[Santzowind]

i have seen a simple experiment showing a glass filled with ice..when the temperature rises the ice melts..but if we freeze the water again it becomes iced water but not solid ice...and that is the problem with the earth's temperature rise ..even if the temperature at the poles falls again the water won't turn into ice...my question is the following...
Is there a way -by chemical or other intervention- to make iced water turn into ice again?

[Donk]

If you take enough heat energy out of a glass of water, it will turn to ice.

I'm trying to guess at what the experiment you saw was trying to demonstrate: Supercooling or Latent Heat.

Supercooling: if you take a glass of very pure water and cool it without agitating, it can get to well below freezing point while remaining liquid. If you then drop something in it (preferably NOT your finger!) the whole mass will suddenly freeze, probably cracking the glass.

Latent Heat: a thermometer in the water shows the temperature dropping by, say, 10 degreesC per minute. It reaches zero, then stops. The water stays liquid, even though heat is being withdrawn from it at the same rate. After eight minutes, when it has lost enough heat energy, it freezes. That energy is called the "latent heat of fusion of ice". It represents the energy change needed to force a change of state from solid to liquid, or vice versa, and represents enough energy to cool water from 80C to zero.