# Evaluating the Effectiveness of Natural Carbon Sinks Through a Temperature-Dependent Model
## 1 Introduction  
Articles are currently being circulated in the media claiming that natural CO\({}_{2}\) sinks have \"suddenly and unexpectedly\" ceased to function. The natural CO\({}_{2}\) reservoirs are the biota, consisting of all living organisms, plants, animals and humans. In addition, the oceans store around 50 times the amount of atmospheric CO\({}_{2}\). It is known and has been proven for many decades that both the biota and the oceans are strong CO\({}_{2}\) sinks. Currently, more than half of all anthropogenic emissions are absorbed by the two major sink systems, ocean and land plants, as reported in [1].  
What has happened that suddenly the sink effect is supposedly diminishing? Even at first glance, the diagram (Figure 3) in [1] reveals that the sink effect, which is attributed to land plants, is subject to extraordinarily strong fluctuations, much more so than in the case of the oceans, for example. This should immediately make us suspicious when we talk about a \"one-off\" event within the past year.  
The scientific basis and trigger for the current discussion is the recent article: \"Low latency carbon budget analysis reveals a large decline of the land carbon sink in 2023\" [2]. The publication essentially states that anthropogenic emissions have been more or less constant over the recent years, but atmospheric CO\({}_{2}\) concentration grew much more than usual in 2023, while between 2016 and 2022 concentration growth was steadily declining. Their conclusion from this observation is that the systems responsible for CO\({}_{2}\) absorption, such as land plants or cold oceans, must have been failing. Another publicationfrom the Alfred Wegener Institute (AWI) in Germany investigated the ocean uptake of CO\({}_{2}\) since 1958 [3]. They came to the conclusion that the ocean sink is diminishing; besides wind, they identified increasing temperature as a sink-diminishing factor.  
Other investigations have found convincing evidence that land sinks have, in fact, significantly increased due to CO\({}_{2}\) fertilization, particularly in tropical forest regions and reduced cold-limitations due to elevated temperature, primarily at higher latitudes [4]. Moreover, this overview article gives good reasons for the future increase of land sinks. In particular, the CMIP6 climate models predict increasing land sinks for at least the next 30 years in the RCP2.6 and higher scenarios [5]. In a recent publication, it was discovered by means of a new analysis that, in fact, the gross primary production (GPP) is 25% larger than previously assumed [6], and in particular, the GPP is 5% larger than soil respiration.  
Such evidence suggests that there may be a forgotten factor in the understanding of the carbon cycle. We may have to look for another explanation causing changes in CO\({}_{2}\) concentration growth. Evaluating the literature on carbon sinks gives some hints on where to look for an answer for the apparent deviations. [PERSON] introduced El N\(\ddot{n}\)o as a possible cause to balance the apparently declining carbon sink activity [7]. [PERSON] used a similar argument to explain short-term atmospheric CO\({}_{2}\) concentration changes depending on temperature anomalies [8], but from that publication, it is not clear exactly what he means by temperature anomaly. In an earlier publication on his blog [9], he indicates (in the legend of the first graph) that his understanding of temperature anomaly is the time derivative of temperature, contrary to the standard definition of temperature anomaly, defined it as the temperature difference to a fixed earlier baseline temperature.