April set a carbon dioxide milestone by averaging 400 parts per million for the entire month. That’s uncharted territory over the course of human history, and a new data visualization makes clear just how high and fast it has risen.
The march to 400 ppm might seem slow by human standards, rising just one or two parts per million each year, but it’s a veritable sprint by geological standards. We know this from ice cores, which contain air bubbles that give snapshots of carbon dioxide levels over the past 800,000 years. Modern atmospheric measurements are taken at observatories around the globe including one at Mauna Loa, Hawaii, which has been taking continuous measurements since the late 1950s.
An animation from the Cooperative Institute for Research in Environmental Sciences makes clear that though there have been variations over time, the current rise is unparalleled. The animation zooms in on the graph of temperatures, often times referred to as the Hockey Stick for its distinctive shape, and shows the granular changes over time. It’s clear that there are long swings taking CO2 levels anywhere from 175 ppm up to 300 ppm.
Over the course of the past 2,000 years, CO2 has stayed roughly around 280 ppm until the Industrial Revolution kickstarted a carbon emissions bonanza, driving levels higher and higher. It soared past 350 ppm — the level scientist James Hansen has said is the safe upper limit of CO2 — in October 1989.
CO2 levels vary throughout the year as trees and plants burst forth in the spring and draw down levels over the following months. That means this year’s CO2 levels will peak in May and then drop below 400 ppm over the summer before trekking back up in the fall. Scientists that work on the CO2 monitoring program at Mauna Loa estimate it will be just a few years before CO2 levels stay above 400 ppm year round.
Rising CO2 levels have been linked to the globe’s average temperature rise as well as a host of other changes to the climate system including sea level rise, shifts in precipitation, ocean acidification, and an increase in extreme heat. Those changes are expected to continue and intensify if emissions from human activities continue.