Saint Louis University

One of the Global Change issues we focus on at SLU's Center for Environmental Sciences (CES) is rising tropospheric ozone levels. Due to fossil fuel burning, the amount of background ozone in the air we breathe has risen since the beginning of the industrial revolution. While ozone is essential in the stratosphere to protect us from harmful ultra-violet radiation, it is a toxic chemical and, close to Earth, is harmful to people and plants. In the Midwestern U.S. and many other parts of the world, background levels of ozone now typically exceed concentrations that are damaging to vegetation (~ 40 ppb) on most days during the growing season. This has consequences to natural ecosystems and agriculture. You can read more about our educational efforts in CES's "Ozone Gardens" webpages.

  • For more information watch Dr. Fishman's talk Tropospheric Ozone in the Anthropocene: Are We Creating a Toxic Atmosphere?
  • Here is a short video by the University Corporation for Atmospheric Research (UCAR) on what ozone is, and the difference between ozone in the stratosphere and troposphere.
  • Rising tropospheric ozone levels was first hypothesized by Fishman and Crutzen in 19781. This has subsequently been verified through a number of observational studies since the 1980'sfor example 2,3,4.

Earth and atmosphere from
The Anthropocene: A time of human global change

Human activity is clearly having a significant impact on Earth and its ecosystems. The "Anthropocene" is increasingly being used to describe this period of Earth's history. The term was popularized by Nobel Prize winning atmospheric chemist Paul Crutzen when he proposed, 15 years ago, it be used to describe the current geologic period of a human-dominated planet5.

Scientists are discussing the merits of making the Anthropocene a formal epoch and, if so, when it would begin. Crutzen originally proposed the end of the eighteenth century, the beginning of the Industrial Revolution, as the boundary of the Anthropocene because this is the time when human activity began causing Earth systems to significantly depart from previous natural behavior. He based this on when air trapped in polar ice begins showing growing concentrations of carbon dioxide and methane. Others have suggested the date be further back in time to the first geological evidence of humans6, and, recently, a group of geologists proposed the date of the first atomic bomb explosion as the start of an official Anthropocene epoch7.

Regardless of its formal starting date, the Anthropocene as it is increasingly used covers the explosion of the human population and its related impacts. These include: massive use of fossil fuels and the resulting carbon emissions; destruction of habitat, loss of biodiversity, and mass extinctions of other species; earth moving - soil erosion and sedimentation; massive production of new materials such as plastics, concrete, and metals; great demands on fresh water; and large-scale agriculture including human-fixed nitrogen, which runs off fertilized fields and alters fresh and salt water ecosystems. 

From a geologic perspective "probably the most significant one that's invisible to us - the change in the composition of the atmosphere"8. When geologists of the future look at the Earth for evidence of the Anthropocene, they will primarily see the consequences of the increasing amounts of carbon dioxide. This will be evident in the fossil record where rising global temperatures are already causing many plants and animals to shift their ranges, or become extinct. It will also be evident in the oceans as a "reef gap". Carbon dioxide seeps in and acidifies oceans, which soon may become too acidic for corals to construct reefs. Each of the past five major extinctions on Earth have been marked with reef gaps.
Read Enter the Anthropocene-Age of Man in National Geographic.

So, what to do? We like journalist Andrew Revkin's proposal that, rather than "mourn the end of nature", we "...have to embrace the characteristics, good and bad, that make humans such a rare thing - a species that has become a planet-scale force. Cyanobacteria were also a planet-scale force, oxygenating the atmosphere some two billion years ago. The difference is that cyanobacteria weren't aware of their potency, while we are at least starting to absorb that reality." He hopes ", say, 100 years in the future...[we] will look back and consider this period...a transition from the lesser Anthropocene to the greater Anthropocene....We have to accept ourselves, flaws and all, in order to move beyond what has been something of an unconscious, species-scale pubescent growth spurt, enabled by fossil fuels in place of testosterone...We're stuck with 'The World With Us'.  It's time to grasp that uncomfortable, but ultimately hopeful, idea."
Read the Dot.Earth post from where this quote was taken.


  1. Fishman J. and Crutzen P.J. 1978. The origin of ozone in the troposphere. Nature, 274:855-858.
  2. Volz, A. and Kley, D. 1988. Evaluation of Montsouris series of ozone measurements made in the nineteenth century. Nature, 332:240-242.
  3. Marenco, A., et al. 1994. Evidence of a long-term increase in tropospheric ozone from Pic du Midi data series - Consequences: Positive radiative forcing. J. Geophys. Res., 99:16,617-16,632.
  4. Parrish, D., et al. 2012. Long-term changes in lower tropospheric ozone concentrations at northern mid-latitudes. Atmos. Chem. Phys., 12:11,485-11,504.
  5. Crutzen, P.J. 2002. Geology of mankind. Nature, 415:23.
  6. Edgeowrth, M., et al. 2015. Diachronous beginnings of the Anthropocene: The lower bounding surface of anthropogenic deposits. Anthropocene Rev., on-line 10/08/2015.
  7. Zalasiewicz, J., et al. 2015. When did the anthropocene begin? A mid-twentieth century boundary level is stratigraphically optimal. Quat. Int., on-line 01/12/2015.
  8. Kolbert, E. March 2011. National Geographic. Enter the Anthropocene-Age of Man.