Climate change and sea-level rise

According to new research, major sea-level rises, catalysed by climate change, will last much longer than the entire history of human civilisation (unless in the next few decades radical global action is undertaken to cut carbon emissions).

"A rise in global mean sea level (GMSL) is projected to occur due to a global decrease in land-water storage, an increase in ocean heat uptake causing thermal expansion (change in shape, volume and area), and an increase in mass loss from land ice (glaciers and ice sheets)"[1]

As a large proportion of the carbon humans are emitting from the burning of fossil fuels will stay in the atmosphere for thousands of years, the effects of climate change will not disappear – at least not for thousands of generations [1].

Even if global climate change is limited to two centuries via tough emissions cuts, sea levels may still rise by 25 metres over the next 2,000 years or so and remain there for at least 10,000 years - twice as long as human history. An even more frightening finding is that if the current burning of fossil fuels is not restrained, global sea levels could rise by 50m, completely altering the form of the world.

When the atmosphere above oceans warms, it takes a long time for the sea temperature to increase and consequently for sea levels to rise. It is this delay in response to climate change that will result in sea levels continuing to rise for centuries to come [2].

To understand the local significance of this change, figure 1 depicts the percentage of population-weighted areas (nations/megacities) below the projected long term local mean sea level. According to this projection, approximately 25-50% of the New Zealand population will be submerged under long-term local sea level projections. That is a huge proportion of the nation to be swallowed by the sea!

[1] Clark, P., et al. 2016: Consequences of twenty-first-century policy for multi-millennial climate and sea-level change. Nature Climate Change.

[2] Ministry for the Environment 2008: Preparing for coastal change. A guid for local government in New Zealand. Retrieved 6 April 2016 from http://www.mfe.govt.nz/publications/climate-change/preparing-coastal-change-guide-local-government-new-zealand/introduction

Figure 1: Population areas affected by sea-level rise

Figure 1: Population areas affected by sea-level rise

Although many of these changes will occur slowly over time, there is still a need to plan for them to reduce risks to communities (both present and future), to direct new developments away from areas prone to flood hazards and to protect existing infrastructure and developments.

Waikato Regional Council, in collaboration with e-Spatial have developed a new online tool to show the degree of possible coastal inundation within the region. The online tool allows people to self-select how different levels of sea-level rise may generally affect coastal areas/individual properties (see Figure 2).

Figure 2: Coastal inundation tool

Figure 2: Coastal inundation tool

Project leader Rick Liefting stated: "Sea level rise is projected in our coastal communities over coming decades and our online tool will be valuable in helping local councils, communities and individual property owners to manage the risk involved. It will also help them make judgments about the risks posed by storm surges and tsunami,"

This tool is a great way to involve the commuinty in understanding the risks of sea-level rise and helping make decisions within areas expected to be affected. If you would like to try it out, click the link below and follow the step by step instructions on the webpage: http://www.waikatoregion.govt.nz/coastal-inundation-tool/