paxera.blogg.se

Increases in early season ecosystem uptake explain recent changes in the seasonal cycle of atmospheric CO2 at high northern latitudes.

Sensitivity of boreal forest carbon balance to soil thaw. If future autumn warming occurs at a faster rate than in spring, the ability of northern ecosystems to sequester carbon may be diminished earlier than previously suggested 9, 10. Our simulations and observations indicate that northern terrestrial ecosystems may currently lose carbon dioxide in response to autumn warming, with a sensitivity of about 0.2 PgC ☌ -1, offsetting 90% of the increased carbon dioxide uptake during spring. In contrast, warming increases photosynthesis more than respiration in spring. We find that both photosynthesis and respiration increase during autumn warming, but the increase in respiration is greater. We use a process-based terrestrial biosphere model and satellite vegetation greenness index observations to investigate further the observed seasonal response of northern ecosystems to autumnal warming. This trend cannot be explained by changes in atmospheric transport alone and, together with the ecosystem flux data, suggest increasing carbon losses in autumn. We find that atmospheric records from the past 20 years show a trend towards an earlier autumn-to-winter carbon dioxide build-up, suggesting a shorter net carbon uptake period. Here we analyse interannual variations in atmospheric carbon dioxide concentration data and ecosystem carbon dioxide fluxes. These observations have led to speculation that spring and autumn warming could enhance carbon sequestration and extend the period of net carbon uptake in the future 8.

A simultaneous greening trend has also been observed, characterized by a longer growing season and greater photosynthetic activity 6, 7.

The carbon balance of terrestrial ecosystems is particularly sensitive to climatic changes in autumn and spring 1, 2, 3, 4, with spring and autumn temperatures over northern latitudes having risen by about 1.1 ☌ and 0.8 ☌, respectively, over the past two decades 5.