为减缓全球变暖，《巴黎协定》正式提出将本世纪末的全球平均气温的升高幅度控制在2℃以内，并努力限制在1.5℃。升温幅度通常以1850-1900年作为基准。然而这一时期的气象观测站点稀疏，北极地区更加缺乏，基于空间插值的温度数据不确定性较大，很难作为升温幅度的准确参照。近几十年的气象观测数据显示，北半球高纬度地区的增温速率远大于中低纬度，该现象被称为“北极放大”效应，但它在气候变暖早期是否在北极同样存在仍然未知。

树木年轮资料在大尺度温度重建中应用广泛，为了准确提取树木年轮中的气候信息，需要去除其年龄趋势。而去趋势的方法众多，不同方法的重建结果差异巨大。过去类似的研究通常只使用单一去趋势方法，对样本的筛选并不严格，因此存在较大的不确定性。本研究采用五种方法对树木年轮数据去趋势，分别是：C-method Standardization（CMS）、区域曲线标准化法（Regional Curve Standardization, RCS）、无信号的区域曲线标准化法（signal-free RCS，sf-RCS）、样条函数法（Spline）和修正负指数曲线法（Modified Negative Exponential curve, ModNegExp），并构建标准树木年轮年表。仅使用与目标格点温度显著相关的年表重建整个北半球及北美洲、欧洲和亚洲的中纬度（30-60°N）和高纬度（60-90°N）地区的夏季温度，评估不同去趋势方法获得的重建结果对于升温幅度估算的影响。结果如下：

1. 整个北半球和北半球各大洲相较于工业化前增温显著，但升温幅度因去趋势方法不同而有所差异。CMS去趋势方法展现出最明显的升温趋势，而Spline去趋势方法升温幅度最弱。

2. 北半球部分地区存在“北极放大”效应，结论也受到去趋势方法的影响：温度重建和再分析数据均显示亚洲高纬度地区的升温幅度要高于中纬度，存在明显的“北极放大”效应；使用三种去趋势方法的温度重建显示欧洲高纬度地区升温幅度低于中纬度，与再分析数据记录一致，不存在“北极放大”效应。

In order to mitigate global warming, the Paris Agreement formally proposes to limit the increase in global average temperature within 2°C by the end of the century and endeavors to limit it to 1.5°C. The warming is usually benchmarked against the period 1850-1900. However, meteorological observation stations were sparse during this period, with an even greater lack in the Arctic, and temperature datasets based on spatial interpolation have large uncertainties, making it difficult to use them as an accurate reference for the warming amplitude. In recent decades, meteorological observations have shown that the rate of warming in the northern hemisphere has been much greater at high latitudes than at low and mid-latitudes, a phenomenon known as the "Arctic amplification" effect, but it is still unknown whether it also existed in the Arctic in the early stages of climate warming.

Tree rings are widely used in global large-scale temperature reconstruction, and in order to accurately extract climate information from tree rings, it is necessary to remove their age trends. There are numerous methods for removing trends, and the corresponding reconstruction results vary greatly. Similar studies in the past usually used only one single detrending method and were not rigorous in screening the samples, resulting in large uncertainties. In this study, we used only tree chronologies that were significantly correlated with the temperature of the target grid points, for which five detrending methods were applied: C-method Standardization (CMS), Regional Curve Standardization (RCS), signal-free RCS (sf-RCS), Spline and Modified Negative Exponential curve (ModNegExp), and standardised to reconstruct mid-latitude (30-60°N) and high-latitude (60-90°N) curves for the entire Northern Hemisphere, as well as for North America, Europe and Asia. And to assess the impact of the reconstructions obtained by different detrending methods on the estimation of the magnitude of warming. The results are as follows:

1. The entire Northern Hemisphere and the Northern Hemisphere continents have warmed significantly compared to the pre-industrial period, and the magnitude of the warming varies depending on the detrending method. The CMS detrending method exhibits the most pronounced warming trend, while the Spline detrending method has the weakest warming.

2. There is an "Arctic amplification" effect in parts of the Northern Hemisphere, and the conclusions are also affected by the detrending methods: temperature reconstructions and instrumental reanalyses records show that warming is higher at high latitudes than at mid-latitudes in Asia, and there is a clear "Arctic amplification" effect; The temperature reconstruction using the three detrending methods shows that the warming in the European high latitudes is lower than that in the mid-latitudes, which is consistent with the reanalyses datasets, and no "Arctic amplification" effect was observed.