Carbon dioxide and Climate change Bubbles of air trapped in ancient glaciers can provide scientists with a record of atmospheric conditions of the planet in the past. For example, scientists have been able to deduce, from these bubbles, the amount of carbon dioxide (CO2) in the atmosphere and the average changes in temperature around the planet over the last 400,000 years. The following graph shows some of these data: changes in global temperature (measured in degrees Celsius, or 0 C) over a time period from 420,000 years ago (left side of graph) to the present century (up to the year 2000, right side of graph). The inset graph highlights these changes in temperature over a much shorter time period - Changes in global temperature in degrees Celsius) Temperature re emperature (°C) 1000 120 100 1600 18 Changes in global temperature (in degrees Celsius) Temperature (0) NO 20.02 Temperature (°C) 0.5 1000 1200 1400 1600 1800 2060 Year 400000 350000 300000 250000 200000 15000 100000 500000 Years before present Henri From the graphs, you see that global temperature has risen and fallen (1). over the past 420,000 years; over the last 100 years, however, global temperature has generally (2) (1) several times; (2) increased (1) once; (2) remained stable (1) twice; (2) decreased