This market will resolve YES if and when the monthly average level of atmospheric CO2, measured at Mauna Loa Observatory and adjusted for the average seasonal cycle, first reaches 427 ppm. The value relevant for resolution is displayed on the blue trend line of the following graph (for September 2024 it is 425,46 ppm): 

https://gml.noaa.gov/ccgg/trends/graph.html

The resolution date for this market will shift based on market odds. It will move closer as the odds increase, and further into the future as the odds decrease. This is intended to allow for an assessment of when the resolution event will likely occur. Initially, with 50% odds, the resolution date is set 50 years in the future. If the odds rise to 75%, the resolution date changes to 25 years in the future. At 80%, it changes to 10 years; at 90%, to 5 years; at 95%, to 1 year; at 96%, to 3 months; at 97%, to 1 month; at 98%, to 1 week and at 99% to 1 day in the future. I have a predefined list of resolution dates for each value between 1% and 99% odds and will adjust the resolution after each trade that changes the odds by at least 1%. 

The market will never resolve NO, since there can be no proof that atmospheric CO2 will never reach 427 ppm.