< p >正如Camilo在评论中提到的,“碳中性”在这种情况下意味着零净碳排放。这是总人为碳排放(化石燃料燃烧和土地利用变化)-碳吸收< em > < / em >通过管理实践。这种区别是非常重要的;你不包括海洋和陆地碳吸收通过< em > < / em >自然过程来抵消总排放量的计算。自2010年以来,联合国环境规划署每年发表了一份“排放缺口”报告,包括一些相关的排放数量:< / p > < blockquote > < p > 2017年排放的温室气体(GHG)排放,不包括土地利用变化——达到创纪录的49.2 GtCO2e……排放从土地利用变化……添加另一个4.2 GtCO2 GtCO2e总数达到53.5。< / p > < p >来源:< a href = " https://www.unenvironment.org/resources/emissions -差距报告- 2018“rel = " nofollow noreferrer " >环境规划署排放差异报告2018年< / > < / p > < /引用> < p >下面是一个不错的各种负面的发射技术的示意图(网),这可以作为缓解总体预算:< / p > < blockquote > < p > < a href = " https://i.stack.imgur.com/HPdgp.jpg " rel = " nofollow noreferrer " > < img src = " https://i.stack.imgur.com/HPdgp.jpg " alt = "在这里输入图像描述" / > < / > < / p > < p >来源:史密斯et al(2016)“生物物理和经济限制负二氧化碳排放”,< a href = " https://www.nature.com/articles/nclimate2870 " rel = " nofollow noreferrer " > https://www.nature.com/articles/nclimate2870 < / > < / p > < /引用> < p >碳捕获和储存(CCS)是在燃烧化石燃料,所以化石总值减少排放。面板(g)叫做LULUCF(土地利用、土地利用变化和林业)的排放差距报告和AFOLU(农业、林业和其他土地使用)在IPCC 1.5特别报道,这实际上是+ 4.2 GtCO2e /年引用。未来的想法是,土地管理必须改变把土地从净源管理温室气体的净碳汇。 As for Bio-energy Carbon Capture Systems (BECCS), the current levels are about zero, although there are a dozen or so demonstrator projects totalling about 0.001 GtCO2/year. So at the moment it barely makes a dent in the overall budget, but mitigation scenarios require it rising to an order of 10 GtCO2/year by 2050: 
The energy production from the use of BECCS over time in a range of mitigation scenarios.
Source: van Vuuren et al (2018) “Alternative pathways to the 1.5 °C target reduce the need for negative emission technologies”, https://www.nature.com/articles/s41558-018-0119-8
The IPCC special report also has a nice schematic of how NETs contribute to emissions scenarios. Although there's no timescale on the schematic, most of the actual scenarios don't show any notable BECCS until 2030.
Figure 2.5 | Evolution and break down of global anthropogenic CO2 emissions until 2100
Source: Rogelj et al (2018) "Mitigation Pathways Compatible with 1.5°C in the Context of Sustainable Development", Chapter 2 of the IPCC Special Report on Global Warming of 1.5°C.