420ppm

420 ppm refers to 420 parts per million, a measurement commonly used to express the concentration of carbon dioxide (CO2) in Earth's atmosphere. This concentration is a key indicator of atmospheric composition and plays a significant role in climate science.

Historically, atmospheric CO2 levels before the Industrial Revolution were around 280 ppm. Since then, human activities, primarily the burning of fossil fuels, deforestation, and industrial processes, have led to a steady increase in CO2 concentrations. The 420 ppm mark represents a level not seen in millions of years of Earth's history.

This elevated level of CO2 is a major contributor to the greenhouse effect, where atmospheric gases trap heat from the sun, warming the planet. Scientists monitor CO2 levels through various methods, including direct atmospheric sampling at observatories around the world. The Intergovernmental Panel on Climate Change (IPCC) regularly reports on these trends and their implications for global temperatures, sea levels, and weather patterns.

The continued rise in atmospheric CO2, including the milestone of 420 ppm, is a central focus of discussions surrounding climate change mitigation and adaptation strategies. Efforts to reduce greenhouse gas emissions aim to stabilize or even lower these concentrations to limit the extent of future climate impacts.