This is because the tropical Pacific ocean is expected to be warmer this year, which leads to hotter and drier conditions that make it more difficult for plants to grow and absorb the excess carbon dioxide released from the burning of fossil fuels, which is fueling climate change.

Professor Richard Betts of the Met Office Hadley Center explained in depth:

https://www.ecowatch.com/atmospheric-co2-levels-2019-2627055991.html