The Climate Question · BBC World Service

Can nature help us to store carbon?

·23 min·2 clips

Dr Steve Smith reveals 15 different ways to pull carbon from the air, from planting trees to chemical capture.

1. The Climate Question from BBC World Service investigates whether kelp and enhanced rock weathering can serve as meaningful carbon dioxide removal solutions. 2. Host Greer Jackson guides the episode, joined by Dr. Steve Smith (Oxford University, Arnell Associate Professor of Greenhouse Gas Removal), Alt Carbon co-founder and CEO Shreya Garwal, and Dr. Raymond Ward (reader in marine sciences, Queen Mary University of London). 3. The episode asks whether nature-accelerated processes — grinding rock and growing seaweed — can absorb enough atmospheric CO2 to matter for the 1.5°C climate goal. 4. Dr. Steve Smith identifies at least 15 distinct carbon dioxide removal pathways, ranging from tree-planting and wood products to mineral reactions and direct air capture chemicals. 5. Enhanced rock weathering works by crushing volcanic basalt — rich in calcium and magnesium — into powder and spreading it on soils, where it reacts with CO2 dissolved in rainwater to form stable carbonate. 6. The reaction either washes the carbonate into the ocean or fixes it as solid carbonated rock, both of which Smith describes as "pretty permanent" forms of carbon storage. 7. Reporter Chavi Sakdev visits the Salem Hill Tea Estate, a 1,000-acre property near Darjeeling where Alt Carbon has been trialing basalt application on 300 acres of tea plantation. 8. Shreya Garwal, a fourth-generation tea planter who bought the garden during COVID-19, says the estate's subtropical temperatures and high monsoon rainfall accelerate rock weathering rates significantly. 9. Garwal says the basalt releases nutrients into degraded soil, producing a 15-20% increase in tea yields and improving tea-leaf colour and biomass quality. 10. Alt Carbon's carbon removal cost is $200-$250 per tonne; Dr. Smith contextualises this as competitive, noting some projects exceed $700 per tonne while newer methods are reaching around $150. 11. Garwal's target is for India to become "the carbon removal hub for the world," citing a goal of removing a billion tonnes per year — comparable to the total annual emissions from global aviation. 12. Dr. Smith says scientific models examined by the IPCC suggest that staying near 1.5°C may require scaling carbon removal to between several hundred million and 10 billion tonnes per year by 2050. 13. Dr. Raymond Ward takes the host diving off Bognor Regis, identifying Laminaria digitata (common kelp) alongside sea oak and a small-spotted catshark below the surface. 14. Ward explains that kelp stores carbon in its holdfast, stipe, and blade, and that during winter storms broken fronds are carried by ocean currents into deep, anoxic (oxygen-free) sediments where bacteria cannot break them down. 15. A study cited from Nature Geoscience estimates that seaweeds worldwide sequester 173 million tonnes of carbon per year — more than the Philippines emitted in 2023. 16. Ward notes kelp also dampens coastal wave energy to reduce erosion, purifies water by absorbing contaminants, and supports commercially important fish species including bass, bream, and wrasse. 17. The episode blends BBC field reporting with studio interviews, combining ambient sound from tea gardens and coastal dives with straightforward expert explanation. 18. The tone is exploratory and journalistic, moving between field scenes and direct Q&A without advocacy or alarm, and the presenter participates physically — swimming in 14°C water off Sussex. 19. Listeners curious about emerging climate technology, nature-based solutions, or the economics of carbon removal will find concrete numbers and on-the-ground reporting. 20. Listeners seeking deep policy analysis or technical debate about carbon accounting methodologies will find the episode too introductory.

As heard by us

Two carbon-removal bets are tested in the field, with a needed reminder that cuts still matter.

The episode makes a large climate question feel concrete by moving between two bets: kelp in cold seas and basalt dust on tea gardens in Darjeeling.

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You get climate solutions you can picture, not just talk about.

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