Met Office researchers expect to see one of the largest increases in atmospheric CO2 concentrations in 2019.
Every year, Earth's natural carbon sinks, such as forests, absorb large amounts of CO2 produced by human activities.
But in the years when the tropical Pacific region is warmer this year, trees and plants grow less and absorb smaller amounts of the gas.
As a result, scientists say 2019 will see a much higher CO2 increase than 2018.
Since 1958, the research observatory in Mauna Loa, Hawaii, has continuously monitored and collected data on the chemical composition of the atmosphere.
In the years since they began filming, the observatory has seen a 30% increase in CO2 concentration in the atmosphere caused by fossil fuel emissions and deforestation.
Scientists argue that the increase would have been even greater without the ability of forests, land and seas to absorb about half of the gas emitted by human activities.
This ability, however, varies according to the seasons of the year.
Forecast CO? concentrations in Mauna Loa throughout 2019 (orange), along with predicted concentrations for 2016 (blue), 2017 (green), 2018 (pink) and measurements from the Scripps Institute (black).
In summer, CO2 levels in the atmosphere fall as trees and plants absorb more carbon as they grow. In winter, when they drop their leaves, they absorb less and the atmospheric levels increase.
But when temperatures are warmer and drier than normal, trees and plants grow less and absorb less. This natural variation is compounded in years when there is an El Niño event, which sees a Pacific heat wave into the atmosphere.
"Sea surface conditions will now continue in the coming months and this will lead to vegetation response," said Chris Jones of the Met Office.
"In a tropical forest, for example, you reduce the natural growth of the vegetation."
According to the Met Office, these limits on the ability to absorb CO2 will see an increase in concentrations this year of 2.75 parts per million, which is higher than the level of 2018.
They are predicting that average CO2 concentrations in 2019 will be 411 ppm. The concentration of carbon dioxide exceeded 400 ppm for the first time in 2013.
The projected increase for this year will not be as great as in the El Niño years of 2015-16 and 1997-98. However, there were only similar increases to this year, about half a dozen times since the records began.
An image showing the 2015 El Niño with rising temperatures in the Pacific
Researchers say the long-term trend is only going in one direction.
"The year-on-year increase in CO2 is steadily increasing, as it has been throughout the 20th century," Dr. Jones said.
"What we are seeing next year will be one of the largest ever recorded and will certainly lead to higher CO2 concentration."
Other researchers say the Met Office results are worrisome.
"Increases in CO2 are a function of our continued dependence on fossil fuels," said Anna Jones of the British Antarctic Survey (BAS).
"A bit of moderation in the rate of increase stems from Earth's ability to absorb CO2 from the atmosphere, but that may change from year to year, as the Met Office forecast shows.
"What is critical, however, is that the persistent increase in atmospheric CO2 is totally at odds with the ambition to limit global warming to 1.5 ° C. We need to see a reduction in the CO2 emissions rate, not an increase."
Met Office scientists say it does not always follow that a record CO2 concentration will lead to a record global temperature in 2019 as there are many natural factors that can affect the final value.
Researchers are pleased that observations over the past four years have shown that their model is accurate. They believe it can be used in the future to help countries accurately assign increases in emissions to their actions or to natural factors.