Across our planet, a range of ancient habitats provide eerie testimonies to the lives of creatures that once ruled the land. In Brazil, more than 100 tree species produce giant fruit that evolved to be dispersed by elephant-sized creatures called gomphotheres, while in Madagascar many plants grow thin zigzag branches to protect themselves from 10ft-high elephant birds, which used to populate the island.

These animals, like the mammoth and mastodon, are now extinct  their disappearances having followed the relentless conquest of the globe by Homo sapiens. Few doubt there is a link. Environmentalist Mark Lynas is certainly convinced that humans slaughtered these huge animals, creatures whose only living legacy today are those specialised fruits and protective thorny bushes that still await their attention. And with no living animals to disperse their seeds properly, these trees and plants are now themselves endangered.

Humans have a lot to answer for, in short. We have wiped out countless species and are now heating the planet, poisoning the oceans, and transforming the atmosphere. Having culled so many of the world's large beasts, we are now preparing to eradicate animals and plants of every size. As Lynas states: "Nature no longer runs the Earth. We do."

And you can see his point. Homo sapiens have acquired God-like powers to transform the world and destroy life. Hence the title of Lynas's book, in which he outlines the measures he believes that humans  as responsible, benign deities  should now adopt to save the planet. Many of these proposals are surprising, coming, as they do, from a former green activist who once trashed GM plant trials and railed against corporate greed.

Consider nuclear power. An anathema to greenies but which turns out to be a particular favourite of Lynas: an energy source that should be seen as "one of the strongest weapons in our armoury against global warming". Those who protest against its introduction are dismissed as doing as much harm to the climate as big oil companies.

Genetically engineered crops also get the thumbs up. Only they can provide the food for the billions of future inhabitants that will populate our planet, Lynas claims. As for those midnight raids he carried out against plant trials, they occurred because "I was caught up more in an outbreak of mass hysteria than anything resembling a rational response to a new technology".

As Damascene conversions go, this is a belter. With luck, it might even start a trend  for as Lynas now admits, it is now "time for a change of tack by the Green movement, for the benefit of farmers, consumers and the environment". Amen, is all I can add.

The core of The God Species relies heavily on the work of the "planetary boundaries" group, a collection of scientists who recently produced strict recommendations about levels of disturbance beyond which humanity should not push the planet. These propose specific limits on carbon dioxide emissions, farming land use, biodiversity loss, chemical pollution, and ocean acidification. Stick to these and earthly life should remain tolerable, Lynas states.

Nor is there a need for an economic revolution to achieve these goals. Good old-fashioned capitalism is quite sufficient. As Lynas says: "A successful environmental movement must work with people's aspirations for prosperity and comfort, not try to suppress these impulses." This is a fair point, though Lynas is vague, to say the least, about how unadulterated capitalism  which has so far failed utterly to halt the planet's current desecration  can achieve this goal.

The God Species nevertheless offers up an intriguing thesis and Lynas outlines it with clarity and panache  though his basic argument is disfigured not just by vagueness about policy measures and specific goals but by a depressing number of silly errors. Industrial pioneer James Watt is said to have invented the steam engine in 1764. He didn't. He invented the secondary condenser, which transformed the efficiency of existing steam engines. And he did it in 1765, a date carved in stone on Glasgow Green where Watt first conceived his great idea.

Similarly, an article I wrote is attributed to the wrong newspaper, while in the same chapter it is "revealed" that the Iberian lynx is hovering on the edge of extinction. In fact, its population numbers have trebled in the past few years, and continue to rise, thanks to a remarkable rescue programme that has saved the animal. I could go on. Suffice to say that these mistakes, while individually trivial, combine to undermine the reader's faith that Lynas fully understands his brief. The problem is haste, I suspect. Certainly, The God Species comes over as a hurriedly written book. On the plus side, this brings a sense of urgency to its pages  time is running out for our world, as Lynas makes clear  but on the other, its mistakes irritate.

Overall, Lynas is to be commended for producing a work that challenges so many green movement taboos and for recognising the importance of hard science  such as nuclear power and genetic engineering  and sound economics as potential saviours of the planet. This is an insightful, honest book. I just wish Lynas had taken a little more care in preparing it.

The political and environmental profile of climate change has been dramatically reconfigured in the past two years. A wave of activism has dissipated and a broad consensus on the necessary measures broken thanks to the failed Copenhagen summit and the anti-global-warming lobby's apparent triumph in the Climategate emails affair. Mark Lynas is one of a growing band of influential figures, along with James Lovelock, Stewart Brand and George Monbiot, who now argue that the approach of most Greens to climate change needs to change.

Lynas puts it briskly in this new book. "Gobal warming is not about overconsumption, morality, ideology or capitalism. It is largely the result of human beings generating energy by burning hydrocarbons and coal." Inevitably, the beliefs of most environmentalists involve a cluster of other goals and ideological imperatives but if some of these are inimical to the need to reduce carbon emissions then, Lynas believes, a decoupling is necessary.

Environmentalists, of course, do want to address global warming: Lynas's other target is the rather large constituency who feel the need to deny it altogether. I'm sure he's right when he divines a reason for the deniers' PR successes: "They tap into a powerful cultural undercurrent that insists we are small and the planet is big, ergo nothing we do  not even in our collective billions  can have a planet-scale impact." Later in the book he gives an excellent refutation of this in the example of Thomas Midgley, who single-handedly almost roasted the entire human race and rendered them brain-damaged. Midgley invented the refrigerants and aerosol propellants (CFCs) that began to eat the ozone layer and was also (this isn't mentioned in The God Species) a key developer of the lead tetraethyl additive for petrol. Lynas goes on to commend the 1987 Montreal Protocol on CFCs as an exemplar of the kind of international action we need on climate change.

He is level-headed about issues that have become intensely emotive, and recognises that the debate around climate change has become polarised on political grounds: libertarians with little understanding of science don't want to acknowledge that there are natural limits to human activity. They then feel free to equate the climate agenda with "socialism by the backdoor". But of course there really are natural limits, in the form of the great natural cycles: carbon, nitrogen, water, and so on.

Many human problems have too many contributory factors to allow cause to be unambiguously linked to effect, but Lynas is surely right that global warming is not one of them. The complexities only emerge in deciding exactly what mix of energy sources will best meet the target of reduced CO2 emissions, and how to fund it. Lynas's first wake-up call came when he became adviser on climate change to the low-lying Maldive Islands. As Dr Johnson might have put it: "When the Maldive Islands are sinking beneath the waves, it concentrates a man's mind wonderfully."

A second wake-up call came at a meeting in Sweden in 2009 when he encountered the Planetary Boundaries Group. This is a body of experts that is campaigning for the recognition that there are nine critical planetary limits. Lynas's purpose in this book is to explain and popularise this concept.

The nine boundaries are: climate change, biodiversity loss, biogeochemical cycles (such as nitrogen and phosphorous), ocean acidification, water consumption, land use, ozone depletion, atmospheric particulate pollution, and chemical pollution. Of these, the group believes that the first three have already passed the planet's limit, the next four haven't, and the last two have not yet been quantified.

It's certainly a useful concept for the kind of planetary management that Lynas believes is now necessary. He is wonderfully sane and cogent on difficult issues, explaining why organic farming is not an option globally and why we need genetically engineered crops. The natural limit to food production is set by nitrogen which, in a form usable by plants, is rare in nature. We owe our present 6.9bn population to the 100-year-old Haber-Bosch process of nitrogen fixation to produce fertilisers. Take that away and the current population is already twice the Earth's carrying capacity. Our best hope for the future is to genetically engineer a nitrogen-fixing plant (the green kind) to replace nitrogen-fixing plant (the heavy industrial kind).

Lynas bravely recounts how, as recently as 2008, he took part in anti-GM activism, which he now attributes to "mass hysteria". He had read not a single scientific paper on the subject until, following negative comments made online after an article he had written in this newspaper, he looked at the evidence and changed his mind. He has written the clearest exposition so far of the choices facing us. We may wince at the book's title (it derives from Stewart Brand's remark: "We are as gods and have to get good at it"), but Lynas is not playing God, simply making a passionate pitch for good global resource management.

Peter Forbes's Dazzled and Deceived: Mimicry and Camouflage (Yale) won the 2011 Warwick prize for writing.