Brown clouds are large patches of pollution clouds, the most distinctive of which are present over the skies of Asia. The pollution clouds can significantly decrease the amount of sunlight that reaches cities, sometimes causing a visible haze that's easily seen from aircraft. Scientists predict that these brown clouds could have serious effects on Chinese and Indian crop yields.
A report by the United Nations Environment Program cites 13 cities in which the brown clouds are likely to have the highest effect because of their density. The cities include Bangkok, Cairo, New Delhi, Seoul and Tehran. The report claims that 10% to 25% of the cities' sunlight has been blocked out due to the clouds' effect.
