Just Half a Degree Difference in Warming Could Raise Sea Levels by 4 Inches

April 22, 2016 | Joanne Kennell

Earth depicted sinking into an ocean
Photo credit: Andrea Della Adriano/flickr (CC BY 2.0)

Yes, the difference between 1.5 and 2 degrees Celsius is a big deal.

(Unless otherwise stated, all temperatures in this article are in Celsius.)

When it comes to how we perceive temperature, a difference of half-a-degree really goes unnoticed. But that is weather — day-to-day variations in temperature, cloud cover, humidity, rainfall, etcetera. Climate, on the other hand, is the average weather that occurs in a region for a particular season, generally over at least 30 years, but sometimes these changes can take place over hundreds and even thousands of years.

But according to a new study, published on April 21 in Earth System Dynamics, an open access journal of the European Geosciences Union, when it comes to climate change and average global temperatures, a half-a-degree variation can have substantially different impacts.

European researchers have found that with a warming of 1.5 degrees Celsius (2.7 degrees Fahrenheit) versus a 2 degrees Celsius (3.6 degrees Fahrenheit) by 2100 — the two temperature limits set in the Paris climate agreements — the additional half degree would mean an additional 4-inch (10-centimetre) global sea-level rise, longer heat waves, and virtually all tropical coral reefs would be risk.

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By considering 11 different indicators including extreme weather events, water availability, crop yields, coral degradation, and sea-level rise, the researchers found "significant differences for all the impacts we considered," said the study's lead author Carl Schleussner, a scientific advisor at Climate Analytics in Germany, in a press release. "We analysed the climate models used in the [Intergovernmental Panel on Climate Change (IPCC)] Fifth Assessment Report, focusing on the projected impacts at 1.5°C and 2°C warming at the regional level."

The team, along with researchers from Germany, Switzerland, Austria, and the Netherlands, identified a number of “hotspots” around the globe where projected climate impacts at 2 degrees are significantly more severe.

The Mediterranean

The Mediterranean is already suffering from the effects of climate change-induced drying. With a global temperature rise of 1.5 degrees, the availability of fresh water in the region would be about 10 percent lower than in the late 20th century. And in a 2-degree world, this number becomes 20 percent.

The Tropics

A half-degree difference in global temperature could have damaging consequences for crop yields, particularly in Central American and West Africa. On average, local tropical maize and wheat yields would reduce twice as much at 2 degrees than at 1.5 degrees.

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Not only that, the tropics would bear the brunt of the additional increase, with warm spells lasting up to 50 percent longer. "For heat-related extremes, the additional [half-a-degree] increase marks the difference between events at the upper limit of present-day natural variability and a new climate regime, particularly in tropical regions," explained Schleussner.

Coral Reefs

The additional warming could also affect tropical coral reefs, which are already experiencing a record bleaching event. Warming limited to 1.5 degrees would allow some tropical coral reefs to adapt to climate change. In contrast, a 2-degree temperature increase by 2100 would put virtually all of these ecosystems at risk of coral bleaching.

Now, on a global scale, the researchers anticipate a sea-level rise of about 20 inches (50 centimeters) by 2100 in a 2-degree world, compared to 16 inches (40 centimeters) with 1.5 degree warming. "Sea level rise will slow down during the 21st century only under a 1.5°C scenario," explained Schleussner.

Unfortunately, with the amount of greenhouse gases being emitted into the atmosphere, the planet will undoubtedly warm 1.5 degrees in the next century, so it is really up to all of us, for the benefit of future generations, to prevent it from rising any further by using and investing in clean and green technologies.

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