Easter Island is now home to an extraterrestrial/futuristic/handwavey device. It continuously and instantly removes CO$_2$ from the atmosphere above the island. To avoid harmful effects on plants, it excludes the 30m of atmosphere closest to the land. If it is unable to process enough atmosphere to remove 40 billion tons of CO$_2$ per year (current global production) it will increase the strength of the prevailing winds within 1000km until it is processing enough.
People will very quickly notice that global CO$_2$ levels are not increasing.
How and how soon will they notice where it is going?