Week 7: Planetary Boundaries Framework Pt. 2 - Post 1

Planetary Boundaries Framework Pt. 2

Lecture 1 – Climate Change

Professor Johan Rockstrom

In this lecture we provide scientific evidence why climate change is a planetary boundary, and the basis for defining the boundary for climate change

Building up evidence:

-Sea level rise

- Following a pathway that is leading us to three or four degrees warming this century

And here science is advancing in a very profound way. We're understanding the climate system much, much more in detail, and particularly how the climate system interacts with the other planetary boundary processes such as land, water, oceans, and biodiversity. And the reason why this is occurring is that we're understanding more and more about resilience, about the risks that we have surprise and thresholds in the Earth system. And this to me is the most fundamental piece of evidence showing that a planetary boundary approach on climate is absolutely necessary because for one, at already very low temperature rises we today have evidence enough to say that the likelihood of large scale catastrophic changes is highly probable. And secondly, it's highly uncertain. It's so complex that we need to apply a precautionary principle where a boundary position is a position of safety beyond which we enter this area of uncertainty.

In fact, some of the large reinsurance companies after the IPCC released its report, clearly pointed out that we're reaching a point of risk which goes beyond the point where they potentially can no longer issue, insurances because they can not be liable for the large scale costs that would be incurred if these kind of catastrophic events would be allowed to happen. So we're entering truly a danger zone with regards to climate.

Conclusion: Now when we all take all this science together and synthesize it to define the boundary, we then apply our theory of a safe operating space, an uncertainty zone, and a danger zone, and we find that the science indicates that at the range of between 350 ppm and 450 ppm the science is well in agreement that here we have a risk of crossing catastrophic thresholds. And therefore we apply the boundary at the safe lower end of that uncertainty which is 350 ppm for carbon dioxide. And there you have it, that's the way we place the boundary for climate change.

Lecture 2 – Ocean Acidification

Professor Kevin Noone

(global carbon budget)

So what happens when you dissolve carbon dioxide in the oceans? Well the carbon dioxide forms a compound with water called carbonic acid, which then dissociates - that means it splits up and forms two ions - a proton H+ and a bicarbonate ion HCO3-. That can dissociate again, giving off another proton and a carbonate ion. And each time a proton is added to water it becomes a little bit more acidic.

keep in mind that a tenth, the 0.1 pH unit, is about a 26% increase in acidity of the oceans.

Consequences- affecting calcification of different organisms as well as biodiversity loss

So the point at which aragonite becomes soluble, or coral reefs might have a very, very difficult time, uh, existing at all, will be about mid-century or so, not too long from now.

Conclusion: What the ocean acidification boundary actually is. It's written in terms of aragonite saturation, that is, it's a chemical equilibrium, and this might be a poster child for planetary boundaries in the fact that that's a very, very easy boundary to define, because it is a chemical equilibrium. If you add a little bit more carbon dioxide to the oceans aragonite becomes saturated, or unsaturated, so this is probably the easiest to define of all the planetary boundaries, and you can see on this slide exactly what it is.

Lecture 3 – Stratospheric Ozone Depletion

Professor Johan Rockstrom

What is the Stratospheric Ozone Layer: All life on Earth depends on the extraordinarily thin layer of livable atmosphere which envelopes the biosphere in our Earth system. But above the atmosphere in the high atmosphere, roughly ten to fifty kilometers above ground, we have the stratospheric ozone layer. And the stratospheric ozone layer is a protective shield that enables life on Earth by reflecting back harmful ultraviolet radiation from the Sun. So clearly the ozone layer is a planetary boundary enabling human prosperity and development on Earth.

(Banning of Chlorofluorocarbons from use because human emissions had caused this depletion)

And this in turn has led to a success story where a boundary of ozone depletion was transgressed in the early '90s and now we're actually moving into a safe operating space, showing that humanity in fact can collectively as all nations on Earth work together to operate within a safe operating space.

+So that's an example of how close we were of what we can call a planetary scale disaster, and why thinking in terms of defining planetary boundaries is so essential.

Conclusion: Science has come to a point where we are at a position where we can define a control variable, which we have chosen as the thickness of the column of ozone across the planet. And this gives us a very good, robust, science-based definition of how much we must maintain in terms of ozone, and thereby also translating that to avoiding chemicals that can destroy the ozone layer.