Morton on the end of the carbon cycle

2009-03-03

in Geek stuff, Science, The environment, Writing

Golden sunset

Among many other things, Oliver Morton’s Eating the Sun discusses the carbon cycle across extremely long timespans. It highlights the existence of positive and negative feedbacks, which have historically constrained atmospheric concentrations of carbon dioxide to a particular range: with a high point established though increased emissions from volcanoes, and a low point established through the absorption of atmospheric carbon dioxide through the weathering of rocks.

The book predicts that, on the basis of astronomical and geological factors, this see-saw will eventually come to rest about a billion years from now: with the victory of erosion, and the permanent elimination of carbon dioxide from the atmosphere. As a consequence, photosynthesis will cease – for lack of building material – and the energy system that supports all complex life will collapse. Morton dubs this ‘the end of plants’ and the explanation of why it is to occur is difficult to compress into a blog post. It’s one of many reasons for which the book is worthwhile reading.

It’s a sobering perspective: akin to the knowledge that our sun will eventually fail, or that the Second Law of Thermodynamics and a universe expanding without end would combine to produce ‘heat death’ and an end to all chemical reactions everywhere.

That being said, it is essentially impossible for our minds to appreciate the meaning of a billion years, or anticipate how life (and humanity) would change across that span. Long, long before this final descent in the carbon cycle could be approached, we would have ceased to resemble our present forms; indeed, our current forms and future forms might not even be able to comprehend one another. After all, the Cambrian explosion, in which complex life forms like molluscs and crustaceans emerged, happened ‘only’ 530 million years ago.

Of course, even starting to approach that post-human future requires surviving the all-too-human threats we have created for ourselves, with climate change foremost among them. The billion-year carbon bust offers no prospect of avoiding the warming we are creating at the level of years and centuries. What Morton’s long-term perspective does offer, however, is a fairly strong assurance that life can adapt to most any set of climatic circumstances we might be able to create. Of course, ‘life’ writ large is far more adaptable and resilient than our present form of civilization, which may be quite impossible to propagate in a world where temperatures are more than 5˚C higher, on average, glaciers and icecaps are gone, the oceans are acid, and precipitation patterns have changed dramatically.

It is both startling and entirely possible that human civilization, for all its accomplishments, will prove less adept at responding to large-scale changes in climate than ancient sharks or turtles have done.

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{ 8 comments… read them below or add one }

mek March 3, 2009 at 9:01 am

Ahhh, the impermanence of all things.

R.K. March 3, 2009 at 9:25 am

With the Cambrian explosion 0.5 billion years ago, and the ‘end of plants’ estimated at 1 billion years from now, are we 1/3 of the way through the period of complex life on Earth?

Anon March 3, 2009 at 11:11 am

If there are still intelligent, technology-using creatures in a billion years, I think they will probably be able to either maintain the habitability of Earth or build self-sufficient colonies.

After all, we only started farming 10,000 years ago.

Milan March 3, 2009 at 12:19 pm

This previously posted video gives a sense of the timespans between the formation of the Earth and the Cambrian, as well as between the Cambrian and now.

. August 20, 2010 at 11:40 am

Fate of Universe revealed by galactic lens
By Howard Falcon-Lang Science reporter

Astronomers used the way that light from distant stars was distorted by a huge galactic cluster known as Abell 1689 to work out the amount of dark energy in the cosmos.

Dark energy is a mysterious force that speeds up the expansion of the Universe.

Understanding the distribution of this force revealed that the likely fate of the Universe was to keep on expanding.

It will eventually become a cold, dead wasteland, researchers say.

. August 25, 2013 at 9:26 pm

Rocks Can Restore Our Climate … After 300,000 Years

July 26, 2013 — A study of a global warming event that happened 93 million years ago suggests that the Earth can recover from high carbon dioxide emissions faster than thought, but that this process takes around 300,000 years after emissions decline.Scientists from Oxford University studied rocks from locations including Beachy Head, near Eastbourne, and South Ferriby, North Lincolnshire, to investigate how chemical weathering of rocks ‘rebalanced’ the climate after vast amounts of carbon dioxide (CO2) were emitted during more than 10,000 years of volcanic eruptions

In chemical weathering CO2 from the atmosphere dissolved in rainwater reacts with rocks such as basalt or granite, dissolving them so that this atmospheric carbon then flows into the oceans, where a large proportion is ‘trapped’ in the bodies of marine organisms.

The team tested the idea that, as CO2 warms the planet, the reactions involved in chemical weathering speed up, causing more CO2 to be ‘locked away’, until, if CO2 emissions decline, the climate begins to cool again. The Oxford team looked at evidence from the ‘Ocean Anoxic Event 2’ in the Late Cretaceous when volcanic activity spewed around 10 gigatonnes of CO2 into the atmosphere every year for over 10,000 years. The researchers found that during this period chemical weathering increased, locking away more CO2 as the world warmed and enabling the Earth to stabilise to a cooler climate within 300,000 years, up to four times faster than previously thought.

. August 25, 2013 at 10:22 pm

Lithium isotope evidence for enhanced weathering during Oceanic Anoxic Event 2

The Ocean Anoxic Event 2 (OAE2) about 93.5 million years ago was marked by high atmospheric CO2 concentration, rapid global warming and marine anoxia and euxinia. The event lasted for about 440,000 years and led to habitat loss and mass extinction. The marine anoxia is thought to be linked to enhanced biological productivity, but it is unclear what triggered the increased production and what allowed the subsequent rapid climate recovery. Here we use lithium isotope measurements from carbonates spanning the interval including OAE2 to assess the role of silicate weathering. We find the lightest values of the Li isotope ratio (δ7Li) during OAE2, indicating high levels of weathering—and therefore atmospheric CO2 removal—which we attribute to an enhanced hydrological cycle. We use a geochemical model to simulate the evolution of δ7Li and the Ca, Sr and Os isotope tracers. Our simulations suggest a scenario in which the eruption of a large igneous province led to high atmospheric CO2 concentrations and rapid global warming, which initiated OAE2. The simulated warming was accompanied by a roughly 200,000 year pulse of accelerated weathering of mafic silicate rocks, which removed CO2 from the atmosphere. The weathering also delivered nutrients to the oceans that stimulated primary productivity. We suggest that this process, together with the burial of organic carbon, allowed the rapid recovery and stabilization from the greenhouse state.

. October 18, 2013 at 2:08 pm

Complicated animals such as humans, animals and most plants have even less time remaining; perhaps a billion years or so. As the sun gradually brightens, the level of carbon dioxide in the air will fall, regardless of any temporary, millennia-long blips caused by footling things such as a civilisation based on fossil fuels. One day, far in the future, the plants that form the base of the food chain will find themselves no longer able to photosynthesise. When that happens, complex life will die out, and the bacteria will re-inherit Earth.

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