Complete the text with the words below.

The greenhouse effect is very important; if it ... occur at all, the temperature of the planet ... be 40 degrees lower and the oceans ... freeze. But an increase in the greenhouse effect may ... to global warming with disastrous consequences. The higher average temperatures produced by global warming could cause ... changes in the weather. Less rain might fall over large land masses. Central Africa, South Asia and some parts of the United States ... risk severe drought and famine. More rain might fall in coastal areas and over the oceans, there ... be more storms and hurricanes in the Pacific. A rise in the earth’s average temperature of only one or two ... would probably melt the polar ice caps and raise sea levels. Sea level throughout the world is already ... by about two millimetres a year. If the polar ice caps melt, sea levels could rise by more than a meter over a few decades.