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Water -Key to Climate Change 

Water has many extraordinary and unique properties and, at present, conditions prevail on the planet of Earth so these properties work to support life here.

Scaled distribution of layers in the atmosphere   T=thermosphere M=mesosphere S=stratosphere W=troposphere where almost all water is found




Web lesson
It's Just a Phase: Water as a Solid, Liquid, and Gas

















NASA site showing how localised water is in the atmosphere




Web lesson How high the atmosphere?
**Be language alert**



Water is part of every living organism, including humans. We are 55-65% water and organs like our brains are 70-80% water. 

Water can exist in all three states (liquid, solid, vapour) at once and does so on Earth.

 It is a liquid between 0°C and 100°C and so can exist as a liquid on most parts of the planet. Oceans cover 71% of Earth’s surface.   

 It conducts thermal energy more easily than any liquid except mercury. This means it acts to moderate temperature differences in the oceans and also within each of us.

It is slow to heat and slow to cool.  This moderates surface temperatures of the planet and it helps each of us resist changes to our own temperatures from sudden weather changes. This property  means that  relatively small changes to the amount of water vapour in the atmosphere can produce large variations in weather.

 It is ‘sticky’ and forms drops. This enables it to form tiny water droplets or ice crystals around tiny dust particles (cloud condensation nuclei) in the air. It also enables water to move through our capillaries.

 The white cloud, ice and snow forms of water scatter sun light around the atmosphere and reflect it back out into space. Also when sunlight strikes water at an angle it tends to be reflected. This helps maintain the thermal balance of Earth.

 It is unique in that its solid form floats on its liquid form i.e. is less dense when solid. This property works to support life on Earth. 

Water vapour absorbs low frequency waves of energy e.g. the infrared waves emitted from the sun and from Earths surface. It re-emits them in all directions, including back to Earth’s surface. Without water vapour in the atmosphere Earth’s surface would be about 31°C cooler! Combined, the other Warmer Trace Gases make about 2°C difference to the global surface temperature.

 It is concentrated in the bottom layer of the atmosphere and then only in certain regions of the globe. 99% of water vapour and ‘weather’ is found in the troposphere i.e. within 8-15kms of Earth’s surface. It is barely detectable in -40°C Antarctic air (0.0001% of the air). It can be 4% of the +40°C Saharan Desert air. 

About 0.001% (13000 cu. kms) of the mass of Earth’s water is in the atmosphere. There is 45000 times as much in the oceans (1400 million cu. kms). Each day about 250 cu. kms evaporates into the atmosphere and this is balanced by precipitation (rain, mist, drizzle, hail, snow falls).

 The movement of both the oceans and the atmosphere transfer thermal energy from warmer regions to cooler regions. In the absence of water the poles would be much cooler and the tropics much warmer. Similarly the extremes between day and night surface temperatures would be much greater.

 Water molecules are cycled in and out of the atmosphere every 6-10 days. By comparison, CO2 molecules have a cycle of 60 years or more.

 The constant interchange between the oceans and the atmosphere is not limited to water molecules. 99% of Earth’s CO2 is dissolved in the oceans. Increasing the thermal energy retained by the oceans reduces their absorption and increases their emission of CO2.

Understanding the role of water is the greatest challenge in the study of Climate Change.  
It is by far the dominant Warmer Trace Gas.
The rapid atmospheric water cycle and the slow ocean thermal cycle can both generate sudden changes.   
Clouds cool Earth’s surface by reflecting solar energy back to space and warm it by retaining infra-red radiation and radiating it back to Earth’s surface.
Both solar and terrestrial activities generate the nuclei or seeds for cloud formation.    
Additional high cloud formation tends to warm up Earth’s surface and low cloud to cool it down.
The challenge is to predict how and where clouds will form in response to a thermal build-up at Earth’s surface and to know whether different regions cool down or warm up.

One thing is certain. The study of the complex role water has in Earth’s energy balance reveals a precious substance of extraordinary beauty and that we are part of an awesome process. 

 This page is part of a programme  Communicating and Teaching the scientific principles underlying Climate Change issues.

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Space =
500-1000 kms (variable)

Centre of Earth =
Approx. 6378kms


























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Web data
The  Oceans

Web lesson
The Water Cycle