Geography of Brazil clearing. Public policies intended to promote sustainable management of timber extraction, as well as sustainable use of nontimber forest products (such as rubber, Brazil nuts, fruits, seeds, oils, and vines), were being discussed intensely in the mid-1990s. However, implementing the principles of sustainable development, without irreversible damage to the environment, proved to be more challenging than establishing international agreements about them. Although 90% of the country is within the tropical zone, the climate of Brazil varies considerably from the mostly tropical North (the equator traverses the mouth of the Amazon) to temperate zones below the Tropic of Capricorn (23°27' S
Geography of Nigeria known as the harmattan. The northward retreat of the tropical continental airmass (CT), is caused by the sun's northward shift from the tropic of capricorn in the southern hemisphere to the tropic of cancer in the northern hemisphere. This shift begins from February and ends in June, when the sun is fully overhead, at the tropic of cancer in the northern hemisphere. During this northward migration of the sun as a result of the earth tilting along its axis, the sun crosses the equator (around March), moving over west Africa at this time on its journey to the northern hemisphere.