En-en adult card 12 carbon sinks
Card #12: Carbon Sinks
Half of the CO2 we emit every year is absorbed by carbon sinks :
- 1/4 by the vegetation (through photosynthesis)
- 1/4 by the ocean
The remaining half (1/2) stays in the atmosphere.
The original IPCC graph represents both CO2 emissions and carbon sinks. The Climate Collage has chosen to split it in two to show where CO2 comes from and where it goes. This is why the two cards are symmetrical: every year, the CO2 emitted by man has to go somewhere. Any CO2 that is not absorbed by the carbon sinks remains in the atmosphere.
The text at the back of the card gives approximate absorption rates. The more detailed percentages are :
- 27.9% for the ocean
- 28.8% for photosynthesis.
This card is to be mirrored with the CO2 emissions card. To make the participants find it, we can show them the card and ask "Do you see anything weird on this card?". Very often participants notice that the legend is written upside down. We can then tell them that it is a puzzle to be solved and that the answer is on the table. In case the participants do not find it, they can be given clues:
- What is the type of representation? A graph
- What type of graph? A "filled" curve
- What is the legend? The same as for CO2 emissions.
Deforestation Participants often think that deforestation reduces carbon sinks. In reality, the impact is minimal because deforested areas represent a very small part of the total forest area. On the other hand, the CO2 emitted is very important.
Agriculture It doesn't matter if this link is not made, but it is true that agriculture can improve storage capacity through photosynthesis. This is the 4 per 1000 principle (if we increased the soil's capacity to sequester carbon by even 4/1000, we would have a significant impact on CO2).
Decline in agricultural yields Studies have shown that yields increase with increased CO2, but that the nutrient content of vegetables is reduced as a result. Indeed, trace elements are not more abundant when yields increase.
To go further
Variation in photosynthesis
On this card, we can see that in some years photosynthesis drops to 0, and varies greatly from one year to another. The explanation comes from the fact that the residual carbon sink is calculated from the remaining value of the other variables. This is why negative values are sometimes found. In this graph, emissions and their distribution only include flows that have varied since 1750, without the natural CO2 flows, such as the absorption of atmospheric CO2 from phasing out, the degassing of CO2 from lakes and rivers, and the degassing of CO2 in the oceans from the carbon brought by rivers. However, the IPCC does not clearly explain why such a variation can be read on the graph.
It can be added that the atmospheric concentration has increased sharply in years with an El Niño phenomenon because it makes it difficult for vegetation to absorb carbon.