Increased carbon dioxide levels in the atmosphere will most likely lead to

Increased carbon dioxide levels in the atmosphere will most likely lead to higher-than-average sea levels.

Explanation:

An increased level of 'carbon dioxide' in the atmosphere would proportionally increase the temperature of the atmosphere due to the action of trapping of heat by the excessive carbon dioxide. This would result in a substantial increase in the rate of melting of the glaciers all over the world. The water from the melting glaciers would ultimately flow into the seas resulting in higher-than-average sea levels.