Perhaps the biggest source of confusion in the public climate discussion is that avoiding catastrophic warming requires stabilizing carbon dioxide concentrations not emissions. Studies find that many, if not most, people are confused about this, including highly informed people, and they mistakenly believe that if we stop increasing emissions, then global warming will stop. In fact, very deep reductions in greenhouse gas (GHG) emissions are needed to stop global warming.
One study published in Climatic Change on the beliefs of Massachusetts Institute of Technology (MIT) graduate students, found that “most subjects believe atmospheric GHG concentrations can be stabilized while emissions into the atmosphere continuously exceed the removal of GHGs from it.” The author, Dr. John Sterman from MIT’s Sloan School of Management, notes that these beliefs are “analogous to arguing a bathtub filled faster than it drains will never overflow” and “support wait-and-see policies but violate conservation of matter.”
Let me expand on the bathtub analogy. Although atmospheric concentrations (the total stock of CO2 already in the air) might be thought of as the water level in the bathtub, emissions (the yearly new ow into the air) are represented by the rate of water flowing into a bathtub from the faucet. There is also a bathtub drain, which is analogous to the so-called carbon “sinks” such as the oceans and the soils. The water level will not drop until the flow through the faucet is less than the ow through the drain.
Similarly, carbon dioxide levels will not stabilize until human-caused emissions are so low that the carbon sinks can essentially absorb them all. Under many scenarios, that requires more than an 80% drop in CO2 emissions. If the goal is stabilization of temperature near or below the 2°C (3.6°F) threshold for dangerous climate change that scientists and governments have identified, then carbon dioxide emissions need to approach zero by 2100. A key related point of confusion is that temperatures do not stop rising once atmospheric carbon dioxide levels have stabilized. It takes a while for the Earth’s climate system to actually reach its equilibrium temperature for a given level of CO2. If CO2 levels stopped rising now, temperatures would keep rising for another few decades, albeit slowly. Put another way, the warming that we have had to date is due to CO2 levels from last century. As long as we keep putting enough carbon dioxide into the air to increase CO2 levels, then this lag will persist and the ultimate warming we face will continue to rise. In addition, certain key impacts, such as the disintegration of the great ice sheets, will also not stop for decades. Moreover, if we wait too long and pass the point of no return, then ice sheet collapse and sea-level rise will continue for centuries, even if temperatures stop rising.
The MIT study, “Understanding Public Complacency About Climate Change: Adults’ Mental Models of Climate Change Violate Conservation of Matter,” notes that there is an apparent “contradiction” in “public attitudes about climate change”:
Surveys show most Americans believe climate change poses serious risks but also that reductions in greenhouse gas (GHG) emissions sufficient to stabilize atmospheric GHG concentrations or net radiative forcing can be deferred until there is greater evidence that climate change is harmful. US policymakers likewise argue it is prudent to wait and see whether climate change will cause substantial economic harm before undertaking policies to reduce emissions. Such wait-and-see policies erroneously presume climate change can be reversed quickly should harm become evident, underestimating substantial delays in the climate’s response to anthropogenic forcing.
Such a misconception of climate dynamics may lead some people to mistakenly believe that action to reduce carbon dioxide emissions does not need to start imminently.