Enhanced weathering

Enhanced weathering

Subject – Environment

Context – An international team, which studied a global temperature rise that occurred 56 million years ago, has found that it took about 20,000 to 50,000 years for the climate to stabilise after the rise of five to eight degrees Celsius.

Concept –

• About 56 million years ago, our Earth experienced a natural period of global warming triggered by a volcanic eruption. This period was known as the Paleocene-Eocene Thermal Maximum (PETM) and there were huge amounts of carbon dioxide released into the atmosphere.
  • This caused about 8° C Surface Ocean warming in the high latitudes.
  • Several studies have shown that during this period ocean acidification caused mass extinctions in the deep ocean and there were changes in the biota in the surface ocean.
• Due to global warming, there would have been weathering of rocks. These dissolving rocks release lithium into surrounding water bodies and by studying the isotopes of lithium we can understand the amount of erosion.
  • Clay minerals from the bottom of the sea were used to study the lithium isotopes stored in water.
• Lithium has the advantage that it is one of the very few elements that is not used by biology or plants at all. So signals from growing or dying plants don’t affect lithium.
  • Also, Lithium isotopes (Li-6 and Li-7) have their relationship (ratio) to each other changed by the weathering process – Li-6 is preferentially retained in clays that form during weathering.
• The difference between the PETM and the present is that the PETM had more warming (up to 8°C) but was slower, but what we’re seeing at the moment is probably 3-4°C (worst case), but much much quicker than the PETM.
• Using weathering to artificially remove CO2 from the atmosphere on more useful timescales – this process is known as ‘enhanced weathering’.
  • You speed up weathering by grinding up rock into powder (so it weathers faster) and ploughing it into fields, where it should remove CO2 and act as a fertiliser. This is now at the field experiment stage in several places around the world.
  • It will never remove all the CO2 we’re adding to the atmosphere, but if we manage to significantly reduce emissions, processes such as enhanced weathering could remove the rest, and help us with ‘negative emissions’, that is removing more CO2 than we add, and reducing CO2 concentrations.