Tukuk-OSThe standard metaphor misleads on one point: the atmosphere is not trapping heat like glass in a garden greenhouse (real greenhouses mostly work by blocking rising air). The honest version: the Sun sends in visible light, Earth’s surface warms and re-emits that energy as infrared, and certain gases — water vapour, carbon dioxide, methane, nitrous oxide — absorb and re-emit infrared, slowing its escape to space. With the natural blanket, Earth’s average surface sits near +15 °C instead of about −18 °C. Life exists in the difference.
The “CO₂ is only 0.04% so it can’t matter” objection fails on measurement, not rhetoric: remove the blanket entirely and our average temperature would drop by tens of degrees. Thin dials matter when they sit on a thermostat. And CO₂ is the dial humans control: water vapour, the biggest natural absorber, responds to temperature but doesn’t initiate change — warm air holds more moisture, roughly 7% per extra degree, which amplifies whatever CO₂ starts. That amplification is why a small forcing moves several degrees, not fractions.
Since 1850 the CO₂ concentration has climbed from around 280 to over 420 ppm — the 426.7 ppm scale visible live on our /air-quality/carbon page — and the fingerprint is checkable in three independent places: the isotopic weight of the added carbon (fossil carbon lacks certain isotopes that living and atmospheric carbon carry), the fact that the upper atmosphere cools while the lower warms (trapping signature, not a brighter Sun), and the oceans absorbing both carbon and heat. Three different measurements, one story.