This photo taken on April 9, 2016 shows a man making his way along a street with white pollen falling from catkin-bearing trees as the return of pleasant weather marks the arrival of the allergy season in Beijing. / AFP PHOTO / FRED DUFOURFRED DUFOUR/AFP/Getty Images

This photo taken on April 9, 2016 shows motorists making their way along a street filled with white pollen falling from catkin-bearing trees as the return of pleasant weather marks the arrival of the allergy season in Beijing. / AFP PHOTO / FRED DUFOURFRED DUFOUR/AFP/Getty Images

This photo taken on April 9, 2016 shows a man (L) making his way along a street with others as white pollen falls from catkin-bearing trees as the return of pleasant weather marks the arrival of the allergy season in Beijing. / AFP PHOTO / FRED DUFOURFRED DUFOUR/AFP/Getty Images

CORRECTION - This photo taken on April 9, 2016 shows a cyclist making his way along a street filled with white pollen falling from catkin-bearing trees as the return of pleasant weather marks the arrival of the allergy season in Beijing. / AFP PHOTO / FRED DUFOUR / The erroneous mention[s] appearing in the metadata of this photo by FRED DUFOUR has been modified in AFP systems. Please immediately remove the erroneous mention[s] from all your online services and delete it from your servers. If you have been authorized by AFP to distribute it (them) to third parties, please ensure that the same actions are carried out by them. Failure to promptly comply with these instructions will entail liability on your part for any continued or post notification usage. Therefore we thank you very much for all your attention and prompt action. We are sorry for the inconvenience this notification may cause and remain at your disposal for any further information you may require.FRED DUFOUR/AFP/Getty Images

TOPSHOT - Children play along the dry banks of the Pahang river as schools remain closed due to the ongoing heatwave in Termerloh, outside Kuala Lumpur, on April 11, 2016. More than 250 Malaysian schools were closed on April 11 due to a heatwave brought on by the El Nino weather phenomenon which is severely affecting food production and causing chronic water shortages in many countries. / AFP PHOTO / MOHD RASFANMOHD RASFAN/AFP/Getty Images

TOPSHOT - A dead fish is seen on the dry banks of the Pahang river during the ongoing heatwave in Termerloh, outside Kuala Lumpur, on April 11, 2016. More than 250 Malaysian schools were closed on April 11 due to a heatwave brought on by the El Nino weather phenomenon which is severely affecting food production and causing chronic water shortages in many countries. / AFP PHOTO / MOHD RASFANMOHD RASFAN/AFP/Getty Images

A buffalo eats grass hidden under a cover of dead leaves as schools remain closed due to the ongoing heatwave in Temerloh, outside Kuala Lumpur, on April 11, 2016. More than 250 Malaysian schools were closed on April 11 due to a heatwave brought on by the El Nino weather phenomenon which is severely affecting food production and causing chronic water shortages in many countries. / AFP PHOTO / MOHD RASFANMOHD RASFAN/AFP/Getty Images

Children walk along the dry banks of the Pahang river as schools remain closed due to the ongoing heatwave in Temerloh, outside Kuala Lumpur, on April 11, 2016. More than 250 Malaysian schools were closed on April 11 due to a heatwave brought on by the El Nino weather phenomenon which is severely affecting food production and causing chronic water shortages in many countries. / AFP PHOTO / MOHD RASFANMOHD RASFAN/AFP/Getty Images