Photo taken on March 27, 2021 shows the Acropolis hill with lights turned off during Earth Hour in Athens, Greece. Lights around the world are turned off at 8:30 p.m. local time on Saturday to mark Earth Hour 2021. (Photos: Xinhua)

Photo taken on March 27, 2021 shows the Acropolis hill with lights illuminated ahead of Earth Hour in Athens, Greece. Lights around the world are turned off at 8:30 p.m. local time on Saturday to mark Earth Hour 2021.

Photo taken on March 27, 2021 shows the Acropolis hill with lights illuminated ahead of Earth Hour in Athens, Greece. Lights around the world are turned off at 8:30 p.m. local time on Saturday to mark Earth Hour 2021.

Photo taken on March 27, 2021 shows the Red Square with lights illuminated ahead of Earth Hour in Moscow, Russia. Lights around the world are turned off at 8:30 p.m. local time on Saturday to mark Earth Hour 2021.

Photo taken on March 27, 2021 shows the Red Square with lights turning off during Earth Hour in Moscow, Russia. Lights around the world are turned off at 8:30 p.m. local time on Saturday to mark Earth Hour 2021.

Photo taken on March 27, 2021 shows the Red Square with lights turning off during Earth Hour in Moscow, Russia. Lights around the world are turned off at 8:30 p.m. local time on Saturday to mark Earth Hour 2021.

Photo taken on March 27, 2021 shows the Red Square with lights illuminated ahead of Earth Hour in Moscow, Russia. Lights around the world are turned off at 8:30 p.m. local time on Saturday to mark Earth Hour 2021.

Photo taken on March 27, 2021 shows the Red Square with lights turned off during Earth Hour in Moscow, Russia. Lights around the world are turned off at 8:30 p.m. local time on Saturday to mark Earth Hour 2021.

Photo taken on March 27, 2021 shows the Red Square with lights turning off during Earth Hour in Moscow, Russia. Lights around the world are turned off at 8:30 p.m. local time on Saturday to mark Earth Hour 2021.