Stronger carbon dioxide pollution due to the golden autumn

The vegetation period, extended by the climate warming, burdens the earth’s atmosphere with additional CO2 emissions

Nature seems to be taking good care of us: Half of the carbon dioxide that we blow into the atmosphere every year to influence the climate is voluntarily taken back by nature. It uses the photosynthesis of its flora, which converts the carbon compound into biomass. Interestingly, the 50 percent mark has remained stable in recent years despite rising man-made emissions – which means that the earth must have increased its absorption capacity as well.

But how long will this trend last?? The researchers’ hopes rested in particular on the question of how longer vegetation periods could increase the buildup of biomass. If spring comes earlier and earlier, won’t the plants have more time to take care of our emissions?? Unfortunately, recent measurements of the seasonally changing CO2 content of the atmosphere, published by an international team of researchers in the journal Nature, show the opposite to be true.

heavier carbon dioxide load due to the golden autumn

A model view of the spatial distribution of the effects of autumn (September to November) temperature warming on gross and net carbon fluxes, obtained with the ORCHIDEE model. a, ORCHIDEE model-derived autumn GPP. b, ORCHIDEE model-derived autumn NPP. c, ORCHIDEE model-derived autumn NEP. d, Sum of satellite-derived autumn normalized difference vegetation index (NDVI). The sensitivity is expressed as the linearly regressed slope of autumn carbon flux or of NDVI against autumn temperature for each pixel over the past two decades. A positive slope of NEP indicates that terrestrial carbon uptake is increasing with warmer temperatures, and vice versa. Areas with a low sensitivity or insignificant (P . 0.05) relationships between the variables are coloured in grey.

Offenbar ist es so, dass sich durch die in nordlichen Breiten um im Mittel 1,1 Grad Celsius (Fruhling) beziehungsweise 0,8 Grad Celsius (Herbst) erhohten Temperaturen die Zeit verkurzt, in der mehr Kohlendioxid aus der Atmosphare aufgenommen als in diese abgegeben wird. You have to know that plants are not only good carbon dioxide swallowers. In addition to absorbing the substance during photosynthesis, they also breathe – and release carbon dioxide in the process. Fortunately, there is a net CO2 uptake overall. In winter, plants release more carbon dioxide on average, while they absorb more during their growth period in spring and summer.

What impact does climate warming have on this fragile process?? The subsequent hope that extended growing seasons could also lead to more CO2 storage did not seem unfounded at first. But data collected by the research team at ten points above 20 degrees north latitude over the past 20 years, among others, now reveal something else: The increasingly golden autumn leads to a reduced CO2 storage overall and thus to a higher proportion of the greenhouse gas in the Earth’s atmosphere.

The scientists also try to explain why this is the case. According to this, the higher temperatures strengthen the effects of photosynthesis in spring – but in autumn they increase the effects of respiration. The warmer it gets, the sooner the plant world crosses the threshold at which it emits more CO2 than it absorbs. It is precisely this limit, as shown by the quantities, that has clearly moved forward in recent years. Still the effect of the golden autumn makes up only 90 per cent of the coarser CO2 admission in the spring again. But simulations show that if the temperature continues to rise, these nine tenths could soon become more than ten tenths. The credit that nature gives us with its CO2 reservoirs would then soon be used up.

However, the picture shown by the volumes in northern latitudes is, by its very nature, not complete. So far, nature’s global capacity to absorb CO2 has continued to increase year after year – so there must be areas on Earth that are producing biomass at an ever-increasing rate. It is possible that these areas are in the tropics – but only time will tell.

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