Sensitive dependence on initial conditions is a well known feature of chaotic dynamical systems. A butterfly flapping its wings in Hong Kong can cause a thunderstorm in Denton several days later. Nevertheless, the behavior of this butterfly should not change the long term averages - how many thunderstorms per year will be observed in Denton in the next 1000 years. However, it may happen that there is also sensitive dependence on parameters. In this case, bringing an additional butterfly to Hong Kong may essentially change those averages. Additionally, one cannot predict whether getting rid of such dangerous species as wing-flapping butterflies from Hong Kong will improve or deteriorate the climate in Denton.