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Are We Headed Toward a New Climate Regime?

The temperature goals established by the Paris climate agreement could affect the planet in dramatically different ways.

By Madeleine Thomas


A school of manini fish pass over a coral reef at Hanauma Bay in Honolulu, Hawaii. (Photo: Donald Miralle/Getty Images)

COP21, the landmark global climate deal discussed in Paris last year, set two critical temperature goals in an attempts to curb the catastrophic consequences of climate change: Cap the average global temperature increase at two degrees Celsius above pre-industrial levels; and try to limit warming to about 1.5 degrees Celsius to stave off global warming’s devastating effects. But by the time Earth Day rolled around in April—the same date in which more than 155 countries met to sign the Paris Agreement—average global temperature change for the first three months of 2016 was already approaching 1.48 degrees. Temperatures in February alone averaged 1.55 degrees, according to Climate Central. Global temperatures are teetering dangerously close to COP21’s threshold.

A recent study published in the journal Earth System Dynamics examines how a 1.5-degrees and a two-degree Celsius temperature change could each affect the planet differently. Even a 0.5-degrees increase, the study notes, could mean the difference between reaching the upper limit of the climate’s natural variability in some regions of the world and entering an entirely new climate regime.

Among the findings:

  • Coral Reefs: Should global warming escalate by two degrees Celsius, “virtually all tropical coral reefs are projected to be at risk of severe degradation due to temperature-induced bleaching from 2050 onwards,” write the study authors, led by Climate Analytics’Carl-Friedrich Schleussner. The future isn’t much brighter for the 1.5-degree mark either. Even then, about 90 percent of the world’s coral reefs are expected to be at risk of long-term degradation by 2050. It’s important to note that those estimates are conservative. They don’t take other environmental degradations into account like ocean acidification, sea level rise, or tropical cyclones — all of which are expected to threaten the world’s reefs even more. As much as 60 percent of the world’s coral reef coverage could be gone within the next 15 years or so, the study notes. Just a few weeks ago, scientists reported with dismay that as much as 93 percent of the Great Barrier Reef — the planet’s largest coral ecosystem — may already be severely bleached.
  • Sea Level Rise: In a two-degree Celsius scenario, the world’s oceans could rise by 50 centimeters by 2100 (compared to sea levels noted in the year 2000). If warming increases by 1.5 degrees, sea level rise could be reduced by as much as 30 percent, comparatively speaking.
  • Water Scarcity: Should global warming surpass two degrees Celsius, subtropics like the Mediterranean, South Africa, Central and Southern America, and South Australia could experience reduced water availability by up to 30 percent. “Regional reduction in median water availability for the Mediterranean is found to nearly double from 9 percent to 17 percent between 1.5 degrees Celsius and 2 degrees Celsius, and the projected lengthening of regional dry spells increases from 7 to 11 percent,” the researchers write.
  • Heat Extremes: Under a two-degree Celsius scenario, the study forecasts temperature extremes of three degrees Celsius and higher throughout the Northern Hemisphere, Central and South America, and South Africa. Warm spells lasting three months or more are also likely to occur at a warming scenario of two degrees. Under a 1.5-degree increase, Amazonia, East and West Africa, and Southeast Asia could also experience warm spells of up to three months. “Given that the [warm spell duration indicator] only measures the longest consecutive interval, such an increase can be interpreted as entering a new climate regime for these tropical regions,” the study authors write.

About 40 percent of the world’s subtropics and tropics could experience an increase in consecutive dry days (the annual number of consecutive days in which precipitation is less than one millimeter per day). This is particularly likely in the Mediterranean, the authors write, as consecutive dry days could increase there by four to 10 percent resulting from a 1.5-degree increase, and six to 15 percent following a two-degree increase.