30 September 2021

Bathtubs and why negative emissions technologies are more important than renewables

By Eddie Gillow

Imagine a bathtub filling up with water. The bathtub represents the climate system, and the water represents levels of CO2. Adding water from the tap is like releasing more CO2 into the atmosphere. If you keep adding water, eventually the tub will overflow. This is the same as in the real world, where total CO2 emissions are rising and will eventually cause levels of warming which will lead to irreparable damage.

Now, we have a range of options that will stop the bath from overflowing. Firstly, we can simply turn the tap off. That would mean that no more water would enter the bath and the water level would stay the same. This is a simple solution, but applied to the real world we see that this would not be possible. We can’t simply expect the world to stop emitting CO2 immediately – this would require us to stop using gas, cars, airplanes, oil, and all the rest of it. This would only be possible in a world where we relied solely on renewable energy – a world which is a long way off.

What seems more reasonable, however, is to turn the tap down and slow down the rate of water entering the bath. This would be the same as asking people to consume less, change their diets, and implement policies such as banning the production of petrol cars. It would also involve the promotion of renewable energy sources so that we don’t have to use so many fossil fuels instead.

But still, if we left the tap running the bath would overflow at some point. Turning the tap down – or using less fossil fuels – would buy us some time. But it won’t stop us from reaching a tipping point.

So what else could we do? The only other option left is to pull the plug out of the bath in order to drain off some of the excess water. Removing water from the bath in this way is the same as removing carbon dioxide from the atmosphere.

More water will need to leave the tub from the drain than is entering the tub from the tap in order to reduce the total amount of water in the tub. Similarly, the atmosphere will ‘overflow’ with CO2 unless we ‘drain’ enough of it through negative emissions technologies such as direct air capture (DAC) or carbon capture utilisation and storage (CCUS).

Whilst reducing our energy consumption and shifting to renewable energy sources is undoubtedly an important step in solving the climate crisis, it’s not enough on its own. We need to balance our emissions with removal of CO2 from the atmosphere if we really want to prevent the climate bathtub from overflowing.

Hopefully this analogy makes it unquestionably clear that removing CO2 from the atmosphere is a fundamentally necessary step if we are serious about preventing the catastrophic effects of global warming. Policy makers need to come to terms with the fact that we need to drain CO2 out of the atmosphere faster than we are pouring it in, and that we cannot focus solely on renewable energy at the expense of negative emissions technologies.

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Eddie Gillow is a Policy Analyst at Public First

Columns are the author's own opinion and do not necessarily reflect the views of CapX.