Recent observational data studies confirm that we are much closer to the temperature tipping point for forest and terrestrial ecosystems than previously reported. These studies employ data spanning 1991 to 2015 from direct measurements via FLUXNET, the largest continuous carbon monitoring network.
At current greenhouse gas emission rates, we will reach a point where the natural carbon ‘sink’ role of more than half of our global terrestrial ecosystem could actually reverse transforming them into carbon ‘sources’ as early as 2040.
Tropical and boreal forests along with other ecosystems trap and sequester 30 percent of human-generated CO2 pollution. Until very recently, it was assumed that there were no limiting factors to this protective function; however, we now know that this is not so. The ability of these massive global systems to mitigate our CO2 output is temperature-dependent. These ecosystems are in danger of losing up to 45 percent of their carbon absorption ability due to the difference between how photosynthesis and respiration respond under higher temperatures.
Photosynthesis in plants uses energy from sunlight and carbon dioxide absorbed by their leaves along with water from the soil to produce sugar, used to boost growth. Oxygen, is a byproduct of this chemical process. Photosynthesis can only take place in daylight.
Respiration is the process that transfers energy to the plant’s cells. CO2 is a byproduct of this process. Respiration happens at all times; daylight or nighttime.
The recent observational studies using the FLUXNET data are essentially tracking the movement of CO2 between ecosystems and the atmosphere. What they show is very worrying to climate scientists. Photosynthesis peaks at specific temperatures over the range of plant species. Above these thresholds, it actually declines.
Plant metabolism increases with temperature; therefore, respiration rates increase across all ecosystems. However, here there is no maximum temperature threshold. This would lead to a situation where CO2 absorption could halve by as early as 2040. CO2 production however, would continue to increase.
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