I’ll begin with a flashback – right back to the Middle Ages. For medieval people, the entire cosmology from creation to apocalypse spanned only a few thousand years. They were bewildered and helpless in the face of floods and plagues and were prone to irrational dread. Large parts of the Earth were terra incognita.

At the same time, they were great architects and builders: they created cathedrals, constructed with primitive technology by masons who knew they wouldn’t live to see them finished. Vast and glorious buildings that still inspire us centuries later.

What will inspire future generations in coming centuries? I’m an astronomer, hence, let’s start with a cosmic perspective. Earth has existed for 45 million centuries. Throughout most of history, the benefits we garner from the natural world have seemed an inexhaustible resource; and the worst terrors to confront humans – floods, earthquakes, and diseases – came from nature, too.

But this is the first century in which humans became the dominant species who can determine, for good or ill, the future of the entire biosphere. We’re deep in what some have called the Anthropocene era.

The worst threats to humanity are no longer natural ones: they are caused or aggravated by us. The backdrop to current geopolitical challenges is a world where humanity’s collective footprint is getting heavier.

There are about eight billion of us on this planet – twice as many as in the 1960s. The collective demands on energy and resources aren’t sustainable without new technology.

Novel bio and cyber technologies are socially transformative but threaten severe damages if misapplied.

Looming over us all is the threat of human-induced climate change. This is potentially like a global fever, in some ways resembling a slow-motion version of Covid-19. For instance, both crises aggravate the level of inequality within and between nations.

Climate change and environmental degradation may well, later this century, have global consequences even graver than those of pandemics and indeed be irreversible in the long term. But a potential slow-motion catastrophe doesn’t engage the public and politicians. Politicians have minimal incentive to address longer-term threats that aren’t likely to occur while they’re still in office, and which are global rather than local.

We’re aware of the threats but fail to prioritize countermeasures because their worst impact stretches beyond the time horizon of political and investment decisions. Our predicament resembles that of the proverbial boiling frog contented in a warming tank until it’s too late to save itself.
 

The most relevant differences between the Apollo era and the mid-2020s are the amazing improvements in our ability to create, launch, and guide robot explorers. These are exemplified by the suite of rovers on Mars. Perseverance, NASA’s latest prospector, can drive itself through rocky Martian terrain with only limited guidance from Earth.

Furthermore, improvements in sensors and in artificial intelligence will enable the robots themselves to identify particularly interesting sites from which to gather samples for return to Earth.

The same is true for the mining of rare minerals. Harrison Schmidt is one of the two last people to walk and drive a buggy on the Moon. As a Senator, today he advocates massive strip mining to extract helium 3 to be used as fuel in fusion reactors.

By 2100, intrepid thrill-seekers may have established bases independent from the Earth. But don’t ever expect mass emigration from our planet. It’s a dangerous delusion to think that space offers an escape from Earth's problems. Dealing with climate change on Earth is a doddle compared to terraforming Mars. There’s no Planet B for ordinary risk-averse people. We must cherish our earthly home.

Still, we and our progeny here on Earth should cheer on the brave space adventurers, because they will play a pivotal role in spearheading the post-human future and determining what happens in the 22nd century and far beyond. This is why.

The pioneer explorers will be ill-adapted to their new habitat. They will have a more compelling incentive than those of us on Earth to re-design themselves. They’ll harness the super-powerful genetic and cyborg technologies that will be developed in coming decades.

This might be the first step towards divergence into a new species. So, it’s these spacefaring adventurers, not those of us comfortably adapted to life on Earth, who will spearhead the post-human era.

But life would be uncomfortable on Mars or even on the Moon. There’s no atmosphere that humans can breathe; they’d face dangerous levels of radiation and a huge range of temperatures. Their lives will need to be spent underground. I don’t think those on Earth will envy them.

We can’t confidently predict what transformative discoveries will have been made by then or the amazing technologies they may have spawned. One must certainly hope that the welfare and resource gap between the prosperous North and the Global South will have been narrowed – a development that will have required massive efforts to construct new infrastructure worldwide.

A benign scenario would nonetheless leave a large fraction of each region close to a natural state, preserving at least the present level of diversity in wildlife and vegetation. Energy would be derived from clean sources. All industrial production would be as pollution-free as possible: indeed, some manufacturing could be carried out in space.

There would be a network of underground fibre and cables to carry energy and information, offering security and high redundancy. Water would, wherever necessary, be pumped great distances to alleviate droughts in any region.

If there is to be widespread adoption of nuclear fission energy to supply base load, the problem of safe underground disposal of radioactive waste will need to have been solved and huge repositories constructed.

Wherever possible, buildings would be long-lived; if they had a short lifetime, they would be built from materials that were recyclable or reusable.

But there is a contrasting scenario, a doom-laden one. Our generation could, through poor planning and lack of foresight this century, bequeath to our descendants a world still dependent on fossil fuels. Continuing rises in CO2 levels would have led to a much-changed climate, triggering tipping points that have induced irreversible changes.

Large areas of our coastal cities will need to be evacuated because of rising sea levels. Among the highest-priority construction projects worldwide would be seawalls and embankments to protect against rising sea levels and more violent storms.

It’s crucial that the governments of our countries ensure that we’re good ancestors, leaving a positive legacy for future generations in coming centuries rather than snuffing out the progress already achieved and leaving a bleak and devastated biosphere.