How water drives our climate

Water has key properties that make it unique, with great implications for the climate and the evolution of life itself. Hear Professor Søren Rud Keiding talk about the importance of water for driving the climate system and keeping our world liveable.

Water is strongly connected to our climate system.
The atmosphere is actually working like a heat pump or an air conditioner but the coolant is different. In the atmosphere, the coolant is actually water. So water changing from liquid water to gas phase water, or back is what drives the entire climate system. One of the things that motivates Grundfos and scientists all over the world is to address the United Nations Development Goals primarily goal number 6 and goal number 13. Goal number 6 is the clean water and sanitation goal and number 13 is the climate change challenges.

All the energy on Earth comes from the sun and in the atmosphere, we use water to redistribute the energy. So what we call weather and climate is actually driven by water. When we heat up water in the atmosphere water will become a gas. So it takes energy to move water from the liquid phase to the gas phase.
If we do the opposite, we condense water so we take water vapor, water gas
and we condense it into a liquid, then energy is released. So when we have storms and when we have winds blowing it's basically just caused by the water molecules going from gas phase to liquid phase. And you can say also combined with the rotation of the Earth. The heat capacity of water is very, very high.
Heat capacity tells us how efficient water is at storing energy.
If we, for example, want to heat up water it takes a lot of energy to heat water because a lot of energy is stored in water. Some of you might know the difference between coastal climate and inland climate. And this is basically driven by the water heat capacity.

If you have a coastal climate, there's a lot of water and it takes a lot of energy to heat up water. Therefore, the temperature will remain more or less constant.
If you go inland, where there's obviously less water then the temperature fluctuations will be much, much higher. If water contains salt it will be heavier, so to speak, it will have a higher density compared to water without salt.
And the fascinating thing is that when salty water is freezing to become ice then the salt will be expelled from the ice cubes. So when ice is freezing, the water underneath it will become denser and it will sink. And this motion of sinking salty water is actually what is driving the Gulf current. So the entire climate system driven by the Gulf current is actually driven by the fact that salty water has a higher density compared to fresh water. You're all familiar with the fact that ice floats on water. To us this is normal but among the 100 million molecules we know nowadays water is the only molecule where this happens where the solid form of the molecule, ice flows on the liquid form of the molecule, water.

It's actually a key property of liquid water that is very, very important for the evolution of life. Liquid water has a density maximum at four degrees. So at four degrees Celsius, the density of liquid water is highest. Liquid water at four degrees will sink. So if you take a small water pond the water at the bottom will be four degrees. And as you go up, the water will become colder and colder.

So water will freeze from the top. All other liquids will freeze from the bottom. And freezing from the top means that water is able to protect whatever biological species you have in the water pond because the ice acts as an insulating layer. So this very unusual property, that water has a density maximum at four degrees is actually essential for the evolution of life.

Course overview

Modules: 6
Completion time
Completion time: 30 minutes
Difficulty level
Difficulty level: Intermediate