CASE STUDY Reports about climate change appear frequently in the media. Climate scientists warn us that major changes will occur in the coming years. For example, scientists predict that the changing climate will probably bring more rain to California, but they don’t know whether the additional rain will come during the winter wet season or extend into the long dry season in spring and summer. Is it possible to investigate the effects of possible future changes in climate now?

Researchers at the University of California, Berkeley carried out an experiment to study the effects of more rain in either season. They randomly assigned plots of open grassland to three treatments. One treatment was to add water equal to 20% of annual rainfall during January to March (winter). A second treatment was to add water equal to 20% of annual rainfall during April to June (spring). The third treatment was to add no water beyond normal rainfall. Eighteen circular plots of area 70 square meters were used for this study, with six plots used for each treatment. One variable the researchers measured was total plant biomass, in grams per square meter, produced in a plot over a year. Total plant biomass for the three treatments was compared to assess the effect of increased rainfall.

Is this a good study? By the end of this chapter, you will be able to determine the strengths and weaknesses of a study such as this.