Week 7: Planetary Boundaries Framework Pt. 2 - Post 2

                                                Planetary Boundaries Framework Pt. 2:

          In total there are nine planetary boundaries, but so far humanity has only pushed three into a danger zone. Climate change, ocean acidification and stratospheric ozone depletion are all within their thresholds, meaning they are outside their safe operating spaces for a stable planet. Now climate change is a term used very commonly in the media to warn of human actions against ecosystems. Since the industrial revolution humans have emitted exponential amounts of greenhouse gases including carbon dioxide and methane. Those gases create a greenhouse effect which traps heat within the atmosphere. This effect creates an imbalance of heat. Essentially, more heat is entering the Earth's atmosphere then is leaving. Over the last one-hundred and fifty years all of the excess heat has added up to an overall global temperature increase of about one degree Celsius. Humanity is already seeing the disastrous effects of this one degree increase, yet emission pathways estimate that the temperature increase will only get higher. Human emissions are following a pathway that will lead to three or four degrees warming this century.  Climate change as a boundary is absolutely necessary because of the already catastrophic events that have happened under just one degree of increase. When scientists take all of the evidence surrounding climate change and synthesize it, they arrive at a quantitative boundary. Then the theory of a safe operating space, an uncertainty zone, and a danger zone are applied. For climate change scientists have found the uncertainty zone of greenhouse gas concentrations to be between 350 ppm and 450 ppm. Within this range is the risk of crossing a very dangerous threshold for humanity. Scientists will then apply the boundary at the safe lower end of the uncertainty zone which is 350 ppm for carbon dioxide. That is how the boundary for climate change is set. Currently, the carbon dioxide concentration is observed as 410 ppm, putting climate change well within the danger zone. Making climate change one of the most important planetary boundaries to pay attention to.
          The second planetary boundary approaching it's threshold is ocean acidification. Not all of the carbon emitted stays in the atmosphere and participates in warming the planet. Actually, about twenty-eight percent of the carbon dioxide is absorbed by the ocean. This process is a vital part of the Earth's resilience to human activity. However, when carbon dioxide is dissolved in the oceans it is not beneficial to the marine organisms. When carbon dioxide is dissolved in salt water it forms a compound called carbonic acid. The carbonic aid will dissociate, or split up and form a proton H+ and a bicarbonate ion HCO3-. The bicarbonate will then dissociate again, giving off another proton and carbonate ion. Each time a proton is added the water becomes more acidic. Since the industrial revolution human carbon emissions have caused the pH in the ocean to increase by 0.1. That seems like a small amount, but just one tenth increase in pH is equal to a 26 percent increase in acidity in the oceans. This increase in acidity has consequences. It affects the calcification, or shell building process, of different marine organisms as well as biodiversity loss. But, what is the official boundary? It is written in terms of aragonite saturation. The more aragonite saturated in the oceans, the greater the danger to marine life; including foundational species like coral. Ocean acidification is considered to be in a danger zone because aragonite levels are expected to reach it's boundary mid century, not very long from now.
          Finally, the third planetary boundary is Stratospheric Ozone Depletion. First there is the ozone layer; a thin livable atmosphere that envelopes Earth, in which all life depends on. Then, roughly 10-50 kilometers above ground, there is the stratospheric ozone layer. This is a protective shield that reflects back harmful ultraviolet, or UV, radiation from the Sun. This ozone layer is extremely important for enabling human prosperity and development. Many may remember, in the early 90s, when the world came together to ban harmful chemicals that were rapidly depleting the stratospheric ozone. While the harmful chemical called chlorofluorocarbons has been discontinued, other ozone depleting chemicals still remain. However, the ability of society to come together across government lines and solve the problem provides hope for sustainability going forward. After much consideration, science has been able to come to a conclusion on a boundary. The control variable is the thickness of the column of ozone across the planet, and thereby science has a quantitative boundary to watch out for.
          Knowing and understanding that these planetary boundaries are nearing a tipping point is vital. Through science, it is known exactly how much greenhouse gas can be emitted, how much carbon dioxide can dissolve in the oceans, and the volume of harmful chemicals that can be allowed to be released in the atmosphere before disaster occurs. By knowing those things, and knowing that humans have neared danger zones for each of those levels, humans can work together to mitigate emissions and work towards preventing the Earth system from crossing into an entirely new and unstable state.