Sunday, July 28, 2019

If It's Not One Tham Ding It's Another: "The Greatest Long-Term Threats Facing Humanity"

Grandmother didn't swear so she said 'tham ding'.
The grandchildren knew what she meant.

From the BBC, July 19:

How long can civilisation survive? To thrive for billions of years, there will be a few troublesome problems to solve – from the death of the Sun to the decay of matter.
Can we actually say anything about the far future? If we can’t predict when it will rain next month, forecasting billions of years hence might seem impossible.

However, not everything is as chaotic as the weather: even predictions very far ahead are sometimes possible, especially in astrophysics and cosmology. We can be confident that there will be a total solar eclipse in the UK on 23 September 2090 because the Moon, Sun and Earth move in stable, predictable orbits with very minor disturbances, and the laws of gravity are now well-tested. Similarly, we can use known astrophysics to predict what will likely happen across the Universe as it expands.
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This approach can be described as “physical eschatology” – a term coined by the astronomer Martin Rees for using astrophysics to model where the Universe is going. Rees took a cue from theology, in which “eschatology” is the study of ultimate things such as the end of the world. And the classic paper on the topic is Freeman Dyson’s 1979 paper on life in open universes, which outlined likely or possible existential catastrophes that could threaten life far into the future, from the death of the Sun to the detachment of stars from galaxies.

So, what are the biggest challenges humanity will face if we survive into the far future? We cannot say how (or if) they will be overcome (I will make some guesses) but we can be confident these threats to our existence are coming.

Problem 1: Survive better than other mammals
The typical lifespan of a mammalian species is about a million years or so. From nuclear war to bioengineered pandemics, humanity clearly has other risks it needs to reduce urgently: right now the natural extinction rate is far smaller than risk we pose to ourselves.

Were we to fix our current existential risk and sustainability problems we would still have to deal with some other challenges to stay around.

For starters, in a few tens of thousands of years we will have to cope with the end of the current interglacial period: we are living during a brief interruption of a long ice age. Our ancestors have survived ice ages, so it is likely not a big deal – except that they were nomadic hunter-gatherers rather than a global civilisation.

We may also face dramatic climate variations between different geological eras. In the past the Earth has been not just colder, but also warmer. During the Eocene, temperatures were 10C warmer, with palms and alligators in the Arctic and equatorial regions too hot for unprotected humans to survive in. Even further in the past there has been “snowball Earth” episodes where almost all of the Earth was covered with ice.
Then there is the risk of supervolcanism, meteor impacts, gamma ray bursts, or emergent ecological disruptions, which we know have led to natural mass extinctions about once every 100 million years....MORE