As regularly as one hour follows the next, e-mails arrive in my inbox from people claiming to have the solution to the world's energy woes in their factory or garden shed or back pocket.

Most, as you'd guess, turn out to be no more convincing than a dentist's reassurance that "this isn't going to hurt" - why on earth does anyone bother inventing perpetual motion machines anymore? - but sometimes, what starts off as an idea with apparently insurmountable technical, political or economic obstacles turns out, eventually, to be a real contender.

Step forward, then, the idea of powering Europe from the Sahara Desert.

I would have to go back at least 10 years to find the first time that someone (an Australian professor, in that case) took me through the sums showing that enough solar energy fell on the sands of North Africa to provide all the world's electricity needs and much, much more.

(I'm sure the concept goes back even further, and I'd be interested to find out just how far back, if anyone has the details to hand.)

Yes, well, I thought; but how much would the electricity cost given the traditionally unfavourable economics of solar energy? What about the major investments needed in plant and transmission lines, and the huge gulf between the political mindsets of the EU and its would-be electricity suppliers?

Now, answers are appearing to some of those questions.

On Monday, a group of companies including some very big industrial concerns - Siemens, RWE, E.On - met with representatives of the German government and other political players to sign a memorandum of understanding that could eventually see the flowering of desert power - the Desertec Industrial Initiative.

Partners will now spend three years putting together viable financial packages that could plant solar facilities across large swathes of the Sahara by 2020.

There is talk of 400bn euros being invested. For comparison, that would dwarf the cost of the Iter fusion power project.

The conventional photovoltaic cell may play some role, but the major technology is likely to be concentrated solar thermal power - probably using approaches where water, or some other fluid, is heated to temperatures measured in hundreds of degrees Celsius and used to turn some kind of turbine.

Remember those startling high-tech photos of mirrors gleaming in a Californian dawn that filled the covers of glossy magazines back in the 1980s? That's a concentrated solar thermal power station.

So is the space-age tower rising from Spanish soil, just outside Seville, which may soon provide enough electricity to meet that city's needs.

The Desertec project's initial goal is "to produce sufficient power to meet around 15% of Europe's electricity requirements and a substantial portion of the power needs of the producer countries".

These will be in North Africa and the Middle East, probably stretching round as far as Jordan, whose Prince Hassan bin Talal declared that "partnerships that will be formed across the regions as a result of the Desertec project will open a new chapter in relations between the people of the EU, West Asia and North Africa".

But the dreams are even bigger. Why not power much more of Europe from the region? Why not electrify much of South America from the Atacama desert and the mountain tops of Patagonia? Sydney and Melbourne from the Simpson desert, and western China from the expanding Gobi?

One reason why not may turn out to be security of supply. Why trade dependence on Middle Eastern gas for dependence on Middle Eastern solar electricity, some would ask.

Another might be that "producer countries" raise concerns about colonialism, about the takeover of their territory to solve Europe's problems - just as some have raised concerns about Western investment in "carbon forests" in poorer tropical nations.

But, if the Jordanian prince is right, Desertec will see development flowing to impoverished desert peoples even as electricity flows in the opposite direction.

Politically, the project will build better bridges between the EU and countries that would like to be closer to it; other benefits could flow over those bridges.

For EU nations, one of the attractions is that it provides a partial route to the target of providing 20% of the bloc's energy by 2020 - a target that, in many observers' eyes, is considerably more ambitious than the 20% greenhouse gas reductions that the EU has also pledged.

Fifteen percent of electricity is a long way from 20% of all energy.

But it is a start. And bear in mind that Europe's electricity consumption is likely to grow; declining reserves of oil and gas will begin to tilt the economics of space heating and transport towards the electric road, and that's a movement that climate policies will probably accelerate.

The next three years, then, will determine if the economics really do stack up.

Many apparently good ideas have perished in the sands of time. One doubts that companies of this scale would be seriously interested in Desertec if they thought it was likely to meet the same end.

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On the face of it, the climate declaration [pdf link] coming out of the G8's Thursday meeting with developing countries appears to be remarkably balanced - it doesn't give anyone what they really wanted.

G8 nations have not persuaded major developing countries to adopt numerical targets on reducing emissions.

Developing countries haven't got the pledges they wanted rich countries to adopt on sharp emission cuts by 2020. Nor have they persuaded G8 leaders to open their wallets and put billions of dollars on the table for green technology and protection against climate impacts.

Some of the environment and development groups that campaign on climate change have savaged the declaration for precisely these reasons.

But in reality, nothing more definite was ever likely to come out of the G8 gathering itself or the larger Major Economies Forum (MEF), the 16-nation-plus-EU group that brings together the biggest greenhouse gas producers from both developed and developing worlds.

The agreement that allowing the global average temperature to rise by more than 2C above pre-industrial levels would be a bad idea provides some indication that all blocs are serious about wanting a deal that will meaningfully constrain emissions.

This at least would not have happened while President Bush lived in the Washington White House and John Howard led Australia.

But all parties acknowledge that the UN process is the real forum for pledges. And what we have seen in L'Aquila is perhaps best viewed as a significant political signpost on the way to December's UN summit in Copenhagen, which is supposed to finalise a comprehensive new global climate treaty.

It is difficult not to conclude that for the Western public, there is a careful bit of news management going on here.

By floating the notion that developing countries would be requested to adopt numerical targets - which they never could, in fact, in this forum - G8 governments have raised the expectation in their electorates that developing countries should adopt numerical targets.

Thus the ground is further prepared for blaming developing countries if the Copenhagen process collapses or produces something with no more bite than an ageing chihuahua.

The key discussions - as they always have been - are about which bloc takes what level of responsibility for climate change, and who puts how much money on the table for what.

In the harsh light of political reality, the difficulties are still that the US and Japan will struggle domestically to set short-term targets big enough to impress developing nations, that in the current economic circumstances they'll struggle also to loosen their purse-strings for what is effectively a new kind of international aid, and that many developing country governments still find it anathema to contemplate meaningful pledges on reducing their own emissions.

The G8 and MEF meetings have confirmed the difficulties that exist. They have not gone very far to resolving them.

Big picture reflections

Although the G8 climate discussions dominated the environmental news this week, I enjoyed reading your comments on my last post asking whether all the political attention on climate change was obscuring discussion of other environmental issues.

In one sense, the G8 discussions threw the topic into a sharper light - and thanks for all your responses.

GaryTW20, you've perfectly encapsulated the arguments made in many quarters against investments to curb population growth - "birth rate control = eugenics = Hitler".

But as several other people observe, including mariansummerlight, programmes being run now by health agencies show that when you give women in poor countries the capacity to choose to have fewer babies, often they do - which benefits their own health, the prospects for their children and reduces population growth

Although still a little too radical for the political mainstream, this view of "population control" is now at least being discussed privately by some European politicians - and maybe the traditional association with eugenics and forced sterilisation will, in the end, be banished.

UI4060183, thanks for your link on Iran's fertility rate - interesting reading.

OneWorldStandards, you remind us - and thank you for it - that there has been a school of economics arguing that population growth is a very good thing because it generates wealth that a) betters the human lot generally, and b) can be used for environmental improvements if so desired.

I would be interested to hear from anyone who has adhered to this school of thought in the past - how much currency it has now, and also what they make of China's spectacular economic growth while practising population restraint.

Maintaining the trend of artistic references - why not branch out into Razia Iqbal's domain sometimes? - omnologos' comment about reducing the average height of a human being reminded me of the Genesis song (showing my age now!) "Get 'Em Out by Friday", in which humans are limited to a maximum height of four feet in order that twice as many can be crammed into the same building... not a happy piece of work.

I feel a lot more empathy for the Hitchhiker's Guide to the Galaxy story quoted by timjenvey... I defy anyone to work in an office or live in a city and not sometimes understand exactly how the Golgafrinchans felt!

On balance, though, probably not a practical option - especially as in some peoples' books, environment journalists would probably be first into the B-Ark...

There's one comment I have to query. stnylan writes: "If the price of our freedom is the devastation of our planet, that is a price worth paying". Really? And what price our freedom once the planet has been devastated?

This is a topic I know we'll come back to in the future - not least because I've spent a large chunk of the week gathering interviews for a BBC Radio Four programme about the very issue.

It's thrown up some fascinating insights and opinions... and I look forward to sharing some of them with you when the programme's due for airing towards the end of August.

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OK. So it's a big question for a Friday afternoon, I know - particularly on a London summer's Friday afternoon that sees the greatest male tennis player in history and the best UK player in a lifetime treading Wimbledon's green swards, and the mighty Blur reuniting for an evening's Britpopping in Hyde Park; but it's with me despite all this, along with a desire to share.

The question is this: how should society prioritise the world''s various environmental woes?

The political space - no doubt about it - is crammed full of climate change.

When you talk about this to people working in other fields - the decline in global biodiversity, the spreading of deserts, the depletion of our oceans - you tend to get two batches of opinions about whether that domination is justified.

One opinion holds that climate change threatens to worsen all other environmental ills to such an extent that it makes sense to prioritise it; and raising its profile will in the end focus attention on all the other issues too.

The other bemoans the comparative lack of attention given to all else in comparison with climate change.

A couple of things have had me mulling the question this week.

First off was a workshop I took part in at the World Conference of Science Journalists in London on the reporting of climate change.

One of the points I raised was that if you look at the biosphere's most recent health check - the UN Global Environment Outlook (GEO-4) report from 2007 - it's obvious that climate shifts are far from being the only kind of environmental trend.

Andy Revkin of the New York Times was also speaking; and he began his talk (as he begins the blurb for his dot.earth blog) by recalling that within a lifetime there will be nine billion people on the planet's surface, all clamouring for its sustenance.

I resurrected, for this workshop, a slide I made a couple of years ago, an attempt to link some of the major environmental trends and their drivers schematically; I've pasted it below.

So whereas we see climate change (the smoke picture) driving water shortages and desertification, we see that deforestation (the tree at bottom left) currently drives climate change more than climate change drives deforestation.

Climate change is projected to become a major driver of biodiversity decline (the cute furry face); but at the moment, the major factor is habitat loss as the human footprint expands.

When it comes to fisheries (forgive the rather gruesome shark head picture), the single biggest driver is undoubtedly over-consumption of what nature provides - the over-use of resources, which also drives climate change and deforestation and just about everything else.

And underlying it all is the growth in the human species.

Have I got this right? I think so - no-one's commented adversely whenever I've brought it forward - but I'll await comment and criticism gladly.

The second thing that brought the question into my head was a party to mark the 85th birthday of Maurice Strong, who (among many other accomplishments) chaired what's commonly cited as the world's first true environment summit, the Stockholm Conference on the Human Environment in 1972.

A few months ago I was reading some material about Stockholm, and it was fascinating to see what issues were prioritised then, and what's changed since.

Fallout from atomic bomb tests, chemical pollution, the expanding human population, whaling, and how urban life could be made sustainable and bearable against the projected expansion of cities - these were all prominent then, with few nods to climatic change or the global loss of species.

In part, priorities have changed with the geopolitical world. Atomic bombs (or as we call them now, nuclear weapons) are no longer tested in open air - in most nuclear states, they're hardly tested at all - and President Obama now holds out the prospect of culling their numbers to levels unimaginable during the period when the concept of Mutually Assured Destruction penetrated far enough into the zeitgeist that rock stars wrote anthems about it.

Science has advanced since then, which has brought bigger declines, better analyses of the problems and a wider range of ideas for solving them. Cleverer fishing methods accelerated the fall in commercial fish stocks; and now clever zoologists are plotting ways to restore some of the degraded species.

Substitutes have been found for some of the most damaging synthetic chemicals, and other regulated out of use.

These trends explain some of the changing priorities. But other changes are less obvious: why, for example, has population growth gone away as a subject of discourse?

I've tried to find rational ways of figuring out answers to the prioritisation conundrum.

One sample question is this: if climate impacts are at present largely reversible but the loss of a species self-evidently isn't, does that make biodiversity loss more important than climate change?

Another is this: if environmental issues are so interlinked, then why do we bother separating them out in the way that the Rio conventions do? Woudn't it be more logical to try to sort everything out en masse?

A third is this: if the fundamental drivers of all the trends are the swelling in the human population and our expanding thirst for raw materials, why aren't these the things that politicians and environmental groups are shouting about and trying to change?

I don't have the answers to any of this; I'm not even sure if such a thing as the "right" answer exists, still less whether a way of finding it logically can be discovered.

Perhaps explanations will be found in cultural and political values rather than logical assessment.

But I think it's important that we at least discuss the point, not least for the very practical reason that some of the policies being considered as a response to climate change - such as biofuels, and carbon sequestration through forestry and ocean fertilisation - could exacerbate other environmental problems.

The weekend awaits; and a glorious one it promises to be here in London. Strawberries and cream, and a double dose of Parklife, may be the immediate priorities.

I look forward to seeing what you've made of the longer term ones by the time a new working week opens for business.

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