There are two tasks in this exercise: Task 1: Read the section of "Are human activities contributing to climate change?" and complete the following summary by filling the gaps with either one or two words. The words required are all used in the original text. Studying the causes of unusual climate change is problematic because change caused by _____________ is often hidden or masked by natural climate variability. In order to separate these two factors, investigations can be divided into __________ and ______________ studies. In the first case, information can be gained by measuring _________________, and in the second situation by finding reasons for the unusual changes in climate that have been noted. In attributing causes resulting from human activity, scientists can make use of ______________. Two examples of this are, firstly, by comparing maps or patterns of temperature change, which is known as _______________, or secondly, by finding characteristic patterns of climate response between observed climate change and predicted change from models, which is referred to as a _________________.