Global Surface Air Temperature (GloSAT)

地表温度是关于气候变化的最长仪器记录，也是《巴黎气候协定》中使用的一种测量方法，旨在“防止气候系统受到危险的人为干扰”。该协定确定了将全球气温变化限制在比工业化前水平高1.5摄氏度或2摄氏度的目标。政府间气候变化专门委员会（IPCC）使用1850-1900年的基线来定义“工业化前”，因为这是现有仪器记录开始的时间。据估计，到目前为止，全球气温可能已经上升了0-0.2摄氏度，但由于缺乏数据，这一数字尚不确定。然而，即使使用1850-1900年的基线，现有的温度数据集对迄今为止的变暖量也存在分歧，这种分歧意味着，仅由于观测到的地表温度变化的不确定性，实现《巴黎协定》目标的允许碳预算有20%以上的不确定性。这些温度数据集之间的差异主要源于两种结构上的不确定性：使用的是海洋表面温度（SST）而不是海洋（特别是冰覆盖地区）的空气温度，以及数据覆盖范围和插值策略的差异。这个项目解决了这两个问题。为了最好地为决策者提供信息，温度变化的记录必须尽可能准确、一致和长。现有的全球数据集从1850年或更晚开始，但我们将把记录再延长70年，回到18世纪晚期。目前对这一时期的了解来自欧洲的仪器测量、古代用物（树木年轮、珊瑚或冰芯）和气候模型。我们将极大地扩展这70年期间早期测量记录的空间覆盖范围，这对于理解自然气候变率和气候对不同辐射强迫的响应具有重要意义。例如，更长的记录包括5次大型火山爆发和多年代际气候振荡的额外周期。新的记录将使我们能够更好地理清人为因素和自然因素对气候系统的影响，并量化人类已经对地球温度产生的影响，从而对未来气候产生的影响。一个主要的不一致之处是，过去使用的是陆地上空的气温，而海洋上空的海温。最近的进展意味着我们可以制作一个海洋气温记录来构建第一个覆盖海洋、陆地和冰的全球气温数据集，时间可以追溯到18世纪晚期。我们的数据集将独立于海温，海温是目前全球温度最不确定的组成部分。我们将改进陆地、海洋和冰冻圈的气温观测，使它们更加均匀，并进一步延长全球记录的时间。这需要基础研究来更好地理解历史观测的偏差和噪声特征，并开发新的误差模型。我们将采用先进的统计技术，即使在观测中有空白，也能估计出各地的气温。我们将通过新的船舶日志和气象站数字化来扩展历史气候记录，重点关注早期数据、稀疏时期和地区，以及陆地、海洋和冰之间的界面。我们会在最近成功的公民科学计划的基础上，让公众参与数码化工作。我们将分析新的地表气温记录，以更好地了解自18世纪末以来气温是如何变化的。更长时间的记录将使人们更好地了解自然气候变化，包括气候系统内部产生的变率以及火山爆发和太阳变化等外部强迫因素造成的变率。这种对自然变率的更好理解将使我们能够更清晰地分离出人为气候变化的特征“指纹”，使我们能够更自信地探测和归因于人为引起的变化。

Surface temperature is the longest instrumental record of climate change and the measure used in the Paris Climate Agreement that aims to 'prevent dangerous anthropogenic interference with the climate system'. The Agreement defines an ambition to limit global temperature change to 1.5C or 2C above pre-industrial levels. The Intergovernmental Panel on Climate Change (IPCC) used a baseline of 1850-1900 for its definition of 'pre-industrial' as this is when existing instrumental records begin. It has been estimated that global temperatures may have already increased by 0.0-0.2C by this time, but this is uncertain due to lack of data. However, even using the 1850-1900 baseline, existing temperature datasets disagree on the amount of warming to date and this disagreement implies more than 20% uncertainty in the allowed carbon budget to meet the goals of the Paris Agreement solely due to uncertainty in observed surface temperature change. These differences between temperature datasets arise mostly from two structural uncertainties: the use of sea surface temperatures (SST) rather than air temperatures over the oceans, especially ice-covered regions, and differences in data coverage and interpolation strategies. This project addresses both.To best inform decision-makers, records of temperature change must be as accurate, consistent, and long as possible. Existing global datasets start in 1850 or later, but we will extend the record a further 70 years back to the late 18th century. Current knowledge of this period comes from instrumental measurements in Europe, palaeo-proxies (tree-rings, corals or ice cores), and climate models. We will dramatically extend the spatial coverage of the early measured record in this 70-year period, which is important for understanding natural climate variability and the climate response to different radiative forcings. For example, the longer record includes the period of 5 large volcanic eruptions and extra cycles of multi-decadal climate oscillations. The new record will allow us to better disentangle the contributions of anthropogenic and natural factors on the climate system and quantify the effect humans have already had on Earth's temperature, and hence on future climate.A major inconsistency has been past use of air temperature over land but SST over oceans. Recent advances mean we can produce a marine air temperature record to construct the first global air temperature dataset over ocean, land and ice, stretching back to the late 18th century. Our dataset will be independent from SST, currently the most uncertain component of global temperature. We will improve land, marine and cryosphere air temperature observations to make them more homogeneous and extend the global record further back in time. This requires fundamental research to better understand the bias and noise characteristics of historical observations and develop new error models. We will adopt sophisticated statistical techniques to allow the estimation of air temperature everywhere, even when there are gaps in the observations. We will expand the historical climate record with new ship's logbook and weather station digitisations focused on early data, sparse periods and regions, and the interfaces between land, ocean and ice. We will engage the public in the digitisation effort building on recent successful citizen science initiatives.We will analyse the new surface air temperature record to better understand how temperatures have changed since the late 18th century. This longer record will give a better understanding of natural climate variations, both variability generated internally within the climate system and that due to external forcing factors such as volcanic eruptions and solar changes. This improved understanding of natural variability will enable us to more cleanly isolate the characteristic "fingerprints" of man-made climate change allowing us to more confidently detect and attribute human-induced changes.