Recently, I came across a foundation, FuturZwei, taking a ‘sideways view’ of sustainability. FuturZwei studies and promotes issues overlooked in official environmental, social and governance metrics. Its key concern seems to be the possibility of ‘running out’ – running out of habitable land; of storage space for CO2, hazardous wastes and landfill and of natural resources.
I decided I had best run the numbers for cement and its principal natural resource, limestone. Using the United States Geological Survey’s 2024 cement and lime production estimates (ignoring their respective 2% and 1% year-on-year declines)1 and a best guess for total global limestone of 67.5 quintillion tonnes,2 the industries will reach material exhaustion in the year 12,243,524. Not this millennium’s problem, or this megaannum’s, then, but worth bearing in mind.
This rests on two large assumptions: firstly, continued population growth and development in a straight line; secondly, a drop-off in technological change. It is as if humanity should keep on expanding to fill its ‘container’ and, for the first time in history, not lift a finger to find a way out.
Then there’s the real runaway feedback loop of rising temperatures and atmospheric CO2. Catastrophising about ‘peak limestone,’ appealing though it may be to our instincts for preservation, is fanciful at best. At worst, it can become the basis for a greenwashing grift to sell advocacy and dubious accreditations.
Still, I found myself thinking about 12,243,524 – not as a mythical tipping point, but as the other end of a comparatively short geological timespan. Is this new, accelerated, anthropogenic limestone cycle itself a cause for concern? It’s really too much stone to conceive of all at once – it will help to zoom in a little.
In South East Asia, 900,000km2 of turrets, gorges and caves extend from southern China to Timor-Leste. This is the karst, a body of limestone deposited over the past 500 million years in which the region lay at its present latitude, mostly submerged below tropical waters.
In Vietnam alone, over 100Mt of the karst’s limestone left the ground at 350 quarries in 2024.3 “Approved quarries have not yet satisfied the long-term demand of production,” according to state-owned cement producer VICEM.
Karsts are ‘biodiversity arks’ for their endemic species, and provide people with food and fertiliser. They can become valuable tourist attractions; they contain invaluable treasures. 51,000-year-old cave art in the Indonesian karst at Maros-Pangkep in Sulawesi, the oldest in the world, is fading, conservators say due to fumes and vibrations from limestone mining.4
Quarrying triggers erosion, which spreads through karsts’ thin soils. Large karsts also form even vaster aquifers, so local disruptions to water flow or quality can spell regional disaster. New mine licences are conditional upon proper management plans to address these issues, but the sheer rate of growth has beguiled efforts at over-arching planning. National parks, nature reserves and conservation areas cover 7% of Vietnam’s land area, leaving at least 56,000km2 of karst unprotected; so are 20,000km2 in Cambodia and 80,000km2 in Myanmar.
The preservation of cultural heritage and tourism were the stated reasons for the Cambodian government’s recent cancellation of licences for six quarries, across 4.6km2 of Kampong Trach, Kampot. Back in Vietnam, the government’s 2030 cement development strategy should place karst management at an ‘international’ standard, on pain of plant closures. Even where South East Asian cement is still expanding, its messaging is increasingly muddled. When Borneo Cement (Sabah) announced its upcoming US$270m Tongod plant in Malaysia, it even advertised its mining operations as a window to Borneo’s limestone-based ecosystems for industrial-ecotourists.
In practice, exploitation continues apace. We hear about natural and cultural products under threat precisely because these are the ones that have been discovered, registered and protected. Elsewhere, exploitation outstrips exploration.
Limestone as a resource will not run out; limestone in its broader sense, as a foundation for complex systems, is declining dangerously. Thought experiments about an Earth where an unchanging cement industry serenely extracts all the limestone down to the last lump are fun – just as long as we don’t forget the scientific and political efforts needed on this Earth!
References
1. USGS, Mineral Commodity Summaries, 31 January 2025, https://pubs.usgs.gov/periodicals/mcs2025/mcs2025.pdf
2. World Economic Forum, ‘Visualizing the abundance of elements in the Earth’s crust,’ 14 December 2021, www.weforum.org/stories/2021/12/abundance-elements-earth-crust/
3. Hanna, ‘Vietnam’s Advantages in Limestone Market,’ 2 October 2023, www.linkedin.com/pulse/vietnams-advantages-limestone-market-hanna/
4. TanaHair, ‘Climate Change and Exploitation Threaten Ancient Cave Paintings in Sulawesi,’ 10 February 2025, tanahair.net/climate-change-
and-exploitation-threaten-ancient-cave-paintings-in-sulawesi/
