According to Henry's law, the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid. In other words, the higher the pressure of the gas, the more soluble it is in the liquid.

This is because when the pressure of a gas is increased, the molecules of the gas are forced closer together, which makes it easier for them to dissolve into the liquid. The increased pressure also increases the number of collisions between the gas molecules and the liquid molecules, which increases the chances of the gas molecules being absorbed by the liquid.

In the case of carbon dioxide, it is more soluble in high pressures because the carbon dioxide molecules are forced closer together at higher pressures, making it easier for them to dissolve into the liquid. Additionally, the increased pressure increases the number of collisions between the carbon dioxide molecules and the water molecules, which increases the chances of the carbon dioxide molecules being absorbed by the water.