His warning comes as the Amazon Rainforest in Brazil is experiencing its worst-ever year for fires, with 72,843 fires detected between January and August a staggering increase of 84 percent on the same period in 2018.
While some of these blazes are wildfires, others are set deliberately to illegally clear the forest for cattle ranching, with many pointing the finger of blame at Brazil's president Jair Bolsonaro, who pledged to develop the region for farming and mining when he took office in January, despite the warnings of conservationists around deforestation.
The issue is so significant because the Amazon Rainforest, the world's largest tropical forest, is not only home to around one million indigenous people and three million species of plants and animals, it also slows down the pace of global warming, as a vital carbon store.
Smalling took to Instagram to discuss the fires with his followers - and ask them to make environmentally-positive changes. "We have to start looking after our planet," he wrote.
"The leading cause of the Amazon's deforestation is cattle ranching, and wild fires are deliberately started in an effort to support this. Animal agriculture is responsible for 18 percent of greenhouse emissions, more than the combined exhaust from all transportation, and the fires alone release huge amounts of CO2 into the atmosphere.
"The Amazon rainforest slows down the pace of global warming, and it's been on fire for over two whole weeks. This post is not about 'you're a footballer, focus on the pitch', I'm a human being with a family that would like to see this planet thriving. If I can use my platform to help, that's what I'm going to do. We need to stop the ignorance and all work to make a change."