Have you ever heard about the bathtub analogy for explaining climate change? It is actually a very simple and informative metaphor for the situation we are in: imagine a bathtub being filled up with  water. At first it is not a problem, after all, the bathtub is made to take up water. Then the water reaches the top of the bathtub and it’s beginning to look critical. The water continues over the edge as long as the tap is still running and now it is all over your floor. The floor starts to crack and water drip down from the ceiling to your downstairs neighbor. Finally, the problem becomes so dire that both of you have to move from your beloved home. Maybe you have already guessed it. The running water represent the increasing greenhouse gas emissions into our atmosphere. The bathtub represents the capacity of our Earth to take up these emissions. The water damage is the immense impacts to our home, the Earth, if we continue to emit greenhouse gases. From this analogy it is very clear: we need to turn off the water – we need to stop emitting greenhouse gases. But have you ever considered that we might also need a bigger bathtub?


What do we do when the bathtub is full?

Trees are natural carbon sinks, which take up carbon through photosynthesis. Berlin is adding more trees to the city, and has also kept wildly regrown areas such as in the Gleisdreieck park, which for several years was abandoned and left to the nature’s power. 


Natural carbon sinks – the bathtub

The bathtub represents the capacity of the Earth to take up greenhouse gases, which is commonly referred to as carbon sinks. These take up more carbon than they emit. The Earth consist of many carbon sinks, in fact, the atmosphere is one of them. But the atmosphere actually only takes up some of our emissions. The remaining goes into the biosphere and the oceans. Vegetation grow by taking up CO2, besides water, light and nutrients, and around half of the carbon is then stored in the wood, leaves and roots. Carbon also build up in the soil when biomass is broken down by microorganisms, which binds some of the carbon into the soil structure. The oceans store most carbon of all the carbon sinks. Either as inorganic carbon dissolved in the water or as limestones at the ocean floor. The oceans also contain large underwater “forests”, especially tiny algae which also take up carbon through photosynthesis. These natural carbon sinks are in a perfect balance with each other, which would normally ensure greenhouse gas concentrations in the atmosphere to be stable, and thus the climate to be stable. The only problem is, that humans are messing with this system by removing carbon sinks and adding more carbon sources.


What do we do when the bathtub is full?

Could we change our way of producing food to instead build up our soils capacity to store carbon? In the Kings Garden in Malmö they produce organically and pesticide free vegetables with regenerative methods that can protect the carbon in the soil. 


Increase the bathtub

Getting back to our analogy. We cannot prevent a water damage if we don’t turn off the tab. But we might give ourselves more time to fix the tab if we get a bigger bathtub. Right now, humans are however making the bathtub smaller by burning down forests, draining wetlands and disturbing soils through agricultural practices. But what if we stopped doing this? What if we instead grew more forest and stopped cutting down what we have already? What if we rewetted areas, so the carbon again would be stored in the ground below? What if we used farming practices which could increase soil carbon instead of depleting it? Then suddenly we would have a larger bathtub.


Add buckets

Besides increasing the bathtub – our natural carbon sinks – we could maybe also add buckets which could capture some of overrunning the water? These could be man-made carbon sinks, commonly referred to as negative emission technologies or for short, NETs. These are for example carbon capture and storage, which consider different technologies that can remove CO2 from emissions, for example at a power plant, and then store the carbon elsewhere, for example back into the geological aquifers where we have extracted oil, gas and coal – the origin of our problem.


What do we do when the bathtub is full?

The ARC incineration plant in Copenhagen are currently testing carbon capture of CO2-emissions from energy production, a so-called negative emission technology. They expect to be ready to use this by 2025 – the same time where Copenhagen is supposed to be CO2-neutral.


To be CO2-neutral we need balance

This brings us to the solution of our problem. Scientists agree that if we want to reduce impacts considerably, we must stay within 1.5 degrees warming – which is what the Paris Agreement is about. In order to do so, all societies must become CO2-neutral at latest by the mid of this century. As we have learned from the bathtub analogy – we must stop our emissions of greenhouse gases. But what we have also learned is that we must also expand our carbon sinks – natural and man-made.


If you want to learn more about how cities cut their emissions and increase their carbon sinks, then join us on our tour 1 in either Copenhagen, Malmö or Berlin. We will have in-persons tours as soon as that is allowed – you can book a spot on a public tour or book a private one https://greenbiketours.org/ We also offer Live virtual tours – public tours are only 9 euros and are offered once a month in all 3 cities https://greenbiketours.org/tour-1-copenhagen-berlin-and-malmo/ or you can book a Live virtual private group tour https://greenbiketours.org/private-group-virtual-tours/