Short answers, pulled from the story.
In 2024, carbon dioxide concentration in Earth's atmosphere reached 430 parts per million, representing a mass of 3,364 gigatonnes. This is 54% higher than the pre-industrial level of 280 parts per million.
Atmospheric carbon dioxide has been rising since the mid-18th century. By May 2022, concentrations were 50% above pre-industrial levels. An estimated 2,650 gigatonnes of carbon dioxide have been emitted by human activity since 1850, with about 1,050 gigatonnes remaining in the atmosphere.
Scientists measure air bubbles trapped in Antarctic and Greenland ice cores for periods up to 800,000 years ago. For older periods they use proxy methods including boron and carbon isotope ratios in marine sediments, stomata counts on fossil plant leaves, and a chlorophyll breakdown product called phytane.
During the Cambrian period, about 500 million years ago, carbon dioxide concentrations reached approximately 4,000 parts per million. This is roughly ten times higher than the current atmospheric concentration of 430 parts per million.
Between 20 and 35% of the fossil carbon transferred to the atmosphere is projected to persist there for many thousands of years after emissions cease. The Bern model estimates that 21.7% of released carbon dioxide stays in the atmosphere indefinitely under current conditions.
Svante Arrhenius published the concept that increased atmospheric carbon dioxide would raise surface temperatures in 1896. His work identified the physical basis: carbon dioxide absorbs and re-emits infrared radiation at wavelengths that overlap with the range in which Earth radiates energy back toward space.