Along with the fireworks and samba party of the opening ceremony of the 2016 Rio Olympics came stark warnings about rising sea levels and global temperatures.

The roughly 3.3 billion people who watched the ceremony saw a video describing rising carbon dioxide levels and showing cities from Lagos, Nigeria, to Rio de Janeiro underwater. It was one of several performances highlighting the vital role that forests, such as the Amazon, the world’s largest rainforest, play in absorbing planet-warming gases.

“City of God” director Fernando Meirelles, one of the creative directors of the opening ceremony, said he wanted to make the rainforest a focus of the ceremonies. He has advocated for forest policies before and is directing a TV series on climate change for the BBC.

“The world is threatened because of global warming. We are calling for action,” he said before the ceremony.

As the 11,000 competitors from the world’s nations entered Maracanã Stadium on Friday in downtown Rio, they each planted a seedling in silver towers representing urban claustrophobia. The towers, laid out in the form of the Olympic rings, erupted into rich green foliage at the end of the ceremony. The seedlings will grow into the Athletes’ Forest in the area of Deodoro.

Environmentalists applauded the spotlight on climate change. Sen. Ed Markey (D-Mass.); the Sierra Club; and Erik Solheim, executive director of the U.N. Environment Programme, among many others, gave somewhat surprised nods to the performance on Twitter. Others criticized the focus on global warming, given the pollution in Rio’s own waters.

Carlos Rittl, executive secretary of the Observatório do Clima, a consortium of environmental groups in Brazil, called the climate change theme “just epic.”

Rittl said there is little cause to celebrate the forest situation in Brazil, with rates of deforestation still high and a tough fire season ahead. But, he said, he hopes the forest segments during the ceremony will spark conversations.

“It gave us some hope, when everyone around the world was watching Brazil, watching Rio, that there will be more opportunities to talk about and act on global warming, forests conservation and restoration, and renewable energy, and to definitively overcome the outdated speech that Brazil has done more than any other country to combat climate change,” he said. “We have reached significant results in the past. But we are far, far away from having done enough.”

A warning seen by more than 3B

The climate change segment aired right before the Parade of Nations and started with a description of rising carbon dioxide levels pushing temperatures higher. Water flooded low-lying areas around the world: Amsterdam; Dubai, United Arab Emirates; Florida; Shanghai; Lagos; and Rio de Janeiro.

“What a challenge for the coastline cities,” said a female narrator. “Is there a way out?”

On cue, a young boy promptly walked out in the center of the arena and sat down to inspect a small plant.

“A flower has sprouted in the street!” rang out the voice of actress Judi Dench as she read Carlos Drummond de Andrade’s classic poem “A Flor e a N´usea” (“The Flower and the Nausea”).

“Buses, streetcars, steel stream of traffic: steer clear!” she said as video showed workers planting trees and crops. “A flower, still pale, has fooled/ the police, it’s breaking through the asphalt.”

The video showed glimpses of seeds expanding from below ground, verdant rainforests and tree-filled stretches of land. It then panned to Rio de Janeiro, home to more than 6 million people.

“I sit down on the ground of the nation’s capital at five in the afternoon/ and fondle with my fingers this precarious form,” Dench said. “It’s ugly, but it’s a flower. ... It broke through the asphalt, tedium, disgust, and hate.”

Reprinted from ClimateWire with permission from Environment & Energy Publishing, LLC. E&E provides daily coverage of essential energy and environmental news at Click here for the original story.