The devastating bushfires in Australia are likely to cause a jump in carbon concentrations in the atmosphere this year, a forecast suggests, bringing the world closer to 1.5C of global heating.

The fires have not only released vast amounts of carbon dioxide and soot, but the unusual extent of the blazes means regrowth is likely to be slower than in previous years. That will reduce the amount of vegetation available to act as a carbon sink, meaning less carbon dioxide is removed from the air.

Experts at the UK’s Met Office have predicted that this year will see another large rise in the carbon content of the atmosphere, which has been measured at the Mauna Loa observatory in Hawaii since 1958. They predict that carbon dioxide will peak at more than 417 parts per million in May, usually the highest point of the year for carbon concentrations, and settle to about 414ppm as the average for 2020.

The predicted year-on-year rise of about 2.74ppm would be one of the biggest on record. Emissions from the Australian bushfires will make up one-fifth of the increase, according to the Met Office. Last year, scientists recorded the second biggest yearly increase on record, of 3.5ppm compared with 2018.

The absorption of carbon dioxide by land ecosystems, such as vegetation and forests, is linked to swings in Pacific Ocean temperatures, the Met Office noted. Many regions become warmer and drier in years with a warmer tropical Pacific, limiting the ability of plants to grow and absorb carbon, while the risk of wildfires increases. That has contributed to the hot dry weather in Australia, making the bushfires more severe.

Since the Mauna Loa records began, human activities have resulted in a yearly rise in the carbon content of the air. Some years have seen only a modest rise, but in recent years the rise has been stronger, despite global efforts to reduce greenhouse gas emissions.

Professor Richard Betts, of the Met Office Hadley Centre, said: “The [annual] rate of rise isn’t perfectly even because there are fluctuations in the response of ecosystem carbon sinks, especially tropical forests. Overall, these are expected to be weaker than normal for the second year running. The year-to-year variability in the rate of rise of CO 2 is affected more by the strength of ecosystem carbon sinks and sources than year-to-year changes in human-induced emissions. Nevertheless, anthropogenic emissions are still the overall driver of the long-term rise in concentrations.”

Each annual rise takes the planet closer to the crucial 450ppm threshold. That is regarded by scientists as the limit of safety, beyond which the impacts of climate change – droughts, floods, heatwaves, fiercer storms, and sea level rises – are likely to become much worse.

“This analysis illustrates how feedback processes can accelerate the rise in greenhouse gas levels and hence the rate of warming,” said Bob Ward, policy director at the Grantham Research Institute on Climate Change at the London School of Economics. “Global warming in Australia, western North America and many other parts of the world is increasing the risk and extent of wildfires, releasing ever more carbon dioxide into the atmosphere. Such feedback processes will lead to the exhaustion of our emissions budgets even more quickly than expected. We are closer than we think to the point of no return.”

Governments pledged at Paris in 2015 to hold global temperature rises to no more than 2C above pre-industrial levels, with an aspiration not to exceed 1.5C. In the years since, greenhouse gas emissions have risen by 4%, according to recent estimates.

Current national pledges under the Paris agreement would take the world to 3C of heating. This November, governments will meet in Glasgow to try to set the world back on track to meet the Paris goals.