Every year, the Earth's natural carbon sinks such as forests soak up large amounts of CO2 produced by human activities. But in years when the tropical Pacific region is warmer, trees and plants grow less and absorb smaller amounts of the gas. As a result, scientists say 2019 will see a much bigger CO2 rise than 2018.

Since 1958, the research observatory at Mauna Loa in Hawaii, has been continuously monitoring and collecting data on the chemical composition of the atmosphere. In the years since they first started recording, the observatory has seen a 30% increase in the concentration of CO2 in the atmosphere caused by emissions of fossil fuels and deforestation. Scientists argue that the increase would have been even larger without the ability of the forests, land and seas to soak up around half of the gas emitted by human activities. This ability however, varies with the seasons.

In the summer, CO2 levels in the atmosphere fall as the trees and plants soak up more of the carbon as they grow. In the winter, when they drop their leaves, they soak up less and atmospheric levels rise. This natural variation is compounded in years when there's an El Niño event, which sees an upwelling of heat from the Pacific into the atmosphere. This year's predicted rise won't be as big as in the El Niño years of 2015-16 and 1997-98.

Researchers claim the long-term trend is only going in one direction and there needs to be a reduction in the CO2 emissions instead of the increase. They are only pleased that observations over the past four years show that their model is accurate. They believe it can be used in the future to help countries accurately attribute increases in emissions to their actions or to natural factors.​

“Worrying Rise” in the Global Carbon Di-oxide in 2019.