You have said climate change is a bigger danger than terrorism. Is George Bush more dangerous than Osama bin Laden? DAVID VAN EGERAAL, London
Global warming represents the biggest challenge our civilisation has ever had to face up to collectively. The absence of leadership from the USA on this issue since the Kyoto agreement was brokered in 1990 has already meant that we are now seriously overdue in managing the problems globally.
Do you agree Britain has to drastically cut its flights if it is to meet its greenhouse gas targets? Are you advising the Government that its huge airport building plans are wrong? C LOWNDES, Bristol
I am advising the Government that we must reduce our emissions through a managed process of moving to low or zero carbon energy sources for the built environment, for industry and for transport, and through improvements in energy efficiency in each of these. Through implementation of these measures we will meet our greenhouse gas targets, and grow our economy.
What do you say to the small band of people who still deny man-made global warming? STUART MEYER, Brussels
We understood the role of greenhouse gases in our atmosphere in keeping out planet warm before the beginning of the 20th century. The vast amount of data and modelling since then has all confirmed this. And now we are experiencing global warming, just as predicted, as CO2 levels rise.
Is it true that the reason Hannibal could cross the Alps was because the planet was warmer then and there were few snow/ice hazards and that the Vikings farmed Iceland, for the same reason? TOM GARVEY, by e-mail
The warming we are experiencing and the expected warming this century are greater than the regional climate variations experienced at earlier times in our civilisation.
Rapid development of new technologies will be essential to avert extreme climate change. But currently if a person has an idea for a new technology, they are required to keep the idea secret. Do you think patent protection law should be reformed to encourage the sharing of ideas which might help these technologies to arrive sooner. CORRY GELLATLY, Newcastle upon Tyne
I have actively pursued the development of an Energy Technologies Institute in the UK, a £1bn public-private partnership that will be launched later this year. Patent protection may need to be used to encourage companies to invest in some of the important new technologies.
Have you revised your stance following concerns that you've become the mouthpiece of the Government to the scientific community instead of vice versa? This is in reference to public comments made by yourself stating that stabilising the atmosphere at anything less than 550 parts per million of CO2 was "politically unrealistic", when the scientific consensus believes that levels of 400-440ppm of CO2 are required to keep temperature rises below the dangerous 2C point. STUART TOMLINSON, by e-mail
Any charge that I have ever subverted my science advice to meet political expediency would be libellous! We have now already exceeded 420ppm CO2 equivalent greenhouse gases, and we cannot guarantee being below a temperature rise of 2C. We should definitely attempt to stay below 550ppm to avoid catastrophic changes in the longer term.
Do you despair that for all their talk, politicians are not taking firm enough action to save the planet? PETER O'NEILL, Dudley
I no longer despair. The tide is now beginning to turn, but there is an enormous amount of work still to be done.
What do you think will happen about avian flu? MATTHEW OSTLER, Frankfurt
So far, it has not transformed into a virus which would lead to a human flu pandemic. But it might. That is why we are spending considerable effort in government preparing for the possibility.
What would you say is the least safe way to travel? COLIN DARLING, Brighton
Judging by the death rate on our roads, the answer has to be, the private car.
Do you think science teaching in Britain is in crisis? Do you panic about the closing of physics departments in universities? USCHI FLEMING, Oxford
We have the second highest proportion of 20-year-olds doing science and science-related degrees in the world! But we need more qualified teachers of maths and physics; and more students in engineering and science degree courses.
How can we get school kids interested in science? EM LUNDGREN, Durham
The challenges of the 21st century will only be resolved through science, technology, medicine, agriculture and engineering. The excitement of meeting these challenges needs to be conveyed at school.
What importance do you place on carbon offsetting schemes? Do you think it provides people with too much of an excuse? JOEL SCRIVEN, Kintbury
Yes, I think it can be an excuse. I am pleased that we will be the first country to regulate these schemes.
Do you agree with Richard Dawkins that science is antithetical to religion? GEOFF DAVIS, by e-mail
Religion has today generally accommodated itself to scientific developments and our liberalised democratic societies. Battle lines are drawn up when it hasn't.
Is there a God? DETLEV ZUMA, by e-mail
Science progresses through study of the natural world, and through challenging those who claim to know the truth. This is the converse of the revealed truth of religion.
Do you share my view that it would be sensible and logical to legalise all drugs? JANE STANTON, Clapham
No I don't. But the work of my Foresight Group on Brain Science, Drugs and Addiction shows that we need a more evidence-based approach to this important issue.
Do you believe time travel is possible? CEARA BLAKE, London
Is homeopathy a con given that it is clearly scientific nonsense? MICHAEL WOOD, Petersfield
There is no scientific evidence whatsoever supporting the use of homeopathy.
You were born in South Africa. Why did you leave and have you met Nelson Mandela? DEE SHEERMAN, Bath
I left after rushing to complete my PhD because it was the softer of the options offered to me by the Apartheid regime. Yes - and what a personality.
What do you think Saddam might have done with his WMD? VIC HAMMOND, by e-mail
I don't think he ever had them. He was bluffing, to make his enemies think he was stronger than he really was, a well-known territorial defence strategy used by many animals.
Is BSE now over? And do you think foot-and-mouth was mishandled? CAROLINE THOMAS, Wiltshire
Yes to your first question. Your second question needs a very long answer. But in brief: Initially the Ministry of Agriculture handled it as if no changes in farming practices or in epidemiological sciences had taken place since the previous FMD outbreak in 1967. Everything did change very quickly after I moved in with a science advisory team about a month after the outbreak.
What on earth is quantum physics about? PETE SCOTT, Edinburgh
Quantum theory provides a remarkably accurate, elegant and complete description of the way the physical universe operates at an atomic and subatomic level. It may be philosophically puzzling, but when combined with modern computers, it is amazingly powerful.
Do you agree with David Miliband that organic food is no safer than chemically treated food? CHRISTOPHER KEEPING, Suffolk
Yes I agree with David.
Do you ever see a tension between what is scientifically necessary, and what politicians are prepared to do? KRISTINA DUBSKI, Manchester
In my six years in government I can only recall one case. We must have every technical tool at our disposal to move towards a zero carbon economy. That includes nuclear power.
Given advances in science and medicine, do you think we should lower the age limit on abortion? KERRY JONES, Kensington
More importantly children are maturing at an earlier age.
What are your vices? MELINDA KILLIAN, Guildford
Sometimes mindlessly watching sports on TV.
You always seem very rational. What makes you want to scream, cry or weep? NICK CHESTON, Norwich
Scream: Liverpool winning the Champions League in 2005. Cry: Watching Woody Allen's Manhattan, listening to Joanna Newsom, Mozart... Weep: The impact of HIV/Aids on my compatriots in South Africa - particularly children and young women.