IPCC的1.5°C報告的一項主要發現是，要將全球暖化控制在「安全限度」內，需要一定程度的「負排放」──「負排放」泛指從大氣中去除二氧化碳並儲存在陸地或海洋中的方法，涵蓋種樹等自然方法到機器吸碳等技術，稱為直接空氣捕獲（direct air capture，DAC）。
根據「決策者摘要」（summary for policymakers, SPM），大規模種樹或造林也可能帶來風險。報告中提到，大規模植樹造林可能「增加土地用途改變的需求」並增加劣化的風險。
而在採取永續土地的氣候變遷解決方案方面，報告強調在其中進一步提升性別平等的重要性。第七章第87頁的註解如下：「性別是社會不平等的一項關鍵，與其他權力和邊緣化系統交會 ──包括種族、文化、階級／社會經濟地位、地理位置、性別和年齡 ，這導致氣候變遷韌性和適應能力的不平等。」
糧食和飲食習慣也是報導焦點。Mother Jones報導，「氣候變遷對糧食、水和土地造成的損失比我們所知更嚴重。海峽時報報導，如果採取正確的農法，可以餵飽全球同時因應氣候變遷 。紐約時報頭條新聞稱「氣候變遷威脅世界糧食供給。BBC報導，轉向以植物為基礎的飲食有助於因應氣候變遷。泰晤士報標題寫道：「聯合國呼籲，少吃肉，救地球」，後續報導指出，減少食物浪費和少吃肉可以避免大片土地因農業而劣化，減少氣候變遷。
有些非政府組織特別關注土地需求衝突的平衡。基督教救助協會（Christian Aid）全球氣候主任克萊摩（Katherine Kramer）博士說：「報告呼籲我們為人類、自然和氣候更妥善地管理土地。在土地利用方式上創造雙贏的方法很多，但我們必須盡快行動，以避免在餵飽人口和減少排放之間取捨。」
其他非政府組織對報告中負碳排技術內容的評論更為直白。 ActionAid的氣候政策協調員安德森（Teresa Anderson）說：「報告發出了嚴肅的警吿－依賴生物能源、碳捕獲和儲存等危險技術，將佔用大量土地，與我們改善糧食安全和保護自然生態系統的需求背道而馳。」「富裕的污染國不能指望南營放棄大片農田來解決氣候問題。」
里茲大學（University of Leeds）氣候變遷福斯特（Piers Forster）教授也提出類似觀點，「為了將升溫限制在1.5°C以下，我們需要大幅改變使用土地的方式……簡言之，我們需要更少的牧場、更多的樹木，實際上這表示我們更加仔細地考慮如何使用每英畝的土地。土地要用來種植糧食，提供生物多樣性和淡水，為數十億人提供工作，並吸收數十億噸碳。」
東英吉利大學皇家學會氣候變遷科學教授、英國氣候變遷委員會（CCC）成員拉奎爾（Corinne Le Quéré）教授表示，「IPCC的調查結果與CCC給政府的建議一致，英國需要減少食物浪費、鼓勵健康飲食，並永續地使用土地，包括種植更多的樹木和復育劣化的土壤。所有這些方法都將有助改善人們的生活，同時減少導致氣候變遷的有害排放。」（系列專文3/3，完）
How could 'negative emissions' affect land, food and wildlife?
A major finding of the IPCC's landmark 1.5C report was that some degree of "negative emissions" will be needed to keep global warming within "safe limits".
"Negative emissions" are a group of methods that aim to remove CO2 from the atmosphere and store it in the land or ocean. They range from the natural-sounding – planting trees, for example – to the technologically advanced, such as using machines to suck CO2 from the air (known as direct air capture, or DAC).
If pursued at scale, most of these techniques would require varying amounts of land – potentially reducing the land left for wildlife and food production.
The land report emphasises that there is no one "silver bullet" when it comes to negative emissions and that, if just one technique were deployed on a vast scale, it could "increase risks for desertification, land degradation, food security and sustainable development".
Many of the modelled pathways for limiting global warming to 1.5C rely heavily on a technique called "bioenergy with carbon capture and storage" (BECCS). (Some research has suggested the 1.5C target can be achieved without BECCS, but only under stretching assumptions for change elsewhere.)
This technique involves growing crops, using them to produce energy and then capturing the resulting CO2 emissions before storing them in the ground or sea. A small number of pilot projects carry out BECCS – but the technique has not yet been proven to work at scale.
How much BECCS is used in the future will depend on a range of complex social and technical factors, the report says. (To read more about the world's possible future socioeconomic pathways, please see: "How important are socioeconomic changes for future land degradation?")
However, if BECCS is pursued at the level "necessary to remove CO2 from the atmosphere at the scale of several billion tonnes of CO2 per year", it could "increase pressure on land" and cause "land degradation", the report says.
Widespread tree planting – also known as "afforestation" – could also come with risks, the SPM says. Large-scale afforestation could "increase demand for land conversion" and raise risks of degradation, the report says.
The graphic below, taken from the SPM, gives an overview of the various impacts of different options for removing CO2 from the atmosphere.
For each technique, the graphic gives an idea of its ability to remove CO2 from the atmosphere ("mitigation"; first column); to help people adapt to climate change ("adaptation"; second column); to avoid desertification (third column); to avoid land degradation (fourth column) and to aid food security (fifth column).
Light to dark turquoise illustrate that the technique has a positive impact in these areas, whereas light to dark red represent a negative impact. (More detail on the scale of impacts is offered in the key.)
The potential cost of implementing the technique is shown with dots on the far right-hand side. Letters represent the level of confidence in the findings (with "L" representing low, "M" representing medium and "H" representing high).
A second figure in the SPM compares the risks of potentially global techniques such as BECCS (top) and afforestation (bottom). This figure shows the risks if the techniques are used at a "high level" versus if they are used at "best practice". This figure makes use of the same colour scale as the previous figure but also uses green to signify potential co-benefits.
The figure shows that both "high level" BECCS and afforestation could come with high risks for food security. The figure also shows, however, that risks to climate change adaptation, desertification and land degradation could be higher with "high level" BECCS than with "high level" afforestation.
If deployed on smaller scales and with "best practice", however, both options could remove CO2 from the atmosphere while providing "co-benefits" for people and wildlife, the SPM says:
"Applied on a limited share of total land, land-based mitigation measures that displace other land uses have fewer adverse side-effects and can have positive co-benefits for adaptation, desertification, land degradation or food security."
For both techniques, it is not just the scale of land used that will be important, but also the way in which they are carried out, says Dr Jo House, lead author of chapter two of the land report and a lead researcher of environmental change from the University of Bristol. She tells a press conference for UK journalists:
"Many of these options can be sustainable depending on the way that we do them. And, if they are done in an integrated sustainable way they could have many co-benefits. However, if they are done on very, very large areas of land and with monocultures, and on areas of land that are already sensitive to desertification, that could have greater impacts.
"The more area of land that is taken, the more risks there are for food security. But it's not just about the scale, it is also about the way in which we do things. That's the really important message: we could do things well or we could do things in a way that increases risks."
There are also several techniques that could, according to the report, remove large quantities of CO2 from the atmosphere while enhancing food security and protecting against degradation.
These include reducing current levels of deforestation and forest degradation and boosting the carbon stores of soils.
Many options exist within agriculture to remove large quantities of CO2 while providing co-benefits for the land, the graphic shows. Such techniques, including increasing food productivity, agro-forestry and improving the management of crops and livestock, are mentioned in more detail below under: "How are the issues linked and what solutions exist?"
The report emphasises that pursuing an "integrated approach" – involving many different land-based negative emissions techniques, could deliver large CO2 removal while minimising risks to people and wildlife.
However, many options for CO2 removal still face large "economic, technological, institutional, socio-cultural, environmental and geophysical barriers", the report says.
If delays to deployment continue, the overall ability of land-based negative emissions to remove CO2 from the atmosphere could start to decrease, says chapter six:
"The potential for some land management options decreases as climate change increases; for example, climate alters the sink capacity for soil and vegetation carbon sequestration, reducing the potential for increased soil organic carbon."
How are the issues linked and what solutions exist?
As the report makes clear, climate change, desertification, land degradation and food insecurity are all overlapping challenges that also tie into wider concerns such as water availability and biodiversity.
Chapter six of the report draws together the various strands, and considers ways to deal with all of these challenges together. The feasibility of each option is assessed, as well as its vulnerability to future climate change.
Strategies to address these issues range from cutting food waste to planting more trees, but each one comes with its own complications, the report notes, often including adverse side-effects that must be taken into consideration. There are also significant regional differences, and the authors note that many of the responses will take time to be effective.
It also considers how such "integrated response options" would affect the UN's sustainable development goals (SDGs) and the concept of nature's contributions to people (NCP) laid out by the Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES).
In total, the report considers 40 specific responses to the issues. Eight of these options yielded medium to large benefits for all of the land challenges being considered: increased food productivity; improved forest management; reduced deforestation; increased soil organic carbon content; enhanced mineral weathering; dietary changes; reduced post-harvest losses; and reduced food waste.
The authors found that "most response options" can be implemented without competing for available land, including improvements to crop management and increasing the carbon content of soils. Others, such as dietary changes and cuts to food waste will actively free up land.
It also finds that, overall, 17 of the strategies could be delivered with no adverse side effects for either SDGs or NCPs.
Having established the potential of different responses to the challenges the planet faces, in chapter seven of the report, it goes on to consider the policy decisions that would need to be made to implement them.
Table 7.5 details policies, programmes and instruments that could be implemented to deal with each of the interlocking issues around climate change and land.
After identifying the various trade-offs in land use in chapter six, they acknowledge that for the most part globally "trade-offs currently do not figure into climate policies and decision making". By way of example, they note that hydropower installations can hamper the movements of fish, and solar and wind farms can affect endangered species and disrupt habitats.
One key message emerging is that "the full mitigation potential assessed in this report will only be realised if agricultural emissions are included in mainstream climate policy". The report concludes that carbon pricing, through markets or taxation, has the potential to cut greenhouse gas emissions while noting it is still relatively untested in this sector.
Many measures are already being implemented, with land-based strategies currently covering up to a quarter of the total mitigation proposed by nations' Nationally Determined Contributions submitted under the Paris Agreement.
The SPM notes that many strategies will require consideration of local environmental and socioeconomic issues before being translated into policy:
"Some options such as soil carbon management are potentially applicable across a broad range of land use types, whereas the efficacy of land management practices relating to organic soils, peatlands and wetlands, and those linked to freshwater resources, depends on specific agro-ecological conditions."
Land degradation neutrality [see Carbon Brief's recent piece on desertification for more on this], is a target with huge benefits but also a major challenge, and one the report says depends on the "integration of multiple responses across local, regional and national scales, multiple sectors including agriculture, pasture, forest and water".
The report concludes that a "suite of coherent climate and land policies" would both advance the goal of the Paris Agreement and the land-related targets of the SDGs, noting that the earlier serious action is taken, the better.
However, it also points out that some strategies, such as BECCS, are a long way from being realised on a large scale, while others face significant "policy lags":
"Even some actions that initially seemed like 'easy wins' have been challenging to implement, with stalled policies for REDD+ providing clear examples of how response options need sufficient funding, institutional support, local buy-in, and clear metrics for success, among other necessary enabling conditions."
What does the report say about sustainable development, gender and the role of indigenous communities?
In a similar vein to the 1.5C report, the land report has a heavy emphasis on the links between addressing climate change and ensuring sustainable development.
The final chapter of the report (chapter seven) is devoted to how land-based decisions for tackling climate change tie-in with sustainable development.
Climate change and land use particularly threaten the world's poor, the report notes.
Future policies for tackling climate change involving the land will need to be carefully designed in order to minimise risks for those living in poverty, the SPM says:
"Due to the complexity of challenges and the diversity of actors involved in addressing land challenges, a mix of policies, rather than single policy approaches, can deliver improved results in addressing the complex challenges of sustainable land management and climate change."
This language mirrors that of the chapter six of the report, which looks at the possible impacts of land-based "negative emissions".
This chapter says that pursuing just one negative emissions technique on a very large scale could come with significant risks for people and wildlife.
It also notes some options for large-scale land-based CO2 removal, including bioenergy or BECCS, could come with trade-offs for several of the UN's sustainable development goals.
Among goals that could be negatively affected is goal 15, which aims to "protect, restore and promote sustainable use of terrestrial ecosystems, sustainably manage forests, combat desertification, and halt and reverse land degradation and halt biodiversity loss".
However, several other land-based negative emissions techniques could remove CO2 while providing co-benefits for this goal, the report says. These include avoiding further deforestation, increasing food productivity and boosting the carbon stores of soils.
(For more information, see: "How could 'negative emissions' impact land, food and wildlife?")
Economic policies for tackling change, too, could be designed in such a way as to minimise the risks to the world's poor, the SPM says:
"Elements of such policy mixes may include weather and health insurance, social protection and adaptive safety nets, contingent finance and reserve funds, universal access to early warning systems combined with effective contingency plans."
The report notes the importance of attaining greater levels of gender equity in sustainable land-based solutions for tackling climate change. A box on gender on page 87 of chapter seven reads:
"Gender is a key axis of social inequality that intersects with other systems of power and marginalisation – including 'race', culture, class/socioeconomic status, location, sexuality, and age – to cause unequal experiences of climate change vulnerability and adaptive capacity."
For example, research has found that the need to adapt to climate change on farms in Australia and Canada falls disproportionately on women's workloads, the report says. In Ethiopia, research found that male-headed households had access to a wider set of adaptation measures than female-headed households, it adds.
Future climate policies should recognise the need for greater gender equality, chapter seven says. This could be achieved through designing policy that enhances female financial empowerment and land ownership, it says.
Throughout the report, there are many references to the importance of including local knowledge – particularly from indigenious communities – in land-based decision making.
The report notes that indigenous knowledge can play a key role in understanding the impacts of climate change on land in regions without long-term instrumental data records. The SPM says:
"Based on indigenous and local knowledge, climate change is affecting food security in drylands, particularly those in Africa, and high mountain regions of Asia and South America."
Greater involvement of indigenous people in the solutions needed to tackle these impacts is vital, says Victoria Tauli-Corpuz, UN special rapporteur on the rights of indigenous peoples. During a press conference held before the report's release, she said:
"No one knows the conflicts playing out among food, fuel and forests better than indigenous peoples and local communities. We're often in the crosshairs of conflicts over land, especially forests. As experts, often guided by hundreds of years of knowledge, we are uniquely suited to manage, protect and restore the world's forests."
What has the reaction been?
There has been extensive global media coverage of the report. (See Carbon Brief's media summary in today's daily briefing newsletter.)
Much of the initial news reports focused on the overlapping nature of risks that the report identified. The Guardian says the report warns that "the climate crisis is damaging the ability of the land to sustain humanity, with cascading risks becoming increasingly severe as global temperatures rise". The Associated Press says the "report examines how global warming and land interact in a vicious cycle. Human-caused climate change is dramatically degrading the land, while the way people use the land is making global warming worse". A second Guardian article warns the impacts of climate change on land "threaten civilisation".
Food and diets also featured prominently in the coverage. Mother Jones's coverage says "climate change is taking a bigger toll on our food, water and land than we realised", while the Straits Times says the world can "feed itself [and] fight climate change if it adopts the right recipe for farming".
Similarly, a New York Times headline says that "climate change threatens the world's food supply". BBC News says that according to the report, a shift to "a plant-based diet can help fight climate change". The Times headline reads: "Eat less meat to save the Earth, urges UN," with the accompanying article noting that cutting food waste and eating less meat could reduce climate change by saving large areas of land from being "degraded by farming".
Elsewhere, NPR begins its coverage of the IPCC findings by saying: "Humans must drastically alter food production in order to prevent the most catastrophic effects of global warming." Reuters reports that "farming and eating need to change to curb global warming", according to the IPCC, with the Washington Post and the Hill taking a similar line.
The Financial Times bucks the trend by running its coverage under the headline: "Climate report warns of rising air over land temperatures," noting that the air over land is warming roughly twice as fast as the global average.
With the initial wave of media coverage, numerous NGOs have released statements in response to the IPCC report.
It "sends a clear message that the way we currently use land is contributing to climate change, while also undermining its ability to support people and nature", says Stephen Cornelius, chief advisor on climate change and IPCC lead at WWF:
"We need to see an urgent transformation in our land use. Priorities include protecting and restoring natural ecosystems and moving to sustainable food production and consumption."
The report "shows that ramping up action in line with the goal to keep temperature rise to 1.5C is crucial to avoid massive disruption to our food chains", says Wendel Trio, director of Climate Action Network (CAN) Europe:
"Already now many farmers in Europe lose their production and revenue due to frequent droughts, floods, heat waves and wildfires. Some of them cannot adapt anymore."
A number of NGOs pick up on what the report says about using the land to absorb and store greater amounts of carbon. Martin Harper, RSPB director of conservation, says:
"Nature-based solutions offer the opportunity to not only restore the natural riches of the world but to also slam the brakes on climate change."
A particular focus for NGOs is the need to balance competing demands for land. As Christian Aid's global climate lead Dr Katherine Kramer puts it:
"Today's report is a clarion call for the need for us to manage land better for people, nature and the climate. There are many opportunities to create win-wins in the ways we use the land, but it's vital we implement these quickly to avoid having to make bleak choices between feeding people and reducing emissions."
Other NGOs are more frank in their assessment of what the report says about negative emissions techniques. Teresa Anderson, ActionAid's climate policy coordinator, says:
"It sends a stark warning that relying on harmful technologies such as bioenergy with carbon capture and storage, which would take up huge amounts of land, are at odds with our need to improve food security and protect our natural ecosystems.
"Rich, polluting countries cannot expect the Global South to give away swathes of farmland to clean up the climate mess."
And Peg Putt, ecosystems coordinator at Climate Action Network, describes BECCS as an "enormous threat to ecosystems, people, and food security", adding:
"As we clearly cannot afford to lose or destroy ecosystems vital to life, the report effectively paints large scale bioenergy and BECCS as completely unacceptable and unworkable."
Mahir Ilgaz, research and grants coordinator at 350.org, also cautions that "false solutions to the climate crisis will add even more pressure to our ailing land and biodiversity systems". Ilgaz says:
"We will need to pursue options that do not force people off their lands and do not swap biodiversity with more monocultures and industrial agriculture."
Linde Zuidema, bioenergy campaigner at Fern, says the report "calls on governments to phase-out harmful subsidies that drive deforestation and forest degradation". Zuidema adds:
"This means the EU should phase out subsidies for bioenergy and focus instead on promoting protection and restoration of forests – which has proven to be positive for nature and people."
In contrast, Will Gardiner – chief executive of the Drax Group, which has gradually been converting its coal-fired power station at Drax to burn wood pellets – argues that the report confirms that "BECCS is an essential technology in tackling the climate emergency the world is facing".
Some scientific institutions and their lead researchers have also put out statements in response to the report. Prof Johan Rockström, director of the Potsdam Institute for Climate Impacts Research (PIK), says:
"The IPCC report on land confirms that we are facing a planetary emergency, that the window for taking decisive action is closing fast and that the costs of inaction will be catastrophic. While the report paints a bleak picture of what could come to pass, it also points a way forward, including opportunities for immediate action."
Prof Sabine Fuss from the Mercator Research Institute on Global Commons and Climate Change warns that "if the rapid transition in agriculture, which accounts for about a fifth of all greenhouse gas emissions, does not succeed, it may result in serious land use competition". She adds:
"At that point, carbon will have to be removed from the atmosphere at large scale, for example through reforestation or cultivation of biomass for bioenergy, which could come at the expense of sufficient food supplies or conserving natural biodiversity."
Prof Piers Forster, professor of climate change at the University of Leeds, strikes a similar tone. The report "shows that to limit temperature change below 1.5C, we need to substantially change the way we use our land", he says:
"In a nutshell we need less pasture and more trees, but really it means thinking much harder about how we use every acre of land. Land needs to grow our food, provide biodiversity and freshwater, give work to billions of people, and suck up billions of tonnes of carbon."
And Prof Corinne Le Quéré, Royal Society professor of climate change science at the University of East Anglia and member of the UK's Committee on Climate Change (CCC) says the "IPCC's findings chime with our [the CCC's] advice to government":
"The UK needs to reduce food waste, promote healthy diets, and use land sustainably, including planting more trees and restoring degraded soils. All of these steps will help to improve people's lives whilst reducing the harmful emissions which cause climate change."