Early geoscientists recognized that salt marsh sediment overlying terrestrial deposits (e.g., soil containing the preserved, in-situ stumps of freshwater trees) represented submergence of the older, buried landscape at a time in the past (e.g., Bartram, 1791; Lyell, 1849). After the development of radiocarbon dating in the late 1940s (e.g., Libby 1961) it became possible to determine when salt marsh sediment was deposited and sea-level research began to focus first on building and then on interpreting Holocene relative sea level (RSL) curves (e.g., Bradley, 1953; Redfield and Rubin, 1962; Bloom and Stuiver, 1963; van de Plassche et al. 1989; Gehrels et al. 1996; Shennan and Horton, 2002). Conceptually relative sea level (RSL) is the elevation of the sea surface relative to the land surface at a specific location and averaged over a period of time to negate the influence of tides and seasonal to annual variability. For example, RSL measured by tide gauges is often expressed as a monthly or annual average, while RSL reconstructions from coastal sediment are inherently time averaged over several years to decades. A variety of physical processes acting on local-to-global spatial scales and on temporal scales from minutes to millennia can cause RSL to change across space and through time. Therefore, measured or reconstructed RSL is specific to a time and place and is often the net outcome of multiple processes acting simultaneously. Proxy-based RSL reconstructions generated by interrogation of salt marsh sediment preserved in the coastal stratigraphic record are valuable in advancing our understanding of Holocene climate (e.g., Kemp et al. 2011), the structure of Earth’s interior (e.g., the viscosity and structure of the mantle; e.g., Shennan and Horton, 2002; Engelhart et al. 2011a), and of physical driving mechanisms of past, present, and future sea-level change (e.g., Kopp et al. 2016).

Historical records show a massive decline in salt marsh area (Pendleton et al. 2012), > 50% in many locations, such as sites in Australia (Saintilan and Williams, 2000; Rogers et al. 2006), the British Isles (Baily and Pearson, 2007), and New England, USA (Bertness et al. 2002). These losses are mainly fueled by an underappreciation of the large contributions of salt marsh to maintaining healthy and productive estuaries. Prior to the middle twentieth century, the value of salt marsh primarily depended on its potential for reclamation. Davis (1910) proclaimed that “…[salt marshes] are conspicuous, being generally unutilized for any purpose except for making a small amount of inferior hay, hence they are practically desert places, except where land values are sufficiently high to make it worth while to raise the surface above high tide level for building purposes, or to dike out the tides.” We now view salt marsh as a valuable estuarine habitat because it provides coastal protection from waves (Shepard et al. 2011), erosion control (Neumeier and Ciavola, 2004), water purification (Sousa et al. 2008), fish and bird habitat (Peterson and Turner, 1994; Van Eerden et al. 2005), carbon sequestration (Mcleod et al. 2011), and tourism/recreation (Barbier et al. 2011; Altieri et al. 2012). Salt marsh is also a coastal depositional environment that can accrete vertically over millennial time scales at rates equal to, or greater than, sea-level rise (Gehrels et al. 1996; Ouyang and Lee, 2014). The relatively high accretion rates and resistance of salt marshes to erosion (Mudd et al. 2010) make them valuable sites for preserving records of sea level (van de Plassche et al. 1998; Engelhart et al. 2011; Kemp et al. 2017), storms (Donnelly et al. 2001; Boldt et al. 2010; de Groot et al. 2011), and tsunamis (Morton et al. 2007; Komatsubara et al. 2008) in their sediments. Salt marsh loss and associated services have been pervasive globally, mainly due to the direct (grazing, ditching, pollution, etc.) and indirect (climate change) effects of human activities, resulting in the recent emphasis on restoration, conservation, and management (Lotze et al. 2006; Airoldi and Beck, 2007; Gedan et al. 2009). Although recent focus has been on better understanding of those mechanisms and processes that are related to salt marsh degradation, reviewing salt marsh formation and the different modes of salt marsh expansion will aid efforts aimed at preserving and increasing salt marsh habitat area and extracting climate and tectonic information from their sedimentary records.

How humanity is fed now and how we can do this better in the future. What can be done and what can everyone do?

We have seen throughout the book so far how urgently we need to learn how to think in ways that let us deal more effectively with the situation we have created for ourselves. We need thinking skills and habits that fit the twenty-first century context of enormous human power and technology on a now-fragile planet. We’ve also seen the global interconnectedness of just about everything we do. It is not at all surprising that ways of thinking that have taken us to this place might not be the same ones that will help us to live well now that we have got here. The brain skills that we developed over the millennia as we expanded on a big, robust world are not the same as the ones that will let us do well on the small delicate spaceship on which we now find ourselves.

Travel and transport accounts for a big enough chunk of the world’s energy use with most of this coming from liquid fossil fuels. These have the huge convenience of being mobile and dense energy stores – ideal for cars, boats and planes. So replacing this will present a raft of technical and infrastructure challenges. All these will be made easier the less travel we actually need.

All the pathways of this book seem to be converging inescapably on the question of values. It turns out to be the crunch point. I haven’t manipulated it that way. In fact, if I could have avoided a values discussion, the book would have been simpler to write. I am conscious of being no more of an ethics professor than I am an economist. But the evidence is pointing towards some values that will help us live well in the Anthropocene, and others that won’t. So, I write this section from a pragmatic perspective. I’m simply asking which values will and which values won’t allow people and planet to thrive in the twenty-first century, and how we can end up with the right ones. Luckily, it turns out that our values are something we can actually shape if we want to.1

When the challenges are so global, and each one of us so small, it can be tempting, but wrong, to think that there is nothing an individual can do to help humans to get a grip. To do so is a cop out. It is one form of human denial of the Anthropocene challenge. The global and systemic nature of our situation does have huge implications for the roles of individuals, organisations and even states. It is true that systemic adjustments can completely undo the direct benefits of many piecemeal actions. So, we need to see everything we do as part of a bigger game.