Page 244 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

Chapter 11. Integration and outlook
Microorganisms have largely influenced and will continue to shape the future climate on our planet. During the Anthropocene, human impacts are unprecedentedly rapidly disturbing the global climate. In less than three centuries – negligible on geological timescales – human activity has affected the Earth’s climate with an unparalleled impact. Increased GHG emissions through human activities are undeniably linked to the warming of our planet. Impacts are clearly visible in, for example, cold ecosystems, which have endured disproportionate warming over the last decades, as well as in coastal ecosystems, which have directly experienced consequences of rising sea levels (ACIA 2005; Graversen et al. 2008).
Climate change is a well-known phenomenon on Earth, but the timescale of the current events is unprecedented. Major past climatic changes include, for example, the collapse of the Carboniferous rainforests, the Younger Dryas, in which the gradual climatic warming after the Last Glacial Maximum was reversed, and likely also the Paleocene-Eocene Thermal Maximum (PETM), in which global temperatures rose with up to 5-8°C (Severinghaus et al. 1998; Sahney, Benton and Falcon-Lang 2010; McInerney and Wing 2011; Lane et al. 2013; Wright and Schaller 2013; Carmichael et al. 2017; Pardo et al. 2019). These changes happened gradually, mostly on million-year timescales, although their exact timing and magnitude are unknown. In contrast, changes within the current human-induced global warming are occuring within decades to centuries. These include the increase of atmospheric water vapor that acts as a greenhouse gas, Amazon forest drought and biodiversity loss, Arctic sea ice melt that is linked to permafrost degradation, and rapid permafrost thaw and carbon release (IPCC 2007; Lawrence et al. 2008; Lovejoy and Nobre 2019).
Most transitions include tipping points that define thresholds of sudden, large-scale environmental changes (Rockström et al. 2009). Identifying thresholds, and especially early warning signals of approaching tipping points, is crucial to adopt climate policies and anticipate consequences of affiliated changes (Wassmann and Lenton 2012; Barrett and Dannenberg 2014).
This PhD project was part of the Netherlands Earth System Science Center (NESSC) gravitation consortium, which aims to better predict future climate scenarios. During this PhD thesis, we investigated the response of methane production and oxidation to environmental factors. We studied how important environmental factors, like temperature and oxygen, affect methane production and oxidation in Arctic ecosystems, wetlands, carbon-rich deposits, and
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