If the upgrading of the Beauly-Denny electricity transmission line is blocked by objectors, then we might as well give up on renewable energy. Scotland's prodigious resources of wind, tide and waves are up north and the electricity needs to be brought down south. It's as simple as that.

In fact, if Beauly-Denny doesn't happen we might as well give up on the planet, because it will indicate an Easter Island state of denial about the nature of the threat posed to the environment. We can't go on giving the view from holiday homes a higher priority than the fate of human civilisation.

I'm sorry if that sounds intemperate - but we are running out of time here. I've been writing about this issue for two years, and yet the planning process has only now begun. The inquiry launched yesterday in Perth will last a year, and then will take another year to report to ministers, who will probably then take another year to respond. If we are going to take five years every time we need to upgrade some pylons, then we are all cooked.

And I speak as someone who values Scotland's wild land very highly and spends as much time as possible getting lost in it. I don't particularly like pylons, especially ones 200 feet high. But I don't believe they constitute the "destruction of the environment", as claimed by groups such as the Ramblers Association. There are already power lines running down this route. We have to get real here.

What will destroy the environment is not pylons but global warming. Already, the character of the Scottish Highlands has been altered forever by the absence of winter. January 2007 was the second warmest on record. If this continues - and it will - then the precious peat bogs and wild habitats will perish altogether as climate change makes them unsustainable. This is not science fiction or alarmist fantasy, but cold, hard fact - staring us in the face, within our lifetimes.

The IPCC report last week ended forever the argument about climate change: it's happening and we are largely responsible for it. Two thousand five hundred scientists made this the most authoritative peer-reviewed examination of the evidence for anthropogenic climate change. We're on our final warning.

If we don't control emissions soon then the concentrations of greenhouse gases in the atmosphere will reach a kind of critical mass. CO2 emissions, currently around 380 parts per million, are projected to rise to 500 ppm before the end of the century, at which level warming would become irreversible. We have no choice but to take charge and stabilise emissions well below current levels.

This will require a massive collective effort, comparable to the mobilisation of industrial populations during a world war. That may sound alarmist, even militaristic - but it is the only comparable emergency within recent memory.

Now, if the country were threatened by military invasion, or if energy supplies were being cut off by a hostile foreign power - not such a daft idea given our dependence on Russian gas - would people object to upgraded power lines? I don't think so. They would probably accept that there had to be some give and take. That there might have to be some temporary sacrifices involved.

And pylons are temporary structures which can be dismantled and removed if and when it becomes technologically possible to transmit the power by alternative means. But these alternatives do not currently exist. Burying transmission lines under the highlands terrain, if it is possible at all, would involve some very substantial earth moving and landscaping which could damage the land far more than erecting pylons. That would be yet more planning inquiries and objections.

Taking the power lines under water down the west coast would also involve a great deal of environmental disturbance if it were technically possible. And the simple reality is that it won't happen because it is too expensive. Burying the Beauly-Denny transmission line would cost at least 12 times the cost of upgrading the existing line.

This inquiry is also a challenge to environmental groups such as WWF, Friends of the Earth. They know better than anyone that if we are serious about renewable energy then it has to be transmitted from where it is generated to where it is needed. But they are holding back - uncomfortable about appearing to side with big business against conservation groups. The woolly jumpers clash with the the suits of Scottish and Southern Electricity, AMEC et al.

But this is no time for sartorial politics. The greens must accept the responsibility that comes from being right. They have won the war on the environment, and the suits have been forced to listen to them. But having argued for renewables, the environmental groups now have a moral obligation to support the only practical prospect of it being developed on a commercial scale. There is no point in developing wind, tidal or wave projects if the electricity can't be transmitted to population centres.

Of course, large-scale solutions aren't the only answer. Home insulation and local power generation are necessary, too, along with clean coal, biomass, zero-carbon transport and curbs on air transport. But even if all these were in place, we would still need every watt of electricity that can be pumped on to the grid from the north of Scotland. These aren't alternatives.

Many scientists believe that, even with renewable energy, conservation and curbs on CO2 emissions, there would still be a gap that can only be bridged by nuclear power. Some objectors to Beauly-Denny may find that more congenial than pylons. Why not just build more nuclear power stations, if they are going to be necessary anyway?

But that is desperately short-sighted. Nuclear power stations are expensive, dangerous and there is no known solution to the problem of nuclear waste, other than to bury it in the ground and hope for the best. They represent the last desperate option if all else fails.

The renewables industry offers the best prospect of reconciling necessary demand for energy with the long-term security of the environment. Wind, wave and tidal power represent a valuable resource for Scotland, and a source of future sustainable employment. If the objectors have their way, this industry will be destroyed.

Of course, this doesn't mean pylons for pylons' sake; but it does mean looking beyond the backyard.

There are times when an entire complex of issues becomes condensed into one simple decision. If the Beauly-Denny transmission line is blocked then the decision will have been made to give up on the future. This is a test of collective resolve. If we don't meet this challenge, if Nimbyism and conservation conservatives succeed, the next generation will not look kindly on us.

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