Global Warming – A Geological Perspective

The carbon-silicate cycle.

A recent study by scientists at Columbia University has come up with an interesting method of removing carbon from the atmosphere, with the aim of reducing greenhouse gases and global warming. When CO2 comes into contact with peridotite, a rock commonly found in the Earth’s mantle but more rarely on the surface, it turns into solid, inert minerals like calcite. The Sultanate of Oman has large amounts of peridotite exposed on the surface and geologist Peter Kelemen and geochemist Juerg Matter say the naturally occurring process can be harnessed to grow underground minerals that can permanently store two billion tonnes of CO2 emitted. by human activity each year. Source-Reuters/IOL Timothy Gardner

Al Gore has been campaigning for reductions in greenhouse gas emissions, and the Kyoto Protocol expires in 2012, and yet we are no closer to achieving a significant reduction in greenhouse gas emissions. . However, I am not going to address the cudgels of climate change at this stage, but rather dwell on an amazing system that, in the long term, ensures that the Earth’s climate stays within certain limits that keep our planet habitable: the carbon silicate. cycle.

We may be able to negatively influence the climate for centuries or even decades, but if we look at the problems from a geological point of view, these human-induced disturbances in the wide variety of geological cycles are inconsequential and will not affect long-term fertility. of the planet. However, we can suffer tremendously during these short-term disturbances: a 5 degree rise will make large portions of our planet uninhabitable. Our distorted sense of importance as a species makes us worry about our future on Planet Earth, but if we can accept that our dominance might be nothing more than a lucky roll of the evolutionary dice, and that the survival of the human species is inconsequential . to the future of the planet, then we can, to some extent, stop worrying about our supposed role in the grand scheme of the universe. Like it or not, we will eventually go extinct, but life in a myriad of different forms will continue until the sun’s last supernova.

But let’s move from philosophy and speculation to some hard facts about our immediate environment and how Earth’s climate stays within all those important limits. Most of us are aware of continental drift and plate tectonics, where the Earth’s crust is recycled by subduction of plates along plate margins. The sinking plate descends into the Earth’s fiery interior where it melts and its constituent elements return to the rock cycle through volcanic action.

One of the most important elements in this cycle is calcium, used extensively by organisms, including humans, to build shells and bones. Add a little carbonic acid to the mixture and you get the formation of calcium carbonate – CaCO3 – the most frequent form is limestone. Limestones are one of the most common sedimentary rocks and generally represent ancient coral reefs preserved in the geological record. Coral reef development sequesters large amounts of atmospheric carbon over millions, sometimes billions, of years until the limestones become trapped in the tectonic mill or exposed to the agents of weathering and erosion. The more CO2 there is in the atmosphere, the faster limestone formation will occur, provided there is enough calcium available.

The question is, what is the source of the calcium? It is derived from igneous, sedimentary, and metamorphic rocks brought to the surface by volcanic action due to plate tectonics. The same eruptions that spew CO2 into the air deliver the chemical needed to remove it, thus keeping things in balance. wow!

Now we need a source of carbonic acid. Weathering of silicates (feldspars and micas) in common rocks such as granites and sandstones produces calcium, silicon, water, and the important carbonic acid. Now, as we have already seen, the more CO2 there is, the faster the limestone forms, thus removing the same CO2 from the system. Similarly, the higher the concentration of CO2, the warmer the planet gets, an unfortunate fact that we are discovering at our expense. This leads to increased evaporation, which leads to increased precipitation and associated increased weathering.

The greater the amount of weathering, the greater the formation of carbonic acid, which in turn leads to faster production of limestone. This of course speeds up the removal of CO2 from the atmosphere and ultimately cools the planet. Cooling then slows the rate of weathering, carbon levels rise, and the Earth warms once again. What a wonderful, self-regulating, fantastic system! But it takes more than a few decades or centuries to smooth out variations in atmospheric carbon. Cold comfort perhaps knowing that high levels of carbon in the atmosphere will ultimately be removed by the silicate carbon cycle, but certainly not in the immediate future. Using peridotite technology may be a short-term but expensive solution to removing carbon from the atmosphere, but it’s clear that there is a much more efficient machine to do it, although those wheels will take several thousand years to turn.