In a new study published in the journal Nature Climate Change, Clark, et al. suggest that our policy orientation in terms of mitigation and adaptation responses to climate change should be expanded to assess the past 20,000 years and the next 10,000 years, well beyond the IPCC’s focus on the 21^st and 22^nd Century. The authors contend that this temporal horizon, “on a geological timescale,” provides a more realistic assessment of the ultimate impacts of anthropogenic emissions, as well as the compelling need to substantially accelerate our commitment to reducing emissions.

The study utilized several different scenarios for temperatures and sea-level change over the course of 10,000 years, as well as referencing of our best understanding of climate change over the past 20,00 years. The study’s projections are based on a suite of four future emissions scenarios with carbon releases between 1,280 and 5,120 PgC, with current the current cumulative human carbon emissions already approaching the low-end scenario.

The researchers argue that projections of climatic change over the next 10,000 years is justified by the inertia of the climatic system. As a consequence, “60-70% of the maximum surface temperature anomaly and nearly 100% of the sea-level rise from any given emission scenario remains after 10,000 years, and that the ultimate return to pre-industrial CO2 concentrations will not occur for hundreds of thousands of years.”

Among the conclusions of the study:

• Projected temperature increases of 2.0-7.5°C over the course of this century will exceed those during even the warmest levels reached in the Holocene, “producing a climate state not previously experienced by human civilizations.” Moreover, temperatures will remain elevated above Holocene levels for more than 10,000 years;
• Even the lowest emissions scenario in the study, 1,280 PgC, results in sea level rise associated with the Greenland ice sheet of 4 meters over 10,000 years. Higher scenarios result in an ice-free Greenland over the course of 2500-6000 years, which could result in approximately 7 meters of sea level rise;
• The lowest emissions scenario yields as much as 24 meters of global mean sea level rise over 10,000 years associated with melting of Antarctic ice sheets;
• An equilibrium climate sensitivity of 3.5°C, consistent with IPCC AR5 scenarios, could yield sea level rise of 25-52 meters within the next 10,000 years, reaching 2-4 meters per century, “values that are unprecedented in more than 8,000 years.
• The only method to avoid a further commitment to sea level rise above the current projections of 1.7 meters “is to achieve net-zero emissions;”
  • There are 122 countries with at least 10% of current population weighted area that will be directly affected by coastal submergence and 25 coastal megacities will have at least 50% of their population-weighted area impacted
• The authors draw several policy implications from this long-term assessment of climatic impacts:
  • On millennial timescales, the use of conventional discounting approaches ensure that “future climate impacts … would be valued at zero, irrespective of the levels of certainty and magnitude.” This poses profound questions in terms of considerations of intergenerational equity and our obligations to future generations;
  • There is a compelling need for global energy policies that result in net-zero or net-negative carbon dioxide emissions; “a marginal reduction in emissions is insufficient to prevent future damages.” Such technologies would need to be kept in place for tens of thousands of years “without fail.” It also suggests radical changes in terms of financial incentives, a need to accelerate research and development of technologies to transform energy systems and infrastructure, and a focus on global equity considerations.”

Among the class discussion questions that might be posed are the following:

1. Is it pertinent for us to consider the potential impacts of climate change on a timescale of 10,000 years? Does it make more sense to formulate policies to protect the current and immediate successor generations?
2. If, as the article suggests, the current rate of discounting future losses is inappropriate for climatic impacts, what alternative system should we employ?
3. What are the most viable “negative emissions” technologies that might be available, and are there any risks in their utilization that should be weighed against their benefits of reducing atmospheric concentrations of carbon dioxide?

The U.S. National Oceanic & Atmospheric Administration publishes an Annual Greenhouse Gas Index (AGGI), “a measure of the warming influence of long-lived trace gases and how that influence is changing each year.” Thus, AGGI is an index that measures climate forcing associated with long-lived greenhouse gases. The Index would be an excellent resource for instructors who involve their students in climate negotiations exercises, as well as a potent reminder of how the promise of Paris is confronted by the practical reality of trends in radiative forcing and atmospheric concentrations of greenhouse gases.

Among the findings of the latest assessment:

1. Carbon dioxide concentrations creased by an average of 1.76 ppm per year from 1979-2015. However, the trend has accelerated in recent years, averaging about 1.5 ppm per year in the 1980s and 1990s, 2.0 ppm per year during the last decade. Moreover, atmospheric carbon dioxide increased 3 ppm in the past year, for only the second time since 1979.
   1. Increases in carbon dioxide concentrations in the atmosphere has resulted in a whopping 50% increase in its direct warming influence on climate since 1990
2. While methane concentrations remained constant in the atmosphere from  1999-2006 (after declining from 1983-1999), they have been increasing since 2007, due to factors such as increasing temperatures in the Arctic in 2007, increased precipitation in the tropics in 2007 and 2007; this trend accelerated between 2014-2015. Nitrous oxides concentrations have also accelerated in recent years.
3. Radiative forcing from chloroflourocabons is in decline, primarily due to the Montreal Protocol on Substances that Deplete the Ozone Layer. The importance of this regime, designed to address threats to the ozone layer, in terms of climate change are clear: without the treaty, climate forcing would have been 0.3 watt m-2 greater, or approximately half of the increase in radiative forcing attributable to carbon dioxide since 1990;
4. Radiative forcing of long-lived, well-mixed greenhouse gases increased 37% from 1990 (the Kyoto baseline year)  to 2015, with carbon dioxide accounting for nearly 80% of this increase;
5. Increases in greenhouse gas concentrations over the past 60 years have accounted for approximately 75% of the total increase in the Index in the past 260 years.

Among the questions for class discussion that this study’s findings might generate are:

• What impacts might purported fugitive methane releases associated with fracking be having on concentrations of atmospheric methane?
• What might the implications be of positive feedback mechanisms that might release substantial amounts of methane from ocean-based methane clathrates?
• Why are concentrations of carbon dioxide accelerating in recent years despite efforts at the national and international level to arrest greenhouse gas emissions?

Most of the scenarios in the IPCC’s Fifth Assessment Report that set out pathways to avoid temperature increases above 2C rely on large-scale use of so-called “negative emissions technologies,” with the lion’s share coming from the use of Bioenergy and Carbon Capture and Sequestration (BECCS) options. However, there is increasing concern that BECCS could have serious negative ramifications for food security for some of the world’s most vulnerable populations. A recent study by Tim Searchinger et al., analyzing results from a suite of models assessing changes in land use, crop production and food consumption associated with the production of biofuels, suggests that these concerns are valid, and may have serious ramifications for the use of BECCS in the future.

Among the findings of the study were the following:

1. Approximately 25-50% of net calories associated with diversion of corn or wheat to ethanol are not replaced through planting of other crops, but rather is taken out of food and feed consumption. Failure to replace crops reduces greenhouse gas emissions from land use change and direct emissions of carbon dioxide by people and livestock;
2. Most analysis of the greenhouse gas emissions implications of biofuel production assume that the emissions associated with fermenting and burning ethanol is offset by carbon absorption by growth of crops diverted to ethanol production. However, this accounting methodology is faulty, because carbon absorbed by crops that would be grown anyway doesn’t constitute a valid offset, because it’s not linked to biofuel production and is not additional.
   1. The only valid form of crop growth offsets would be either from growth of additional crops to replace those diverted to biofuels production, or increases on crop yields on existing croplands;
   2. Moreover, converting forests or grasslands to produce additional food crops would also release carbon, “reducing or negating the net offset from producing more crops;”
3. One study suggests that approximately 20% of calories diverted by biofuel production are not replaced. “Food reductions result not from a tailored tax on overconsumption or high-carbon foods but from broad global increases in crop prices.”

Among the class discussion questions that might be pertinent to this article are the following:

• What would the food implications be of a large-scale commitment to BECCS?
• What are the prospects to avoid food security issues outlined in this study by techniques such as increasing crop yields or using alternative bioenergy feedstocks, such as algae or cellulosic sources?;
• If trade-offs are indeed inevitable in terms of food production and greenhouse gas emissions, how should the world community make decisions under such conditions?

I have recently published an online commentary on Article 8 of the Paris Agreement on The Conversation site, which addresses the issue of “loss and damage.” I think that loss and damage is an excellent issue to discuss with students because it provides a device to discuss many “meta issues,” including the potential role of State responsibility and liability for climate damages, the role of climate justice, and the effectiveness of risk-pooling mechanisms, such as insurance.

Incidentally, The Conversation site has a lot of interesting energy and climate commentary by academics. Because it’s designed to be accessible to wider audiences, much of the content might be particularly appropriate for undergraduate students.

This site’s Compendium on the Paris Agreement, which seeks to bring together key online resources on the agreement, has been expanded recently to more than 130 links. The Compendium is available at: https://teachingclimatelaw.org/wp-admin/post.php?post=2993&action=edit

Any suggestions for additional resources are greatly appreciated, and can be submitted to the Compendium’s creator, Wil Burns, at: [email protected].

In a new article (subscription only, but link here will take you to a pre-edited version on Professor Anderson’s home page) published in the journal Nature Geoscience, Kevin Anderson of Tyndall Centre for Climate Change Research at the University of Manchester, argues that many of the recent scenarios for limiting temperatures to 2C or below are far too insouciant about the challenges ahead. Anderson contends that such “up-beat — and largely uncontested — headlines . . . are delivered through unrealistically early peaks in global emissions, or through the large-scale rollout of speculative technologies intended to remove CO2 from the atmosphere …”

By contrast, Anderson contends that the carbon budgets consistent with a 2C scenario requires “profound and immediate changes to the consumption and production of energy.” Among Anderson’s conclusions:

1. The IPCC’s 1000 Gt cumulative carbon budget (for having a 66% chance or better of avoiding passing the 2C threshold) requires cessation of all carbon emissions from energy systems by 2050, five decades earlier than projected by the IPCC in its 5th Synthesis Report;
2. Of 400 IPCC scenarios that have 50% chance or more of keeping temperatures below 2C, a whopping 344 require large-scale deployment of so-called negative emissions technologies (poster’s note: these include technologies such as Direct Air Capture and Bioenergy and Carbon Capture and Sequestration);
3. Limiting emissions to 1000 GtCO2, with energy production alone chewing up 140 GtCO2 of this budget from 2011 to 2014 alone (overall a fifth of the budget has been emitted in four years), “suggests a profoundly more challenging timeframe and rate of mitigation than that typically asserted by many within the scientific community;”
   1. To avoid exceeding the remaining 650 GtCO2 in the budget would require ratcheting up emissions reduction rates to 10% annually by 2025, continuing this rate to virtual elimination of carbon dioxide by 2050. This would most likely exclude the use of fossil fuels in the post-2050 period, even with deployment of carbon capture and storage, unless its life cycle carbon emissions could be reduced by an order of magnitude;
4. Given the need to avoid further imperiling the welfare of the global poor, developing countries should need to reduce carbon intensity by approximately 13% annually, higher still for the wealthiest developed countries.

Anderson’s piece could be an excellent reading for a module on long-term responses to climate change and what it will mean to reach the overarching objectives of the Paris Agreement. Among the questions that would be ripe for class discussion:

1. What would be the policy implications of seeking to meet the more ambitious objective under Paris of limiting temperature increases to 1.5C above pre-industrial levels?;
2. Anderson portrays negative emissions options as “speculative” or a deus ex machina; do you agree? Assuming that negative technologies can help to remove carbon from the atmosphere, are there any downsides to this approach?;
3. What are some of the measures that could be taken to effectuate the radical transformation of the world’s economy that could meet the objective of limiting temperatures to 2C?

One of the ongoing debates in climate science, and by extension, climate policy making, is the role of anthropogenic greenhouse gas emissions in historically unprecedented increases in temperature over the past few decades. A recent study by Michael Mann, et al. in the journal Scientific Reports seeks to

The recognition that most IPCC scenarios for to avoid exceeding the 2°C “guardrail” require large-scale deployment of negative emissions technologies (NETs) has led to extensive recent discussion of the potential effectiveness and risks associated with a range of option. However, as the authors of a new study published in the journal Global Change Biology conclude, most studies to date have focused on bioenergy with carbon capture and sequestration (BECCS), direct air capture, enhanced weathering of minerals, and afforestation and reforestation. This study, by Pete Smith at the University of Aberdeen, expands the scope of inquiry to two other NETs options: 1. soil carbon sequestration (SCS), through methods such as alternation of agricultural practices, including no-till or low-till with residue management, organic amendment and fire management; and 2. Biochar, which is production of charcoal as soil amendment via the process of pyrolysis which can, inter alia, sequester carbon. Biochar, at least, is often included under the rubric of “climate geoengineering” options, in the subcategory of carbon dioxide removal (CDR) approaches.

Among the study’s findings:

1. SCS at global scale could sequester from 0.4-0.7GtCeq. yr^-1, with technical potential of 1.37GtCeq. yr^-1, at a cost of ~$70-370 per ton of Ceq. Biochar could effectuate sequestration of ~1 GtCeq yr^-1, with a maximum potential of 1.8 GtCeq yr^-1
2. By contrast, BECCS might be able to sequester 3.3 GtCeq yr^-1 by 2100, and direct air capture a comparable amount. However, the potential of SCS and biochar are higher than either enhanced weathering and comparable to afforestation and deforestation;
3. About 20% of the mitigation to be derived from SCS could occur at negative cost, and 80% between $0-40 tCeq. Biochar costs range from -$581-1560 billion;
4. In terms of water requirements, SCS and biochar are virtually zero, while direct air capture has medium to high water demands, and BECCS creating “a very large water footprint;”
5. In terms of energy requirements, SCS has a negligible energy impact, and biochar can actually produce energy during the pyrolysis process; by contrast, both direct air capture and enhancing mineral weathering have significant energy requirements;
6. One significant issue in terms of both SCS and biochar is “sink saturation,” i.e. decreased carbon sequestration potential as soils approach a new, higher equilibrium level. This can occur after 10-100 years for SCS, and is also an issue for biochar. This has implications for deployment of these technologies, as most scenarios for use of NETs envision primary importance in the second half of this century, meaning that deployment of some approaches in the next few years might have little impact later this century.

Overall, the author of the study concludes that SCS and biochar should be given serious consideration in integrated assessment models given their advantages over some other NET approaches.

Among the classroom questions that this study might generate:

1. How do we determine the optimal mix of R&D funding for NETs?
2. What should be the most important criteria for determining if we proceed with research on individual NETs options?
3. What kind of governance architecture should be established for NETs research and development and/or deployment?

I recently delivered a lecture at University of Wisconsin, entitled “Into the Great Wide Open: The Potential Promise and Peril of Climate Geoengineering.” It provides an overview of climate geoengineering options and potential avenues for governance. The video for the lecture, including the Power Point presentation, is available here.