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I recently finished a free on-line course through edx.org called Making Sense of Climate Denial. I highly recommend the course to anyone interested in climate change and especially those interested in what science says about communicating the science of controversial issues.

One example is that presenting myths in the wrong way can create more belief in the myth even if the author is trying to do the opposite. My attempt at debunking a sea-level-rise myth is below. While many of the impacts of climate change are under-estimated by many people, I chose one claim that could be called “alarmist.” That means that the myth overestimates the impact. To learn more about the fact-myth-fallacy structure, please check out the course!



FACT: Climate scientists expect global sea level to increase between 0.26 meters (0.85 feet) and 0.98 meters (3.2 feet) by 2100.

In the 2013 IPCC report, estimated sea level rise by 2100 is estimated to be between one and three feet. This compares to a 0.2 meter (0.6 feet) increase from 1901 to 2010. The main contributors to sea level rise are thermal expansion of oceans and glacier melting. Another increasing contributor is ice sheet melting.

Running several scenarios including atmospheric CO2 concentrations greater than 700 ppm and including “ice-sheet dynamical changes”, models suggest that sea level rise will likely not be greater than 0.98 meters (3.2 feet) by 2100.

There *will* be regional variation in sea level rise as winds, ocean currents, and landmass change. Some areas will experience greater change and others will experience less change or even sea level decrease. However, average global sea level rise by 2100 will be moderate – not extreme.

The reports adds that with medium confidence, extra sea level rise from collapse of the Antarctic ice-sheet would contribute less than several tenths of a meter (1 foot) additional sea level rise by 2100.

One myth suggests that expected sea level rise will be 20 feet (6.1 meters).

This myth doesn’t include a time frame. However, it implies that this may happen in a single lifetime. This myth cherry picks from the model results because sea level may well reach this magnitude, but not for at least 500 years. Even in the worst scenarios considered, global sea level in 2100 will only reach 1.3 meters (4.3 feet).

People who cite this 20-foot-rise statistic are trying to make this impact seem scary, but other factors like changes in storm surges and increased weather extremes will have more worrisome effects.

So the next time you stand on a beach with your toes in the water, imagine the ocean at waist level in 2100. This is definitely worrisome, but the sea level will *not* have increased by the height of a two-story house.