The BBC has convened an expert panel to examine issues raised in James Lovelock's latest book, The Revenge of Gaia.
Professor James Lovelock, author of The Revenge of Gaia
Professor Lovelock argues that climate change, combined with other environmental factors, is a major threat to human society and the natural world.
We asked for your views and questions. Here are extracts from the discussion which address some of your points.
Size of the human footprint
While it is clear that there is significant climate change occurring and that humans have had some role to play in this, do we yet know the extent to which humans are the root cause? Rajat, Toronto
While I am prepared to accept that there may be global warming, nothing I have seen shows a causal connection. Tim, UK
One of the most persistent arguments made by those who do not believe that climate change is caused by human activity is that there is "no consensus" amongst climatologists about this. How would you respond to this? Tim Dennell, Sheffield, United Kingdom
Five hundred years ago the scientific consensus was that the world was flat. Thirty years ago, we were about to enter another ice age. Twenty years from now we will all have a good laugh about "global warming". Thumper3181
There are a lot of people who are very sceptical about climate models, and it is very difficult to build a true Earth simulator; after all, the Earth system has the potential to have in it processes that we do not even see at the moment, and so cannot model.
But what we do know is that in the last 100 years, we have shifted the carbon dioxide concentration up by the same amount as it normally varies on a 100,000-year cycle.
So we have done something in about one thousandth of the time that the natural system takes, and it is bound to have an effect because we have seen those effects on global temperature. In fact, the global temperature changed by 5C or more when carbon dioxide varied by that much in the past.
I would not want anyone to think that we are relying on computer models to tell us this is a dangerous situation. It is very simple; we are hitting the system with a whacking great hammer, and it is bound to respond.
The point to emphasise is that the basic physics associated with the accumulation of CO2 in the atmosphere and its effect on the Earth's temperature has been known for well over 100 years.
And the temperature rises that we see today and which are predicted by our sophisticated computer models are very much of the same order predicted at the end of the 19th Century - this is not something new.
We are not talking about whether this is a serious problem, but whether it is serious or very serious.
End of the scale
Surely if the book is at the "upper end of expectation", then it is actually possible. Chris Wills, Fareham
Vicky Pope: Bleak picture of our future is "possible"
This book paints a very bleak picture of the future - bleak but possible, and I think that is the point; it is possible.
If it is possible, then we should take it very seriously.
'No science' of prediction
Since the weather today cannot be predicted reliably for more than 12 hours, the science of predicting 100 years or more seems no science at all. Chuck Rogers, Jacksonville, Florida, US
We have two messages emerging from our discussions.
One is something we are familiar with - 'systems are incredibly complex, there is a huge amount that needs to be understood about the science' - on the other hand, we are certainly being told by Jim Lovelock and by others that there is a certain urgency to this problem.
These things seem somewhat incompatible to me. In some ways we are asking questions of the science that the science cannot answer, either because they are not fundamentally scientific questions, they are political or ethical questions; or because we are asking science to resolve questions on a timescale on which it cannot resolve them.
Could the Earth achieve a "balanced" state where it handles the human impact through natural processes? Eric Nondahl, Middleton, WI, US
The real difference between now and the geological past is the speed of the change. The only geological event of comparable impact and speed really has to be the impact of a meteorite or something of that kind.
And all of the changes we know about in the past have taken place, even the very fast ones, over tens of thousands of years; and over that sort of period, organisms have time to change, to accommodate, to evolve slightly.
We do not see that at the moment; that is the big difference.
Adapt and survive
Does it not seem prudent that every government should be preparing for the eventuality that the global warming scenario may be real? Herb, Los Angeles, California
Hans von Storch
We need to talk about adaptation. But when we talk about heatwaves in Europe for example, we have to ask ourselves: 'how is it possible that people can live in conditions where we have such thermal regimes nowadays?'
Obviously people can do that and they live very happily and productively, and that means we have somehow to change how we live in Europe. Maybe we have different houses and things of that sort.
Hans von Storch: Is regular flooding so terrible?
Then let us talk about coastal inundation, which has been studied on the German Bight. Water levels in storm surges in the year 2080 may amount to 70cm and that is something we have to be concerned about.
I would say we have no big chance of avoiding it. We could increase the dikes but sometimes it is not possible; so in certain areas people have to expect that they will be flooded every 20 years. Is that particularly bad?
I think Mr Lovelock has a very good point, even if he may make it a little too strongly and emotionally. However, to effect real change globally we need to change the behaviours of three nations above all others: the US, China, and India. Martin W, Coventry
How do we persuade those (such as our president) who claim that climate change is a natural process, and that the effects of human activity on this process haven't been proven? Charles Peach, Charlotte, North Carolina, US
I believe we know quite enough to persuade any politician who is paying any attention that this is one of the most serious things, the most serious thing that will come across their desk.
We don't know the details of what we are doing, but by God we know we're doing it. Any other issue that crossed their desk that has a 95% certainty attached to it - they would just throw up their hands and say it's incredible.
Nuclear fission is the only way through the problem of global warming which can cope with the ever-increasing world population. Gaz, Liverpool
I am in full agreement with Professor Lovelock's position, but I fear the short-term solution of nuclear power. The waste disposal problem has not been solved so would we not be replacing excess heat with radioactive poisoning? Alex McKeon, Los Gatos, CA, US
Nuclear energy is said to be the more efficient energy compared to the other sources. But how safe is it to depend on nuclear fission, looking into long-term effects caused by the radiation let out from it? Anil Kumar, Bangalore
I think the nuclear option raises a number of real problems.
There is of course the problem of the public and political acceptability of nuclear power, and in a democracy we cannot just wish those concerns away. For example, how would we deal with the consultation and planning processes that we would need in order to bring forward a nuclear power programme?
Susan Owens: Problems with the nuclear option
There are also issues of cost - I do not agree with Jim Lovelock that nuclear is the cheapest source of electricity - and if you went for a quick nuclear programme there are questions about the sheer capacity to deliver in terms of construction capacity and skills.
Jim presents nuclear as a short-term bridging option, but it is difficult to see how a major nuclear programme could be a short-term solution because of the very long lead times.
I also feel this concentration on how we supply electricity is taking our eye off major issues like transport, where we are letting those sectors develop in energy-profligate ways.
I think it is fair to make the point that modern nuclear technology is as unlike traditional designs as a modern car is to a vintage car.
Nuclear has undergone a major transformation, and there are not many of the problems around today that there were 20 or 30 years ago.
I find the stress on nuclear power is perhaps not helpful.
I think the first thing we have to concentrate on is being more miserly with the energy we have, and secondly we should be looking for a diverse energy system.
Electricity is part of the whole energy mix which we have to deal with, and nuclear may be part of that energy mix for electricity.
But I think diversity is the important thing, and we should explore a lot of the technologies and see what we can get into play as early as possible; it is incredibly important for example that we try carbon sequestration on fossil fuel plants as soon as we can.
The issue of the public perception of nuclear power is a very ephemeral, trivial thing.
We have found in the last two years by stressing the need for nuclear that it has been possible to swing public opinion in the UK round from something like 98% against to something like 40% in favour; so public opinion is easily changed.
On energy conservation, I agree entirely, and I don't see why we cannot use other sources of energy.
I am talking about nuclear only in the context of electricity, and electricity is vital for modern civilisation. We have become hooked on it, we are utterly dependent on it, and we have to think really seriously about the consequences of any major cutback in electricity supplies; it would hit hard and immediately, within a period as short as a week.
Ultimately we could have a civilisation - I grew up in one - where there was very little electricity at all, and it worked very nicely; but it takes a hell of a time to switch back to something like that.
Nuclear power is NOT the answer. Instead we should set about massively and rapidly reducing our excessive consumption of all resources, but particularly of fuel. We should start by introducing fuel rationing. Tony Hamilton, Broadstone, Dorset, UK
Wouldn't it be better to develop a fundamental new energy system based on a holistic approach to sustainable energy production and use? Simon Carroll, Stockholm
Micropower to the people and help save the planet! Clare Finley, Hereford, UK
I think that we are going to need every source of energy we can get.
Ron Oxburgh and Brian Hoskins listen to discussions
Wind power is one of those which may never be a huge source of energy; but if you can save a few tonnes of carbon dioxide here and there by using wind energy, I think that is good.
We should in particular be encouraging microgeneration of energy on individual houses; it is not the case that huge turbines are the only way of exploiting wind energy.
We have no option to nuclear; wind just cannot compare in quantity, and we would never be able to get a constant, stable supply of wind.
If we depended wholly on windmills, what would happen during warm, still summer weather? The windmills stop working and there is no electricity, whereas nuclear keeps steadily going, as it has done for 40 years, keeping things working.
Ultimately it's our own fault because of our obsession with consumerism, so perhaps we should just take our lumps like grown ups. Jez Lawrence, Leeds, UK
We live in a culture of consumption; and particularly we live in a culture of high energy consumption.
So people get very mixed messages; they read a book like Jim's, saying 'what we are doing is destroying the planet, it is very dangerous'; but they go about their daily lives and they are locked into patterns of high energy consumption and they are being persuaded to consume more.
People exist within a cultural and social context, and they cannot simply change their behaviour to respond to messages like the ones in Jim's book, or indeed to messages that the government gives out about 'being responsible and doing your bit and changing your behaviour'.
I tend to think in terms of the higher part of the range given by the Intergovernmental Panel on Climate Change for temperature rise over this century - that is between 3C and 5C - because I think that we as peoples will not take the necessary measures in time to stop carbon dioxide increasing.
Many of the lower predictions are based on very optimistic assumptions about what the people of the world are going to do about emissions and various other things.
I do not believe they will happen, and I think emissions will if anything tend to grow.
If you are a reader of The Economist magazine, you get the impression that all of prosperity depends on finding more and more carbon fuel as quickly as possible everywhere.
The BBC panel comprised:
Brian Hoskins (Chair)
Royal Society Research Professor, Reading University
Professor of Environment and Policy, Cambridge University
University scientist; former chairman of Shell
Head, Climate Prediction Programme, Hadley Centre
Director, British Antarctic Survey
Hans von Storch
Director, Institute for Coastal Research, Geesthacht, Germany
Professor of Environmental Sciences, University of East Anglia