Another scary climate milestone looks imminent. While there have been sporadic measurements of atmospheric concentrations above 400ppm, the weekly average value has yet to reach this limit at Mauna Loa. Looking at the last week or so of data, it looks like we wont be able to say this for long.
Last year, atmospheric CO2 concentrations topped 400ppm in the Arctic. While this was a very significant milestone for climate, global CO2 levels did not reach the same values. In the Arctic, wind and fronts tend to cause CO2 to reach slightly higher concentrations in this region compared to the global average.
Scientists are predicting the Earth to reach a weekly mean CO2 concentration above 400ppm some time during May.
Each year, the Earth experiences a natural fluctuation in CO2 as the planet “breathes”. In Northern Hemisphere autumn/winter, trees drop their leaves, releasing large volumes of CO2 back into the atmosphere. During spring/summer, as trees grow new leaves they take in the CO2 that was released earlier in the year. What results is a pattern of CO2 concentrations that naturally fluctuates each year.
Underlying this natural seasonal fluctuation is the anthropogenic CO2 signal (i.e. CO2 released from humans). This signal is pushing the CO2 concentrations closer and closer to the 400ppm milestone.
From ice cores we can measure CO2 levels in the atmosphere as far back as 800,000 years ago. During this time, CO2 levels naturally fluctuated between 180ppm and 300ppm. Further back in time, we can indirectly measure CO2 concentrations by looking at indicators of CO2 concentrations, including the carbonate skeletons of tiny marine organisms. Using this method, scientists estimate that current levels of CO2 have not existed on earth since the Pliocene – more than 2.5 MILLION years ago.
The consensus amongst climate scientists is that 400ppm is an achievable CO2 target to aim for in order to limit the worst effects of climate change. 350ppm would be even better.
As CO2 levels in the atmosphere continue to rise unchecked, the emissions reductions measures required to limit CO2 concentrations in the atmosphere become more and more significant.