We will all face the consequences of runaway climate change. Unless, maybe, you live in one of Elon Musk's new homes on Mars. But for the rest of us poor souls, tackling global heating is pretty much the top priority.

The bad news is that we are not on track to limit global temperature rise to 1.5°C. A new report has also revealed that temperatures in Europe are rising twice as fast as the rest of the world.

We need to make drastic cuts in emissions. We also need to pull out some of the carbon we've already put in. This may conjure up visions of giant, air con-like machines sucking carbon out of the air. But carbon removal comes in many forms.

Remove, an Amsterdam-based accelerator programme for carbon removal startups, recently unveiled its latest cohort. It consists of 20 early-stage companies championing everything from microalgae biorefineries to biochar-based concrete.

Some of them are simply weird — and many, wonderfully simple.

Burying trees underground

A Dutch startup is planning an obscure but straightforward way to keep the carbon trees pull from the air locked away. They will bury it underground.

Trees are great at absorbing huge quantities of CO2, but they release the carbon again when they die and rot. Burying them could fix this problem.

Underground Forest plans to cut down old spruce trees, dig holes in wetlands, and drive the poles into the soil. It will plant new trees in their place.

“We can permanently remove up to a gigaton [of CO2] per year,” Kees de Gruiter, founder of Underground Forest, told TNW. He sees biomass burial working alongside other carbon removal technologies like Direct Air Capture (DAC).

De Gruiter says the wooden piles can also act as a foundation for houses. Over a thousand years ago, the people of Venice, Italy, built the city on over 10 million similar wooden piles.

While biomass burial is largely unproven, it's nevertheless attracting attention from climate tech investors. One startup, US-based Kodama Systems, has raised over $6mn from Bill Gates' Breakthrough Energy to scale its biomass burial system.

Another budding company, Switzerland-based RECOAL, has developed a way to turn waste biomass into “negative emission coal.” The company then plans to store this coal in permanent underground deposits.

“With the available waste biomass worldwide and the possibility to store the coal as a filling material in abandoned mines and gravel pits, the process is highly scalable,” explains RECOAL founder Joachim Hanssler.

While the likes of Underground Forest and RECOAL are looking beneath our feet, others have their sights set on the ocean.

Sealife, bro

The ocean is great at sequestering carbon. It has already absorbed 30% of the CO2 —  and 90% of excess heat — emitted by human activities. Organisms living in the sea itself do most of that work.

For instance, seagrass — a type of seaweed — can remove carbon 30 times faster than a rainforest. The UN once called it a “secret weapon in the fight against global heating.”

Several projects have attempted to grow seagrass with varying degrees of success. One problem is that farming by hand on the seafloor isn't that easy.

That's why Ulysses Ecosystem Engineering is working on a way to plant and manage seagrass fields using “cutting-edge robotics.”

Details are scant at this point. “[We are] currently in stealth,” the startup says on its Instagram.

Another innovative approach has emerged in the UK. London-based startup Blusink is trying to kill two birds with one stone. The company has developed apple-sized “carbon-sinking” pebbles it calls “blusinkies”.

The company plans to spread piles of blusinkies on the seafloor. Over time, the pebbles form so-called “rhodolith beds.” These beds act as an ideal habitat for organisms like coralline algae, that suck up carbon.

But the little pebbles have another trick up their sleeve: they're composed primarily of calcium oxide. When in contact with this chemical compound, carbon dioxide mineralises into solid carbon. The company plans to source calcium oxide as waste from the construction industry.

“Our production and operation costs are extremely low compared to DAC and other technologies,” the company's founder, Lorena Neira Ramírez, told TNW. She estimates Blusink can remove carbon at a cost of €180 per ton. To put that into perspective, DAC unicorn Climeworks currently removes carbon at a cost of €1000-1300 per ton.

Unlike seagrass carbon capture projects, Blusink says its pebbles foster the growth of entire ecosystems, not just monocultures. “It creates environmental benefits well beyond carbon capture,” said Ramírez.

Other startups like Italy's Limenet or the Netherlands' Brineworks plan to throw lime dust into the ocean to absorb carbon dioxide and reduce acidity at the same time. (Ocean acidification contributes to coral bleaching.)

Key to these efforts is calcium oxide's natural ability to solidify CO2.

Turning buildings into carbon sinks

UK-headquartered startup Calcin8 is tackling the problem the other way around. Rather than capturing CO2 from the atmosphere, it is developing a low-carbon lime to prevent more emissions in the first place.

Lime (or calcium oxide) is used for a variety of industrial processes, including making cement. However, current methods for producing 1 ton of lime emit approximately 1 ton of CO2.

Founded in 2021, Calcin8 has developed a kiln that captures CO2 before it escapes into the air.

“We have rejigged the production process entirely, turning lime into a carbon sponge,” the company's founder, Behn Mapus-Smith, told TNW.

When Calcin8's lime is used in construction, for example, it will react with CO2 in the air and absorb it — turning buildings into carbon sinks.

“Carbon dioxide removal will only have a meaningful impact if it scales to the gigaton level, which is a huge challenge for everyone involved in the industry,” said Mapus-Smith.

The International Energy Agency strongly supports carbon removal technologies to curb global heating. But, most of these technologies remain untested on a large scale.

“The startups emerging in the carbon removal space will play a crucial role in assisting businesses and governments in achieving their goals of reaching net zero emissions,” said Hans Westerhof, co-founder and managing director of Remove.

With almost 40 billion tons of CO2 emitted in 2023 alone, the budding industry has a huge task on its hands.

“All hands on deck are needed to achieve the removal scale required to address the climate crisis,” said Westerhof.