Climate scientists warn of large decline in global carbon sink

Newly released data reveals that global carbon sinks in 2023 were at their weakest since 2003 according to a new pre-print paper available on the arXiv server.

Carbon sinks are anything natural or artificial which absorbs more greenhouse gases than it releases. Examples of carbon sinks are plants, soil and the oceans. They are vital to attempts to mitigate human-induced climate change, in particular when oceans and forests are healthy.

Global emissions estimates are based partly on expectations that carbon sinks would soak up carbon dioxide and help mitigate climate change. They were not expected to shrink as much as they have.

The pre-print paper content, revealed today by its worried authors, shows that, despite relatively moderate El Niño and global greening at its third highest since records began in the 1980s, land carbon sinks absorbed about 0.44 gigatonnes of carbon in 2023 – the lowest level since 2003.

Over the period 2010–2022, the average land carbon sink level was almost 5 times higher at 2.04 gigatonnes of carbon per year.

Last year was the hottest year on record.

“A weaker carbon sink in 2023 echoes the impact of extreme warming, globally 0.6°C above the 1991–2020 average and 1.48°C warmer than the 1850-1900 pre-industrial level, with extreme summer temperatures and drought in the northern mid latitudes,” the authors write.

Several factors are noted by the study authors which might have contributed to the weak carbon sink, particularly on land, which will have to be taken into account in future estimates of the global carbon sink.

These factors include the massive wildfires of 2023 and satellite imagery showing low water levels on land over the year which can cause plant water stress.

In other words, the authors suggest, the warming already caused by the emissions of greenhouse gases may be creating a feedback loop in which increased temperatures and dryness are weakening carbon sinks which leads to increased emissions of carbon dioxide (CO₂) into the atmosphere.

The authors warn: “If very high warming rates continue in the next decade and negatively impact the land sink as they did in 2023, it calls for urgent action to enhance carbon sequestration and reduce greenhouse gasses emissions to net zero before reaching a dangerous level of warming at which natural CO₂ sinks may no longer provide to humanity the mitigation service they have offered so far by absorbing half of human induced CO₂ emissions.”