In January of last year (2016) atmospheric CO2 levels finally reached 400 ppm. This was not the first time that we’ve reached this threshold, as we watched our measuring stations flirt with 400 since about 2013. However, for the first time in human history we’ve reached 400 ppm and we’re not going back…at least not for the foreseeable future.

I woke up this morning thinking about the implications of this, having learned last night that Mauna Loa Observatory, the Hawaiian atmospheric observatory, has been measuring approximately 410 ppm for the latter half of the month of April. Now in case you don’t know, Mauna Loa Observatory has been measuring atmospheric CO2 since 1959, which means it has a 58 year modern record of atmospheric chemistry. Along with Mauna Loa there are 5 other global observatories operated by NOAA and the ESRL (Earth System Research Laboratory) that collect hourly measurements of Earth’s atmospheric conditions. All of these observatories mean that there is a lot of data, which means we can extrapolate something like the rate of atmospheric CO2 growth over the period of measurement from 1959 to 2017.

Amazingly, fellow scientists at Mauna Loa Observatory already do this as a way to compare present rates of CO2 increase to the past (this concept is also applied to data extrapolated from ice cores). From 1959 to 2015 the average rate of increase in atmospheric CO2 has been approximately 1.5 ppm/yr. (you can view all of this data HERE) During that span of 56 years there were times when that number was either a little higher or a little lower, but that’s why it is an average rate of growth. What sticks out the most about the data is the average growth rate for the past 2 years (2015 and 2016) coming in just over 3.0 ppm/yr, and with new measurements reaching 410 ppm, it looks like we are on course to observe one of the largest increases in a single year (since we started measuring) for the year of 2017. Of course I suspect this trend will continue, with each new year beating, or at least comparing, to the previous one.

So what does this mean for us? The immediate and most obvious answer is more warming (which leads to a host of other feedbacks). However it’s not like the Earth hasn’t seen this before. We probably all remember our grand parents telling us about the troubling days way back ~66 Million years ago during the Paleocene Eocene Thermal Maximum (PETM). Wait…hominins didn’t even evolve until about 2 million years ago! During the PETM the geologic record indicates there was an extinction event that occurred between deep sea benthic organisms and some mammals on land. Interestingly this change took place over the course of about 6,000 years. It’s been less than 200 years since the dawn of the industrial revolution, just in case you were wondering.

Sources:

Higgins, J. A., and Schrag, D. P., 2006, Beyond methane: Towards a theory for the Paleocene- Eocene Thermal Maximum: Earth and Planetary Science Letters, v. 245, p. 523-537

Kennett, J. P., and Stott, L. D., 1991, Abrupt Deep Sea Warming, Paleo-Oceanographic Changes and Benthic Extinctions at the end of the Paleocene: Nature, v. 355, p. 225-228

Rea, et al., 1990, Global Change at the Paleocene – Eocene Boundary: climatic and evolutionary consequences of tectonic events: Paleogeography, Paleoclimatology, Paleoecolgy, v. 79 p. 117 – 128

NOAA, 2017, Trends in atmospheric carbon dioxide: https://www.esrl.noaa.gov/gmd/ccgg/trends/index.html (accessed May 2017)