What factor that has increased over recent years is thought to be affecting the thickness and area of ice covering the sea?

The factor that has increased over recent years and is thought to be affecting the thickness and area of ice covering the sea is global warming. Here are the steps explaining this:

1. Global warming refers to the long-term increase in Earth's average temperature. It's primarily caused by human activities, especially the burning of fossil fuels like coal, oil, and gas, which release greenhouse gases (GHGs) into the Earth's atmosphere.

2. These GHGs, especially carbon dioxide (CO2) and methane (CH4), trap heat from the sun's rays within the atmosphere. This is known as the greenhouse effect.

3. Over recent years, the concentration of these GHGs in the atmosphere has been increasing, leading to an increase in Earth's average temperature.

4. This rise in temperature is causing the polar ice caps to melt at an accelerated rate.

5. As the ice melts, the area and thickness of ice covering the sea decreases. This is particularly noticeable in the Arctic, where the extent and thickness of sea ice have been shrinking rapidly over the past few decades.

6. Therefore, the increase in global warming is thought to be affecting the thickness and area of ice covering the sea.