22 - Rising Sea Levels

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It is important to note that the forecasts for the rise in water levels are very conservative. Some phenomena, understood qualitatively but not quantitatively, are simply not quantified in the IPCC report. This is the case for moulins, for example. Moulins, or glacier mills, are shafts that carry melted water from the surface of a glacier or an ice sheet down to the bedrock. Once the water enters these passages, it lubricates the contact between the bedrock and the ice sheet, making it easier for the glaciers to drift towards the sea. The figures for sea level rise will therefore most likely be revised upwards in future reports. For the US, you can use the Sea Level Rise Viewer to show the extent of the phenomenon.

Earth from Space
The physical processes causing global sea-level rise are highlighted in this animation. The main causes are thermal expansion of oceans, as they accumulate the excess heat caused by greenhouse gas emissions, the melting of ice from the ice sheets and glaciers, as well as changes in land water storage such as lakes. Global mean sea-level has risen by more than 30 millimetres per decade since precise satellite measurements began in the 1990s. A good third of this rise in sea level is down to thermal expansion – as seawater warms, it expands. Nearly two thirds of the rise is because of freshwater being added to the ocean, mainly through the melting of land ice. Another addition of water to the ocean results from a decrease of water on land, such as groundwater storage.
Credits :© ESA CCI Sea Level Budget Closure Project/Planetary Visions
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3
Causes

Rising Sea Levels

A melting of 100 gigatons of ice per year is equivalent to about 0.28 mm per year of mean sea level rise. Thus, 15 to 35% of sea level rise is linked to the melting of glaciers, according the IPCC scenarios. 30% to 35% is linked to the expansion of water. The remainder is linked to the melting of the ice caps.

Rising Sea Levels

Rising Sea Levels

1
Consequence

Rising Sea Levels

2
Wrong causes

Rising Sea Levels

This it the trap in which participants can fall while playing with cards set n1. Therefore, do not ask them to read the cards from the beginning. Once they have put them in place, ask them to read the texts.

Rising Sea Levels

No, more rain is not going to cause the oceans to overflow! This is a rare mistake to be made, but if it happens to you, ask the players where rainclouds come from...