It's been a week of doom as far as the public face of science is concerned. On Tuesday we had Sir David Attenborough's depressing prognostications that the future is going to be worse for our children and their children (especially if we insist on producing more children in the first place).

Now the comments by the astronomer royal, Martin Rees, take the apocalyptic tone to a new level, one which resonates with his medieval title. With a Nostradamus-like gloom, he intimates it may be too late to naturally reverse the effects of climate change – and believes that radical geoengineering may be the only way we can cope with the desperate scenario. It is one which Lord Rees does not relish: "Geoengineering would be an utter political nightmare", he acknowledges, as well as stirring up practical and ethical dilemmas we can't begin to imagine. But that doesn't stop us trying.

Geoengineering – planet-hacking, in other words – is another of those scientific ventures that pursues the fantastical and seeks to implement it in reality. It's a kind of steampunk for boffins and entrepreneurs – Jules Verne gone viral. It ranges from the ostensibly practical, to the practically insane – but it reminds us that we humans have that one extraordinary superpower which might yet get us out of this fix: imagination itself.

So (every science statement begins thus nowadays), what are the ideas?

1. The giant sunshade

One of Lord Rees's fellow astronomers, the aptly named Roger Angel, has come up with a vast sunshade to be constructed from 16tr glass discs, assembled in space, and sent into orbit using electromagnetic launchers. This has a beautiful, obvious simplicity. Angel believes that by blocking just 2% of the sun's rays, global warming could be reduced to manageable proportions. That we could regulate the earth's temperature, much as we do with the blinds in a sunny conservatory. All well and good – but issues of maintenance and other practicalities – asteroids, for one – cast a shadow on this mega-space umbrella.

Practicality rating: 5/10

Apocalypse rating: 3/10

Cost: 8/10

2. Iron fertilisation

This is the idea that by infusing the ocean with iron filings, we could stimulate phytoplankton blooms, increasing bio-productivity and create a green carbon sink, in the process absorbing large amounts of CO2. It may sound like a school lab experiment gone crazy, but since the 1990s, this has been one of the most favoured geoengineering techniques.

However, it completely ignores its effect on marine life. Surely one reason we're trying to save the planet is to preserve the reasons why we liked it in the first place. And anyway, sperm whales have been doing this naturally for millennia. A recent Australian report estimated the southern ocean population of whales release enough faeces to absorb 400,000 tonnes of carbon a year. Although no-one's proposing training huge pods of the creatures to do our dirty work. Yet.

Nevertheless, more localised environmental concerns didn't stop Russ George of Planktos dumping 100 tonnes of iron sulphate in the Pacific last year, an act which has been accused of violating the UN's convention on biological diversity and other international conventions that forbid dumping at sea. Good old human bureaucracy may yet stymie the wilder excesses of geoengineering. Meanwhile, other scientists claim that diatoms – photosynthetic plankton – may merely absorb the iron into their shells and sink to the sea bed, negating the intended effect.

Practicality rating: 8/10

Apocalypse rating: 6/10

Cost: 3/10

3. Seaweed farms

Proposals for giant seaweed farms work on a similar principle to iron fertilisation, and would cultivate larger, more CO2-absorbing plant forms than phytoplankton. They also sound rather more directly appealing (at least for lovers of Japanese cuisine) in that they'd have the added bonus of furnishing us with food as a byproduct.

Practicality rating: 8/10

Apocalypse rating: 2/10

Cost: 2/10

4. Solar radiation management

Surely the most practical solutions are the simplest. Reflecting the sun's rays back into space could help lower the temperature on earth. White roofs would reflect up to 80% of the sun's rays, compared to dark roofs, which only reflect 20% at most, according to the Lawrence Berkley national laboratory in California. They also reduce the need for air-conditioning by making the rooms within cooler. But a pot of whitewash isn't exactly sexy stuff in the heady, macho world of planet hacking. The sense of emergency evoked by Lord Rees's remarks will surely encourage those with plans for a fleet of cloud-making ships to do a similar job, or schemes to turn great swaths of desert lands green and soak up more of those pesky rays.

Practicality rating: 7/10

Apocalypse rating: 4/10

Cost: 3/10

5. Artificial volcano

Perhaps the most extraordinary project on the geoengineers' cyber drawing board, however, is the artificial volcano. Another version of solar radiation management, it would pump ash into the atmosphere, reflecting the sun's rays back into space. One of the idea's supporters Samuel Thernstrom, co-director of the Geoengineering Project in Washington DC, declares: "There is no argument for ignorance – we should know more about geo-engineering."

However, anyone whose travels were disrupted by the eruption of the Icelandic volcano Eyjafjallajökull in 2010 would certainly have their reservations. Would we have to call out a futuristic Bruce Willis to sort it all out for us? And there's a more serious note of caution to be made here, too. It was a natural volcanic explosion in Indonesia in 1815 which created "the Year without a Summer" of 1816. Those broody skies and stormy nights over the Villa Diodati on the banks of Lake Geneva inspired Mary Shelley to write Frankenstein; or, the Modern Prometheus – a book freighted with ominous warnings about the consequences of human beings using science to manipulate the world to their own ends.

Practicality rating: 6/10

Apocalypse rating: 7/10

Cost: 6/10