This Is What the World Looks Like if We
Pass the Crucial 1.5-Degree Climate Threshold

Lauren Sommer / NPR

 (November 9, 2021) — There’s one number heard more than any other from the podiums at the United Nations climate summit in Glasgow, Scotland: 1.5 degrees Celsius. 

That’s the global climate change goal world leaders agreed to strive for. By limiting the planet’s warming to 1.5 degrees Celsius, or 2.7 degrees Fahrenheit, by 2100, the hope is to stave off severe climate disruptions that could exacerbate hunger, conflict and drought worldwide.

The 1.5-degree target has long been championed by developing nations, where millions of people are among the most vulnerable to climate change. At the 2015 Paris climate negotiations, they pushed industrialized countries to improve on the 2 degree Celsius goal held at the time, since wealthier nations are responsible for most greenhouse gas emissions since the Industrial Revolution. 

At the climate negotiations now underway, nations are touting new commitments to cut their heat-trapping emissions by switching to clean energy and reducing deforestation. India is pledging, for the first time, to be carbon neutral by 2070. More than 100 countries, including the United States, joined a global pact to cut methane, a potent greenhouse gas.

Still, added together, the recent pledges don’t go far enough. Even with more ambitious emissions cuts from some countries, warming is still on track for more than 2 degrees Celsius (or 3.6 Fahrenheit) by the end of the century. The Earth is already 1.1 degrees Celsius hotter than it was 150 years ago.

Though a half-degree Celsius difference in temperature increase might seem inconsequential, the difference for life on Earth could be huge. Here’s what scientists expect, if average global temperatures exceed 1.5 degree Celsius warming by 2100.

Coral Reefs Face Almost Complete Die-off

Off the coast of Australia, the Great Barrier Reef is known for being large enough to be seen from space. It’s the size of Germany — a biodiversity hotspot that was once thought to be too big to fail. But over the last few decades, marine biologists like Ove Hoegh-Guldberg of the University of Queensland have watched its rapid decline.

“My career is one of going from a period of when it was wonderful and abundant to now, staring down the barrel,” Hoegh-Guldberg says. “We’re staring down the barrel of something really horrific.”

Oceans are warming along with the atmosphere, since they absorb much of the excess heat from climate change. Repeated marine heat waves over the last five years have turned much of the Great Barrier Reef a ghostly white color. When temperatures rise, corals expel the microscopic algae inside them, losing their food source in the process. Sometimes the corals can recover, but increasingly, they’re dying off.

“Something around 50% of the shallow water corals were killed literally over a couple of months, in some cases over a couple of weeks,” Hoegh-Guldberg says. “If you extend that out into the future, we’ll get to a point where the damage overwhelms the ability of corals to bounce back.”

Marine heat waves have already doubled in number since 1980 and are expected to become more intense as temperatures rise. At 1.5 degrees Celsius, it’s likely that 70 to 90% of coral reefs will die off worldwide. At 2 degrees Celsius of warming, 99% are lost.

“If we delay even a year or two more, we really are going down a pathway where there will be no return,” Hoegh-Guldberg says. “We need to act and we need to act decisively, without question and solve this problem.”

‘Unheard-of’ Storms Become More Common

Water has taken a heavy toll in 2021, all over the world. In September, the remnants of Hurricane Ida swept into the Northeast, killing more than 50 people in New Jersey, New York and other states. Many drowned in cars and basement apartments, overwhelmed by rushing water. In August, two dozen people died when heavy rains caused flash flooding in Tennessee. 

Scientists warn that a hotter atmosphere is a wetter atmosphere. Warmer air can hold more water, helping produce more intense rainfall and stronger storms. With ocean temperatures higher in the Gulf of Mexico, hurricanes are intensifying at a more rapid rate. 

As the climate warms, storms once thought to be extremely rare are expected to become more frequent. And the chances don’t just go up a little bit.

The Threat Level As Perceived in 2018

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