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Why two degrees of global warming is worse than it sounds » Yale Climate Connections


A cartoon featuring two parents working and looking stressed. In the background is a sick child laying on a couch. A caption reads:

A couple of degrees Celsius might not sound like a lot. But in terms of global warming, it’s a big deal.

In fact, every tenth of a degree that the Earth warms in the future will make a difference in the impacts that people experience worldwide and in your neck of the woods.

Picture yourself:

  • In Phoenix, Arizona, where you have to endure roughly nine additional days of over 110 degrees Fahrenheit per year than people here used to. 
  • In Montecito, California, where if you’re not shopping for new air filters due to expected wildfire smoke, you’re practicing your evacuation plan in preparation for the mudslides that are becoming more common on fire-scarred hillsides.
  • In a Gulf Coast community, where hurricanes are getting more frequent and more severe — like Hurricane Ian, which was 10% wetter than it would have been if not for climate change.

Those are just some of the impacts we’re already seeing as a result of the one degree Celsius the world has already warmed since the late 19th century.

And the consequences to everyday life will only get more severe with every degree of change. That’s why the world’s governments pledged in the Paris climate agreement to limit global warming below 2 degrees Celsius (3.6 degrees Fahrenheit) — and preferably to 1.5 degrees C (2.7 F).

Yet current policies and pathways put the world on track to a 2.8 C/5 F temperature rise by the end of the century, according to the United Nations Environment Program’s Emissions Gap Report 2022.

So it’s important to understand what a difference a couple of degrees really can make.

It’s warmed ONE degree Celsius so far, and we can already feel the impacts.

Today’s world is roughly 1 C/1.8 F warmer than it was back in 1880 when people started burning fossil fuels in earnest as part of the Industrial Revolution.

This change may look small on a thermometer, but it makes a big difference here and now in communities across the planet.

According to NASA, 19 of the warmest years on record have taken place since 2000.

Colorado, New Mexico, Tennessee, and Texas all experienced their hottest-ever summer nights in 2022. Hurricane Ian tied for the fifth-strongest hurricane on record to hit the U.S. and has been projected to be one of the costliest to ever hit Florida. And communities across the Western U.S. are grappling with increasing drought and growing threats to crops.

Meanwhile, ice is melting at both poles, with Antarctica losing ice mass to the tune of about 150 billion tons per year and Greenland losing roughly 280 billion tons annually. And summer Arctic sea ice extent is shrinking by 12.6% per decade.

All that melting ice contributes to sea level rise, threatening coastal communities and low-lying islands globally. Longtime residents of the Isles de Jean Charles in Louisiana, for example, have already had to abandon their homes for higher ground, due to a combination of sinking land and sea level rise.

Meanwhile, the last decade was the ocean’s warmest since at least the 1800s, with 2021 the warmest on record. Water expands as it gets warmer, so warming oceans are responsible for between one-third and one-half of sea level rise, whose rates of rise NASA calls “unprecedented” over the last 2,500-plus years.

That’s just from one degree Celsius of change.

And impacts will only intensify as the temperature continues to tick up. A 2022 Intergovernmental Panel on Climate Change report notes that even the most ambitious plan of limiting warming to 1.5 C/2.7 F includes “unavoidable multiple climate hazards over the next two decades.”

These risks include threats of sea level rise to infrastructure and low-lying coastal communities, as well as more extreme weather, drought, and related health impacts.

What difference does a degree of change make? Ask the humans of 2100.

In a world that’s 1.5 C/2.7 F warmer than in pre-industrial times, storms, heat waves, and droughts will be even more extreme than they are today. More homes will be lost to sea level rise and wildfire. And more people are likely to suffer from heat-related illnesses, infectious diseases, and starvation.

Life in the 2020s already looks different. With every additional degree — and each fraction of a degree — of warming, the consequences will become yet more palpable in 2100.

Let’s say, for instance, that people manage to keep warming below 1.5 C/2.7 F. Today’s young children could live to see nearly four times the number of extreme storms they see now, according to the Intergovernmental Panel on Climate Change research. And that’s just with an additional 0.5 C of warming from where we are today. With 3 C/5.4 F of warming, however, today’s kids would inherit a world with five times the likelihood of hurricanes and other severe storms.

The following are other examples of the difference a degree or two could make in terms of real-world harm:

  • More extreme heat. In a 1.5 C/2.7 F scenario, about 14% of the world’s population will face severe heat waves at least once every five years. In a 2 C/3.6 F of warming scenario, however, that number shoots up to 37%. [NASA]
  • Increasing sea level rise. By 2100, millions more people will be exposed to flooding from sea level rise in a 2 C/3.6 F scenario (32–80 million people worldwide compared with 31–69 million under a 1.5 C/2.7 F warming). [IPCC]
  • Intensifying drought. Worldwide, 800 million to 3 billion people would experience chronic water scarcity at 2 C/3.6 F warming, a figure that jumps up to as high as 4 billion in with 4 C/7.2 F warming. [IPCC
  • Vicious cycles – Like a runaway train, some climate impacts can speed up warming. For example, some scientists are concerned that climate impacts like melting permafrost will make warming even worse. [Skeptical Science]

With every degree of warming, there’s also an increased likelihood of reduced crop yields, loss of biodiversity, and coral reef die-off, underscoring the fact that a seemingly small change can have major consequences.

The bottom line: A couple of degrees makes a profound difference

Every fraction of a degree of warming matters — but that goes both ways.

By transitioning off fossil fuels and to clean energy, sucking carbon out of the air, and drastically slashing emissions, the world has a chance to limit global warming — averting the worst impacts and helping to preserve a safe and livable world.

Tom Toro is a cartoonist and writer who has published over 200 cartoons in The New Yorker since 2010.



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