They aren't just happening now. They have been an issue for years, but the particularly dry weather has meant that more of the fires spread and aren't as easily contained. Many of the fires are set on purpose by locals who are trying to clear the land so they can plant crops or grow livestock.

Around 20% of the oxygen in the world is generated by the Amazon, so it could cause an increase in the CO2 in the atmosphere. It wouldn't help with global climate issues.