The series of annual levels of carbon dioxide have seen a year-on-year increase since 1958, driven by fossil fuel burning and deforestation.
Australian wildfires will help push up carbon dioxide levels in the atmosphere to new highs in 2020, the Met Office has said.
Its annual forecast for concentrations of the key greenhouse gas in the atmosphere predicts 2020 will see one of the highest annual increases in levels since records began more than 60 years ago.
This year levels of carbon dioxide are set to rise by 2.7 parts per million compared to 2019, averaging 414 parts per million in the atmosphere over the year - ever higher above pre-industrial levels of around 280 parts per million.
Levels are set to remain above 410 parts per million throughout the year for the first time, the Met Office said.
Human activities such as burning fossil fuels have been pushing up levels of carbon dioxide in the atmosphere every year since records began at Mauna Loa in Hawaii in 1958.
But around a tenth of the projected increase in 2020 is due to weather patterns that create conditions in which plants grow less and absorb less carbon and make blazes such as Australia's devastating bush fires more likely.
Weather patterns linked to swings in temperatures in the Pacific Ocean affect the rise in carbon dioxide levels, because in years with a warmer tropical Pacific many regions become warmer and drier.
This limits the ability of plants in "carbon sinks" such as tropical forests to grow and take carbon dioxide out of the atmosphere. It also increases the risk of wildfires which create more emissions.
This kind of weather pattern has - along with human-caused climate change pushing up temperatures - contributed to the hot, dry weather in Australia which played a key role in how severe the fires were, the Met Office said.
The fires that have been raging in Australia will contribute around 1-2 percent of the overall rise in concentrations of the greenhouse gas in 2020, the Met Office said.
Professor Richard Betts, of the Met Office Hadley Centre and University of Exeter, said: "Although the series of annual levels of carbon dioxide have always seen a year-on-year increase since 1958, driven by fossil fuel burning and deforestation, the rate of rise isn't perfectly even because there are fluctuations in the response of ecosystem carbon sinks, especially tropical forests."
Warmer temperatures in the Pacific mean that for a second year running, these carbon sinks are likely to absorb less carbon dioxide than normal, the Met Office said.
While natural sources and stores of carbon create fluctuations, human activity is the driver of the long-term rise in carbon dioxide concentrations in the atmosphere, Professor Betts added.
Carbon dioxide concentrations at Mauna Loa are measured by the Scripps Institution for Oceanography at UC San Diego and the National Oceanographic and Atmospheric Administration (NOAA), while emissions from fires are monitored by the Global Fire Emissions Database (GFED).
Emily Beament is the PA environment correspondent.