SCIENTIFIC THINKING Will increasing atmospheric levels of CO2 make you sneeze as well as itch? Scientists studying the effects of rising CO2 levels have looked at ragweed, whose pollen is the primary allergen for fall hay fever. They grew ragweed in three levels of CO2: a pre-industrial concentration of 280 ppm, a year 2000 level of 370 ppm, and a projected level of 600 ppm. They found that pollen production increased by 131% and 320% in the plants exposed to the recent and projected CO2 levels, respectively. What was the hypothesis of this experiment? Do the results support the hypothesis? Given what you know about climate change, what other variables would you like to test, and what other measurements would you like to take?