Why is CO2 accumulating in the atmosphere and what can be done about it ? This slideshow is designed to help students see how the processes that move carbon at the scale of a plant or a person are related to those that move carbon at the scale of the entire globe, and the consequences those movements are having for our globe.

Questions to consider: The graph below shows carbon dioxide concentrations in the atmosphere in parts per million (ppm) from 1958 until the present. This is a record since the late 1950s of carbon dioxide concentration as measured on the upper slopes of Mauna Loa, Hawaii. It is a reasonable average for the amount of CO2 in the atmosphere of the northern hemisphere, since it is far from concentrated sources of CO2 (i.e. industry, heavy traffic, etc). Answers to Qs (don’t necessarily need to answer these for students at first, later slides will help them answer this): each year concentration oscillates up and down in response to more photosynthesis in spring and summer (in northern hemisphere), and less in the winter. All indications are that CO2 concentration will continue to rise as humans continue to combust more fossil fuels than natural systems can take up. Questions to consider: Explain the annual periodicity of the above curve? What inferences can you make about CO2 concentrations for the next 50 years ?

Stored CO2 – Fossil Fuels 1. Review Processes ATMOSPHERIC CO2 Direct Air to Sea Exchange (dissolution) Process Process Process Plants and Animals Human use Oceans This is a very simplified version of a carbon cycle diagram. Here the blue boxes represent “pools” or reservoirs where carbon can be found on earth, and the red arrows show movements of carbon between those pools. Each arrow represents a process that can transform carbon in one pool into carbon in another. KEY (clockwise from left side of diagram): Respiration, photosynthesis, combustion (or respiration) and combustion. Process Stored CO2 – Fossil Fuels

Accumulation Basic principle: Accumulation happens when inputs are greater than outputs For carbon cycle: -Inputs to atmosphere = sources -Outputs from atmosphere = sinks (land and ocean) This slide focuses on the bottom line for carbon accumulation in the atmosphere – more is coming in from sources than is leaving to sinks.

Before human civilization... 120 90 Plants and animals Oil Oceans Human energy use The atmosphere Coal Natural Gas These numbers are approximate, but the big idea is that without humans combusting materials inputs and outputs to the atmosphere were roughly equivalent and thus concentrations were stable. Fossil fuels were essentially locked out of circulation at this point. Before human civilization...

In the year 2005 121 122 90 92 Plants and animals Oil Oceans Human energy use The atmosphere Coal Natural Gas 7 More CO2 dissolved in oceans 1 Gt/yr from deforestation By modern times, the balance has shifted as combustion of materials has increased. Note that the release of carbon from lands and oceans has stayed almost the same since prehistory, but the middle box has changed dramatically. Deforestation – increases emissions into the atmosphere due to the decay of organic matter; combustion of trees (slash and burn) and increased rate of organic carbon decomposition in the soil as well as reduced carbon sequestration 2 Gt/yr from regrowth of forests In the year 2005

90 92 Plants and animals Oil Oceans Human energy use The atmosphere Coal Natural Gas What numbers must be present in the empty boxes to make the movement of carbon into and out of the atmosphere balance?

One possible solution 90 92 Plants and animals Oil Oceans Human energy use The atmosphere Coal Natural Gas 120 122 4 Reduce deforestation Questions to raise: Can we continue to add more biomass to forests indefinitely into the future ? Will the ocean sink (92 – 90) continue into the future? Answers: 1) No, eventually places that were deforested will be grown back. Biomass added to forests will probably gradually decrease. 2) No, eventually the ocean will be in equilibrium with the atmosphere and there will no longer be a net flux of CO2 into the ocean. Reduce emissions from energy use Maintain regrowth of forests

Concentration stabilization scenario Movement of Carbon in every year during the years 2020 - 2030 Figure 4. This shows the concentration of carbon dioxide in the atmosphere in parts per million (ppm) if levels are stabilized by 2020. Figure 3. This shows the movement of carbon in every year for the years 2020 – 2030. The numbers stand for billions of tons of carbon. 122 4 In order to begin holding the [CO2] steady, inputs from the air must match outputs to the air, meaning that human emissions of carbon must slow.

Challenge #1 - How to make this fun, relevant, and not depressing

CO2 CO2 CO2 electricity CO2 CO2 here’s a fun way of considering how many of our actions touch on the carbon cycle, both directly and indirectly

Understanding how the earth works and how humans fit in is cool Sustainability will provide new opportunities You are not a bad person if you drive a car; you are just a contemporary human. What will a future human drive? materials Individual behavior matters. Collective behavior matters more. Modern human societies are dependent on fossil fuels. Although individual behavior is important, policy-level changes are probably needed. Not an individual moral issue – maybe a societal moral issue. Be a little easy on ourselves, the world has never done this before. Arnold story. Roles for everyone. Green jobs and careers. This is exciting. Knowing more about the earth and how humans connect is a fascinating topic. Enjoy the ride – we will figure it out. The curve will flatten. There will still be electric guitars in the future. We will figure this out. Enjoy the ride. Be part of it.

Challenge #2 Finding Solutions  How can we stabilize carbon emissions over the next 50 years to maintain Carbon emissions instead of continuing on our current path? The triangle shown in yellow on this diagram represents the carbon emissions that are likely to occur unless human society as a whole takes steps to curtail or replace carbon emissions in ways that will not release more carbon. This is the premise of the “Stabilization Wedges” game that you can do next. http://cmi.princeton.edu/wedges/slides.php