You will see crosshairs which you can move on the screen. Moving them chooses a target level for average CO2 in the atmosphere. The 2009 level is 386. (This means 386 molecules of CO2 per million molecules in the atmosphere; "parts per million" or ppm.)
Setting the crosshairs at 450 (a common recommendation) makes a line move on another part of the same screen, showing how the world's Carbon emissions need to drop each year, to stabilize at your chosen level.
Another line on the same screen shows the resulting rise in temperature, relative to 1750 or any later year.
Then try other targets, like 350 or 550, and see how emissions and temperatures are affected.
The options are discussed more on our Goals page.
Go to the Climate Model.