The world’s oceans take up twenty five percent of our annual CO2 emissions to the atmosphere. This helps slow down global warming. Keeping track of this uptake is essential for understanding climate change.
Every year, the numbers are presented in the Global Carbon Budget. This helps us determine what actions we need to take.
But, how do we know how much CO2 is taken up by the ocean?
Observing lines of data points
To measure this, scientists have established a global network to collect data that can be used to determine the ocean CO2 uptake. Advanced instruments are installed on cargo ships, ferries and cruise ships, and on research vessels. These instruments measure CO2 concentrations in surface water along the journey. The data enable us to determine how much CO2 the ocean takes up from the atmosphere.
This particular cargo ship, the Transcarrier, sails along the Norwegian coast every week. In the end, we will get a line of data points. Throughout the year such instruments record more than a million data points from all over the world.
In the next step, these data points are checked by scientists around the globe. Researcher Meike Becker is at her computer, doing her piece of the puzzle. She is verifying her portion of data, to make sure that every data point from the ocean surface is reliable. We have millions of verified data points. These are published as the surface ocean CO2 atlas, SOCAT.
But, for every year, only a fraction of the vast global ocean is surveyed. How do we go from these spotty measurements to an estimate of the carbon uptake of the full ocean? How do the researchers estimate the carbon uptake?
The clue is neural networks.
Artificial intelligence recognising patterns
With the help of algorithms, it is possible to find patterns in the data. These patterns allow us to reconstruct CO2 concentrations in areas where we have no data, from satellite measurements that cover the entire globe. Throughout the year, satellites measure surface ocean temperature and chlorophyll, green algaes, that give a measurement of the primary production in the ocean surface.
When combined with the CO2 data from the shipping lines, the neural networks find patterns of how these three properties – that is CO2, temperature and chlorophyll – appear together.
The neural network is then applied on the satellite data and gives a CO2 concentration for every point in the surface ocean. This is then used to determine the global ocean CO2 uptake.
By taking up 25% of our CO2 emissions the ocean is doing us a huge favour. Without this uptake, atmospheric CO2 would have been more than 500 parts per million instead of the 420 now observed. This would have caused global warming far beyond 2 degrees.
It is essential that we continue to assess the efficiency of this important carbon sink. A reduced ocean carbon uptake, for instance, will translate into a stronger need for emission cuts to reach net-zero and the two degree target.
We need to be able to detect any such changes at an early stage. It has never been more important that we continue to measure our oceans.
Animated and edited by Eli Kristin Muriaas. Produced with support from the Research Council of Norway (RapidVERIFY, #309571). Thanks to ICOS; Glen Peters, CICERO; Peter Landschützer, VLIZ: Corinne Le Quere, University of East Anglia; and the University of Exeter.