Human extinction: is it possible?

An artist's rendition shows lightning striking the surface of planet Venus. Could Earth end up being as inhospitable toward life as Venus? Photo: European Space Agency

Human extinction: is it possible?
Julian Cribb, April 2, 2014 smh.com.au

Over the Earth’s history, about 99.9 per cent of all species to emerge have gone extinct. Many humans, however, cherish a notion that this doesn’t apply to us.

Typically, species survive for about 10 million years before they succumb to Mr Darwin – though there are notable long-distance champions, like sharks (420 million years), jellyfish (550 million years) and algae (2+ billion years). In evolutionary terms this means the human race is barely out of the starting blocks compared with these venerable competitors, having so far successfully covered less than a tenth of the standard course.

In recent years a number of prominent figures have warned of the possibility of human extinction as a result of man-made climate change. (I use the term "man-made" advisedly, as most of the people who excavate carbon for a living are males. Climate change is a gender issue too.) How could it come about that a species so intelligent, flexible and well-equipped could potentially destroy itself? Surely, it must be grand hype?

Jellyfish have existed on Earth for 550 million years.

Well, no. Not really. But extinction theory doesn’t depend entirely on climate change, at least in the first instance; rather, it depends on human behaviour and our response to peril.

The idea that man-made carbon emissions could trigger catastrophic global warming is based on two particular facts:

1. The fact that it has happened before, about 50 million years ago during an event called the Palaeocene-Eocene Thermal Maximum, PETM for short, when the Earth’s temperature increased by at least 5 degrees, and possibly as much as 9 or 10 degrees. This lasted about 200,000 years. The icecaps vanished, the oceans warmed as high as 35 degrees, corals almost disappeared. PETM was probably driven or accelerated by a vast release of seabed methane – a greenhouse gas more than 20 times more potent than CO2. Although PETM caused a severe setback to life in general, it wasn’t as bad as the KT extinction which occurred about 10 million years earlier and removed the dinosaurs.

2. The fact that there are vast stores of methane in the Arctic permafrost and as frozen gas deposits on the sea bed, known as clathrates or gas hydrates. These are basically the accumulated detritus from billions of years of decomposition of dead organisms – plants, animals and algae. Clathrate deposits are estimated at between 500-2400 billion tonnes of methane – or around three times the size of the planet’s estimated natural gas reserves. On top of these are tundra methane deposits estimated at 1500 billion tonnes. Together these two immense sources of carbon could boot global temperatures up by 5-10 degrees if they melt as a result of man-made warming of the Arctic and shallow seas around the continents.

What happens next is somewhat speculative, because it depends on incalculable factors in the Earth’s system – and in the human character. The issue is whether such large increases in global temperatures in turn trigger further irreversible feedbacks, releasing yet more greenhouse gases, in an episode known as runaway global warming. For example, the oceans begin to evaporate more rapidly and water vapour, being another greenhouse gas, accelerates warming.

The current scientific worst case scenario here is an increase in global temperatures of about 16 degrees, which would render much of the planet uninhabitable by humans and eliminate agricultural food production. Such a scenario might not spell extinction however – Siberia, the Canadian north and Antarctica might remain habitable for survivors using advanced technologies to produce food.

To view the absolute downside, you only have to go outside on a clear evening and look west. That bright star is Venus, where it is 465 degrees in the shade; the Venusian atmosphere is mostly CO₂ and 90 times heavier than ours. Being similar in mineral composition to Earth, Venus probably once had water and maybe oceans; faint traces remain in its atmosphere, the last vestiges of a catastrophic planetary warming episode. The message to Earthlings from the Evening Star is plain: this is what can happen to a planet if you release all your carbon and boil off your oceans.

However our own behaviour is liable to be a far more immediate determinant of human survival or extinction. Above two degrees – which we have already locked in – the world’s food harvest is going to become increasingly unreliable, as the Intergovernmental Panel on Climate Change warned this week. That means mid-century famines in places like India, China, the Middle East and Africa. But what scientists cannot predict is how humans living in the tropics and subtropics will respond to this form of stress. So let us turn to the strategic and military think tanks, who like to explore such scenarios, instead.

The Age of Consequences study by the US Centre for Strategic and International Studies says that under a 2.6 degree rise “nations around the world will be overwhelmed by the scale of change and pernicious challenges, such as pandemic disease. The internal cohesion of nations will be under great stress…as a result of a dramatic rise in migration and changes in agricultural patterns and water availability. The flooding of coastal communities around the world… has the potential to challenge regional and even national identities. Armed conflict between nations over resources… is likely and nuclear war is possible. The social consequences range from increased religious fervour to outright chaos.” Of five degrees – which the world is on course for by 2100 if present carbon emissions continue – it simply says the consequences are "inconceivable".

Eighteen nations currently have nuclear weapons technology or access to it, raising the stakes on nuclear conflict to the highest level since the end of the Cold War. At the same time, with more than 4 billion people living in the world’s most vulnerable regions, scope for refugee tsunamis and pandemic disease is also large. It is on the basis of scenarios such as these that scientists like Peter Schellnhuber – science advisor to German President Angela Merkel – and Canadian author Gwynne Dyer have warned of the potential loss of most of the human population in the conflicts, famines and pandemics spinning out of climate impacts. Whether that adds up to extinction or not rather depends on how many of the world’s 20,000 nukes are let off in the process. These issues all involve assumptions about human, national and religious behaviour and are thus beyond the remit of scientific bodies like the IPCC, which can only hint at what they truly think will happen. So you are not getting the full picture from them.

However in a classic case of improvident human behaviour, a global energy stampede is taking place as oil, gas, coal, tar sands and other miners (who, being technical folk, understand quite clearly what they are doing to the planet) rush to release as much carbon as possible as profitably as possible before society takes the inevitable decision to ban it altogether. Thanks to them, humanity isn’t sleep-walking to disaster so much as racing headlong to embrace it. Do the rest of us have the foresight, and the guts, to stop them? Our ultimate survival will be predicated entirely on our behaviour – not only on how well we adapt to unavoidable change, but also how quickly we apply the brakes.

Which form of human behaviour prevails will probably settle the extinction argument, one way or the other. It’s our call.