Due to the greenhouse effect, the average temperature of the planet has risen by about one degree Celsius over the last century. This may seem to be another negligible increase, but the climate is a very delicate mechanism that depends on very many interconnecting variables: if any of them are altered, there may be unforeseeable consequences, while others are already evident, such as the increase in the frequency of extreme weather events. In fact there may be long periods of draught, sudden exceptional rainfall, floods, waves of excessive heat and cold. Tropical cyclones may be strengthened by violent rainfall, winds and the sea level.
