The team of US experts secretly working on the development of the atomic bomb made a profoundly worrying discovery in 1942: an atomic explosion would create temperatures on Earth (15 million ºC) hotter than at the centre of the sun.

What might such an unprecedented inferno trigger? Scientists openly speculated that it could well ignite the hydrogen in the world’s oceans, or nitrogen in the atmosphere, setting off a cataclysmic fireball capable of extinguishing life on Earth almost entirely.

Despite being aware of the existential risk this entailed, on July 16th, 1945, the Trinity nuclear test went ahead. As author Toby Ord notes, “this was a new kind of dilemma for modern science”.

As the atomic fireball rose into the desert sky, one observer, Harvard University president James Conant, feared the worst. “My instantaneous reaction was that something had gone wrong, and that the thermal nuclear transformation of the atmosphere…had actually occurred.”

These fears turned out to be groundless, and within weeks the US had dropped two of its deadly new weapons on Japanese cities.

Ord assigns July 16th, 1945, as the beginning of what he terms the “precipice”, our new era of heightened existential risk. Humanity, Ord argues, “is akin to an adolescent, with rapidly developing physical abilities, lagging wisdom and self-control, little thought for its long-term future and an unhealthy appetite for risk”.

While adults impose constrains to keep adolescents in check, no such mechanism exists for humanity to collectively lay down and enforce the rules to keep its awesome destructive power in check, Ord adds. He cites the 1972 Biological Weapons Convention: “This global convention to protect humanity has just four employees, and a smaller budget than an average McDonald’s.”

Adolescence

Ord is a moral philosopher at the Future of Humanity Institute at Oxford University, and while teasing out the many risks humanity faces (he estimates we have a one in six chance of total extinction this century), his overall analysis is sweepingly optimistic. If we can survive our own turbulent adolescence as a species, he believes humanity has quite literally a place among the stars, and a future without limits.

It is a bold, relentlessly upbeat hypothesis. “This book is not just a familiar story of the perils of climate change or nuclear war. These risks that first awoke us to the possibilities of destroying ourselves are just the beginning.”

Rapidly emerging risks from biotechnology to novel pandemics to advanced artificial intelligence, he argues not entirely convincingly, “may pose much greater risk to humanity in the coming century”.

Latterly, carbon emissions, which Ord describes as a minor side effect of industrialisation, have “eventually grown to become a global threat to health, the environment, international stability and maybe even humanity itself”.

Ord’s thesis is that humanity stands at the edge of the eponymous precipice, facing on the one hand extinction, yet on the other a future full of possibilities beyond our present capacity to even imagine. “Humanity opening its eyes, coming into its maturity, and guaranteeing its long and flourishing future. This is the meaning of our time,” he posits.

Ord’s chapter outlining the key anthropogenic threats lucidly sets out the risks arising from climate breakdown. Reviewing the available evidence, he points out that “we could plausibly end up with anywhere up to 13ºC of warming by 2300 – and even that is not a strict upper limit”.

Ecosystems

The overwhelming consensus among climatologists is that a global temperature increase of 4-6ºC or higher is likely to be lethal to most species and ecosystems on earth, and will virtually wipe out agricultural systems. Yet having grasped this point, Ord lets it slip in concluding that when assessing climate and ecological risks “none of these threaten extinction or irrevocable collapse”.

In his concluding chapter Ord looks beyond the skies, suggesting rather improbably that if we could reach one nearby star, “this entire galaxy would open up to us…if we could travel just six light years at a time, then almost all the stars in our galaxy would be reachable”.

The author believes that humanity is unique not just on Earth but perhaps in the cosmos. “The main obstacle to leaving our solar system,” he concedes, “is surviving long enough to do so.” This view of human exceptionalism might be better leavened with more humility about our all-too-human shortcomings.

Yet Ord is a defiant Utopian, choosing to believe that humanity yearns “to end the evils of our world and build a society that it truly just and human”, adding that “many of the harshest injustices visited on our fellow humans are behind us”.

The Precipice is a well-researched and extensively annotated survey of global existential risk. Yet some of its key conclusions appear ultimately to be as much the product of earnest wishful thinking and techno-optimism as philosophical reflection.

John Gibbons is an environmental journalist and commentator