Natural weathering processes are removing CO2 from the air in a wide range of environments across continents and ocean. Until recently these 'CO2 vacuum cleaners' were often studied separately, without properly examining their complex interactions. Now, an international team of earth scientists is proposing an integrated vision of the many factors that influence the removal of atmospheric CO2 from the highest mountain peaks to the deep ocean floor, including their various interactions. The so-called weathering continuum provides a much more complete picture on what controls and regulates the natural removal of CO2, which could help in the development of enhancing weathering techniques.
The type of rock worn away by wind and water, the chemical reactions that break down rocks and convert them into soils and muds: all of this influences the rate at which CO2 is removed naturally from the air and is stored in the soils or the ocean. The efficiency of these CO2 vacuum cleaners has varied substantially in the Earth's past, which had researchers puzzled for over a century.
Weathering Continuum
Viewing the numerous chemical reactions of minerals on land and in the ocean as a single entity - a weathering continuum - now emerges from a new research paper, published in Nature Geoscience, involving numerous experts from various disciplines. "The main conclusion from our work is that the various CO2 fluxes on land and in the ocean are very closely linked. This governs the efficiency of the removal of CO2 from the atmosphere," says Dr Gerrit Trapp-Müller, a postdoctoral researcher at the Georgia Institute of Technology and the lead author of the study, which he did when he was still affiliated with Utrecht University.
Previous research had already shown that it is possible that the natural weathering processes can practically come to a halt – and sometimes even reverse, when the ocean starts to emit CO2. "Using the analogy of the vacuum cleaner, if intense vacuum cleaning has already filled up the device's storage unit, it eventually becomes less effective in cleaning - and may even blow out the dust back into your flat."
Reducing greenhouse effect
Compared to emissions from human activities, the natural processes that remove CO2 are relatively slow. Could this new research help us harness these natural CO2 vacuums to reduce the still increasing amounts of greenhouse gases in the atmosphere?
'Enhanced weathering' technologies could help to get somewhere close to the 1.5 or 2.0°C targets of the Paris Agreement, agrees Trapp-Müller. But he also cautions: "If weathering accelerates in some place, it can have consequences for the rest of the chain and the net amount of carbon stored." The weathering continuum warns of unforeseen consequences of enhanced weathering sites, but also provides guidance for how to harness the full potential of these techniques.
