Written by Tom Gill Updated on 30 November 2022 The climate crisis is the biggest challenge humanity has ever faced, with time to avoid a 1.5°C global temperature rise rapidly running out.Some experts think the planet has already passed the threshold, and that now we need to work towards capturing the carbon already present in the atmosphere, instead of just reducing our current emissions.While the bulk of work needs to be done by the most polluting countries and corporations, innovators and scientists are still working hard to find ingenious ways to combat climate change by capturing carbon.We’ve looked into five clever ways to undo the effects of climate change, from seaweed farms and mushrooms that eat plastic, to installing millions of arctic water cannons. What's on this page? 01 Farming seaweed 02 Plastic-eating mushrooms 03 Building with hemp 04 Capturing carbon in the air 05 Using water cannons at the poles 06 Summary Farming seaweedSeaweed has been one of the biggest CO2 absorbers for the past 500 million years, sucking in around 173 million tonnes of the stuff annually.That led businessman John Auckland to use what he describes as the “wondrous properties” of seaweed to capture carbon on an industrial scale.Through a project called Seafields, his ambition is to farm sargassum, a type of floating seaweed that can be grown in large enough quantities to cover a massive area of the ocean.Auckland wants to cover 55,000 sq km (21,200 sq miles) with sargassum, which he says will be enough to absorb an astonishing gigatonne of carbon dioxide from the atmosphere. That’s a billion tonnes of CO2 every single year.For context, all the forests of the world combined currently take out roughly 2.3 gigatonnes of CO2 from the atmosphere.We still collectively put around 50 gigatonnes of CO2 into the atmosphere per year — an astronomical amount — but it’s impressive to think seaweed alone could remove 2%.Despite this, sargassum has a problematic relationship with many coastal societies. When it washes up on the shore, it brings with it a foul stench that has plagued tourism-focused communities in locations such as the Caribbean.Containing the sargassum is imperative, which is why Auckland and his team plan to grow the seaweed farms in the ocean’s gyres. These are vast rotating currents best known for accumulating giant islands of plastic.If his Seafields use these gyres properly and combine them with other containment methods, this should prevent the sargassum ending up on shores around the world — while also massively reducing the amount of CO2 in the atmosphere.As the seaweed dies and sinks to the ocean floor, all the absorbed carbon is held down by the immense pressures at those depths, keeping it out of the atmosphere. It’s kept from rising throughout the ocean by these same pressures. Plastic-eating mushroomsMushrooms have all sorts of wonderful properties, but few would expect the ability to eat plastic to be among them.And yet, scientists have been working on this over the past few years, looking into which species of mushrooms are the best at consuming plastic.Pestalotiopsis, a genus of fungi found in decomposing tea and avocados, is leading the charge. It can grow on and digest polyurethane, a type of plastic found in electronics, insulation, and food packaging all over the globe.Oyster mushrooms can do the same, except they can also convert plastic into human-grade food. This not only has the potential to reduce plastic pollution, but to help feed people too.We’ve dumped 7.5 billion tonnes of plastic into the environment since 1960, so there’s a lot for the mushrooms to get munching on.One place to start is the infamous Great Pacific Garbage Patch, a colossal area of plastic waste collected over an area bigger than Spain.The idea is to grow the right type of fungus on the worst-affected areas of the patch, then let the magical mushrooms eat through the trillions of microplastics and nurdles, converting them into harmless organic matter. Building with hempHemp is one of the most effective, durable, and efficient building materials on the planet, capable of insulating a property while producing far fewer emissions than traditional bricks.It’s brilliant from a climate point of view, because like all plants it captures carbon dioxide from the atmosphere and acts as a carbon sink — or carbon store — trapping carbon dioxide in the soil throughout its life.Hemp is a superstar in this field, as it's capable of taking in up to four times more CO2 than trees. A single acre of hemp can remove 10 tonnes from the air, eclipsing the 2.6 tonnes that an acre of mature trees can absorb.The picture gets even better when you consider how quickly hemp grows, going from seed to maturity in just four months. There’s no need for pesticides either, which contribute to agriculture’s poor reputation for emissions.A study by the International Assessment of Agricultural Knowledge, Science and Technologya for Development found pesticides play a huge part in agricultural emissions, which make up 30% of the planet’s total.Hemp combats soil degradation as well, because its deep root system strengthens the soil it grows in. What’s even more impressive is that hemp helps with land reclamation, as it’ll confidently grow in infertile soil, and enrich the ground with nutrients when it dies. Capturing carbon in the airMost forms of carbon capture focus on capturing it at the source, but one technique extracts it straight out of the air.Called Direct Air Capture (DAC), this method sucks CO2 from the atmosphere, storing it in deep geological formations to achieve carbon dioxide removal (CDR).DAC is a great option because it’s able to store large amounts of CO2 without taking up much land or water space. It’s also simple to use the stored CO2 for food processing, or to combine it with hydrogen to make synthetic fuels.It sounds promising, but DAC is definitely in its infancy right now, with only 18 air capture plants operating worldwide, extracting around 0.01 megatonnes of CO2 a year. This is only the equivalent annual emissions of around 1,234 UK households.The costs involved are heavy too, with a recent study estimating that it costs between £78 and £193 per tonne of CO2 removed from the air — which means paying £1.35 million to remove 0.01 megatonnes of CO2.Scale that up to what’s needed, and it’s clear the costs must go down for DAC to become a viable CDR method. It would cost £1.35 billion to remove 2% of the world’s annual CO2 emissions using DAC.If costs are reduced however, then a widespread DAC network can be one of the most effective and unobtrusive ways to extract and repurpose CO2 from the atmosphere. Not just cost, but energy too, because it would require 10% of the world’s current energy consumption to remove a gigatonne of CO2. Using water cannons at the polesThis one is on the novel side, but there is sound science behind it. The idea is to install millions of water cannons to blast the surface of arctic and antarctic ice sheets with seawater, which would then freeze.As the water freezes, more seawater is blasted on top of the sheet, adding layers and further thickening the ice. The thicker the ice gets, the longer it lasts.This would lead to more sunlight being reflected from the larger ice sheets, which would reduce global warming, plus we’d be freezing water that would otherwise melt down and contribute to rising ocean levels.However, it’s not cheap. £417 billion is the projected price tag, and it’s easy to argue this kind of money could be used elsewhere.For instance, the Loss and Damage Fund announced at COP27 is a better use of these billions, because building climate resilience for disproportionately affected countries is essential right now. SummaryThese creative ways to undo the effects of climate change are exciting prospects, but they shouldn’t distract from the fact we need to switch to clean energy sources and reduce our fossil fuel appetite now.Climate scientists understandably worry these ideas discourage people from changing their energy consumption habits, because they’re often presented as cure-alls.Nonetheless, these initiatives could act as a buffer, giving us more time to make the shift to renewable energy sources.If some of the ideas can be scaled down to local levels as well, it’d be great to see smaller communities take the fight against climate change into their own hands. Written by: Tom Gill Writer Tom joined The Eco Experts over a year ago and has since covered the carbon footprint of the Roman Empire, profiled the world’s largest solar farms, and investigated what a 100% renewable UK would look like. Tom has a particular interest in the global energy market and how it works, including the ongoing semiconductor shortage, the future of hydrogen, and Cornwall's growing lithium industry.