Climate Change

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Personally I think we can all expect a disastrous deterioration in climate over the next 10 to 20 years and it'll get much worse if we don't try and find alternative energy sources. Last year Britain recorded it's hottest temperature ever, 102F, and this August was the wettest in history. We've been hit constantly by floods and even tornados. Clearly something is going very wrong.
Option 1 for me.
Plant billions of trees to soak up the CO2 and start switching to renewable energy sources before it's too late.

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The evidence is indisputable in my opinion. I do believe we are entering a naturally warmer period (the period 1300-1800 was very cold), however that's probably just 10% of the overall change. 90% is due to human activities.

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Man is not that important. A couple of major volcanoes... now THAT'S important.

Volcanic eruptions reduce the temperature of the earth, however it's only temporary. The eruption of Krakatoa in the late 19th century was by all accounts cataclysmic, equivalent to thousands of Hiroshimas, however it only effected world climate for 5 or so years. The effect of releasing CO2 into the atmosphere is irreversable in the short term. It takes thousands of years to correct.

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I agree, it's hardly rocket science.
We are digging up millions of tonnes of fossilised plant matter, burning it and releasing the CO2 locked inside it into our atmosphere. Once it's released it cannot be put back again.
The fact remains, there is no doubt whatsoever that CO2 creates global warming, it's a scientific fact. It's the reason our planet is warm in the first place. If the Earth's atmosphere didn't contain CO2 as soon as night fell the temperature would plunge to about -100C!!
Any 'environmentalist' worth his or her salt would know this, so your 'lefty' mate clearly isn't that clued up on the subject.
I concede the exact dynamics of global warming are not known, some areas will get colder due to changing ocean currents, however globally the temperature is increasing and that's the important thing.
Global warming is happening, it's a proven fact.

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It's getting warmer but I believe it's primarily natural.

Significant warming would be trouble for some areas but a benefit for others. The likely migrations would cause political problems. There are also offsetting factors, like the theory that the Gulf Stream would shut down. But a lot of it is just theory. In the 1970's the prediction was that human activity would result in an ice age. Now it's global warming. Many of the Chicken Littles are watermelons (green outside, red inside).

Swarch, well how do you explain the fact that the earth has warmed more in the past 10 years than in the previous 100? If the warming was natural then surely it would be a linear event?
The gulf stream is a localised phenomonan. Some areas probably will cool such as Nth Wst Europe as they're artificially warm at the moment, but the global temperature will rise.
In any case, it's not beneficial since it means sea levels will rise reducing the amount of land we have to live on. Additionally it means extremes of weather will occur more often and of greater severity.

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He's right nuclear power does produce large amounts of CO2. Not directly obviously, however huge amounts of energy are required to mine the uranium and purify it. Then decomissioning nuclear power stations is a vastly expensive, time consuming business. Spent fuel for example is usually melted down and solidified in glass. This itself uses up extraordinary amounts of energy. Fission reactors are pretty much obsolete.

Until we can develop fusion reactors (perhaps 20 years time?), wind power, dams and tidal barrages are the way to go.

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It's getting warmer but I believe it's primarily natural.

Significant warming would be trouble for some areas but a benefit for others. The likely migrations would cause political problems. There are also offsetting factors, like the theory that the Gulf Stream would shut down. But a lot of it is just theory. In the 1970's the prediction was that human activity would result in an ice age. Now it's global warming. Many of the Chicken Littles are watermelons (green outside, red inside).

Swarch, well how do you explain the fact that the earth has warmed more in the past 10 years than in the previous 100? If the warming was natural then surely it would be a linear event?
The gulf stream is a localised phenomonan. Some areas probably will cool such as Nth Wst Europe as they're artificially warm at the moment, but the global temperature will rise.
In any case, it's not beneficial since it means sea levels will rise reducing the amount of land we have to live on. Additionally it means extremes of weather will occur more often and of greater severity.

I can't explain why it's warmed up quickly, but that isn't evidence of it being a man-made problem. In many areas, there's a lot less pollution now than there was in the past, so why didn't it happen earlier? I agree it would be detrimental on balance, but places like Canada and Russia should benefit. And would it really be more extreme? Wouldn't the temperature range just shift up--hotter in summer, hotter in winter?

Swarch, firstly, yes, localised pollution is much reduced in developed countries simply because we burn cleaner fuels (gas etc) and the process is far more efficient. This means you don't get millions of soot particles flying about. CO2 pollution however is far, far worse, simply because we use so much energy. New York uses more electricity in a day than smoggy London did in a month in 1950.
As for the weather being more extreme, it's because hotter climates are far more dynamic and unstable due to the greater energy content of the atmosphere. This is why tropical climates suffer hurricanes, torrential rain, massive hailstorms and catastrophic droughts. Cold climates like Canada have predictable, boring climates. You basically know it's going to snow in winter and be warm and sunny in summer. Nothing exciting happens apart from a blizzard or an ice storm.

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He's right nuclear power does produce large amounts of CO2. Not directly obviously, however huge amounts of energy are required to mine the uranium and purify it. Then decomissioning nuclear power stations is a vastly expensive, time consuming business. Spent fuel for example is usually melted down and solidified in glass. This itself uses up extraordinary amounts of energy. Fission reactors are pretty much obsolete..

I ask again, can you provide a citation for this claim.  Mining and transporting coal takes energy as well, and given the high energy density of uranium, it takes a lot less effort to mine uranium than the equivalent amount of coal on a per unit of energy basis. Right now the only technology that could hope to replace coal-fired electric generators in the quantities needed to merely maintain current levels of power generation is nuclear fission.  Wind power, dams and tidal barrages are all low density power sources that require vast areas of terrain to be developed.  They can contribute to energy production, but they aren't a viable solution.

AG Ernest, nuclear fuel isn't the answer to the problem, since it requires huge amounts of time, money and energy to deal with the lethal by-products when the power station is decommissioned. Dams and tidal barrages are NOT low density power sources! The 3-gorges dam in China apparently will produce the same amount of electricity as 200 coal-fired power stations at full capacity!

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Oh and we're still in an inter-glacial period (and an unusually cold one at that).
Within a geological timescale all the current climate changes are little details, as in a few thousand years the Ice will return.
And that's also a fact.

True. It's thought that most ice ages are caused by temporary decreases in the sun's radiation, co-inciding with a increase in sun spots. It happens every few thousand years. Massive volcanic eruptions also cause mini ice ages. This is thought to have been the reason for the 1300-1800 'cold episode'.