Changes in forest cover have a strong effect on climate through the alteration of surface biogeophysical and biogeochemical properties that affect energy, water and carbon exchange with the atmosphere. To quantify biogeophysical and biogeochemical effects of deforestation in a consistent setup, nine Earth system models (ESMs) carried out an idealized experiment in the framework of the Coupled Model Intercomparison Project, phase 6 (CMIP6). Starting from their pre-industrial state, models linearly replace 20×10⁶ km² of forest area in densely forested regions with grasslands over a period of 50 years followed by a stabilization period of 30 years. Most of the deforested area is in the tropics, with a secondary peak in the boreal region. The effect on global annual near-surface temperature ranges from no significant change to a cooling by 0.55 ^∘C, with a multi-model mean of $-\mathrm{0.22}\pm \mathrm{0.21}$ ^∘C. Five models simulate a temperature increase over deforested land in the tropics and a cooling over deforested boreal land. In these models, the latitude at which the temperature response changes sign ranges from 11 to 43^∘ N, with a multi-model mean of 23^∘ N. A multi-ensemble analysis reveals that the detection of near-surface temperature changes even under such a strong deforestation scenario may take decades and thus longer than current policy horizons. The observed changes emerge first in the centre of deforestation in tropical regions and propagate edges, indicating the influence of non-local effects. The biogeochemical effect of deforestation are land carbon losses of 259±80 PgC that emerge already within the first decade. Based on the transient climate response to cumulative emissions (TCRE) this would yield a warming by 0.46 ± 0.22 ^∘C, suggesting a net warming effect of deforestation. Lastly, this study introduces the “forest sensitivity” (as a measure of climate or carbon change per fraction or area of deforestation), which has the potential to provide lookup tables for deforestation–climate emulators in the absence of strong non-local climate feedbacks. While there is general agreement across models in their response to deforestation in terms of change in global temperatures and land carbon pools, the underlying changes in energy and carbon fluxes diverge substantially across models and geographical regions. Future analyses of the global deforestation experiments could further explore the effect on changes in seasonality of the climate response as well as large-scale circulation changes to advance our understanding and quantification of deforestation effects in the ESM frameworks.

中文翻译：

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CMIP6模型中对理想化森林砍伐的全球气候响应

森林覆盖的变化通过改变影响大气中能量，水和碳交换的表面生物地球物理和生物地球化学特性，对气候产生强烈影响。为了以一致的方式量化森林砍伐的生物地球物理和生物地球化学效应，九个地球系统模型（ESM）在耦合模型比较项目第六阶段（CMIP6）的框架内进行了理想化实验。从工业化前的状态开始，模型线性替换20×10 ⁶  km ²草地茂密的森林地区的森林面积持续50年，然后稳定30年。大部分森林砍伐地区位于热带地区，北部地区有次要高峰。对全球年度近地表温度的影响范围^从无显着变化到降温 ^0.55∘C，具有多个模型平均值：$--\mathrm{0.22}\pm \mathrm{0.21}$ ^∘C .五个模型模拟了热带地区森林砍伐土地上的温度升高和森林砍伐的北方土地上的降温。在这些模型中，温度响应变化符号的纬度范围为11至^43∘N  ，多模型平均值为^23∘N  。多集合分析表明，即使在这样的温度下，近地表温度变化的检测也是如此。强烈的毁林情景可能需要数十年的时间，因此比当前的政策期限更长。观测到的变化首先出现在热带地区森林砍伐的中心并传播边缘，这表明了非本地效应的影响。毁林的生物地球化学效应是259±80的土地碳损失  在第一个十年内就已经出现了PgC。基于所述瞬变气候响应于累积排放（TCRE），这将通过0.46得到变暖 ±  0.22  ^∘ C，这表明砍伐森林的净变暖效应。最后，本研究介绍了“森林敏感性”（作为对森林砍伐的每部分或每区域的气候或碳变化的度量），它有可能在没有强大的非本地气候反馈的情况下为森林砍伐－气候模拟器提供查找表。尽管就全球温度和陆地碳库的变化而言，各模型在应对森林砍伐方面已达成共识，但潜在的能源和碳通量变化在各模型和地理区域之间存在很大差异。未来对全球森林砍伐实验的分析可以进一步探索对气候响应季节变化以及大规模环流变化的影响，以增进我们在ESM框架中对森林砍伐影响的理解和量化。