As it turns out, quite a lot.
China has switched its soy imports from US to Brazil due to trade-war tariffs
Researchers warn Brazil will need to open up millions of hectares to soy growing to meet China supply
Brazil's right-wing President Jair Bolsonaro has already begun weakening the country's environmental protections
The US-China trade war has a lot to do with soybeans, and soybeans have a lot to do with the Amazon.
Brazil, where most of the Amazon rainforest lies, is the world's biggest soybean producer, and growing soybeans is one of the leading causes of deforestation in Brazil, behind cattle grazing.
Until last year, the world's biggest buyer of soybeans, China, was splitting its soy imports mostly between Brazilian and US growers, taking more than 31 million tonnes off US hands in 2017 alone.
But as the trade war escalated between Washington and Beijing, the US slapped a 25 per cent tariff on goods imported into the United States from China, and China responded in kind, with its own 25 per cent tariff on US products, including soy.
As a result, China's soy imports from the US crashed and they looked for cheaper alternatives, namely Brazil, to plug the gap.
While all this was going on, Brazil elected a right-wing president, Jair Bolsonaro, who had promised to water down protections for the Amazon, and described indigenous land rights in Brazil, including the Amazon, as "an obstacle to agribusiness".
His first move after being elected was to hand control of the department charged with protecting indigenous rights over to the Ministry of Agriculture.
Now according to researchers writing in Nature today, this has set the stage for a potential rush on deforestation in the Amazon rainforest.
Now for the bad news
A birdseye view of a vast forest stretching into the distance.
Researchers fear an area as big as Greece could be cleared in the Amazon to grow soy. (Reuters: Bruno Kelly)
In a worst-case-scenario, Brazil will need another 12.9 million hectares of land dedicated to growing soy to meet China's needs, according to researcher Richard Fuchs from the Karlsruhe Institute of Technology in Germany.
"Everything that more or less was the shortfall from the US [soy supply in 2018] was covered by Brazil," he said.
"It's a kind of early warning sign that, at least in the short term, China will try to satisfy their demand by turning towards Brazil."
In 2006, Brazil implemented a soy moratorium, meaning that Amazon forest couldn't be directly cleared to grow the crop.
A single tree standing in flattened landscape.
A 2006 soy moratorium means the Amazon can't be directly cleared for its farming, but there are other ways soy production could encroach on the forest. (Getty Images: Raphael Alves)
The moratorium has largely been successful in slowing Brazil's rate of deforestation, although research has found that nearly 60,000 hectares of forest have been illegally converted to soy plantations in the Brazilian state of Mato Grosso since the moratorium came into place.
But Mr Bolsonaro could ignore the moratorium, or soy expansion could have a less direct impact on the Amazon, according to Dr Fuchs.
"Often [soy is] not driving deforestation directly, but indirectly by expanding into pastureland, and then pastureland is driven into the rainforest," he said.
For the worst-case-scenario to happen, Brazil alone would have to make up for the US soy shortfall and new growing regions would have to be concentrated in the Amazon rainforest.
But there are several factors at play that make the worst-case-scenario, at least in the short term, unlikely.
Firstly, Brazil could replace existing crops like maize with soy, thus negating the need to clear more land.
But more immediately, if the US-China trade war cools, China is likely to resume its soy trade with the US before Brazil can significantly expand its own industry, according to Rod Keenan from the University of Melbourne.
"The timeframes are the issue. It depends how long these trade tariffs stay in place," Professor Keenan said.
He also said there were significant hurdles in the way that limit how much product Brazil can export.
"One of the big restrictions on soy production in Brazil is getting the stuff out — the infrastructure's not there at the moment."
China expansion could flourish under 'Tropical Trump'
Bolsonaro and Trump side by side.
President Bolsonaro's environmental credentials have many ecologists worried for the health of the Amazon. (AP: Evan Vucci)
China's massive demand for soy is a result of its growing middle class with an increasingly westernised, meat-rich diet.
The soy is used as a feed-stock for pigs, poultry and cattle.
As climate change and growing population make food security one of the biggest challenges of the next century, China is intent on a plan it calls the "Belt and Road" initiative, locking in its global food supply through a vast network of land and sea trade routes across 152 countries.
And Brazil is set firmly in its sights.
In 2015, China's Premier Li Keqiang secured agreement from Brazil and Peru to begin feasibility studies into a railway line crossing South America from Brazil's east coast, 5,200 kilometres through the Amazon to Peru's west coast.
A worker feeding pigs in China.
Researchers have suggested eating less meat as a way to combat growing soy demand. (Reuters: Stringer)
The railway would allow exports from Brazil to travel straight to the west coast, opening up a direct route to China by ship, rather than via the Panama Canal, under the South American continent, or around Africa.
Brazil and Peru both found the project to be unfeasible, but some of the environmental obstacles standing in its way will be of little concern to Mr Bolsonaro, according to Bill Laurence from James Cook University.
Mr Bolsonaro's a really big worry. He's the worst environmental president I think in living memory. People call him the Tropical Trump for good reason," Professor Laurence said.
"Environment, development and indigenous people...things that have held up these projects in the past he doesn't see as an obstacle."
Even if the US-China trade war is settled soon, the long-term environmental impact of China's expansion into South America is likely to be significant.
Despite Chinese President Xi Jinping's assurances that the 21st century silk road would be "green, healthy, intelligent, and peaceful", huge environmental concerns have already been raised around the world.
A hydroelectric power plant and dam being built under the Belt and Road initiative by state-controlled Chinese companies in Sumatra, Indonesia, is threatening the only known habitat of the world's rarest orangutan, and the endangered Sunda pangolin, for instance.
If little regard is shown for development in the Amazon, the entire dynamic of the forest ecosystem could be altered, according to Clive McAlpine from the University of Queensland.
"You've got deforestation, which is releasing carbon back into the atmosphere. The impacts on the environment are quite significant," Professor McAlpine said.
"It will make that environment hotter and drier. Forests keep the land surface cooler, and impact cloud formation. You will lose all those benefits of the forest on the climate."