The rising oceans: Coastal societies must adapt to the reality of rising sea levels and more frequent coastal flooding
By Dr John Church, CSIRO Fellow at the Centre for Australian Weather and Climate Research
08 February 2011 Today there are more than 140 million people and a trillion dollars in infrastructure in the first one metre above high tide level around the world. Coastal areas (people, infrastructure and the environment) are already affected by extreme events such as coastal flooding and coastal erosion. For example, Hurricane Katrina caused over $100 billion of damage and the loss of over 1,000 lives along the USA Gulf coast and cyclone Nargis resulted in the loss of well over 100,000 lives in Burma. And just last week, Cyclone Yasi caused widespread damage and storm surge flooding along north Queensland’s coast. These events remind us that coastal societies in both developed and developing nations are vulnerable to extreme coastal sea levels. This vulnerability will increase with rising sea level as a result of anthropogenic climate change. With greenhouse gas emissions continuing to rise, it is becoming increasingly clear that modern coastal societies will need to adapt to rising sea levels. To cost effectively adapt, we need to know what to adapt to. How, why and where sea level has changed in the past, how it is changing now, and how it will change in the future. Currently, more than 200 million people are already vulnerable to flooding by extreme sea levels around the globe. This population could grow to 800 million by the 2080s. Over the last 140,000 years, sea level has varied over a range of 100 metres as ice sheets waxed and waned. While these changing sea levels allowed migration of early humans out of Africa and to distant continents such as Australia and North America, our modern society has only developed since climate stabilised after the end of the last ice age. During this period, and particularly over the last 2000 years, global averaged sea level has been relatively stable allowing society to develop coastal infrastructure close to present day sea level. The rate of global averaged sea-level rise has increased from the 19th to 20th century and during the 20th century. Since late 1992 when we began observing global sea levels with satellite, sea level has been rising at over three millimetres a year — an order of magnitude larger than the pre-industrial period. While this rise is barely noticeable each year, it accumulates over time, like interest on an unpaid credit card debt. The impact is felt most acutely during extreme events such as storms and the associated surges at the coast or in estuaries. … Reducing our emissions of greenhouse gases can decrease the rates and amounts of rise but it is clear we cannot stop all sea-level rise. We will need to adapt. There are three basic options available to adapt to rising sea levels. We have already adopted these options during the 20th century and will continue to use them during the 21st century. Firstly, we can protect coastal populations and valuable coastal infrastructure, such as that in the low-lying Netherlands. The city of London has the Thames barrage which protects more than 100 billion pounds of assets. However, when these coastal defences fail in extreme events such as Hurricane Katrina, the impacts can be catastrophic. Secondly, we can prepare for rising sea levels by changing the way we use the coastal region and designing appropriate infrastructure. Such infrastructure includes shelters where people can retreat to in times of severe storm surges and that have saved thousands of lives in Bangladesh. Thirdly, it will be too expensive to protect all the world’s coastlines and parts will be abandoned to the rising ocean, as is already being done in the UK. …
