Brazil is still weeks away from its traditional fire season, but hundreds of blazes, fanned by searing temperatures, are already laying waste to the Pantanal, the world’s largest tropical wetlands, and to parts of the Amazon rainforest.

Scientists say the burning of such vast swaths of land may represent a new normal under rising global temperatures and uneven rain, making efforts to save some of the world’s most important ecosystems much harder.

There were more wildfires in Brazil’s share of the Pantanal, an enormous trove of biodiversity stretching across three countries, between January and June of this year than during the same period in any other year, according to the National Institute for Space Research, which has been tracking fires in Brazil since 1998.

The highest number of fires in at least two decades was also recorded in the Amazon and in the Cerrado savanna, a patchwork of shrubs, grasslands and gnarled trees encompassing 1.2 million square miles in Brazil’s central and northeastern regions.

“It’s really worrying this early on,” said Ane Alencar, the science director at the Amazon Environmental Research Institute in Brazil. Fires at this scale, she said, do not usually occur until August or September, the peak fire months.

But extreme weather has caused fires recklessly ignited by people to quickly spread out of control, Dr. Alencar said, “creating the ideal conditions for any spark to become a wildfire.”