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The view on mitigating climate change has entered a new phase
Up to now, the future has been framed in terms of how long we can continue to emit CO2 at the present rate, while limiting the rise in global temperature to 1.5°C.
This blithely optimistic view is no longer tenable. “We have already hit the buffers. We have practically used up our emissions budget,” says Julia Pongratz, Chair of Physical Geography and Land-Use Systems at LMU.
Changes in global surface temperature over the past 170 years
Source: Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), August 2021, Working Group 1 (Summary for Policymakers)
Too much CO2
How much of this is attributable to land use?
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0 GtCO2 emissions per year (global)
Current concentration of greenhouse gases in the atmosphere since the pre-industrial level: 48%
Human activities are now responsible for the release of some 40 gigatons of CO2 per year. The current concentration of greenhouse gases in the atmosphere is 48% higher than the pre-industrial level. As a consequence, global temperature has risen by approximately 1.2°C since the mid-19th century.
Although the international community agreed to limit the rise in global temperature in 2015, too little has been done, and time is running out. “It’s a tragedy,” says Pongratz. “Reductions in the rate of emission are no longer sufficient. On its own, that approach is not effective enough to make the required difference. In addition to further drastic reductions in CO2 emissions, we need to concentrate on the active sequestration of CO2 from the atmosphere.” On both counts, land use has a crucial role to play. -
1 %accounts for greenhouse gas emissions because of land use
“The exploitation of fossil carbon sources accounts for the majority of emissions since the middle of the 20th century. But changes in land use have also made a substantial contribution to the rise in levels of greenhouse gases in the atmosphere,” she says. The latter factor is responsible for approximately 15% of total CO2 emissions, and this proportion rises to approximately 25% when other greenhouse gases, such as methane and nitrous oxide (N2O), are included.
Rise in CO2 emissions
Historic development from 1850 to the present day
Humankind was already influencing the concentration of greenhouse gases in the atmosphere even before the industrial age began. As people built settlements and farmed the land, they intervened in the natural carbon cycle. Industrialization then led to a dramatic rise in CO2 emissions.
— Fossil emissions
— Emissions from land use
— Emissions from land use
The figure above shows how CO2 emissions have increased since the dawn of industrialization.
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Source: Friedlingstein et al.: Global Carbon Budget 2021, Earth Syst. Sci. Data, 2021.
https://doi.org/10.5194/essd-2021-386; globalcarbonatlas.org (Carbon Story)
Interview
Prof. Dr. Julia Pongratz
holds the Chair of Physical Geography and Land-Use Systems at LMU. Her research focuses on the development of methods for the precise estimation of the contribution of agriculture and forestry to CO2 emissions, and the potential ability of land-use systems to absorb the gas from the atmosphere.
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Interview
“The exploitation of fossil carbon sources accounts for the majority of emissions since the middle of the 20th century. But changes in land use have also made a substantial contribution to the rise in levels of greenhouse gases in the atmosphere.”
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Plants absorb CO2
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Indeed, forests can store enormous amounts of carbon, and therefore serve as a vital carbon sink. These natural sinks can be enlarged by reforestation.
So knowledge of how different types of vegetation affect the carbon balance is now relevant in two ways – in relation to emissions, and in terms of their potential to remove CO2 from the atmosphere.
How land and oceans absorb CO2
How natural carbon sinks absorb CO2
Play Video about Video: natürliche Kohlenstoffsenken
Plants absorb CO2
Indeed, forests can store enormous amounts of carbon, and therefore serve as a vital carbon sink. These natural sinks can be enlarged by reforestation. So knowledge of how different types of vegetation affect the carbon balance is now relevant in two ways – in relation to emissions, and in terms of their potential to remove CO2 from the atmosphere.
How land and oceans absorb CO2
How natural carbon sinks absorb CO2
Play Video about Video: natürliche Kohlenstoffsenken
Extreme weather events on the rise
More and more people are suffering the consequences of a changing climate.
Although Germany does not lie in a region that is projected to be at highest risk, the recent catastrophic floods in parts of the country have underlined the startling consequences of global warming for society.
The first part of the 6th Assessment Report issued by Working Group 1 of the Intergovernmental Panel on Climate Change (IPCC) in August confirmed that human-induced climate change is amplifying the frequency of such extreme weather events.
Forests under twofold pressure
In her own research, LMU scientist Julia Pongratz is confronted with the fact that forested areas are now doubly under pressure: They are being both assailed by climate change and converted into agricultural land.
Climate change is leading to more droughts, which impair the natural capacity of the land and the oceans to absorb CO2. This, too, is shown in the IPCC’s latest report: In scenarios where emissions of greenhouse gases are high, the proportion of CO2 emissions absorbed by the oceans and by vegetation and the soil on land is significantly smaller. In other words, more CO2 remains in the atmosphere and will exacerbate global warming beyond the increase expected from a higher volume of emissions alone.
Climate change is leading to more droughts, which impair the natural capacity of the land and the oceans to absorb CO2. This, too, is shown in the IPCC’s latest report: In scenarios where emissions of greenhouse gases are high, the proportion of CO2 emissions absorbed by the oceans and by vegetation and the soil on land is significantly smaller. In other words, more CO2 remains in the atmosphere and will exacerbate global warming beyond the increase expected from a higher volume of emissions alone.
And then there is the issue of anthropogenic deforestation to create more agricultural land, which also generates further CO2 emissions. This has been the primary focus to date. “Up to now, attention has been focused on deforestation – the transformation of forests into agricultural land. But researchers found that the total area affected by forest degradation is much larger. Here, the forest as such remains, but its structure is altered, owing for example to increased fire frequency or the selective logging of specific types of trees. “Degradation probably leads to even greater loss of CO2 than wholesale deforestation does,” is Julia Pongratz’s comment on this hitherto underestimated process. Furthermore, degradation is also occurring in the temperate and boreal woods of Europe, not only in the carbon-rich rainforests of America, Asia and Africa. These practices have a negative impact on the ability of forests to store carbon. “We must pay much more attention to the permanence of natural carbon sinks. We only have to look at what is happening to the forests on our doorsteps, which have been battered by droughts in three of the last 10 years. We can no longer take their capacity as carbon sinks for granted.”
Indeed, according to a recent report, even the Amazonian rainforest is showing signs of losing its function as a carbon sink, and some parts of it are already emitting more CO2 than they absorb. “In the year 2020, the rate of deforestation in the Amazon Basin reached its highest level in the last 10 years,” Pongratz says, and the trend in South Asia is similar. “In both regions, exports of food and fiber cause an expansion of agricultural land, and unfortunately that affects rainforests, which are particularly rich in carbon,” she adds.
The role of exports also reveals a peculiarity in the political attribution of CO2 emissions. At the moment, the CO2 emitted as a result of the consumption in Europe of foodstuffs grown elsewhere – soybeans in Brazil, for example – appears on the producing country’s balance sheet. The working group around Julia Pongratz was instrumental in producing an article recently published in Science magazine demonstrating that, because of global trade, 27 percent of emissions from land use and forestry alone – not counting emissions from fossil fuels – are not attributed to those countries in which the products are consumed. “Some 40% of the emissions that are directly linked to consumption in Germany actually originate in other countries,” Pongratz says. If these emissions were accredited to the factor ‘consumption’ instead of ‘production’, the contribution to global warming attributable to Germany would increase. The same conclusion can be drawn when looking back in history: “The regions that bear most of the responsibility for climate change are the US and Europe – owing to their long history of industrialization – because the driving force behind global warming is the cumulative amount of carbon emissions.”
“The regions that bear most of the responsibility for climate change are the US and Europe – owing to their long history of industrialization – because the driving force behind global warming is the cumulative amount of carbon emissions.”
Map of the world
Continents
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Per-capita CO2 emissions in different countries (tons of CO2)
The map of the world translates CO2 emissions into per-capita consumption in different countries in 2019. (Countries for which no data is available have been left blank.)
Source: Global Carbon Project 2019 http://www.globalcarbonatlas.org/en/CO2-emissions
Updated by Peters et al. (2012) and Peters et al. (2011)
Peters, GP, Minx, JC, Weber, L, and Edenhofer, O, 2011. Growth in emission transfers via international trade from 1990 to 2008. Proceedings of the National Academy of Sciences USA. DOI:10.1073/pnas.1006388108. Available at: http://www.pnas.org/content/108/21/8903 -
Per-capita CO2 emissions by continent (tons of CO2)
The figure depicts per-capita CO2 emissions across the different continents in 2019.
Source: Global Carbon Project 2019 http://www.globalcarbonatlas.org/en/CO2-emissions
Updated by Peters et al. (2012) and Peters et al. (2011)
Peters, GP, Minx, JC, Weber, L, and Edenhofer, O. 2011. Growth in emission transfers via international trade from 1990 to 2008. Proceedings of the National Academy of Sciences USA. DOI:10.1073/pnas.1006388108. Available at: http://www.pnas.org/content/108/21/8903
Learning
from the past
In her efforts to assess as accurately as possible current and future levels of carbon emissions attributable to land use, and estimate the potential of diverse land-use practices to store carbon, Pongratz looks to the past for guidance for the future. The idea is to analyze historical data in order to learn how diverse classes of vegetation, and interactions between them, affect the carbon balance, and on this basis develop recommendations and forecasts for the future. For this purpose, she uses geophysical models into which current observations can be integrated. These models are so complex that the analyses require the use of supercomputers.
In addition to established strategies such as reforestation, Julia Pongratz will evaluate the potential of new technologies for the extraction of atmospheric CO2 that much hope is set on, such as sequestration in suitable geological settings. However, she emphasizes that all such measures involve specific risks and side-effects. “In particular, we have no unifying framework that would allow us to identify possible conflicts and synergies between biodiversity, water quality, recreational value, economics and many other factors – and that could be applied to all conceivable measures in a comparative way.”
In a nationwide research program which Pongratz is coordinating, a team of scientists across a variety of disciplines is therefore studying not only what measures can be used to remove carbon dioxide from the atmosphere, but also how they can be implemented at societal level.
"In particular, we have no unifying framework that would allow us to identify possible conflicts and synergies between biodiversity, water quality, recreational value, economics and many other factors – and that could be applied to all conceivable measures in a comparative way."
The question is:
"What is to be done?"
One thing is clear: The transformation of land use will play a key role along the road to climate neutrality. It will involve stopping the emissions caused by deforestation and degradation – i.e. protecting existing carbon sinks – and, in the future, harnessing land-use practices to remove CO2 from the atmosphere.
Julia Pongratz gives lots of lectures – many of them for the general public – on the consequences of climate change, and she explains the causal connections between CO2 emissions, rising temperatures and the process of climate change.
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Learning from crises
When Pongratz has completed her outline of the science of climate change and its repercussions in her lectures, the audience is often baffled, and at a loss to answer the question of what can be done to mitigate the consequences of the process. “This is where I start discussing directly with the audience,” she says.
She is all too well aware of the highly complex tangle of conflicting interests that make it so difficult for politicians and society as a whole to respond effectively to the challenges posed by climate change. On the other hand, climate researchers have closely followed the reactions of politicians to the coronavirus pandemic, and taken note of how different their approaches to the two societal crises have been.
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“Taken together, the financial recovery packages that were instituted to cope with the repercussions of the pandemic are about 10 times larger than what would be needed annually over the next few years to transform the global energy system to meet the goals set out in the Paris Agreement,” Pongratz emphasizes. Moreover, many Covid-19 recovery plans are actually incompatible with national emissions targets.
In a blogpost, she pointed out what can be learned from the responses to the coronavirus crisis. “No one questioned the notion that short-term investments may be necessary to avert worse damage in the long term” during the crisis. She went on to argue that “the same cost-benefit analysis must be applied to the mitigation of climate change.”
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%
Amazonas rainforest
already vanished
Among the topics she is often asked are ‘tipping points’. In the language of dynamical systems like the Earth’s climate, this term refers to a state that can rapidly undergo a transition to a very different state when a particular parameter exceeds a certain threshold.
In the case of the rainforests of Amazonia, such a tipping point might be reached when deforestation has eliminated between 20 and 40% of their original area. The rationale for this idea derives from the fact that the extensive tracts of rainforest themselves generate much of the rainfall needed to sustain the forest. Without this source of precipitation, the Amazon Basin is likely to be transformed into savannah – and some 17% of its forests have already vanished.
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“The possible significance of tipping points is one of the aspects of climate change that are less well understood,” says Pongratz. “Because human-induced climate change is an unprecedented situation, there are no empirical data to go on.”
Researchers have begun to place more emphasis on the potential risk of domino effects. For example, if rainforests are degraded to the point that they become carbon sources rather than carbon sinks, global temperatures might reach levels high enough to melt the world’s permafrost regions, releasing yet more CO2 and methane.
What to be done?
One thing is clear: The transformation of land use will play a key role along the road to climate neutrality. It will involve stopping the emissions caused by deforestation and degradation – i.e. protecting existing carbon sinks – and, in the future, harnessing land-use practices to remove CO2 from the atmosphere.
Julia Pongratz gives lots of lectures – many of them for the general public – on the consequences of climate change, and she explains the causal connections between CO2 emissions, rising temperatures and the process of climate change.
Julia Pongratz gives lots of lectures – many of them for the general public – on the consequences of climate change, and she explains the causal connections between CO2 emissions, rising temperatures and the process of climate change.
1
%
Amazonas rainforest already vanished
Among the topics she is often asked are ‘tipping points’. In the language of dynamical systems like the Earth’s climate, this term refers to a state that can rapidly undergo a transition to a very different state when a particular parameter exceeds a certain threshold.
In the case of the rainforests of Amazonia, such a tipping point might be reached when deforestation has eliminated between 20 and 40% of their original area. The rationale for this idea derives from the fact that the extensive tracts of rainforest themselves generate much of the rainfall needed to sustain the forest. Without this source of precipitation, the Amazon Basin is likely to be transformed into savannah – and some 17% of its forests have already vanished.
In the case of the rainforests of Amazonia, such a tipping point might be reached when deforestation has eliminated between 20 and 40% of their original area. The rationale for this idea derives from the fact that the extensive tracts of rainforest themselves generate much of the rainfall needed to sustain the forest. Without this source of precipitation, the Amazon Basin is likely to be transformed into savannah – and some 17% of its forests have already vanished.
“The possible significance of tipping points is one of the aspects of climate change that are less well understood,” says Pongratz. “Because human-induced climate change is an unprecedented situation, there are no empirical data to go on.”
Researchers have begun to place more emphasis on the potential risk of domino effects. For example, if rainforests are degraded to the point that they become carbon sources rather than carbon sinks, global temperatures might reach levels high enough to melt the world’s permafrost regions, releasing yet more CO2 and methane.
Researchers have begun to place more emphasis on the potential risk of domino effects. For example, if rainforests are degraded to the point that they become carbon sources rather than carbon sinks, global temperatures might reach levels high enough to melt the world’s permafrost regions, releasing yet more CO2 and methane.
Learning from crises
When Pongratz has completed her outline of the science of climate change and its repercussions in her lectures, the audience is often baffled, and at a loss to answer the question of what can be done to mitigate the consequences of the process. “This is where I start discussing directly with the audience,” she says.
She is all too well aware of the highly complex tangle of conflicting interests that make it so difficult for politicians and society as a whole to respond effectively to the challenges posed by climate change. On the other hand, climate researchers have closely followed the reactions of politicians to the coronavirus pandemic, and taken note of how different their approaches to the two societal crises have been.
She is all too well aware of the highly complex tangle of conflicting interests that make it so difficult for politicians and society as a whole to respond effectively to the challenges posed by climate change. On the other hand, climate researchers have closely followed the reactions of politicians to the coronavirus pandemic, and taken note of how different their approaches to the two societal crises have been.
“Taken together, the financial recovery packages that were instituted to cope with the repercussions of the pandemic are about 10 times larger than what would be needed annually over the next few years to transform the global energy system to meet the goals set out in the Paris Agreement,” Pongratz emphasizes. Moreover, many Covid-19 recovery plans are actually incompatible with national emissions targets.
In a blogpost, she pointed out what can be learned from the responses to the coronavirus crisis. “No one questioned the notion that short-term investments may be necessary to avert worse damage in the long term” during the crisis. She went on to argue that “the same cost-benefit analysis must be applied to the mitigation of climate change.”
In a blogpost, she pointed out what can be learned from the responses to the coronavirus crisis. “No one questioned the notion that short-term investments may be necessary to avert worse damage in the long term” during the crisis. She went on to argue that “the same cost-benefit analysis must be applied to the mitigation of climate change.”
No time to lose
The threat that faces us
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Regardless of the numbers presented by climate researchers to policymakers and the general public – time is running out.
“We know that we are still emitting too much CO2 and that the target to limit global warming to 1.5°C over pre-industrial levels cannot be met without rapid, substantial and sustained reductions in emissions,” Pongratz says. In her discussions with the – only initially – perplexed audiences, many topics are brought up, ranging from mobility and eating habits to recycling. Many of these have a large impact on one’s personal CO2 footprint, while others have more to do with environmental issues than with the mitigation of climate change.
But the central message is the same: “It is perfectly clear that profound structural changes are required. We need policies that define an effective framework for action, and we as voters must ratify them. But we can only change direction successfully if every one of us, too, is willing to make the behavioral adjustments required to meet the necessary targets.”"We know that we are still emitting too much CO2 and that the target to limit global warming to 1.5°C over pre-industrial levels cannot be met without rapid, substantial and sustained reductions in emissions."
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Source: Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), 2021
The degree to which the Earth actually heats up depends on measures to mitigate climate change. The figure shows simulations of how the planet’s mean temperature will increase as a function of the decrease in CO2 emissions. In the optimistic scenario at left, global warming is constrained to slightly below one degree compared to the period from 1995 to 2014. On the right, a pessimistic scenario puts global warming at over ten degrees in the worst-affected regions.
What if CO2 emissions continue to rise?
Largely owing to the increase in the rate of emission of CO2, average global temperatures have risen by approximately 1.2°C since the middle of the 19th century. This warming trend is set to persist, since CO2 is long-lived and will become more abundant as emissions continue to build up. The effects will be felt on all of the continents, which will heat up faster than the oceans, and temperatures in the Arctic and the Antarctic will rise faster than in the tropics. Global warming will also lead to an increase in the frequency of extreme weather events.
At this point, the rise in global temperature can only be limited to 1.5°C if effective steps are taken to reduce the emission of greenhouse gases rapidly and enduringly.
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