Clouds are not as light as they look

“I am the daughter of Earth and Water, 

And the nursling of the Sky; 

I pass through the pores of the ocean and shores; 

I change, but I cannot die.” 

This is what poet PB Shelly wrote about clouds. Made up of air and tiny droplets of water, they have been the fodder for imagination to poets and common man alike. The effortless ease with which those clouds float across the sky makes us feel that they do not have any weight. However, this is far from truth. These ‘daughters of earth and water’, which come in various shapes and sizes, also have their own weight. However, the weight varies depending on the type of clouds.  

Types of cloud 
Based on the height at which clouds exist in the troposphere, the atmospheric layer closest to the earth, there are different types of clouds.  

• At around 16,500-45,000 feet, we find cirrus, cirrostratus, and cirrocumulus clouds. 
• At around 6,500-23,000 feet, we find altocumulus, altostratus and nimbostratus clouds. 
• At or less than 6,500 feet, we find status, cumulonimbus, stratocumulus and cumulus clouds. 
• Special types of clouds include contrails, mammatus, lenticular and orographic clouds. 

Cumulus: The most commonly seen clouds and their weight 
These low-level clouds are fluffy and look like white cotton balls and are seen mostly during the summer. The density of other types of clouds would be differ. So, let's stick to the cumulus clouds while it comes to measuring weight. 

 A cumulus cloud has approximately a quarter of a gram of water for every cubic metre of cloud. The total weight of the water will depend on the size of the cloud. Summer cumulus clouds vary in size, but a typical one would be about one kilometre across and about the same tall. When measured in terms of cubic metres, that comes to 1000 x 1000 x 1000 cubic metres or 1 billion cubic metres. So the weight of water at half a gram per cubic metre is about 250 million grams or 250 tonnes. That’s about the same weight as two adult blue whales. 

Now, we must add the weight of the water in the cloud to the weight of air. The weight of air is the barometric pressure present at a certain altitude in the atmosphere. The closer we measure to the sea level, the high the pressure. The weight of air at the altitude which cumulus clouds float at, is around 1 kilogram for every cubic metre. That makes the weight of air in the same cloud 1 billion kilograms, or, 1 million tonnes. Thus, an average cumulus cloud weighs 1,000,250 tonnes. But they are relatively light-weight clouds.  

Grey thunderstorm clouds hold a lot more water content, about two grams per cubic metre, and they are much larger in size too, about 10 km tall and the same across. This means they hold 2 million tonnes of water and 1 billion tonnes of air. That’s 1,002,000,000 tonnes in all. Yeah, clouds are much heavier than we think!