Human Cooperation Can Restore Climate Patterns: The Case of the Ozone Layer and the Southern Jet Stream

Emissions from the chlorofluorocarbons and hydrochlorofluorocarbons used as refrigerants and aerosols didn't just burn a hole in the ozone layer. They also shifted the Southern Hemisphere's jet stream south towards Antarctica.
Now, a study published in Nature Wednesday found that the 1987 Montreal Protocol banning those substances wasn't just successful in helping to repair the ozone hole. It also paused this jet stream shift.
"This is an object lesson in how the international community should react to global environmental challenges," the study's authors concluded. "Restricting dangerous emissions and changing business practices is also the way to combat global warming caused by greenhouse gases."
Previous research had shown that the jet stream in the Southern Hemisphere had been shifting south by one degree of latitude each decade until 2000, The Guardian reported. This caused changes to storms and rainfall in South America, East Africa and Australia.
But after 2000, the shift stopped, and researchers were able to use a combination of models and computer simulations to determine this pause was down to the shrinking ozone hole, and not natural causes, ScienceAlert explained. In fact, the shift may have even begun to reverse.
This is a relief to some parts of the world.
"The 'weather bands' that bring our cold fronts have been narrowing towards the south pole, and that's why southern Australia has experienced decreasing rainfall over the last thirty years or so," Ian Rae, an organic chemist from the University of Melbourne who was not involved in the study, said, according to ScienceAlert! "If the ozone layer is recovering, and the circulation is moving north, that's good news on two fronts (pun not intended)."
In Chile and Argentina, the reversal will bring more rain and less ultraviolet light, but farther north in South America and in parts of East Africa the change could actually reverse the greater rain and area available for agriculture that it had brought, The Guardian explained.
On a global scale, however, the news is a hopeful example of how we might act on the climate crisis.
"This is good news, definitely," paper reviewer Alexey Karpechko of the Finnish Meteorological Institute told The Guardian. "It shows our actions can stop climate change. We can see coordinated action works. It is a strong message to us as emitters of greenhouse gases. This shows we can manipulate the climate both ways: in a wrong way and by reversing the damage we have done."
However, our failure to act collectively on greenhouse gasses so far means that the reversal in the jet stream's shift is not guaranteed to last: While the recovering ozone layer pushes it back to normal, greenhouse gas emissions draw it south again.
"We term this a 'pause' because the poleward circulation trends might resume, stay flat, or reverse," lead author Antara Banerjee, a NOAA scientist and visiting fellow at the University of Colorado Boulder, said in a university press release. "It's the tug of war between the opposing effects of ozone recovery and rising greenhouse gases that will determine future trends."
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The speed and scale of the response to COVID-19 by governments, businesses and individuals seems to provide hope that we can react to the climate change crisis in a similarly decisive manner - but history tells us that humans do not react to slow-moving and distant threats.
A Game of Jenga
<p>Think of it as a game of Jenga and the planet's climate system as the tower. For generations, we have been slowly removing blocks. But at some point, we will remove a pivotal block, such as the collapse of one of the major global ocean circulation systems, for example the Atlantic Meridional Overturning Circulation (AMOC), that will cause all or part of the global climate system to fall into a planetary emergency.</p><p>But worse still, it could cause runaway damage: Where the tipping points form a domino-like cascade, where breaching one triggers breaches of others, creating an unstoppable shift to a radically and swiftly changing climate.</p><p>One of the most concerning tipping points is mass methane release. Methane can be found in deep freeze storage within permafrost and at the bottom of the deepest oceans in the form of methane hydrates. But rising sea and air temperatures are beginning to thaw these stores of methane.</p><p>This would release a powerful greenhouse gas into the atmosphere, 30-times more potent than carbon dioxide as a global warming agent. This would drastically increase temperatures and rush us towards the breach of other tipping points.</p><p>This could include the acceleration of ice thaw on all three of the globe's large, land-based ice sheets – Greenland, West Antarctica and the Wilkes Basin in East Antarctica. The potential collapse of the West Antarctic ice sheet is seen as a key tipping point, as its loss could eventually <a href="https://science.sciencemag.org/content/324/5929/901" target="_blank">raise global sea levels by 3.3 meters</a> with important regional variations.</p><p>More than that, we would be on the irreversible path to full land-ice melt, causing sea levels to rise by up to 30 meters, roughly at the rate of two meters per century, or maybe faster. Just look at the raised beaches around the world, at the last high stand of global sea level, at the end of the Pleistocene period around 120,0000 years ago, to see the evidence of such a warm world, which was just 2°C warmer than the present day.</p>Cutting Off Circulation
<p>As well as devastating low-lying and coastal areas around the world, melting polar ice could set off another tipping point: a disablement to the AMOC.</p><p>This circulation system drives a northward flow of warm, salty water on the upper layers of the ocean from the tropics to the northeast Atlantic region, and a southward flow of cold water deep in the ocean.</p><p>The ocean conveyor belt has a major effect on the climate, seasonal cycles and temperature in western and northern Europe. It means the region is warmer than other areas of similar latitude.</p><p>But melting ice from the Greenland ice sheet could threaten the AMOC system. It would dilute the salty sea water in the north Atlantic, making the water lighter and less able or unable to sink. This would slow the engine that drives this ocean circulation.</p><p><a href="https://www.carbonbrief.org/atlantic-conveyor-belt-has-slowed-15-per-cent-since-mid-twentieth-century" target="_blank">Recent research</a> suggests the AMOC has already weakened by around 15% since the middle of the 20th century. If this continues, it could have a major impact on the climate of the northern hemisphere, but particularly Europe. It may even lead to the <a href="https://ore.exeter.ac.uk/repository/handle/10871/39731?show=full" target="_blank" rel="noopener noreferrer">cessation of arable farming</a> in the UK, for instance.</p><p>It may also reduce rainfall over the Amazon basin, impact the monsoon systems in Asia and, by bringing warm waters into the Southern Ocean, further destabilize ice in Antarctica and accelerate global sea level rise.</p>The Atlantic Meridional Overturning Circulation has a major effect on the climate. Praetorius (2018)
Is it Time to Declare a Climate Emergency?
<p>At what stage, and at what rise in global temperatures, will these tipping points be reached? No one is entirely sure. It may take centuries, millennia or it could be imminent.</p><p>But as COVID-19 taught us, we need to prepare for the expected. We were aware of the risk of a pandemic. We also knew that we were not sufficiently prepared. But we didn't act in a meaningful manner. Thankfully, we have been able to fast-track the production of vaccines to combat COVID-19. But there is no vaccine for climate change once we have passed these tipping points.</p><p><a href="https://www.weforum.org/reports/the-global-risks-report-2021" target="_blank">We need to act now on our climate</a>. Act like these tipping points are imminent. And stop thinking of climate change as a slow-moving, long-term threat that enables us to kick the problem down the road and let future generations deal with it. We must take immediate action to reduce global warming and fulfill our commitments to the <a href="https://www.ipcc.ch/sr15/" target="_blank" rel="noopener noreferrer">Paris Agreement</a>, and build resilience with these tipping points in mind.</p><p>We need to plan now to mitigate greenhouse gas emissions, but we also need to plan for the impacts, such as the ability to feed everyone on the planet, develop plans to manage flood risk, as well as manage the social and geopolitical impacts of human migrations that will be a consequence of fight or flight decisions.</p><p>Breaching these tipping points would be cataclysmic and potentially far more devastating than COVID-19. Some may not enjoy hearing these messages, or consider them to be in the realm of science fiction. But if it injects a sense of urgency to make us respond to climate change like we have done to the pandemic, then we must talk more about what has happened before and will happen again.</p><p>Otherwise we will continue playing Jenga with our planet. And ultimately, there will only be one loser – us.</p>By John R. Platt
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