Latent heat



Above image shows a number of feedbacks that are accelerating warming in the Arctic. Feedback #14 refers to (latent) heat that previously went into melting. The reason this heat is called latent (hidden), is that it doesn't raise the temperature of the water, but instead goes into the process of melting the ice. 

With the demise of the snow and ice cover, an increasing proportion of this heat will no longer go into melting, but will instead get absorbed and thus contribute to accelerated warming in the Arctic.

As the sea ice heats up, 2.06 J/g of heat goes into every degree Celsius that the temperature of the ice rises. While the ice is melting, all energy (at 334J/g) goes into changing ice into water and the temperature remains at 0°C (273.15K, 32°F). 

Once all ice has turned into water, all subsequent heat goes into heating up the water, at 4.18 J/g for every degree Celsius that the temperature of water rises.

The amount of energy absorbed by melting ice is as much as it takes to heat an equivalent mass of water from zero to 80°C. The energy required to melt a volume of ice can raise the temperature of the same volume of rock by 150º C. 



Above video, created by Stuart Trupp, shows how added heat at first (A) goes mainly into warming up water that contains ice cubes. From about 38 seconds into the movie, all heat starts going into the transformation of the ice cubes into water, while the temperature of the water doesn't rise (B). More than a minute later, as the ice cubes have melted (C), the temperature of the water starts rising rapidly again. 

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