Every time I mention a Brian Aldiss novel, I have to be careful to check the original title against the one published in the US. The terrific novel Non-Stop (1958) became Starship in the States, rather reducing the suspense of decoding its strange setting. Hothouse (1962) became The Long Afternoon of Earth when abridged in the US following serialization in The Magazine of Fantasy & Science Fiction. I much prefer the poetic US title with its air of brooding fin de siècle decline as Aldiss imagines our deep, deep future.
Imagine an Earth orbiting a Sun far hotter than it is today, a world where our planet is now tidally locked to that Sun, which Aldiss describes as “paralyzing half the heaven.” The planet is choked with vegetation so dense and rapidly evolving that humans are on the edge of extinction, living within a continent-spanning tree. The memory of reading all this always stays with me when I think about distant futures, which by most accounts involve an ever-hotter Sun and the eventual collapse of our biosphere.
Image: The dust jacket of the first edition of Brian Aldiss’ novel Hothouse.
Indeed, warming over the next billion years will inevitably affect the carbon-silicate cycle. Its regulation of atmospheric carbon dioxide is a process that takes CO2 all the way from rainfall through ocean sediments, their subduction into the mantle and the eventual return of CO2 to the atmosphere by means of volcanism. Scientists have thought that the warming Sun will cause CO2 to be drawn out of the atmosphere at rates sufficient to starve out land plants, spelling an end to habitability. That long afternoon of Earth, though, may be longer than we have hitherto assumed.
A new study now questions not only whether CO2 starvation is the greatest threat but also manages to extend the lifetime of a habitable Earth far beyond the generally cited one billion years. The scientists involved apply ‘global mean models,’ which help to analyze how vegetation affects the carbon cycle. Lead author Robert Graham (University of Chicago), working with colleagues at Israel’s Weizmann Institute of Science, is attempting to better understand the mechanisms of plant extinction. Their new constraints on silicate weathering push the conclusion that the terrestrial biosphere will eventually succumb to temperatures near runaway greenhouse conditions. The biosphere dies from simple overheating rather than CO2 starvation.
The implications are intriguing and offer fodder for a new generation of science fiction writers working far-future themes. For in the authors’ models, the lifespan of our biosphere may be almost twice as long as has been previously expected. Decreases in plant productivity act to slow and eventually (if only temporarily) reverse the future decrease in CO2 as the Sun continues to brighten.
Here’s the crux of the matter: Rocks undergo weathering as CO2 laden rainwater carrying carbonic acid reacts with silicate minerals, part of the complicated process of sequestering CO2 in the oceans. The authors’ models show that if this process of silicate weathering is only weakly dependent on temperature – so that even large temperature changes have comparatively little effect – or strongly CO2 dependent, then “…progressive decreases in plant productivity can slow, halt, and even temporarily reverse the expected future decrease in CO2 as insolation continues to increase.”
From the paper:
Although this compromises the ability of the silicate weathering feedback to slow the warming of the Earth induced by higher insolation, it can also delay or prevent CO2 starvation of land plants, allowing the continued existence of a complex land biosphere until the surface temperature becomes too hot. In this regime, contrary to previous results, expected future decreases in CO2 outgassing and increases in land area would result in longer lifespans for the biosphere by delaying the point when land plants overheat.
How much heat can plants take? The paper cites a grass called Dichanthelium lanuginosum that grows in geothermal settings (with the aid of a symbiotic relationship with a fungus) as holding the record for survival, at temperatures as high as 338 K. The authors take this as the upper temperature limit for plants, adding this:
Importantly, with a revised thermotolerance limit for vascular land plants of 338 K, these results imply that the biotic feedback on weathering may allow complex land life to persist up to the moist or runaway greenhouse transition on Earth (and potentially Earth-like exoplanets). (Italics mine)
The long afternoon of Earth indeed. The authors point out that the adaptation of land plants (Aldiss’ continent-spanning tree, for example) could push their extinction to even later dates, limited perhaps by the eventual loss of Earth’s oceans.
…an important implication of our work is that the factors controlling Earth’s transitions into exotic hot climate states could be a primary control on the lifespan of the complex biosphere, motivating further study of the moist and runaway greenhouse transitions with 3D models. Generalizing to exoplanets, this suggests that the inner edge of the “complex life habitable zone” may be coterminous with the inner edge of the classical circumstellar habitable zone, with relevance for where exoplanet astronomers might expect to find plant biosignatures like the “vegetation red edge” (Seager et al. 2005).
The paper is Graham, Halevy & Abbot, “Substantial extension of the lifetime of the terrestrial biosphere,” accepted at Planetary Science Journal (preprint).
Hothouse is an excellent novel. Obviously quite dated now, but still a good read
Yes, as are so many of the Aldiss novels of that period. Well worth re-reading.
How is a story set 3 billion years in the future dated? :^)
https://brianaldiss.co.uk/writing/novels/novels-h-l/hothouse/
At 338 K (65 C), mammals will no longer be part of the biosphere unless there are refuges where the temperature is much lower. The Eocene Thermal Maximum was about 6C greater than today, and even the Permian extinction had estimated average surface temperatures of up to 25 C. Any animals will have to adapt to this extreme heating, probably retreating to the poles, underground, and in the deep ocean.
But we should disabuse ourselves of the vision of complex life on the surface, like the dense tropical vegetation in “Hothouse”. We know extremophiles can survive in temperatures of up to 121 C. The temperatures below ground are far more stable and likely protective. This suggests microorganisms, probably bacterial or archaeal, will be the last type of life on Earth.
If Earth was to become tidally locked, that would be a saving grace, as it would allow for temperate conditions along the terminator. The problem is the transition from current day-night cycles to reach that point. Mobile animals like fish might migrate to maintain their temperatures, but this is not an option for land-living animals, plants, and relatively immobile animals.
Cixin Liu’s “Wandering Earth” nooks seem like the better path if we could manage it. Move the Earth outwards to maintain an equitable temperature, slowly enough to allow for annual reproduction rates to evolve with the longer years, or perhaps engage in “star lifting” to remove mass from the sun to offset its heating. One can only hope our descendants have the technology to ensure that our terrestrial life is not lost and can be spread to other star systems that are currently sterile.
Even if humans last another million years, this is an eyeblink in the deep time being envisaged. Surely within that time, we will have come up with solutions for protecting our biosphere, from sunshades to more drastic approaches as the sun becomes a red giant billions of years in the future.
If we are to become gods, we really should learn to act beneficently towards our home world.
@Tolley. Earth husbandry versus resource exploitation; a lot has to change.
It is interesting that the dense vegetation, usually in tropical jungles, is the setting for “the unknown”. Aldiss had uncontrolled vines invading the corridors of the starship in “Non-Stop”. He revisited a tropical world in “Helliconia Summer”.
4 posts ago, the intro included Burroughs’ Mars (Barsoom) stories. Mars was depicted as a drying world much like Lowell’s speculations. But Burroughs’ other famous stories were his Tarzan stories set in the African jungle, a place where there could be undiscovered people and wonders just over the hill.
I suspect our East African Plains Ape ancestry is responsible for this viewpoint. Unlike our ape cousins, we left the dense forests to live on the Savannahs. The greater distances we could see are reflected in our preferred landscapes and landscape paintings. Conversely, the forests are places of fear, where bad things happen. We admonished our children to stay away from the forests with tales like “Red Riding Hood” and “Hansel and Gretel”. Movies like “The Cabin in the Woods” and of course, the Jurassic Park franchise emphasize the darkness of the forest and the dangers hiding nearby.
The contemporary Amazon basin in Brazil, as well as the jungles of Mexico, once almost impenetrable mysteries away from the rivers, are now revealing their secrets as LIDAR reveals structures beneath the tree canopy. Our distance vision is restored with different wavelengths, as well as our ability to fly and orbit over the Earth.
It is ironic that we are now pushing for greater reforestation to try to ameliorate rising CO2 levels. The new fashion for building engineered wood high rises to consume new forest growth and store carbon in wood is a related part of that response.
Yes, I thought about that Non-Stop connection and almost mentioned it. You clearly know your Aldiss, Alex!
Exploring deep time is something that may save science fiction. I’m interested in exploring where the genre can take us when so many themes have been shut off or moved into the realm of fantasy?
Themes closed off:
time travel is likely impossible (we haven’t been visited),
interstellar transportation of life is impossible (also, we haven’t been visited),
mind reading, teleportation, and other psychic abilities are impossible (never demonstrated credibly) and
various kinds of super powers are impossible (by correct understanding of physics and biology).
Where does the genre go from here. I’m nostalgic for “Starman Jones”, Heinlein, 1953.
I’ve had two separate conversations about Starman Jones in the past month with people who are likewise nostalgic. I absolutely loved that one and have re-read it a number of times since.