Coastal infrastructure15 years from now, our impact on regional sea level will be clear

By John Church and Xuebin Zhang

Published 14 October 2014

Coastal communities and industries require information on regional sea-level change to develop strategies for reducing the risk to population, infrastructure and the environment. This requires modeling projections of sea-level rise, estimating the costs and benefits of adaptation options, and understanding the impacts on coastal ecosystems. Inundation maps that can be used to identify areas that are most vulnerable to rising sea levels are particularly valuable. Adaptation measures may include land-use planning such as preventing building in low lying areas, increasing or maintaining a vegetated coastal margin that serves as a buffer zone against extreme sea levels, or using protective sea walls in the long run if certain sea level rise thresholds are exceeded.

Drs. Xuebin Zheng (l.) and John Church, guest authors // Source: HSNW composite

Human activity is driving sea levels higher. Australia’s seas are likely to rise by around seventy centimeters by 2100 if nothing is done to combat climate change. But 2100 can seem a long way off.

At the moment, regional sea-level rise driven by warming oceans and melting ice is hidden by natural variability such as the El Niño, which causes year-to-year changes in sea level of several centimeters.

So at any particular place, the sea level might go up in one year, and down in the next. On Australia’s northwest coast, for example, the sea level was three centimeters below normal during 1998, but four centimeters above normal the following year.

At the same time, human-caused climate change is driving sea level relentlessly upwards in most regions, eventually pushing it far outside the bounds of historical variation. But when will the difference become clear?

Our new analysis of sea-level projections, published in Nature Climate Change on Sunday, 12 October, indicates that regional sea-level rise will be generally noticeable before 2030. By then the average sea-level rise globally will be about 13 centimeters higher than the average sea level calculated between 1986 and 2005.

Sea-level rise: depends on your perspective

First, it’s important to note that global sea-level rise is already attributed to anthropogenic climate change.

Like temperature changes, the sea-level changes are not uniform across the world. One region may experience a very different sea-level change from other regions.

When averaged around the globe, sea level has been rising at a rate of about 1.7 millimeters per year between 1901 and 2010, and about 3.2 millimeters per year between 1993 and 2014.

This is a clear signal of climate change, driven by expansion of ocean waters as they warm and from the increase in the mass of the ocean as water is added from glaciers and ice sheets. Over recent decades, these changes are largely a result of increasing concentrations of greenhouse gases.

As well as this gradual and relatively steady rise in global sea levels, in any part of the ocean there are also natural variations in sea level. This is associated with climate phenomena such as El Niño and La Niña, storm surges and tides that can dominate any sea level variations over short periods.