The Plant That Could Save The World

Azolla: A plant that could reverse climate change

Will Lockett
Jan 12 · 8 min read

Climate change is the biggest threat to mankind. It’s a looming armageddon. It’s the elephant in every room, only much more deadly. The good news is that globally we are doing a lot to slow down the effects. The bad news is we may have already passed the ‘tipping point’ as our C0² exceeds 400 parts per million (ppm). This means it could get hot enough to melt ancient ice, releasing vast amounts of C0² and methane that has been trapped for millions of years, triggering a runaway greenhouse effect, which will boil the Earth. So, to save ourselves and the World, we not only need to stop the damage we are doing now but reverse decades of human planetary abuse. How on Earth can we do that?!

Well, our planet has dramatically cooled in the past so why don’t we replicate the mechanisms that caused one of these events?

One of the larger of these events was the Azolla Event 49 million years ago. A tiny cute plant called the Azolla fern caused the world to go from a hot-house, with palm trees and turtles living at the poles, to the beginning of the fridged Ice Ages. The epitome of tiny yet mighty, you can still find these adorable plants in rivers and lakes around the world.

But how does a tiny plant cool the world? Its superpower is that it is great at growing and really good at dying… Let me explain.

49 million years ago the Arctic looked very different, all the landmasses were bunched up around it, there were no ice caps and it had a pleasant climate. This made the Pole resemble a temperate sea cut-off from the rest of the oceans. It had a few straights to connect it, but nothing more. This meant that currents like the Gulf Stream couldn’t mix up the Arctic waters so it was very still. What's more, high rainfall on the continents poured tonnes of nutrient-rich freshwater (namely phosphorus and sulphur compounds) into this calm saltwater.

What this created was a unique environmental cocktail as the freshwater and saltwater didn’t mix — in fact think fancy cocktail, James Bond-style, but crucially, not shaken and not stirred. The heavy denser saltwater sank to the bottom and stayed there just like your sugary cocktail syrups and the freshwater stayed on the top like your lighter spirits.

As there was no mixing the saltwater layer had next to no oxygen. However, the surface layer of freshwater was highly oxygenated and received months of continual sunshine! In these balmy waters, Azolla flourished. This little plant grows quickly, reproduces really quickly and dies remarkably quickly too. To top it off, Azolla needs minimal nutrients, and they get all of their nitrogen from the atmosphere. This means they can bloom and die off without draining too much of the nutrients out of the water. So, every summer there was a huge Azolla bloom across the Arctic, potentially covering the entire sea. Then this expansive mass of Azolla rapidly died.

When these ferns died they sank into the syrupy saltwater below. As there was virtually no oxygen, there was no bacteria to breakdown the plant matter. So, every year thousands of tonnes of Azolla ferns piled up on the seafloor without decomposing.

This lack of decomposing is the reason the Azolla had such a huge impact on the atmosphere as it locked CO² into the seabed. Let's dig a bit deeper…

The vast majority of any organism is made of carbon and plants get their carbon from the air. They take in CO², use the carbon to build their body and release the oxygen. Usually, when a plant dies it is consumed by an animal, fungi or bacteria — to cut a long story short these organisms return the plants carbon to the atmosphere in the form of CO² and methane through respiration or decomposition. This is known as the Carbon Cycle. But Azollas weren’t recycling the carbon, but instead were burying it in the seafloor. This is shown in the diagram above as ‘Net Ocean Uptake.’

So, Azolla’s talent for growing fast with little nutrients and dying quickly, combined with a salty seafloor and a freshwater top layer made a super-efficient carbon sink.

This effect was so great that over the course of the Azolla Event (800,000 years) these ferns pulled 80% of the CO² out of the atmosphere! The CO² concentration went from a wapping 3500 parts per million to 650 parts per million. This rapid decrease triggered the freezing of the Poles and was one of the catalysts for the Ice Ages.

We are currently around 410 parts per million CO² which is lower than when these Azolla ferns were around. But they lived in a hot-house Earth (no polar ice caps) and we live in a cold-house Earth (year-round polar ice caps). Our ecosystems have evolved for this colder climate and warming them up too quickly can wreak havoc. To get our CO² levels back to pre-industrial revolution amounts (in other words to reverse human-made climate change) we need to get to sub 300 parts per million.

Now, we don’t want to cause another Ice Age. I think I speak for everyone when I say I like my summer holidays! But could we harness such a natural carbon sink to combat our climate change issue? Time for a little maths, but don’t worry, I have done it all for you!

Well, on average, the Azolla Event reduced global CO² every year by 0.0035625 parts per million. That means to take our 410 ppm to 300ppm would take 30,877 years.

Let that sink in for a second. If we replicated one of the fastest cooling events in Earth’s history it would take over 30,000 years to undo the atmospheric damage we have done in the last 70 years. This should show you just how fast the planet is changing up right now and how hard it is to reverse the changes we have put in motion.

If we can neutralise our own CO² emissions over the next few decades, we could keep CO² levels below 450 ppm. But even then it will still take tens-of-thousands of years to restabilise the atmosphere — but in geologic time scales that is nothing. If we want the human race to survive long-term, and not just be a blip in the Earth’s long history, we need to reset the global climate to protect us and the ecosystems we depend upon.

So, if we can neutralise our CO² at 450ppm, replicate the Azolla Event and be very patient we can reverse climate change!

But there is just one problem. Can we really replicate the Azolla Event? After all, the global cooling of the Azolla Event came from an entire sea being turned into an Azolla farm.

Well again let's use some back of the envelope calculations to see. We need to replicate the Arctic sea 49 million years ago and its’ conditions without having a global effect.

Sadly, there is no part of the world today that closely resembles the Arctic 49 million years ago, so we will have to be a little more hands-on here. We can’t section off a part of the oceans as we will disrupt the important oceanic balance and potentially affect the whole of the ocean’s biodiversity. But, lucky for us, Azollas are freshwater plants. Could we build a giant artificial lake in a desert? Unfortunately, such a huge presence of water would distrust weather patterns and global nutrients. For example, the Amazon is fed nutrients by the dry, dusty wind that sweeps from the Sahara Desert.

So rather than using an artificial lake, we can engineer some of the world's largest lakes to be our farm. This means the ocean isn’t affected by our farm, and unlike making entirely new human-made lakes, we won’t be messing with weather patterns too much.

The ancient Arctic sea was 4,000,000 km² (1,500,000 sq mi) which is huge! There is a total of 5,170,000 km² of lakes in the world. We would need to use 77% of all lakes in the world to get enough surface area to replicate our sea!

We can engineer these lakes into huge Azolla farms. Firstly we need to kill off all native life, and then by closely monitoring what goes into the lakes, we can engineer the oxygen dead zones on the bottom and the nutrients needed to kick start an Azolla Bloom. What's more, with modern farming methods, we could have an even higher rate of CO² absorption than the original Azolla Event by ensuring that we always have perfect conditions.

Now, destroying unique ecosystems in these lakes doesn't sound like a great way to save the planet, does it? But to make these Azolla powered carbon sink, you need to. Is this sacrifice worth the reward? I don’t know, that isn’t for me to decide.

So, can Azolla save the world? Quite possibly, but it would come at a huge sacrifice and with a level of commitment never done by humans before. We would need to desecrate some of the world’s most unique habitats and work tirelessly for tens-of-thousands of years just to reverse 70 years of human activity. So it is questionable whether this method can be used or even should be used. At the very least this puts the scale of climate change into sharp focus.

Having said that, there could be another way to produce Azolla carbon sinks, like closed-off tubes of hydroponics, that could work in less biodiverse areas like desserts without changing global weather patterns. There are also many other methods of pulling carbon out of the atmosphere like using atmospheric carbon to make graphene batteries. Azolla is just one of the many tools we have to solve our biggest problem.


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Will Lockett

Written by

Science writer of space, environment, and technology. I show you the wonders and terrors of our universe & its future. Follow me at



where the future is written

Will Lockett

Written by

Science writer of space, environment, and technology. I show you the wonders and terrors of our universe & its future. Follow me at



where the future is written

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