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Evidence & Impacts: Feedback effects

Image: Michael Held

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Feedback effects – fire & ice

Summary

  • Feedback effects occur when a change triggers an effect that reinforces the initial change, leading to dangerous tipping points.
  • A feedback that increases an initial warming is a ‘positive feedback.’
  • A feedback that reduces an initial warming is a ‘negative feedback’.
  • The main positive feedback in global warming is the increase in the amount of water vapour in the atmosphere, which in turn leads to further warming for reasons explained here.
  • Once certain tipping points are reached, the feedback effect becomes self-sustaining. That is, it can’t be reversed.
  • Two profound and unprecedented feedback effects now underway are melting ice from the albedo effect, and the increasing number and intensity of raging wildfires, particularly in the Arctic. Both trigger a series of cascading positive feedbacks in other earth systems. Both examples are explained below.

Native terrestrial biodiversity in Canterbury was deemed to be at major risk due to drought, increased fire weather and reduced snow and ice. Climate-induced impacts on biodiversity are highly uncertain, but terrestrial biological and ecological impacts could have flow-on impacts to the food system (Landcare, 2019). – Tonkin & Taylor 2020

Example #1: the Albedo Effect—ice and snow

Clean ice and snow have a very high albedo, that is, they reflect up to 90% of solar radiation back into space. The ocean is much darker, so it has a very low albedo, reflecting only about 6% of the incoming solar radiation and absorbing the other 94%, warming it (Fig. 1).

Warming over the past 40 years has led to a very large decrease in the  amount of summer sea ice in the Arctic (Video 1). It’s not just the total area of cover that’s decline, it’s also the thickness of the ice, so the total volume of sea ice in the Arctic has declined 95% in the past 33 years.

Home > Climate wiki > Evidence > Feedback effects

Summary

  • Feedback effects occur when a change triggers an effect that reinforces the initial change, leading to dangerous tipping points.
  • A feedback that increases an initial warming is a ‘positive feedback.’
  • A feedback that reduces an initial warming is a ‘negative feedback’.
  • The main positive feedback in global warming is the increase in the amount of water vapour in the atmosphere, which in turn leads to further warming for reasons explained here.
  • Once certain tipping points are reached, the feedback effect becomes self-sustaining. That is, it can’t be reversed.
  • Two profound and unprecedented feedback effects now underway are melting ice from the albedo effect, and the increasing number and intensity of raging wildfires, particularly in the Arctic. Both trigger a series of cascading positive feedbacks in other earth systems. Both examples are explained below.

Native terrestrial biodiversity in Canterbury was deemed to be at major risk due to drought, increased fire weather and reduced snow and ice. Climate-induced impacts on biodiversity are highly uncertain, but terrestrial biological and ecological impacts could have flow-on impacts to the food system (Landcare, 2019). – Tonkin & Taylor 2020

Fig 1: The Albedo Effect over snow and ice versus water. (Image: NASA)
Fig 1: The Albedo Effect over snow and ice versus water. (Image: NASA)

Video 1: Loss of sea ice in the Arctic is creating a positive feedback effect, leading to more warming.

This loss means more heat-absorbing open ocean is exposed (as ice thins, it has a progressively lower albedo), leading to more warming, and so on every year in a downward spiral. This triggers a cascading series of feedbacks that affects weather, changes how ocean currents work, and melts permafrost and methane clathrates, which is releasing more of the greenhouse gases carbon dioxide and methane into the atmosphere. This in turn leads to even more warming, which in turn melts more ice, in a positive feedback loop.
 

The overall impact is that warming in the Arctic is twice to three times the global average (Fig. 2), which continues to enhance the positive (warming) feedback loop.

Fig. 2: The Arctic is warming twice as fast on average as elsewhere. (Image: NASA)
Fig. 2: The Arctic is warming twice as fast on average as elsewhere. (Image: NASA)

Example #1: the Albedo Effect—ice and snow

Clean ice and snow have a very high albedo, that is, they reflect up to 90% of solar radiation back into space. The ocean is much darker, so it has a very low albedo, reflecting only about 6% of the incoming solar radiation and absorbing the other 94%, warming it (Fig. 1).

Warming over the past 40 years has led to a very large decrease in the  amount of summer sea ice in the Arctic (Video 1). It’s not just the total area of cover that’s decline, it’s also the thickness of the ice, so the total volume of sea ice in the Arctic has declined 95% in the past 33 years.

Video 1: Loss of sea ice in the Arctic is creating a positive feedback effect, leading to more warming.

Fig 1: The Albedo Effect over snow and ice versus water. (Image: NASA)
Fig 1: The Albedo Effect over snow and ice versus water. (Image: NASA)
This loss means more heat-absorbing open ocean is exposed (as ice thins, it has a progressively lower albedo), leading to more warming, and so on every year in a downward spiral. This triggers a cascading series of feedbacks that affects weather, changes how ocean currents work, and melts permafrost and methane clathrates, which is releasing more of the greenhouse gases carbon dioxide and methane into the atmosphere. This in turn leads to even more warming, which in turn melts more ice, in a positive feedback loop.
 

The overall impact is that warming in the Arctic is twice to three times the global average (Fig. 2), which continues to enhance the positive (warming) feedback loop.

Fig. 2: The Arctic is warming twice as fast on average as elsewhere. (Image: NASA)
Fig. 2: The Arctic is warming twice as fast on average as elsewhere. (Image: NASA)

Example # 2: wildfires

As the climate warms, evaporation dries out vegetation, making it more prone to fires. This triggers a range of positive (warming) feedback effects, depending on where the fires are located. One feedback is the explosive growth of forest fires globally, in areas that have rarely experienced them. Fires are becoming so large entire ecosystems are being destroyed, unable to recover because temperatures are now too high to support their recovery. 

Research of the impacts is now underway; contact Lynda Petherick (Victoria University of Wellington) or Phil Novis (Manaaki Whenua Landcare Research) for more information.

To fully explore this global problem, see ‘How climate change is affecting wildfires around the world’ (Carbon Brief).

Fig 3: Smoke plumes from bushfires in southeast Australia on January 4, 2020, sent ash over New Zealand. (Image: NASA Earth Observatory)

Wildfires in Australia impact Aoteaora

Until 2019, Australia’s national fire-related carbon emissions averaged 439 million tonnes/year. In the first 6 weeks of 2020 alone, fires emitted 830 million tonnes

The effects were felt here in New Zealand when ash and smoke blew across the Tasman (Fig. 3). One afternoon our skies turned orange and for the next few weeks, ash fell over already retreating glaciers, reducing their albedo, leading to faster melting (Fig. 4).

It also extended the hole in the ozone layer over Antarctica.

As the climate warms, the weather system in the Indian Ocean, the Indian Dipole (the Pacific ‘sister’ of El Niño/La Niña) is expected see more strong “positive” events similar to the one seen in 2019 that contributed to the Australian drought and bushfires.

Fig 4: Ash landed on Franz Josef glacier. The albedo effect increases the melt rate of snow and ice on New Zealand’s glaciers. This in turn has a feedback effect by changing river flows and water storage. (Image: Twitter/ @Rachelhatesit)

Wildfires in the Arctic

“As we move into the 2020 Boreal and Arctic wildfire season in the Northern Hemisphere, parts of the Arctic Circle have been more than ten degrees warmer than usual over the last couple of weeks.”  Copernicus Atmospheric Monitoring Service, May 2020

Wildfires that incinerated tundra along the Arctic Circle this summer released a record 244 megatonnes of carbon dioxide—35% more than last year, which was also a record breaker.” Nature, September 2020

Every year, the wildfire season in the Northern Hemisphere (Alaska, Canada, and Russia) begins earlier, ends later, and is more intense. The June 2021 heatwave in the Pacific Northwest generated a record number of wildfires. One feedback effect is that the soot or ‘black carbon‘ that falls on ice as far away as Greenland (Fig. 5) reduces the albedo and enhances surface melting, which in turn speeds up the disintegration of outlet glaciers that hold back the massive Greenland ice sheet leading to increasing meltwater that increases the speed of rising sea levels. Large volumes of freshwater melting is also changing the AMOC ocean current with multiple profound effects around the globe.

Fig 5: Meltwater lakes and dark snow dramatically reduces albedo so heat is absorbed promoting more melting. (Image: Kintisch Greenland).

In addition to losing forest, fires in boreal regions are threatening to turn peat, which had once been a carbon sink, into a major source of atmospheric methane and carbon dioxide. The peat in this region is largely permafrost, but that’s now melting at an alarming rate, both from atmospheric warming and from increasingly uncontrollable forest fires melting the upper layers of the soil (Video 2).

“The entire Canadian Boreal contains 307 billion tonnes  of carbon…as much carbon as the world emits in 36 years.”  – Anthony Swift, Natural Resources Defense Council, Canada

Video 2: As Arctic summers get warmer and drier, boreal forest fires are becoming more intense, meaning they burn deeper into the soil. (NASA)

“Boreal forest fires emit large amounts of carbon into the atmosphere primarily through the combustion of soil organic matter… Climate warming and drying has led to more severe and frequent forest fires, which threaten to shift the carbon balance of the boreal ecosystem from net accumulation to net loss, resulting in a positive climate feedback… This implies a shift to a domain of carbon cycling in which these forests become a net source—instead of a sink—of carbon to the atmosphere over consecutive fires.”                              Walker et al, 2019