2005; Jevrejeva et al., 2006). Because sea level exhibits considerable interannual and decadal variability, the calculated rate of change depends on the length and start date of the record used. For example, Church and White (2006) found that the global rate of sea-level rise was 1.7 ± 0.3 mm yr-1 for the 20th century, 0.71 ± 0.4 mm yr-1 for 1870–1935, and 1.84 ± 0.19 mm yr-1 for 1936–2001. Their results are shown in Figure 2.1, compared to other independent estimates of global sea-level rise from tide gages.
The time dependency of global sea level can be seen in the analysis of Church and White (2011), who calculated the sea-level rise using 16-year moving windows of data, as shown in Figure 2.2 (see also Box A.1 in Appendix A). In this example, the linear trend in global sea-level rise was 1.7 mm yr-1 from 1900 to 2009, with some 16-year intervals yielding rates of 2–3 mm yr-1 in the 1940s, 1970s, and 1990s. This variability has been attributed to natural climate variability (e.g., El Niño-Southern Oscillation [ENSO]), which causes short-term variations in global mean temperature, and to large volcanic eruptions, which briefly cool the Earth’s surface and troposphere (e.g., Hegerl et al., 2007).
FIGURE 2.1 Global sea-level time series from Church and White (2006; red) compared with independent global sea-level time series from (a) Trupin and Wahr (1992), (b) Holgate (2007), (c) Gornitz and Lebedeff (1987), and (d) Jevrejeva et al. (2006) in black. Time series are arbitrarily shifted vertically for clarity. SOURCE: Woodworth et al. (2009).
FIGURE 2.2 Sixteen-year running averages of global sea-level rise trends showing variability in rates over short timescales. SOURCE: Church and White (2011).