The Planet's Breath Stumbles: How El Niño Stilled Earth's Lungs ✛
From July 2023 to July 2024, Earth's atmosphere gained carbon dioxide at a rate of 3.66 parts per million per year. That is the fastest pace since 1979. The reason is not that factories and cars suddenly started emitting more CO₂. The planet's lungs—forests and soils—took a shallower breath.
The planet breathes through its green cover. Leaves take in carbon dioxide, while roots and microbes breathe it back out. In a normal year, the land absorbs more than it releases, slowing the accumulation of CO₂ in the air. But in 2023/24, that balance was disrupted: the terrestrial carbon sink shrank by 2.24 gigatonnes of carbon per year compared to the 2015–2022 average. It is as if all the world's forests simultaneously took a breath a third shorter than usual.
The culprit was El Niño, the warm phase of the Pacific climate cycle. It brought drought to tropical forests. When trees lack water, they close the pores on their leaves to avoid drying out. With water, CO₂ uptake also stops. Photosynthesis slows, while soil respiration continues. The forest turns from a sink into a source.
The drought area in the Amazon reached 68.2% of the region, larger than in any El Niño since 1997. Rivers shrank so much that shipping stopped in some places. Trees not only stopped growing; they began to die. Dead wood decomposes and releases stored carbon back into the atmosphere, a process that will stretch over years.
To see this so quickly, scientists combined three independent assessment methods: computer models of plant growth, fast substitutes for ocean models, and satellite measurements of CO₂ concentration in the air column. Previously, such a complete balance was published with a delay of a year or more. Now the planet's sensors work like a pulse oximeter on a patient's finger: a breathing failure is visible almost immediately.
Now that the planet's lungs have lost their rhythm, doctors have a device for early diagnosis. If the next El Niño strikes the tropics again, we will see it not a year later in reports but within months. And we will be able to tell whether this is a temporary shortness of breath or the onset of a chronic disease.
The 2023 Amazon drought was so severe that river levels fell to historic lows, and in some areas navigation completely ceased. The area affected by water deficit reached 68.2% of the region, more than in any previous El Niño since 1997.
A scenario in which tropical forests turn from a carbon sink into a source is explored in Kim Stanley Robinson's novel 'The Ministry for the Future', where a heat wave in India triggers a cascade of climate disasters. This work shows that such a transition is already occurring in reality during strong El Niño events.