Our planet has a lot of water. Around 71 per cent of the Earth’s surface is covered in it.
Most of it is in the oceans, it is salty and undrinkable; only about 3.5 per cent is fresh water.
This fresh water is found in lakes, rivers and streams or hidden deep underground where it is hard to reach. Some of the water is so obvious that you might not even think about it – it’s in the water vapour that makes up the clouds.
Some is in the cells of your body. Did you know that you are about 60 per cent water?
Around 70 per cent of the fresh water is actually frozen. It’s locked away in glaciers, icecaps, icebergs, permafrost and snow. Around 95 per cent of the ice is based on land, and most of that is in Greenland and Antarctica. The ice at the Arctic is not sitting on land, it is floating in the sea.
Around 70 per cent of the fresh water is actually frozen. It’s locked away in glaciers, icecaps, icebergs, permafrost and snow. Around 95 per cent of the ice is based on land, and most of that is in Greenland and Antarctica. The ice at the Arctic is not sitting on land, it is floating in the sea.
As global temperatures rise, some of the ice on Earth will melt. Exactly how much is still debated by climate scientists. Depending on which kind of ice melts, it will have a different effect on sea levels.
In July 2017, part of the Larsen C ice shelf in Antarctica broke off in a process known as calving. An ice shelf is a thick floating tongue of ice that connects to a landmass or grounded glacier. The calving was not a surprise as scientists had been tracking the fracture for a long time. It is part of the natural lifecycle of an ice shelf and experts in Antarctic science say it is not necessarily the result of climate change.
The calving event created one of the largest icebergs ever recorded. It is estimated to weigh more than a million million tonnes and has an area of 5,800 km2. That’s more than twice the size of Luxembourg. (Big then, ed).
This picture of the ice shelf below was taken with the Thermal Infrared Sensor on the Landsat 8 satellite. The cold areas appear dark, these are the ice shelf (left) and the iceberg (central). The white areas are the warmer seawater (in the fracture and to the right).
As the ice was already floating in the sea, the new iceberg will not affect the sea levels much as it melts. You can see how this works in our experiment.
However, the story is more complicated than simply ‘it won’t cause sea levels to rise’ because a large ice shelf like this protects the glacier behind it. When an ice shelf collapses, the back pressure disappears and the glacier can now flow more easily towards the sea adding its water to the oceans more quickly.
Remember that 95 per cent of the ice sits on land? When that melts, it will have a very different effect on sea level, as you can discover from our experiment.
– Two identical pots that fit into….
– Two identical large drinking glasses
– Water
– Food dye (optional)
– Small sieve
–Tray to collect drips
Fill your two identical pots to exactly the same level. Add food dye if you wish. This will be your iceberg and your glacier. Put them in the freezer overnight.
Half fill one glass with water and stand it next to the other empty glass on a tray.
Carefully remove the ice from one pot. Place your ‘iceberg’ into the glass that has water in it. What has happened to the water level? The iceberg has displaced some water, it has taken up the room where the water was before, moving the water level up the glass. This is why the water level rises when you lay down in the bath – have you ever noticed it?
Now fill the second glass to the same level and place the sieve on top. Place the ‘glacier’ ice cube in the sieve.
Now leave the ice in each glass to melt. What happens to the water level in each glass?
You should notice that the ice floating in the water does not change the water level much. This is because it had already displaced the water and made the level rise before we started. This is what will happen with the iceberg from the Larsen C ice shelf, it will not change sea level directly by melting. In the glass where the ice was on land (i.e. in the sieve) the water level has risen, this is what happens when glaciers and land-based ice sheets melt. They will contribute to sea level rise.
Taking it further: Have a think about what is likely to happen to our planet if the sea levels continue to rise. What can we do to help prevent climate change?
If you enjoyed this brilliant blog, then why not think about a subscription to AQUILA magazine!
Words: Dr Sarah Bearchell. Illustration: Sophie Bryant-Funnell.
New Leaf Publishing Ltd 2024