10 New Insights in Climate Science 2020

Slide 2 Improved models strengthen support for ambitious emission cuts to meet Paris Agreement
Climate models anticipate CO2 and other greenhouse gases being released as permanently frozen ground – permafrost – thaws. However, the calculations have not yet included processes where the ground collapses abruptly and exposes deep layers of permafrost, as these have previously been difficult to quantify. Recent advances make it possible to better understand the impact of these processes on emissions and they are significant enough to have an impact on climate negotiations.
Climate models anticipate CO2 and other greenhouse gases being released as permanently frozen ground – permafrost – thaws. However, the calculations have not yet included processes where the ground collapses abruptly and exposes deep layers of permafrost, as these have previously been difficult to quantify. Recent advances make it possible to better understand the impact of these processes on emissions and they are significant enough to have an impact on climate negotiations.
Key new insights
Image
  • Emissions of greenhouse gases from permafrost will be larger than earlier projections because of abrupt thaw processes, which are not yet included in global climate models.
  • These abrupt thaw effects could as much as double the emissions from permafrost thaw under moderate and high emissions scenarios.
  • Emissions from permafrost thaw could be yet higher due to effects on plant root activity, which increases soil respiration.
Key new insights
Image
  • Emissions of greenhouse gases from permafrost will be larger than earlier projections because of abrupt thaw processes, which are not yet included in global climate models.
  • These abrupt thaw effects could as much as double the emissions from permafrost thaw under moderate and high emissions scenarios.
  • Emissions from permafrost thaw could be yet higher due to effects on plant root activity, which increases soil respiration.
Image
Thawing coastal permafrost in Arctic Canada with person for scale. Credit: G. Hugelius

Thawing permafrost in the Arctic is expected to release significant quantities of greenhouse gases over the coming decades, enough to merit consideration in climate negotiations. Recent research shows it will be larger than earlier projections due to abrupt permafrost thaw processes.

Permafrost is a perpetually frozen layer beneath the seasonally thawed surface layer of the ground, covering 18 million square kilometers in the northern hemisphere and storing 1,460–1,600 petagrams of carbon (PgC) – one third of the world’s soil carbon. The Arctic is responding quickly to climate change, with air temperatures warming more than twice as fast as the global average. Unusually warm summers – such as the record-breaking 2020 heatwave in Siberia and Svalbard – are happening more often. This is causing Arctic permafrost to thaw in some northernmost regions almost a century earlier than some climate models projected.

Landscape-changing thaw on the up
Abrupt permafrost thaw happens when melting ground ice causes the ground surface above to collapse. This liberates previously frozen soil carbon, creating a socalled “thermokarst” landscape of slumps and gullies in upland areas and collapsed scar wetlands and lakes in less well-drained areas. Satellite observations of these landscape-scale changes have shown an acceleration in these processes over the past two decades; they are expected to substantially increase this century as climate warms. These processes increase thaw rates by exposing deeper regions of permafrost – which would otherwise be shielded by surface layers – to warm summer air. While climate models do include gradual permafrost thaw, they do not include the more complex thermokarst-inducing processes. When thermokarst is included, by the year 2100 up to three times more carbon becomes exposed assuming moderate future warming at Representative Concentration Pathway (RCP) 4.5 and up to 12 times more carbon is exposed under a high warming scenario of RCP8.5. Abrupt permafrost thaw also causes ecosystem shifts to conditions more conducive to producing strong greenhouse gas emissions, notably methane. Accounting for these processes nearly doubles the annual projected 2100 greenhouse gas emissions from permafrost thaw (for a high warming RCP8.5 scenario).
Peatlands and increased soil respiration mean even higher emissions

Peatlands have year-round waterlogged conditions that slow plant decomposition, allowing peat to accumulate – one of the largest natural carbon stores on land. Nearly half of northern peatlands are underlain by permafrost. Abrupt thaw could shift the entire northern hemisphere peatland carbon sink into a net source of global warming, dominated by methane, lasting several centuries.

An ecological feedback associated with permafrost thaw that is not yet included in global climate models is a priming effect on soil respiration, caused by an increase in root activity. This amplifies soil carbon loss, with an additional 40 Pg carbon loss (corresponding to 147 Gton CO2) projected from Arctic permafrost by 2100 for RCP8.5.

In the Special Report on 1.5°C, the IPCC assumed that permafrost thaw will release 100 Gton of CO2 equivalents cumulatively to year 2100. Abrupt thaw processes could, under moderate to high emissions scenarios, approximately double the cumulative carbon emissions compared to gradual thaw alone. This may also apply to emissions scenarios consistent with 1.5°C or 2°C warming targets, which would impose tighter restrictions on the remaining anthropogenic carbon emission budgets.

Image
Figure 2. The thermokarst forming process proceeds in several stages. In the earliest stages, deeper layers are completely frozen and thawing proceeds top-down through gradual thaw. When thaw affects massive ice bodies in the ground, such as ice wedges, the loss of volume as the ice melts away causes the ground to collapse and thermokarst lakes, wetlands, or thaw slumps start to form. Once these thermokarst start growing, they enhance the thawing process by transporting heat to the thawing front through the movement of the water, causing it to thaw faster than surrounding permafrost at the same depth. Adapted from Zandt and coauthors, 2020.2

Thawing permafrost in the Arctic is expected to release significant quantities of greenhouse gases over the coming decades, enough to merit consideration in climate negotiations. Recent research shows it will be larger than earlier projections due to abrupt permafrost thaw processes.

Permafrost is a perpetually frozen layer beneath the seasonally thawed surface layer of the ground, covering 18 million square kilometers in the northern hemisphere and storing 1,460–1,600 petagrams of carbon (PgC) – one third of the world’s soil carbon. The Arctic is responding quickly to climate change, with air temperatures warming more than twice as fast as the global average. Unusually warm summers – such as the record-breaking 2020 heatwave in Siberia and Svalbard – are happening more often. This is causing Arctic permafrost to thaw in some northernmost regions almost a century earlier than some climate models projected.

Landscape-changing thaw on the up
Abrupt permafrost thaw happens when melting ground ice causes the ground surface above to collapse. This liberates previously frozen soil carbon, creating a socalled “thermokarst” landscape of slumps and gullies in upland areas and collapsed scar wetlands and lakes in less well-drained areas. Satellite observations of these landscape-scale changes have shown an acceleration in these processes over the past two decades; they are expected to substantially increase this century as climate warms. These processes increase thaw rates by exposing deeper regions of permafrost – which would otherwise be shielded by surface layers – to warm summer air. While climate models do include gradual permafrost thaw, they do not include the more complex thermokarst-inducing processes. When thermokarst is included, by the year 2100 up to three times more carbon becomes exposed assuming moderate future warming at Representative Concentration Pathway (RCP) 4.5 and up to 12 times more carbon is exposed under a high warming scenario of RCP8.5. Abrupt permafrost thaw also causes ecosystem shifts to conditions more conducive to producing strong greenhouse gas emissions, notably methane. Accounting for these processes nearly doubles the annual projected 2100 greenhouse gas emissions from permafrost thaw (for a high warming RCP8.5 scenario).
Peatlands and increased soil respiration mean even higher emissions

Peatlands have year-round waterlogged conditions that slow plant decomposition, allowing peat to accumulate – one of the largest natural carbon stores on land. Nearly half of northern peatlands are underlain by permafrost. Abrupt thaw could shift the entire northern hemisphere peatland carbon sink into a net source of global warming, dominated by methane, lasting several centuries.

An ecological feedback associated with permafrost thaw that is not yet included in global climate models is a priming effect on soil respiration, caused by an increase in root activity. This amplifies soil carbon loss, with an additional 40 Pg carbon loss (corresponding to 147 Gton CO2) projected from Arctic permafrost by 2100 for RCP8.5.

In the Special Report on 1.5°C, the IPCC assumed that permafrost thaw will release 100 Gton of CO2 equivalents cumulatively to year 2100. Abrupt thaw processes could, under moderate to high emissions scenarios, approximately double the cumulative carbon emissions compared to gradual thaw alone. This may also apply to emissions scenarios consistent with 1.5°C or 2°C warming targets, which would impose tighter restrictions on the remaining anthropogenic carbon emission budgets.

Image
Figure 2. The thermokarst forming process proceeds in several stages. In the earliest stages, deeper layers are completely frozen and thawing proceeds top-down through gradual thaw. When thaw affects massive ice bodies in the ground, such as ice wedges, the loss of volume as the ice melts away causes the ground to collapse and thermokarst lakes, wetlands, or thaw slumps start to form. Once these thermokarst start growing, they enhance the thawing process by transporting heat to the thawing front through the movement of the water, causing it to thaw faster than surrounding permafrost at the same depth. Adapted from Zandt and coauthors, 2020.2
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Slide 5 Climate change can profoundly affect our mental health 1 Improved models strengthen support for ambitious emission cuts to meet Paris Agreement 2 Emissions from thawing permafrost likely to be worse than expected 3 Deforestation is degrading the tropical carbon sink 4 Climate change will severely exacerbate the water crisis Slide 10 Going to court to defend human rights can be an essential climate action 6 Governments are not yet seizing the opportunity for a green recovery from COVID-19 7 COVID-19 and climate change demonstrate the need for a new social contract 8 Economic stimulus focused primarily on growth would jeopardize the Paris Agreement 9 Electrification in cities is pivotal for just sustainability transitions