Impacts of climate variability and extremes on carbon uptake by land ecosystems

Tese de doutoramento, Ciências Geofísicas e da Geoinformação (Deteção Remota), Universidade de Lisboa, Faculdade de Ciências, 2015

Global land ecosystems are particularly important in the regulation of the atmospheric carbon dioxide (CO2) balance, removing every year about one quarter of anthropogenic CO2 emissions. Although the oceans constitute a CO2 sink of approximately the same magnitude, most of the inter-annual variability observed in atmospheric CO2 growth rates is due to variability in the land-sink. While the patterns governing variability of vegetation CO2 exchange at the sub-seasonal to seasonal time scales are relatively well understood, large uncertainties remain about the dynamics and drivers of CO2 uptake by ecosystems at continental to global scale, and on time-scales from annual to decadal. This is partly due to the complexity of the interactions between the different processes that regulate CO2 exchange ar the ecosystem level and their physical drivers, as well as to the presence of natural variability in the climate system. In this context, understanding the link between the main modes of coupled atmospheric-ocean circulation and CO2 uptake by ecosystems, as well as the way ecosystems respond to extreme events, is particularly relevant. This Thesis analyses in detail the influence of the El-Niño/Southern Oscillation on the global land-sink and explores the relationship between the European sink and the main large-scale atmospheric circulation patterns in the North-Atlantic sector, in particular the North-Atlantic Oscillation and the East-Atlantic pattern. Furthermore, this work performs a comparative study of the two most outstanding extreme events affecting Europe in the past century - the 2003 heatwave over western Europe, and the 2010 event over western Russia. The results highlight the potential of analyzing ecological variability in the framework of climate variability patterns, which may help to better interpret past and present trends in the land-sink and pave the way to better constrain future projections in Earth-System models.

Fundação para a Ciência e a Tecnologia (FCT), SFRH/BD/78068/2011, PTDC/AAGGLO/4155/2012