How do we know what the temperature of the Earth was in the past? What is the relationship between CO2 (carbon dioxide) and temperature on Earth?

What is the greenhouse effect?

Why are global sea levels rising?

How do we know what the temperature of the Earth was in the past? - One way to measure past temperatures is to study ice cores. Whenever snow falls, small bubbles filled with atmospheric gases get trapped within it. In some places, so much snow falls that the older layers become buried and compressed into ice, locking away air bubbles in ice sheets and glaciers

What is the relationship between CO2 (carbon dioxide) and temperature on Earth? - When the carbon dioxide concentration goes up, temperature goes up. When the carbon dioxide concentration goes down, temperature goes down.

What is the greenhouse effect? - the trapping of the sun's warmth in a planet's lower atmosphere, due to the greater transparency of the atmosphere to visible radiation from the sun than to infrared radiation emitted from the planet's surface.

Why are global sea levels rising? - Global warming is causing global mean sea level to rise in two ways. First, glaciers and ice sheets worldwide are melting and adding water to the ocean. Second, the volume of the ocean is expanding as the water warms.