With the Amazon rainforest experiencing its worst drought for 40 years, Brazil has declared many cities in the region's largest state, Amazonas, as disaster areas.
Droughts in the Amazon are usually associated with El Niño, a periodic warming of southern Pacific waters. But no such warming has been detected this year.
However, the North Atlantic has been unusually warm, making water evaporate more than usual. This might have had the knock-on effect of providing less rainwater to the Amazon region.
Paul Lefebvre, a researcher who runs a monitoring station in the Amazon, says the drought could damage local fish supplies and human health.
He adds that the drought could slow tree growth, which could eventually contribute to climate change by making the forest less able to absorb carbon dioxide.
The fear is that the Amazon could become part of the problem of climate change rather than part of the solution, as many scientists have proposed.