Evidence > Sea Level
Sea Level is rising
- Sea level has risen by 3.16 mm a year since 1993
- The sea level rose 1.7 mm a year between 1870 and 2000
- The rate of sea level rise has almost doubled (from 1.7 to 3.16 mm a year)
Here is how sea levels have moved since 1993.
A rise of 3.16 mm per year may not sound like much – but the ocean covers about 70 percent of Earth’s surface. The 3.16 mm rise may seem tiny, but it is a lot of water.
Sea level rise is the yardstick for global warming.
Sea level rise is the ruler by which we measure how much human activity has changed the climate.
- In a thermometer, when the mercury warms, the mercury expands, pushes higher up the calibrated thermometer scale, and we can read the temperature on the scale.
- Like mercury, water expands as it warms.
- So, as the ocean warms, the ocean water expands, tending to increase sea levels.
- Over 90% of the current build up of heat in our planet, due to greenhouse gases in our atmosphere, is absorbed by the oceans.
- A little of the heat build up melts ice in places like Antarctica and Greenland, the melt water runs into the ocean and this too tends to increase sea levels
- Perhaps 5% of the heat accumulation stays in the atmosphere or is absorbed into the ground and so does not directly change sea levels.
- So, The ocean heats up and causes sea level rise. Ice melts and causes sea level rise. We can see the results at the shoreline.
- Sea level rise is a good measure of global warming as about 95% of the heat accumulating in our planet leads to sea level rise
- Extreme rain events can drop huge amounts of water onto the land and significantly decrease sea level, for example the 2010 / 2011 floods in Australia. However, these sea level drops only last for a few months as evaporation and rivers remove the water from the land and it returns to the oceans.
- Our oceans act as an inbuilt thermometer for the planet
- Sea level rise is the yardstick for global warming
Sea Levels give no hint of a pause in warming
While the “average global temperature” records have been the basis for suggestions that global warming paused after 1998, the sea level gives no hint of any pause in global warming.
Air temperatures are important for humans as we live in this air. However, air temperature is an unstable measure of global warming.
This is because the oceans have a far greater capacity to retain heat than the atmosphere and, for example during an El Nino period, movement of heat from the oceans into the atmosphere can significantly increase global air temperatures.
Rising sea levels already a problem
- The Intergovernmental Panel on Climate Change (IPCC) predicts that sea levels will rise a total of 0.18 to 0.6 meters (7 inches to 2 feet) between 1990 and 2100.
- Rising sea levels already cause problems in low-lying coastal areas of the world.
- For instance, the population of Bangladesh is 157 million and about half of them live less than 5 meters (16.5 feet) above sea level.
- In 1995, Bangladesh’s Bhola Island was half-submerged by rising sea levels, leaving 500,000 people homeless.
- Scientists predict Bangladesh will lose 17 percent of its land by 2050 due to flooding caused by climate change.
- The loss of land could lead to as many as 20 million climate refugees from Bangladesh.”
(National Geographic Society: Encyclopaedia: Climate Refugees)
Climate change could greatly increase the number of refugees heading for places like Australia.
Climate change risks to coastal regions
In late 2009, the Australian Government completed a national assessment of the climate change risks to Australia’s coast. The assessment identified the climate change risks to coastal settlements, infrastructure, industries and ecosystems; it found that by 2100, rising sea levels may threaten up to 247,000 residential buildings in Australia, with an estimated replacement value of $63 billion (2008 values)
Australian Government National Assessment of Climate Risks to Australia’s Coasts
Ultimate sea level rise could be 66 metres
If we destabilise the ice in Greenland and Antarctica, sea level could ultimately rise by 66 metres.
*** It is not sustainable for us to have sea level rising at 3 mm a year, and more important, to have this sea level rise headed for 4 mm a year and higher.