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The Black Summer fires’ smoke may have increased the likelihood of the triple La Nina, according to research.


black summer smoke Credit: NASA

The 2019-2020 wildfire season has been devastating. Vast swaths of pristine forest burned, many for the first time in memory. By some estimates, a billion domestic animals have perished up and down Australia’s east coast. Dozens of people died.

While Sydney’s skies are blue again, Australia’s black summer has kept scientists around the world busy. The sheer scale of these huge fires led to horrific effects. Recently, researchers have found huge amounts of smoke ate away in our protective ozone layer.

now, New search By American scientists indicates that the black summer fires were huge enough to affect the El Niño Southern Oscillation cycle. It’s one of the main drivers of unusual weather around the world – and one Australians know firsthand.

The three consecutive years of La Niña we just had? Their likelihood could have been increased by the fires of the Black Summer. Surprisingly, the cause is smoke.

But it is important not to say that the link is proven. While pioneering, this research relies on a single model. It is too early to say clearly that wildfire smoke can lead to La Niña.

Where there is fire, there is smoke

We’ve known for a long time that the massive volume of ash spewed high into the upper atmosphere by a major volcanic eruption can cool the Earth’s surface for months, or even years.

We also know volcanoes can influence Equatorial Pacific Ocean, and thus affect the occurrence of El Niño or La Niña phase.

how? by blocking light. Ash particles reduce the amount of light that reaches the surface.

Volcanic ash flies high in the stratosphere, the part of the atmosphere just above the clouds where long-haul aircraft fly. The sunlight is then reflected before it reaches the ground, thus cooling the surface like an umbrella can.

The smoke from the Black Summer fires could have heightened the potential for a La Nina trilogy

So many forests and trees were burned during the Black Summer that plumes of smoke can be seen from space. Credit: NASA

Is wildfire smoke the same as volcanic ash?

It is tempting to equate smoke with ash, and assume that a large enough bush fire will have effects similar to a volcano.

But there are important differences. Wildfires obviously don’t smell like rotten eggs.

This may seem insignificant, but the smell of rotten eggs – which comes from the sulfur – indicates significant differences in the composition of volcanic ash and wildfire smoke.

Different chemicals can mean very different responses to sunlight once in the atmosphere, which in turn can affect how much light is reflected.

Second, wildfires don’t break out.

A decent volcano erupts with enough force to blow smoke high into the stratosphere. Wildfires do not have the same driving force.

However, wildfire smoke is hot, and hot smoke rises nicely. Some smoke from the black summer fires The stratosphere has reachedalthough after a much longer period of volcanic eruptions.

So, do large wildfires have the same effect on climate as a volcano?

The US researchers begin by checking the similarities using climate simulations. They found that wildfire smoke does indeed shade the surface from sunlight in this simulation.

how much? Over the Southeast Pacific, about 150 terawatts of sunlight has been bounced back into space — the equivalent of about 100,000 coal power plants.

The smoke from the Black Summer fires could have heightened the potential for a La Nina trilogy

The whiter and thicker clouds make the ocean surface cooler. Credit: Shutterstock

Clouds matter

The surprising discovery is how this happens. Unlike volcanic eruptions, wildfire smoke did not directly reflect sunlight. Instead, the clouds were responsible.

How does this work? This is where the magic of the climate system begins. Our atmosphere, oceans, and land are constantly interacting with each other.

In the simulations, black summer smoke was first blown eastward by strong winds in the atmosphere. Under certain conditions, some smoke particles can interact with the droplets in the clouds and make the clouds thicker and brighter. One area where this can happen is the subtropical Southeast Pacific.

The researchers were able to show that the clouds over this region increased in brightness significantly around the time the smoke particles arrived.

These brighter, whiter clouds reflect more sunlight back into space and shade the surface beneath. Net effect: cooler sea water.

The effect was particularly significant because of the timing. Smoky clouds appear around the summer solstice in late December, the same time of year when the intensity of incoming sunlight reaches its peak in the Southern Hemisphere.

How does this relate to La Niña?

Follow the chain: Huge amounts of smoke billow eastward as they whiten clouds, cool seawater, and cause less water to evaporate.

Surface winds carried this cooler, drier air over the tropical Pacific Ocean, where they cooled the ocean surface again, and made it difficult for tropical storms to form.

A cooler sea surface in the tropical Pacific Ocean is a defining feature of La Niña, the cold phase of the El Niño Southern Oscillation cycle.

This is how this research was able to track the link between summer black smoke and rare cascading La Niña events in 2019-20 and 2020-20. As you know, we ended up having a rare three times for La Niña in 2021-22, even though the hunt ends before that.

The smoke from the Black Summer fires could have heightened the potential for a La Nina trilogy

Plumes of smoke reached as far as South America. Credit: NASA

Is the link installed now? not exactly

This study provides a consistent physical explanation for how wildfires affect the El Niño cycle.

It’s another example of how complex climate science can be, and how much we can still be surprised and challenged by what Mother Nature has to offer us.

But there are some caveats to keep in mind.

On the one hand, the ENSO cycle in the simulation was heading for a double La Niña even without the smoke effect. The simulation ends in the winter of 2021, just before the real-world El Niño turns into a third La Niña.

What does it mean? In short, we can’t know for sure if the effect of wildfire smoke actually caused the triple La Niña.

Another caveat is the fact that the study relied on a single climate model, and relies heavily on the representation of clouds in that model.

This is a potential problem, because we know that clouds – and especially their interactions with aerosols such as smoke – continue to be the biggest source of uncertainties and model errors.

To prove or disprove the link, we’ll have to simulate the effect of ballooning plumes of black summer smoke across many different models.

Introduction to the conversation

This article has been republished from Conversation Under Creative Commons Licence. Read the The original article.Conversation

the quote: Research suggests smoke from Black Summer fires may have made La Nina trilogy more likely (2023, May 13) Retrieved May 13, 2023 from https://phys.org/news/2023-05-black-summer -triple-la-nina.html

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