Former Labour Environment Minister Michael Meacher and Dr S. Fred Singer, president of the US-based Science and Environment Policy Project, answered your questions in a special interactive programme.
Climate change poses a bigger threat to the planet than terrorism - so says the UK government's chief scientific adviser, Sir David King.
Droughts, forest-fires, heat waves, floods and storms have all hit the headlines in recent years.
The World Health Organisation's Europe Global Change and Health Programme has estimated that more than 25,000 people died in last year's European heat wave.
Most mainstream scientists believe that human activity - notably emissions of greenhouse gases - has contributed to a detectable increase in the average surface temperature of the planet.
British Prime Minister Tony Blair says addressing climate change is his key priority during the UK's chairing of the G8.
The Pentagon says climate change should be "elevated beyond a scientific debate to a national security concern."
How serious is the threat of climate change? Whose job is it to tackle it - governments, companies or individuals? Do you believe your actions can make a difference - and do you care enough to try?
This debate is now closed. Thank you for your comments.
Who is to say that the current warming trend, whether a natural cycle or man made, won't also provide more benefit than harm? In any case it is a very gradual shift and we can deal with it in time if necessary.
David, Houston, Texas USA
We have it within our collective power, agreement and behaviour to stop all terrorist activity. We are unable to stop the forces of nature which will be unleashed because of our negligence, greed and loss of soul, earth spirit and understanding of what the totality of life on earth is all about.
If America do not respect the planet how can they respect man kind?
Terrance Webster, Oxford, UK
Global warming is like a religion. It can't be proven, yet people radically change their lifestyle because of it. Like most zealots, global warming activists associate differing beliefs with low morality. Natural disasters are credited to global warming, just like any other deity. And of course, the last chapter of the global warming story is a doomsday scenario.
Jim, NJ, USA
On the D-Day beaches the sea level has dropped 30ft over 60 years, and the great lakes in the US/Canada have dropped 10 feet over 10 years, how and why is this possible?
Gerry Lancaster, Ashford, England
I would like to point out that saying that global warming will destroy the earth is a bit misleading. It will destroy plants, animals and us humans. The earth will just go on spinning and forget about us like the bad dream that we are.
Emmanuel Quartey, Tema, Ghana
Even if terrorists were to kill hundreds of millions of people and destroy a limitless amount of property, humanity would still live on. However, we have only one Earth to live on and we are killing it. I believe that global warming is a bigger threat than terrorism. It scares me when a large, relatively civilised, country like the US refuses to sign the Kyoto protocol. They are gladly driving their petrol devouring cars towards our extinction.
Beatrice Olofsson, Sweden
We accept damage to the environment because we enjoy all the factors that cause it. However, I feel our lifestyle and greed created the breeding grounds for both threats. We should look into this deeply and carefully.
Ahmad Hmoud, Amman, Jordan
I resent that America has NOT enforced the Kyoto accords. My people were conquered and forced into the American Union. Most of our land in Alaska, 91%, was stolen from us by America. This land is subject, today, to the whims of the majority American immigrants, who want to exploit and tear up our land in the name of economic development. But, at what price can we say we prosper economically? This mentality that our Earth is an inexhaustible resource to be exploited has to stop!
Today, our shores erode daily from higher sea levels. More of our land is drying up and burning in forest fires every year. The sea ice, which is our lifeblood, arrives later EVERY year, and becomes useless much earlier in the spring. When all is said and done, and every rich man has his dollar, who will remember the Yupik and other coastal people when our history is erased beneath the waves?
Pengetaghaq, Tapraq, Alaska
I think too many people say too much about what they "think". Would it not make more sense to look at data, facts, numbers, history and trends to come to a sensible conclusion? Terrorism is obvious. Global warming is subtle, and this is probably why many people "think" it is either not happening or that it is a natural cycle not influenced by humans. I would gladly have accepted solar heating panels from Mr Clarke, in the UK.
I thought that the eruption of Mt. St. Helens in 1981 threw more "greenhouse" gasses into the atmosphere in one day than the world's cars had done in 100 years?
If we are worried about fuel usage surely we should think about a)living closer to where we work and b)only eating locally grown produce. Why switch the "Standby" off on your tv if you cheerfully travel 100 miles each way to work? Or eat strawberries in December that have been flown in from Peru?
Finally, if you buy a bike please realise that there is an environmental cost in manufacture that is not justified if you leave in the garden shed after the first week.
Tony Ward, Birmingham
The pollution caused by humans has proven links to increases in cancer, child birth deformities, asthma, allergies and animal habitat destruction.
Even if 90% of global warming is a myth we are still destroying our own habitat like it or not. We are all consuming foods laden with artificial chemicals, breathing air laced with poison and wonder why health care keeps going up.
Population control (especially in developing countries) and green technology should be our priorities for the next 50 years.
N Lowe, Bedfordshire
It is not a matter of denying the reality of man-made global warming, it is a question of facing up to the reality that, to stop (man-made) emissions, we have to stop the growth of industry. Would anybody really have preferred the Industrial Revolution and the massive economic growth since then, not to have taken place, in order to prevent the Earth from warming up a couple of degrees? Developing countries will soon become the biggest emitters of greenhouse gas; would you deny this same opportunity of economic growth and prosperity to them? If we want to leave the Earth completely free of damage, we should all be living at subsistence level.
Mariam Mahmood, London, UK
I get really tired of people saying get out of your car and use public transport. They should try living in a rural area. Some villages only have two buses a week. Public Transport is not a viable option to get to work in rural areas. And it is poorly paid rural workers hit hardest by fuel duty rises.
Geoff, Sleaford, Lincolnshire
Over the next thirty years, greenhouse gas emissions and pollution levels will more than double, due to the expansion of China and other world economies. People who say this has always happened are obtuse. This generation has already done enough damage to the future of the world. The changes now being seen are significant. We ignore the scientists' warnings at our own, or our children's peril.
Nigel, Redhill, UK
Someone has recently come up with an improved electric milkfloat that can go up to 70 miles an hour. So why aren't there cars on the market that can do the same? Come on you car manufacturers, I'd buy an electric car if you designed one at a reasonable price. We would also not be so dependent on other counties for oil!
Melanie Hassan, London
I know of not a single death that has been proven to be caused directly by global warming. I can think of at least 3,000 attributed to terrorism in September of 2001 alone. What a silly argument this is.
Lyn, New York City
Yes, climate fluctuation happens naturally - but natural changes occur over thousands of years. The recent sharp rise in global temperature has occurred during just the past century - a minuscule interval of geologic time. Nothing like that has ever happened before, and the rise corresponds precisely with the rapid growth of industry and pollution. Those who deny the reality of global warming are not examining the facts.
Matt Simon, Boston, US
How can you compare the two? There are so many differences between these threats and the manifestations and of course outcome of these threats. However they do have 2 similarities 1. They are both a very real threat. 2. Both problems are being compounded by incompetent, greedy governments. Who will only act on these issues if it secures a positive election campaign or brings in the money.
Global warming is far a bigger threat to humans than terrorism is. Most people might not look at global warming as a big threat because it is abstract to them, than terrorism. Humans can try to win a fight against terrorism, but it is absolutely absurd to fight against the force of nature. At one point, the world will reach a point where it can't handle anymore, and this will be a disaster. Let us think about our future generations and care as our fore-fathers did care for us to reduce much pollution. Reinford Mwangonde, USA.
Reinford Mwangonde, St.Louis, USA
I absolutely do no think so. As Gary and Paul (UK) have put it, climate fluctuations have been happening throughout history, and will still happen. Global warming is just causing global hysteria.
Eugenia Kothe, Idstein, Germany
The hysteria generated over this issue is astounding!
Gary Walker, Harlow, Essex, UK
Throughout history the Earth's temperature has fluctuated, ice ages one epoch, rainforests the next. Are we so arrogant that we think we can affect the Earth's climate?
Paul Weaver, London, UK
I work as a HECA officer for a local authority. It is my job to raise awareness of energy efficiency measures, climate change issues and fuel poverty. It's a hard job as the media in the main dismiss scientific research by teams across the world and the Chief Scientific adviser as unsubstantiated tree-hugging nonsense.
I recently obtained £40k in grant from government to pay for solar thermal heating and 8 households that I offered FREE solar heating systems to refused it saying that they didn't believe in global warming...it was a waste of time!
I asked a man - "did he not care about his children's future?", and he replied I'll be dead! So who cares!
Richard Clarke, Petersfield, Hants, UK
'Global warming' is most likely a symptom of climate change that naturally occurs across the planet over millions of years, the same change that causes an 'ice age' and the subsequent thaw. To believe that humans could be responsible for such a massive impact upon the world is the ultimate arrogance.
Chris Phillips, Gloucester, UK
Those who claim that it is arrogant to imagine that humans can affect the earth's climate forget that the earth has never before had to cope with such a huge population.
Jane, Wales, UK
The last period of global warming started in the 10th Century (obviously the Vikings were burning too many villages)
This continued until the 15th Century when we had the "Little Ice Age" leading to our misconception of the White Christmas.
Since the 18th Century the temperatures have risen again, so it looks to me that Global Warming is a myth perpetuated as an excuse to over-tax motorists.
Iain, Rochdale, UK
Climate change does not pose a threat to the planet? It only poses a threat to the people that live on it!
We cannot do anything to change the processes of climate and weather (humans do not control nature), but we can reduce pollution and toxic waste, and make the planet a nicer and cleaner place in which to live.
Terrorism IS controllable - through security measures, changing policies, building trust and rapprochement over time. Unless we act on climate change, and take action now, we are storing up a frightening legacy for the next generation and beyond. Unless we reverse the trend, the temperature rise will have a universal impact that will affect all ecosystems and inhabitants on the earth. It's far beyond a political or ideological struggle.
Joanna Watson, London, UK
If only America, so keen to make the world a better place with its war on terror, was half as concerned about this problem and took the Kyoto agreement seriously.
They, not even 5% of the world's population, produce a quarter of worldwide CO2 emissions and refuse to do anything about it! Long term, that attitude will cause more death than any WMD.
Climate change in one form or another has been happening to this planet for millions of years, and it is arrogant to think that this is all our doing. Every variation in the weather is put down to global warming.
If we really are causing climate change, we all know what we need to do. No more cars, no more burning of fossil fuels anywhere. Electricity must be rationed so the renewable sources can cope. In other words, our way of life must end. Of course we will not change in anything more than a token fashion. So let's prepare for what we believe will come. Violent weather, changes in sea level, climate change now seem inevitable. We did it all by ourselves.
David, Cornwall, UK
Global warming has killed fewer people than lack of sanitation. It can be addressed, and there is time to do so. Terrorists on the other hand pose an immediate threat in many parts of the world. So terrorism is the more critical threat at present.
Eran, Jerusalem, Israel
Climate change is happening and will affect us all. Whereas you cannot pass laws that do away with terrorism you can make legislation that will force corporations and people to live and conduct business in ways that are more environmentally friendly and much less damaging to the planet. Of course this won't come cheaply and the economic cost will be hard but when you weigh this against our children's future (or lack thereof) which is worth more?
Mark, Hong Kong
Global warming is already killing millions of people every year - as droughts and floods around the world are increasing. Every scientist I know who I've spoken to about the climate is very worried indeed. I've climbed on glaciers that are melting, and staying in countries where the rainy season has literally swapped with the dry season. Yet the developed world, and particularly the USA continues to do nothing about it.
Pete, London, UK
Global climate change is a much greater threat than terrorism. The vast majority of the population of this planet will remain untouched by terrorism but vast numbers will be affected by sea level rise, drought, famine, crop failures and severe storms. Furthermore, the effects of climate change will lead to greater migration putting pressure on dwindling productive land and increasing the threat of disputes, war and terrorism.
Declan Allison, Belfast, Northern Ireland
No way. The environmental lobby are the like the boy who cried wolf. According to many studies in the late 70's and 80's were all supposed to be dead right now. I'm not saying that pollution is not a problem, but with advances in technology, I would hope that we could decrease the amount pollution that is created.
Mike Daly, Miami, FL
Yes it is. Scientists and good people have been worrying about this for the last 50 years, and not without good reason. If we had pulled our fingers out of the oil wells and worked towards alternative energies all this time, this would not be a problem right now. But when the governments of western nations are funded by or even run by the CEO's of oil companies, it's difficult to get any kind of environmentally friendly legislation put in place.
Lloyd Evans, Brighton, UK
Global warming is something that is hyped out of all proportion by the media. There is nothing new happening with the weather or climate change. Everything that is happening now has happened before and there was no influence from the so called greenhouse effect. Nothing we do can change the natural cycle of events that will inevitably take place just the same as it did in the past. We can neither defeat nor overcome nature, what will be will be.
Keith, Sunderland, UK
Of course global warming (which threatens us all) is more serious than terrorism (which will kill only a very small percentage of us). Wind turbines are not the answer; neither is building a new load of nuclear power stations. Strange that no politician dare suggest the one "cure" for global warming that might work - namely tax incentives to reduce the world population to sustainable levels. Aim for 10 million (down by 83%) in the UK by 2100.
Brian Beesley, UK
"Think global, act local" - This phrase encapsulates it all - your actions do make a very real difference.
Peter Holten, Milton Keynes, UK
After going through two historically cold New England winters in a row, coldest and most snow in over 100 years, and the mild, cool, summers that followed global warming isn't worrying me as much as terrorism. Both are overblown by the press, neither is understood as well as the experts pretend and It is unlikely that most people will ever experience either.
Steve Mac, Boston MA USA
Global warming will continue as long as humans exist on this planet. However I do not believe it will bring an end to civilization. Disasters are a normal part of life and do not signal a beginning of the end.
Charles, Montreal, Canada
Governments must take the lead. Emissions must be addressed as well as alternative fuel sources. Conservation should be legislated if need be. Perhaps we should be educating our very young children, who will one day inherit this planet from us, about what they will be facing. If they grow up with the knowledge and understanding of what is bad for the environment and what responsibility they have to protecting it, it could mean a world of difference in the future.
Beth, Kansas City, USA
There is a very slight risk that I or someone I know will be directly impacted by a terrorist attack. On the other hand, it is inevitable that sooner or later every person on the planet will be impacted by climate change - maybe not next year, or in 10 years, but sometime pretty soon. And here's the problem. Politicians have to worry about the whim of the electorate - there are no votes to be won by introducing punitive taxes now to save the planet in 100 years time.