An interpreter in a hall tries to convey the speaker's words, but the hall is noisy: someone coughs, chairs creak, and the street outside is loud. If the speaker lowers their voice, the interpreter keeps translating, but their voice gets lost in the noise. The atmosphere is the same: it 'translates' our carbon dioxide emissions into rising concentrations, but that signal is drowned out by the breathing of forests, the ocean, and global climate swings.
Scientists took data from 2015 to 2024 and divided all land into squares of 1°×1°. For each square, they calculated how fast CO₂ concentrations were rising in the air above it, how much carbon dioxide humans were emitting, how actively local plants were absorbing carbon (which is visible through their glow, reflecting photosynthesis), and how the global climate cycle known as the Southern Oscillation influences it. They found that CO₂ growth varies greatly from place to place, but these variations are mostly driven by natural processes, not local emissions. Even in 2020, when emissions dropped sharply due to the pandemic, the human contribution to the model actually increased in many cities.
For climate policy, this means that we cannot verify how much countries are reducing emissions solely through atmospheric observations: we need to account for what is happening in each region. If the interpreter cannot hear the speaker's quiet remark, it does not mean the speaker is silent; it just means the noise in the hall is too strong.
The Southern Oscillation, which the authors use as a climate driver, is measured by the difference in atmospheric pressure between Tahiti and Darwin. This index was proposed back in 1987 and remains one of the simplest and most reliable indicators of El Niño.