As you read these words, a huge asteroid with Earth’s name on it could be hurtling towards us from outer space, whose impact with Earth will eliminate humanity, just as another asteroid killed off the non-avian dinosaurs 65 million years ago. Collision with an asteroid is one of many apocalyptic scenarios that could wipe out humankind, and it is no surprise to learn that a branch of academia is devoted to studying how such scenarios might arise.

Two bodies located at the University of Oxford, the Global Priorities Project and the Future of Humanity Institute, have just issued a Global Catastrophic Risk 2016 Report. The authors make the sobering calculation that the risk of extinction of humankind during the next 100 years is 9.5 per cent, which puts our water charges controversy into context.

Apart from killer asteroids, what other scenarios might trigger an extinction event? Well, for example, we might have a global nuclear war followed by nuclear winter, runaway global warming, a mistake with a huge geo-engineering project to change Earth’s climate, the eruption of a super-volcano, the release of a genetically engineered killer microbe, or artificial intelligence might decide to eliminate humans, and so on.

It is estimated that the risk of extinction of the human race is 0.1 per cent to 0.2 per cent per year. While this risk seems small, the Catastrophic Risk Report points out that these figures imply that an individual is more than five times as likely to die in an extinction event than in a car crash. And because all these small probabilities add up, the chance of global extinction within the next 100 years is 9.5 per cent.

So, what should we do about existential risks that have a low probability? Some philosophers have suggested we have a moral imperative, of higher priority than any other global good, to reduce existential risk as much as possible. I agree we should take existential threats very seriously, but I would also urge caution.

Expert estimates of the risk that any particular extinction scenario will occur rely on certain assumptions, and mistakes can be made here. For example, predictions of an impending global population explosion were widespread in the scientific community in the 1960s. The biologist Paul Ehrlich pictured this scenario in his 1968 best-selling book The Population Bomb, predicting famines in which hundreds of millions of people would perish. To avert disaster, western governments urged population control in the developing world, and the Indian government instituted a campaign of compulsory sterilisation. However, the dire predictions never materialised, because the doomsayers had not anticipated falling birth rates and the Green Revolution.

That said, let me return to an apocalyptic scenario that is a current real possibility – runaway climate change. Human emissions of greenhouse gases are steadily warming the Earth. The rate of warming is speeding up, and if we don’t control the situation soon we may trigger a “tipping point” in our planetary regulatory systems leading to runaway warming and the possible extinction of life on Earth.

Rapid warming occurred 55 million years ago in the Paleocene-Eocene Thermal Maximum when large-scale emissions of carbon to the atmosphere, as carbon dioxide and methane, warmed the earth by between five and nine degrees. Most species were able to adapt because global warming developed then about 10 times slower than the Earth is warming today. Current warming rates would overwhelm biological species. Ominously, several times atmospheric methane is currently frozen in Arctic permafrost and sub-seafloor frozen solid methane gas hydrate. The permafrost is thawing and the methane hydrate is destabilising as Arctic temperatures rise.

Global warming is accelerating and 2016 will be the warmest year ever recorded. The 2015 UN Climate Change Conference in Paris set a target of limiting global warming to less than 1.5 degrees over pre-industrial temperatures. This target will not be met and we will struggle to restrict warming to 2 degrees. We need to declare a global warming emergency and to initiate drastic remedial action.

William Reville is an emeritus professor of biochemistry at UCC. http://understandingscience.ucc.ie