Title: SOLUTION: Bathtub experiment interpretation
Course: Project week - Leuphana-Copy > Section: What is renewable energy? (science focus)

[fa-info-circle] Make this page visible or print it out for your students upon completing the bathtub experiment task cycle.

There are three important points to be made when interpreting the bathtub/climate analogy:

1. The concentration of carbon dioxide in the atmosphere is rising because more is going in than is coming out. The experiment showed that if the rate of inflow is greater than the rate of outflow, the stock size will grow. In the case of our climate system, emissions exceed removals.
2. To stabilize the carbon dioxide concentration in the atmosphere, emissions will need to equal removals. (In the experiment, the rate of in- and outflow must be the same so that the stock size is in a state of dynamic equilibrium.)
3. To stabilize carbon dioxide in the atmosphere by getting emissions to equal removals, it will be necessary to make significant reductions (over 50%) in emissions.In other words, it is not enough to level off carbon dioxide emissions. Thus, the statement in part one of the TASK: The bathtub experiment – Interpretation is false.

The three scenarios explored in the simulation are: (a) allow increasing carbon dioxide emissions, (b) level off carbon dioxide emissions, (c) reduce carbon dioxide emissions. Climate Interactive provides the following descriptions of these scenarios:

(a) Allow Increasing Carbon Dioxide Emissions

One scenario is to allow human emissions of carbon dioxide to increase at roughly current levels. This means that governments around the world would not regulate carbon dioxide emissions, and businesses and individuals would not take any special action to reduce carbon dioxide emissions. Everything would continue on as it has been going. This “business as usual” or “status quo” approach asks: What if we did nothing?

The numbers used in this scenario were the “business as usual” estimates of the Intergovernmental Panel on Climate Change (IPCC), the international group dedicated to studying this issue. In this scenario, removals increase naturally, but are never able to keep up with the increase. By the year 2045 the levels would reach 450 ppm. This amount would cause significant changes in the atmosphere, and global warming would cause dramatic changes to the environment.

In our climate simulation, the bathtub would overflow by 2045, and we would experience even more significant climate change. This future is what the IPCC scientists expect will happen if we make no major changes to avert climate change.

(b) Level Off carbon dioxide Emissions

Another option is to gradually stop the increase of human-caused emissions of carbon dioxide in the decades following 2007.This scenario is based loosely on the Kyoto Protocol, an international treaty to reduce carbon dioxide emissions. The treaty was negotiated by the United Nations Framework Convention on Climate Change (UNFCCC) in 1997 and went into effect in 2005. More than 150 nations were involved in creating the Kyoto Protocol, and 84 countries signed the agreement. However, the agreement also needed to be ratified by each country, and not all who signed the protocol ratified or approved it at home. The leading industrialized countries that have

include Russia, Japan, and the members of the European Union. Other countries have since joined the agreement, bringing the total to more than 165. The United States and Australia are among the industrialized countries that signed but did not ratify the Kyoto Protocol.

The countries that did agree to follow the protocol produce about 60% of the world’s greenhouse gases. The agreement is for industrialized countries to reduce greenhouse gas emissions to 5.2% lower than 1990 levels by 2012. This would roughly level off carbon dioxide emissions. But is stabilizing emissions enough to prevent carbon dioxide levels from going above 450 ppm?

(c) Reduce carbon dioxide Emissions

What if all the governments in the world agreed to significantly reduce carbon dioxide emissions? A plan like this has been proposed by former U.S. vice president Al Gore. Climatologist David Stern has proposed something similar. This scenario calls for reducing emissions of carbon dioxide by 58% of the 2007 level by 2070. What would happen to our bathtub? Would it still overflow?

For more information, view the Climate Interactive teaching guide on this simulation.