How can you increase the solubility of a gas?
By decreasing the temperature of the liquid or by increasing the partial pressure of the gas above the liquid.
The best example of the pressure is when you take the cap off a bottle of fizzy water. Water is pressurized under an atmosphere or so of carbon dioxide and then capped. Unscrew the lid, the external pressure of carbon dioxide reduces by 2 orders of magnitude. The result? The water fizzes!
Here is a demonstration of this concept.