCH4 yr11; ref. 3).

Budiansky argues that, with moreintensive farming methods and ascountries become wealthier, the world’spopulation could significantly increase per capita consumption without increasedland requirements.

I doubt whether he has included in hiscalculations the loss of usable land owingto sea-level rise, as predicted by theIntergovernmental Panel on ClimateChange, and to desertification resultingfrom global warming4.David S. ReayInstitute of Ecology and Resource Management,University of Edinburgh, Edinburgh EH6 3JU, UK

1. Budiansky, S. Nature 416, 581 (2002).

2. Kroeze, C. A, Mosier, A. R. & Bouwman, L. Global Biogeochem.

Cycles 13, 1–8 (1999).

3. Mosier, A. R. et al. Climatic Change 40, 39–80 (1998).

4. IPCC. Climate Change 2001: The Scientific Basis (Cambridge

Univ. Press, 2001).

will come from the US Department ofEnergy. These funds have no direct‘crossover’ to biomedical research orbiology. Every one of the five synchrotronX-ray sources in the United States was built and is operated by agencies that donot deal with biology.

One can make arguments for theadvantages of using electrons, as outlinedby Henderson, or others for using X-raypulses. One can estimate that the conventional handicap of X-rays overelectrons could be reversed3 and made intoa net gain on very small samples, whenextremely intense and very short X-raypulses will be produced. This is the domainof the X-ray FELs.

There is surely room for more than one avenue to be explored — differenttechniques will be appropriate for different biological structures andprocesses. This flexibility is intrinsic to the nature of research and essential forscientific progress. There are no threatshere, only challenges.Janos HajduBiomedical Center, Uppsala University, Box 576, S-751 23 Uppsala, Sweden1. Henderson, R. Nature 415, 833 (2002).2. Patel, N. Nature 415, 110–111 (2002).3. Neutze, R., Wouts, R., van der Spoel, D., Weckert, E. & Hajdu, J.

Nature 406, 752–757 (2000).

correspondence

Intensive farming, US-style, is not sustainable worldwideMore greenhouse gases will increase loss of usable land.

Don’t punish scientistsfor government actionsSir — You mention in News in Brief(Nature 416, 574; 2002) a letter from 125academics published in the UK nationalnewspaper The Guardian, urging asuspension in European funding for Israeliresearch programmes.

Richard Dawkins, a signatory of thatletter, once notoriously advised the Princeof Wales: “Of course we must be open-minded, but not so open-minded that ourbrains drop out.” With this in mind, I wouldlike to point out to the 125 distinguishedsignatories that Israel is not a freeloadingrecipient of European research funds, butrather a participating country that pays adesignated contribution to the overallbudget of the European Union (EU).

A suspension of our ‘associated nation’status in the EU will free our governmentfrom the obligation to transfer these funds to the EU. Because academicresearch and academic freedom are notpriorities of the Sharon government, toput it mildly, the net result will be apunitive blow to Israeli researchers (not a group noted for blind support of thegovernment), while freeing up funds thatthe Sharon government will undoubtedlychannel into defence needs.

Perhaps the 125 Guardian authors need to bear in mind another (slightlymodified) quotation, “put brain into gearbefore setting pen to paper”. Mike FainzilberDepartment of Biological Chemistry, WeizmannInstitute of Science, 76100 Rehovot, Israel

The challenge offered by X-ray lasersSir — In his Correspondence “Excitementover X-ray lasers is excessive” (ref. 1),responding to your News Feature2 aboutthe applications of X-ray free-electronlasers (FELs), Richard Henderson raisestwo points. First, that the development of X-ray FELs for biological applicationsthreatens the field of structural biologybecause it will use up money needed forexisting techniques; and second, that thedevelopment of existing techniques will be more fruitful than investing in anexpensive, unproven technology such as X-ray FELs. I believe that both of thesearguments are incorrect.

Synchrotron machines were developedby physicists and materials scientists, and have evolved to benefit biology. Whenthe first dedicated synchrotron lightsources came to life more than 20 yearsago, they produced X-rays with intensities

50–100 times greater than a rotating anode generator. Yet synchrotronradiation triggered a revolution in the life sciences, and today almost 15,000 X-ray structures feature in the protein data bank as a result.

Did the construction of synchrotronsharm biology? Certainly not. Should one be afraid of a much bigger step aheadwhen the first X-ray FEL comes to life? Idon’t think so.

If one takes the speed of walking andmultiplies it by 1010, the result is a speed100 times faster than the speed of light.The expected improvement in peakbrilliance offered by X-ray FELs overexisting synchrotrons is of this magnitude.These machines will bring us into a worldfor which only predictions exist.

A lack of hands-on experimental data on the behaviour of matter underthese conditions makes very detailedforecasts difficult. But one thing is certain:X-ray FELs will generate fresh thinking,new science and a new scientificcommunity. To imply that there is nothing that X-ray FELs can discover in biology is misguided.

The money for building and runningthe Linac Coherent Light Source atStanford (first of the planned X-ray FELs)

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