Gap-fill exercise

Look at the graph and complete the commentary by filling in the gaps, then press "Check" to check your answers. Use the "Hint" button to get a free letter if an answer is giving you trouble. Note that you will lose points if you do!

However, statistics on the increase of cirrus levels as a result of stratospheric aircraft movements are still meagre and their statistical significance is not always proven. Yet at Salt Lake City and between and do an in cirrus cloudiness which paralleled the in jet aircraft activity ( 7.5). The expected rapid development of civil aviation in future decades may make this an important element of anthropogenic atmospheric modification.

(From: Andrew Goudie, The human impact on the natural environment. Basil Blackwell, 1981)