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管理森林与击倒 - 树干
有砍伐的树干的管理森林。 信誉:安德鲁乱族顿/ alamy股票照片。
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2021年4月26日16:00

客座帖子:一个“Rosetta Stone”,用于将土地缓解途径带入线路

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0.4.。26.21
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26.04.2021 |4:00 PM
客人帖子 客座帖子:一个“Rosetta Stone”,用于将土地缓解途径带入线路

科学家知道世界的陆地表面吸收近三分之一人类引起的二氧化碳排放量每年。这款碳“水槽” - 主要来自森林 - 是人类活动每年涌出的排放的重要缓冲区。

但是求凿出的陆地水池完全是“自然”,有多少“人为” - 这是由人类影响的 - 很棘手。

为了回答这个问题,已经为建模小组和国家“库存”制定了不同的方法,即各国用于估计每年在其边界内排放和吸收的温室气体(GHG)。

这两种方法具有完全不同的定义和估计。它可能听起来像一个小细节,但是巴黎协议, it makes a difference for monitoring collective progress towards global emissions reductions.

在我们的新论文中,发表在自然气候变化,我们呈现“Rosetta Stone“调整用于翻译基于模型的土地利用缓解途径,以估计与国家级温室气体清单更媲美。

While our approach does not change the existing global decarbonisation pathways, it does reallocate part of the model-based land sink to be consistent with GHG inventories.

This adjustment lowers the original model-based pathways, slightly anticipating the point when net-zero emissions is to be reached. As a result, the cumulative allowable global emissions until then – that is to say, the remaining GHG budget – is reduced, under the national inventory definition, by about 12-13% relative to the original model pathways for meeting the 1.5C or 2C limits.

全球剩余的碳或温室气体预算本身不会改变,但其感知大小取决于哪些会计系统用于排放。

如果我们使用在全球脱碳途径中模型应用的系统,与早期估计相比没有变化。但是,如果我们使用国家级GHG库存,我们的调整可确保与模型的途径相比,可以改变各国关于所需的净排放水平的看法。

为什么CO2'removals'估计如此重要?

巴黎协议规定,在旨在为1.5℃的旨在实现“远低于2C”的目标,以“远低于2C”,需要在下半年实现“通过温室气体(GHG)的汇率下降来源的人为排放的平衡”世纪”。

结果,各国现在正在宣布一连串净零目标。实现这些目标将需要减少排放和促进二氧化碳“去除”的组合 - 将CO2从大气中取出的流程,目前依赖于土地部门。

词汇表
Integrated Assessment ModelsIAMS.是计算机模型,用于分析广泛的数据 - 例如,物理,经济和社会 - 制作可用于帮助决策的信息。For climate research, specifically,…Read More

一年一次,定期检查巴黎协定目标的进展“全球臭味“。这个过程的第一次迭代,它将明确依赖于最佳可用科学,将于2022-23开始。亚慱彩票APP它涉及各国的历史和计划缓解努力与科学表明是必要的,以达到约定的目标。亚慱彩票APP预计识别的任何差距都将被承认,并希望能够激励更强的气候行动。

通过历史进度通过在巴黎协议下报告国家GHG报告, hereafter collectively called “national GHG inventories” (NGHGIs). Assessments of planned future effort uses countries’ pledged climate targets, which include “国家决定捐款“(NDCS)在2025或2030年和long-term strategiesfor mid-century or thereafter. Scientific estimates of emission pathways consistent with limiting warming to 1.5C and well-below 2C are provided by综合评估模型(IAM)。

虽然这个计划看起来很声音,但在IAM和NG​​HGIS的土地部门的“人为移除”概念中存在棘手的细节。也就是说,如何从人类活动影响的土地分配二氧化碳吸收。

所涉及的二氧化碳量是显着的。例如,土地二氧化碳净渠道的模型与国家级估算之间的差异 -flux” is the exchange of CO2 between the land and atmosphere – is currently equivalent to more than 10% of global anthropogenic CO2 emissions.

为什么全球模型和国家在土地二氧化碳估计中有所不同?

下图突出了全球人为陆二氧化碳“净助焊剂”估计之间的差距 - 正助焊剂表明更多的二氧化碳被发射到大气中而不是除去,而相对适用于负通量。

蓝线代表来自使用的模型的历史净助焊剂的估计special report on climate change and land由这件事政府间气候变化小组(IPCC), while the red lines show projections from IAMs under different scenarios. The grey line shows flux estimates from NGHGIs and the black lines show projections under the NDCs.

红色和蓝线之间的间隙和灰色和黑色的差距均为每年约55亿吨的二氧化碳(GTCO2 / YR)。这种不匹配的禁止准确评估巴黎协定下的进度。

Mismatch in the land CO2 flux estimates between NGHGIs and pledged future NDCs and global models
显示NGHGIS(灰线)与未来国内确定捐款(NDC,黑线)和全球模型(红线)之间的土地二氧化碳通量估算中的图表。历史模型助焊剂(蓝线)来自用于簿记模型IPCC关于气候变化和土地的特别报告(IPCC SRCCL), while future pathways (red) are from IAMs for various共享社会经济途径(here, only SSP2 scenarios). LULUCF stands for “land use, land-use change and forestry”, which is the term for land-related CO2 fluxes in NGHGIs. Unconditional pledges are the minimum countries pledge to do, conditional pledges are stronger action based on, for example, finance. Positive fluxes indicate net emissions, whereas negative fluxes indicate net removals of CO2 from the atmosphere. Source: Grassi et al (2021.)。

Our study identifies a major and resolvable reason for this gap, linked to the conceptual inconsistencies between IAMs and NGHGIs in estimating the anthropogenic CO2 sink.

排放量from fossil fuels and industry are unmistakably caused by humans and, thus, are classed as “anthropogenic”. However, for land CO2 fluxes, things are far more complicated – they involve both human-caused and natural processes that can be difficult to disentangle.

这些过程包括直接人类诱导的效果 - 例如森林砍伐,森林收获和再生 - 但也是间接影响。这些包括二氧化碳施肥温暖引起的温度和降雨模式的变化,往往刺激植物生长。

两个基本上独立的科学社区发展了不同的方法,以估计来自土地的人为二氧化碳通量 - 以不同的目的和范围 - 这在他们自己的具体背景下有效。

第一个社区涉及全球碳周期和综合评估的科学建模,包括IAM。通过复杂的模型,他们开发了从天然助熔剂(包括间接人类诱导的效果)的大约单独的人体助条质(仅限人类诱导的效果)的方法,其目的是提供包含在内的全球一致的估计IPCC assessment reports

另一个社区与发展有关IPCC用于NGHGIS的方法论指南– with the aim to provide pragmatic and consistent methodologies that are applicable by all countries for报告他们的温室气体排放量

在这种实际的现实世界背景下,在这第二个社区运作的情况下,在管理的森林中对二氧化碳净助剂的直接和间接人为效应的分离是不可能的,即不受森林或造林的森林。这是因为,通过直接观察测量森林生物量随时间的变化 - 例如国家森林清单通常是基于基于NGHGIS的 - 一个人不能说出有多少生物量变化是由于更好的管理以及环境所致的多少因素。

因此,非法的IPCC指南采用了妥协,其中人类被人类被定义为“管理”的所有GHG助量被认为是人为的。来自“非托管”土地的GHG助焊剂不会被认为是人为的,因此在NGHGIS中没有报告。虽然这个代理显然是不完善的IPCC专家组已经结束了,目前,NGHGIS没有更好和广泛适用的替代品。

在实践中,在森林中保持不变area, IAMs only consider the CO2 fluxes associated with intensive harvesting activities and the subsequent regrowth (direct effects) to be anthropogenic. This is a relatively limited area globally. NGHGIs, on the other hand, include all CO2 fluxes on a broader managed area – including, for example, less intensively managed forest – such as areas subject to thinning and selecting logging – or protected areas. And, importantly, the NGHGIs consider both the direct and the indirect human-induced effects on this larger area, in line with the IPCC “managed land” compromise.

There is a considerable difference between the managed forest areas considered by the IAMs – around 0.5bn hectares – and the NGHGIs – around 3bn hectares. These differences are summarised in the figure below, which also include完整的森林,我们用作各国未托管森林的代理。

IAMS和NGHGIS在估算人为土地CO2通量的不同方法的插图
IAMS和NGHGIS在估算人为陆二氧化碳通量的不同方法的插图。基于Bassi等人(2021.)and Ogle & Kurz (2021.)。

这种在人为土地CO2助焊剂中的这种不匹配是利用IAM在评估进度方面的关键障碍,并且在巴黎协定下的目标中更加雄心壮志。

此问题已受到最高级别的确认,例如在最近的IPCC特别报告中(ON)全球变暖1.5℃和上气候变化和土地)在2019年期间plenary sessionof the联合国气候变化框架公约(UNFCCC).

IPCC和政策制定者都需要一种可行的解决方案。然而,这个问题不是为了决定哪种方法更好,也不要强迫一个社区或者另一个使用特定的方法,但能够平衡他们的估计,以便可以比较它们。

如何确保一致的比较?

在改变国家的方法的过程中,可以是可取的直接和间接影响的方式,这在短期内是不切实际的。因此,我们探讨了如何使用全局模型的输出来促进类似于类似的比较。

In essence, the problem is that countries call “anthropogenic” the part of the land CO2 sink that IAMs call “non-anthropogenic”. Luckily, these emissions are not “lost” in the overall calculations by IAMs, but are captured by other kinds of models, such as动态全球植被模型(DGVM)和Earth system models(ESMS)。

这些模型专门估计土地对人类诱导的环境变化(间接影响)的自然反应 - 也就是说,大多数国家通常是“人为”的那些二氧化碳势态。虽然大多数IAM没有明确地模拟这些势态,但它们是使用ESMS和DGVMS的信息来陈述 - 在开发与特定温度限制一致的发射路径。

由于这主要是如何标记通量的问题,因此只需通过重新分配陆地汇来实现更一致的比较。这在下面的图表中示出。

The left-hand charts (a and b) show the modelling approach for anthropogenic (top) and natural fluxes (bottom), while the right-hand charts (c and d) show the models’ results adjusted to the NGHGIs approach. To make the modelling of anthropogenic fluxes conceptually more comparable with NGHGIs, we relocate part of the global models’ natural sinks – due to indirect human-induced effects on non-intact forests (the dashed green area in chart b) – to the anthropogenic component (chart c).

It is important to note that our approach relocates part of the forest sink by global models (from the non-anthropogenic to the anthropogenic component), but does not change the emission pathways for energy and industry, nor the land-use emissions due to direct effects (grey and yellow areas in the figure below, respectively). In addition, because the changes in natural and anthropogenic fluxes fully compensate, the CO2 remaining in the atmosphere (red lines in b and d) also remains unchanged.

调整建模的IAM IAM CO2通量可与NGHGI方法相媲美
Example of adjusting modelled IAMs’ land CO2 fluxes (left-hand charts) to be comparable to the NGHGI approach (right-hand). The green arrow shows the relocation of part of the global models’ natural sinks (green shading with hatching) to the anthropogenic component. Non-intact forests are used here as a proxy for countries’ managed forests. From Grassi et al (2021.),用于SSP2-2.6场景。

Does the relocation of fluxes change our understanding of the global carbon budget?

我们拟议的调整确保了IAM和NG​​HGIS之间适当的类似比较,但不会改变对当前和未来的科学了解剩下的全球碳或累积温室气体排放(即,排放直到净零碳或GHG排放与某种气候目标一致)。但是,它确实有影响了解国家所需的缓解努力。

下图总结了所有的步骤above. Starting from a large gap in anthropogenic land CO2 fluxes (chart a) between NGHGIs (black line) and IAMs (coloured lines, representing different emissions pathways), our approach adds the fluxes from indirect effects estimated by DGVMs on non-intact forests (chart b) to the original IAMs’ results (chart c). The resulting “adjusted” IAMs estimates (dotted lines in chart c) are then conceptually and quantitatively more comparable with NGHGIs (black line in chart c).

这些变化不会影响非Lulucf(土地使用,土地使用变化和林业)排放(图表D)。但是,Lulucf和非Lulucf排放的总和(即“经济范围的”排放)确实发生变化,并且对经济范围的排放(图表E中虚线的无数的减缓途径低于原始排放量(实线)。相同的推理适用于累积温室气体排放。

For example, for the scenariosSSP2-1.9和SSP2-2.6- 表示保持升温至约1.5℃和2C的途径,分别累积温室气体排放,直到以NGHGI可比较的方式表达的Net-oots表示为120-192 GTCO2,与IAMS(图F)描述如何。这意味着,尽管我们的解决方案不改变原始脱碳途径,但由于NGHGIS的镜头,相对于原来的IAM考虑,它会降低给定的温控极限的总人为排放和允许的经济范围内净排放量途径。

Charts summarising the adjustment of IAM pathways to be NGHGI compatible
Charts summarising the adjustment of IAM pathways to be NGHGI compatible: Starting from the current large gap in land CO2 fluxes between IAMs and NGHGIs (chart a), the indirect effects estimated by DGVMs from non-intact forests (chart b) are added to the original land IAM pathways (solid lines in chart c) to obtain adjusted, NGHGI-comparable land IAM pathways (dotted lines in chart c). Considering the wider implications: By summing the other GHG emissions which remain unchanged (in chart d) to the land IAM pathways we obtain NGHGI-comparable economy-wide IAM pathways including all the sectors (dotted lines in chart e). Table f then represents the impact of our approach (as GtCO2 or %) on the NGHGI-comparable remaining cumulative GHG emissions relative to the original ones. It is worth noting that the forest sink in chart b is very uncertain beyond 2050. Adapted from Grassi et al (2021.)。

这种调整的含义是什么?

我们拟议的调整并不意味着应在气候目标中或不应包括间接效应,而是简单地促进了类似的效果 - 以及因此科学更准确的 - 对IAM途径的不同国家气候目标进行比较。

In the absence of these adjustments, comparing IAM-based pathways to current emissions based on NGHGIs would give the impression that collective progress is more on-track than it actually is.

However, the adjusted IAM pathways become harder to interpret, because the CO2 sink due to indirect effects depends on the level of climate change. For example, under more ambitious pathways, the CO2 fertilisation effect decreases and therewith also the CO2 sink (see the blue and green lines in chart b above). As a consequence, the adjusted LULUCF pathways do not include this clear dependency on the level of climate action and, thus, the effort required is less visible compared to the original LULUCF pathways (chart c).

IAMS缓解途径对气候政策具有巨大的重要性,作为评估巴黎协定下的集体进展的基准和比较。然而,为了满足这种作用,他们应该与NGHGIS和气候目标相媲美。

总的来说,可以从我们的研究中获取两条消息。首先,可以在全球模型和国家级温室气体清单之间进行人为土地CO2助理的核性:当制造类似的比较时,原始的大差距消失。

其次,由于大多数国家通过其NGHGI会计系统的镜头考虑排放和气候目标,因此需要与调整后的NGHGI兼容的途径和剩余累积温室气体排放进行比较。该调整能够更准确地评估巴黎协议的全球储存下的集体气候进展,从而改善国家对全球排放水平的理解,他们仍然可以为特定的温度目标发出。

Grassi,G.等人。(2021)评估国家气候进步的土地缓解途径的关键调整,自然气候变化,doi:10.1038/s41558-021-01033-6

来自这个故事的Sharelines
  • 客座帖子:一个“Rosetta Stone”,用于将土地缓解途径带入线路
  • 帖子邮政:为什么对齐土地缓解途径是评估气候进步的关键

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