Quantcast
Environmental News for a Healthier Planet and Life

Help Support EcoWatch

Global Warming Slowdown Attributed to Phase-Out of CFCs

Climate

By Tim Radford

What appears to be a slowdown in the rate of atmospheric warming this century may have a simple explanation, Mexican scientists say. It could be the consequence of protecting the ozone layer.

Scientists who looked at the whole history of climate in the twentieth century have come up with a new possible explanation for the apparent slowdown in global warming. It is because, they say, of the Montreal Protocol that banned chlorofluorocarbons (CFCs) and saved the ozone layer.

The slowdown in the rate of atmospheric warming this century may be due to the Montreal Protocal in 1987, which phased out Ozone-depleting CFCs internationally. The slowdown is a favored case of climate change deniers.

The ozone layer was the second great atmospheric crisis of the late twentieth century (the first involved the urban smog and acid rain that triggered clean air legislation in Europe and the U.S.). CFCs were the safe, enduring gases used as refrigerants: their only problem was that—once they reached the stratosphere—they unexpectedly began to destroy the ozone layer that screens out harmful ultraviolet light.

Within four years of the dramatic discovery of a huge “hole” in the ozone layer over the Antarctic, these gases were phased out, in a rare act of international agreement, by the 1989 Montreal Protocol.

But CFCs had a second unexpected property. They were greenhouse gases of unusual potency: molecule for molecule, one of them was rated at more than 17,000 times more effective at trapping infrared radiation than carbon dioxide. CFCs were released only in comparatively tiny quantities, but they were calculated to account for up to 24 percent of global warming.

Francisco Estrada of the National Autonomous University of Mexico and colleagues report in Nature Geoscience that they spotted the signal of the missing CFCs when they used statistical analysis to examine average temperature records in the two hemispheres from 1880 to 2010.

Tentative Results, Clear Pattern

Exercises such as these are not simple: the scientists had to find a way of eliminating natural cycles that keep the weather in a permanent pattern of change, and identify long-term trends that could be identified as evidence of human activity.

In the first place, for a mix of reasons, rates of change in the two hemispheres are out of step; in the second place there are natural cycles linked to ocean and atmospheric circulation such as the Atlantic Multidecadal Oscillation that are associated with extended periods of warming and cooling; in the third place things like greenhouse gas emissions are tied into cycles of economic growth, and affected again in many cases by legislation, perhaps to reduce the aerosols that make citizens cough and splutter, but that also block sunlight and have a mild cooling effect.

And to get the results that they did, the researchers had to use advanced statistical methods (for example, they say, the “Perron-Yabu testing procedure, valid with integrated or stationary noise”) that would baffle most of the human race.

So like all research results, the findings are tentative and published to provoke more research. But even so, the graphs in Nature Geoscience show a pattern of human influence in global average temperatures.

In the last century, the planet warmed overall by 0.8 degrees Celsius. In the trend discernible in the sometimes dramatic oscillations of temperature, there is evidence of a slowdown in this warming during two world wars, and the Great Depression of the 1930s, when world trade came to a standstill, factories closed everywhere and chimneys stopped smoking.

The authors see a pronounced rise in both greenhouse gas emissions and in global temperatures in the 1960s—the start of sustained global warming. But they also see a distinct slowdown that begins in the 1990s in response to the Montreal Protocol, which began the phase-out of the CFCs and the slow restoration of the ozone screen.

There is evidence that the ocean is warming 15 times faster than at any time in the last 10,000 years, which suggests that ocean circulation may be carrying away the heat that meteorologists expected to record in the atmosphere.

Slowdown Caused by Humans

The Montreal Protocol is not the only possible explanation for the apparent slowdown. There is also evidence that at least one sector of deep ocean is warming 15 times faster than at any time in the last 10,000 years, which suggests that ocean circulation may be carrying away the heat that meteorologists expected to record in the atmosphere.

Two scientists in October proposed that the slowdown in the rate of global warming could possibly be explained by a much longer-term natural cycle that nobody had yet identified: a climate signal could propagate across the northern hemisphere in a self-organising way, just as the so-called “stadium wave” propagates around a sports arena as excited spectators stand and sit down again.

They say in Climate Dynamics that such a phenomenon could be linked to a brake-and-accelerator pattern of influence of northern sea ice on atmosphere and ocean circulation.

If this pattern exists, it would explain why climate modellers had not predicted the present lull or slowdown in global warming. But the wave itself would have nothing to do with global warming, the two authors say. It would just offer a new perspective for climate science.

The Nature Geoscience paper, however, does once again confirm the link between average temperatures and greenhouse gas emissions. “Paradoxically the recent decrease in warming, presented by global warming skeptics as proof that humankind cannot affect the climate system, is shown to have a direct human origin,” the authors conclude.

Visit EcoWatch’s CLIMATE CHANGE page for more related news on this topic.

EcoWatch Daily Newsletter

A man pushes his mother in a wheelchair down Ocean Drive in South Beach, Miami on May 19, 2020, amid the novel coronavirus pandemic. CHANDAN KHANNA / AFP via Getty Images

The U.S. reported more than 55,000 new coronavirus cases on Thursday, in a sign that the outbreak is not letting up as the Fourth of July weekend kicks off.

Read More Show Less
To better understand how people influence the overall health of dolphins, Oklahoma State University's Unmanned Systems Research Institute is developing a drone to collect samples from the spray that comes from their blowholes. Ken Y. / CC by 2.0

By Jason Bruck

Human actions have taken a steep toll on whales and dolphins. Some studies estimate that small whale abundance, which includes dolphins, has fallen 87% since 1980 and thousands of whales die from rope entanglement annually. But humans also cause less obvious harm. Researchers have found changes in the stress levels, reproductive health and respiratory health of these animals, but this valuable data is extremely hard to collect.

Read More Show Less

Sunscreen pollution is accelerating the demise of coral reefs globally by causing permanent DNA damage to coral. gonzalo martinez / iStock / Getty Images Plus

On July 29, Florida Governor Ron DeSantis signed into law a controversial bill prohibiting local governments from banning certain types of sunscreens.

Read More Show Less
Oat milk is popping up at coffee shops and grocery stores alike, quickly becoming one of the trendiest plant-based milks. jacqueline / CC by 2.0

By Kelli McGrane

Oat milk is popping up at coffee shops and grocery stores alike, quickly becoming one of the trendiest plant-based milks.

Read More Show Less

"Emissions from pyrotechnic displays are composed of numerous organic compounds as well as metals," a new study reports. Nodar Chernishev / EyeEm / Getty Images

Fireworks have taken a lot of heat recently. In South Dakota, fire experts have said President Trump's plan to hold a fireworks show is dangerous and public health experts have criticized the lack of plans to enforce mask wearing or social distancing. Now, a new study shows that shooting off fireworks at home may expose you and your family to dangerous levels of lead, copper and other toxins.

Read More Show Less
Billions worth of valuable metals such as gold, silver and copper were dumped or burned last year as electronic waste produced globally jumped to a record 53.6 million tons. Curtis Palmer / CC by 2.0

By Ashutosh Pandey

Billions worth of valuable metals such as gold, silver and copper were dumped or burned last year as electronic waste produced globally jumped to a record 53.6 million tons (Mt), or 7.3 kilogram per person, a UN report showed on Thursday.

Read More Show Less

Trending

A women walks with COVID-19 care kits distributed by Boston's Office of Neighborhood Services in Boston, Massachusetts on May 28, 2020. The pandemic has led to a rise in single-use plastic items, but reusable bags and cloth masks can be two ways to reduce waste. JOSEPH PREZIOSO / AFP via Getty Images

This month is Plastic Free July, the 31 days every year when millions of people pledge to give up single-use plastics.

Read More Show Less