Skyscrapers Shanghai World Financial Center (R) and Jin Mao Tower are seen during heavy rain at the financial district of Pudong in Shanghai May 15, 2015. REUTERS/Aly Song TPX IMAGES OF THE DAY

Heavy fog rolls by early in the morning near the Dubai Marina November 21, 2007. Once filled with the cacophony of cranes and construction labourers, Dubai today hums to the work of a quieter crowd. The brash Gulf emirate, renowned for extravagant real estate projects and flashy living, has turned into a city of auditors. Picture taken November 21, 2007. To match Special Report DUBAI/ REUTERS/Steve Crisp/Files (UNITED ARAB EMIRATES - Tags: BUSINESS CITYSCAPE SOCIETY ENVIRONMENT)

Fog clears around the Houses of Parliament in central London December 11, 2013. REUTERS/Olivia Harris (BRITAIN - Tags: CITYSCAPE ENVIRONMENT SOCIETY)

People walk on a pier in the Hudson River as clouds shroud One World Trade Center (C) and the skyline of Lower Manhattan in New York as seen from Hoboken, New Jersey, May 25, 2012. REUTERS/Gary Hershorn (UNITED STATES - Tags: CITYSPACE ENVIRONMENT)

An aerial view of the famous Christ the Redeemer atop of Corcovado mountain in Rio de Janeiro, January 12, 2011. REUTERS/Bruno Domingos (BRAZIL - Tags: SOCIETY RELIGION TRAVEL IMAGES OF THE DAY)

Low level clouds float over Dubai's Marina area as the sun sets on Dubai on New Year's Eve, December 31, 2008. Dubai's ruler on Tuesday ordered the cancellation of all New Year celebrations in the Gulf's tourism hub in solidarity with Palestinians facing Israeli military attacks in the Gaza Strip. REUTERS/Steve Crisp (UNITED ARAB EMIRATES)

A bird flies in front of city sky scrapers covered by fog in the center of Warsaw February 23, 2015. REUTERS/Kacper Pempel (POLAND - Tags: ENVIRONMENT ANIMALS CITYSCAPE)

A long exposure picture shows a seasonal fog illuminated by the lights of Cape Town harbour as the city prepares for the start of the southern hemisphere winter, May 8, 2012. REUTERS/Mike Hutchings (SOUTH AFRICA - Tags: ENVIRONMENT CITYSPACE)

Low level clouds float over Dubai's Marina area as the sun sets on Dubai on New Year's Eve, December 31, 2008. Dubai's ruler on Tuesday ordered the cancellation of all New Year celebrations in the Gulf's tourism hub in solidarity with Palestinians facing Israeli military attacks in the Gaza Strip. REUTERS/Steve Crisp (UNITED ARAB EMIRATES)

A migrant labourer works at a construction site near The Bund on the banks of the Huangpu River in Shanghai December 27, 2009. REUTERS/Aly Song (CHINA - Tags: BUSINESS CONSTRUCTION)

The skyline of San Francisco appears above the evening fog as the suns sets on the Marin Headlands in Sausalito, California April 18, 2009. REUTERS/Robert Galbraith (UNITED STATES ENVIRONMENT SOCIETY)

Heavy fog rolls by high-rise constructions near the Dubai Marina in this November 21, 2007 file photo. With their ban on interest, the Gulf's Islamic banks that managed to avoid the types of debt which proved toxic for their conventional counterparts are now praying the global crisis will bypass their property holdings. To match feature FINANCIAL/ISLAMICBANKS-GULF/ REUTERS/Steve Crisp (UNITED ARAB EMIRATES)

Shanghai's skyscrapers Shanghai World Financial Center (L), Shanghai Tower (R) and Jin Mao Tower (top) are seen at the financial district of Pudong during Earth Hour in Shanghai March 29, 2014. Earth Hour, when everyone around the world is asked to turn off lights for an hour from 8.30 p.m. local time, is meant as a show of support for tougher action to confront climate change. REUTERS/Carlos Barria (CHINA - Tags: SOCIETY BUSINESS TPX IMAGES OF THE DAY)

Early morning fog enshrouds Cape Town's Green Point 2010 FIFA Soccer World Cup Stadium, August 25, 2009. South Africa is hosting soccer's showpiece event, which kicks off on June 11, 2010. REUTERS/Mike Hutchings (SOUTH AFRICA SPORT SOCCER IMAGES OF THE DAY)

A cruise ship makes its way past New York's Lower Manhattan and One World Trade Center as steam rises from the Hudson River as seen from Hoboken, New Jersey, January 11, 2014. REUTERS/Gary Hershorn (UNITED STATES - Tags: ENVIRONMENT CITYSCAPE TPX IMAGES OF THE DAY)

The pods on the London Eye tourist attraction cast shadows against a thick morning fog as the spring sun shine begins to burn it off in central London, March 15, 2012. REUTERS/Andrew Winning (BRITAIN - Tags: ENVIRONMENT SOCIETY TRAVEL TPX IMAGES OF THE DAY)

Heavy fog rolls by early in the morning near the Dubai Marina, November 21, 2007. Fog across the United Arab Emirates has disrupted traffic and delayed many flights over the last few days. REUTERS/Steve Crisp (UNITED ARAB EMIRATES)