Make a model of the greenhouse effect. You will need two nonmercury thermometers, one large plastic bag such as a produce bag, one small plastic bag such as a sandwich bag, and two twist ties. Place one thermometer in the small bag. Blow into the bag to inflate it, and tie it with a twist tie. Put the inflated bag inside the larger plastic bag. Inflate the large bag, and seal it with a twist tie. Now lay the bags containing the thermometer on a sunny windowsill or outside. Lay the unbagged thermometer next to it. Observe the temperature reading of both thermometers after 30 minutes. Explain your results.