Final answer:
Sea levels are rising at a rate of 3.4 mm per year due to the melting of land and sea ice, as well as thermal expansion of the warmer water. This increase in sea level is primarily caused by climate change.
Step-by-step explanation:
Sea level is rising at a rate of 3.4 mm per year due to two main factors: melting ice and thermal expansion. Melting land ice, such as glaciers, contributes to sea level rise as the water from the melted ice flows into the ocean.
Melting sea ice, like the arctic ice, does not directly raise sea levels, but it affects climate patterns and can contribute to the melting of land ice, thus indirectly raising sea levels. Additionally, as global temperatures increase, the warmer water expands and takes up more space, leading to a rise in sea level.