映射:'代理'数据如何揭示地球遥远的遥远的气氛

由Robert McSweeney和Zeke Hausfather。汤姆普拉特设计。

在任何一个时刻,都采取了数以千计的测量世界的天气。跨越土地,海洋和天空,数据正在手动和自动使用一系列技术,从谦逊的温度计到最新多百万磅卫星

这些测量多年来聚集在一起a record of the Earth’s climate以及它是如何变化的。

但即使是世界上最长的气候档案 -central England temperature record-only goes back to 1659. This is a mere snapshot in time considering the hundreds of thousands of years that humans have roamed the planet.

幸运的是,地球一直在保留自己的记录。在各种各样的地方藏起来 - 从贝壳和钟乳石到花粉和封口封封 - 自然世界已经记录了千年之千年的潮流和流动。

这被称为“代理数据” - 在生物圈不同部分印记的气候间接记录。

以同样的方式“史前”与书面历史之前的时间涉及一段时间,代理数据在专用记录之前提供了进入气候的洞察。它形成了过去的气候研究的基本部分,被称为“古世教徒学”,同时还帮助支持科学家的理解未来气候如何变化。

In this in-depth Q&A, Carbon Brief explores what proxy data is, the different types, how scientists draw climate data from them, and what they can tell us about the Earth’s climate in the past, present and future.

In addition, Carbon Brief has produced an interactive map of the US国家海洋和大气管理局(noaa)存档超过10,000个代理数据集

什么是代理数据?

In 1714, German physicistDaniel Gabriel华氏温度invented what is considered to be thefirst example of the modern thermometer。它在玻璃管中封闭汞,并在侧面延伸标准化秤。十年后,他会增加熊的温度尺度。(瑞典天文学家安德斯摄氏度不会再制定他另外二十年的替代规模。)

温度计,以及其他仪器如barometerfor measuring air pressure andhygrometer对于湿度,继续成为正式气象站的关键部分。这些站 - 屏蔽了一个百叶窗史蒂文森屏幕-were first installed in Europe and the US in the 1800s, and spread around the world throughout the century and beyond.

A Stevenson screen, containing meteorological instruments. Credit: Universal Images Group North America LLC / DeAgostini / Alamy Stock Photo.
A Stevenson screen, containing meteorological instruments. Credit: Universal Images Group North America LLC / DeAgostini / Alamy Stock Photo.

经过the middle of the 19th century, there were sufficient weather stations and enough observations being recorded on land – and- 产生可靠的全球温度测量。这全球温度最长记录-共同生产由这件事UK Met Office Hadley Centre东安格利亚大学’s气候研究单位- 从1850年开始。其他,例如由此产生的那些NASA国家海洋和大气管理局(NOAA), start in 1880.

年度全球平均水平表面温度从1850 - 2012年起。数据来自NASA Gistemp.noaa globaltemp.Hadley / Uea Hadcrut5伯克利地球和碳简短乐动体育下载app的原始温度记录。1979-2000温度从Copernicus Era5.(随着重新分析记录于乐动体育app苹果j1979年开始)。异常绘制了1880-1899个基线以显示自预生产以来的变暖。

这意味着科学家的强大陈述了过去一个世纪的全球气温如何发生变化。但是,当然,地球比那个年龄较大。甚至还要回顾一下 - 对于没有仪器的地方,直到相对近最近 - 科学家需要将他们的眼睛施放到直接观察到间接证据,这些证据被锁定在地球上的各种形式。这是“代理”数据。

这word “proxy” is typically defined as an intermediary or substitute – often in reference to a person given the authority to vote or speak on behalf of someone else. Proxy data, therefore, is information that is a substitute for direct observations of the Earth’s climate.

“气候代理是我们用来重建过去的有效因素的变化,如温度,降水,二氧化碳水平 - 或者其他任何意义,”解释说保罗Pearson教授来自地球和海洋科学院的乐动体育 英超Cardiff University。他讲碳简短:乐动体育下载app

“Obviously, these things can't be measured directly without a time machine, so we need to find something that survives from the past that is dateable and contains something we can measure that would have responded to the variable we are interested in – hence, the name ‘proxy’.”

因此,科学家们认为气候“在环境中留下了标记”的方式。Dr Maisa Rojas,地球物理部副教授智利大学and a lead author on the古爱宝质章节(pdf) of the气候变化政府间议会(IPCC)第五次评估报告(AR5)。她讲碳简短:乐动体育下载app

“这living part of our world – the biosphere – responds to the climate and, as such, it leaves marks in a number of environmental indicators that we can then use to reconstruct back the climate.”

这些线索过去的气候被散落在地球上,从湖泊底部的巨大冰盖和沉积物的层,到树木的响亮和洞穴中高耸的石笋。(看later section有关不同的代理数据来源。)

比利时汉族洞穴洞穴的石笋。信用:Bombaert Patrick / Alamy股票照片。
比利时汉族洞穴洞穴的石笋。信用:Bombaert Patrick / Alamy股票照片。

这些信息允许科学家们“在过去几百年和千年中研究气候,从而进一步回到时间内,而不是仅使用乐器气候数据”,解释说瓦莱丽教授臭味那a professor in the树圈研究实验室亚利桑那大学和作者树木故事,关于树戒指的书。她补充说:

“通过在20世纪之前研究气候,当气象站数据变得可用时,我们可以将目前的气候变化放在长期背景下,研究自然,非人为驱动,气候变异性。”

这way that the climate can leave its mark on the Earth’s surface has long been observed. In the 15th century, for example, Italian artist and inventor Leonardo da Vinci记录树圈的厚度 - 发现穿过树干的同心圆 - 随着降雨而变化。

树木戒指约会的科学纪律称为“dendrochronology” - 稍后被美国天文学家开创e douglass.in the early 20th century.His research试图通过气候和树木模式的波动连接太阳黑子周期的模式。从这个最早的工作来看,Douglass继续发现上面提到的树林研究实验室。

(从左到右):Leonardo da Vinci,Harold Urey和Andrew Ellicott Douglass。
(从左到右):Leonardo da Vinci,Harold Urey和Andrew Ellicott Douglass。乐动体育下载app碳短暂复合。

Another proxy with a long history is “the oxygen isotope composition ofcalcite皮尔森说,壳牌“在海洋生物中说:

“这种方法由[美国化学家]开创Harold Ureyin the immediate post-war years and helped launch the entire field of古籍方式。”

乌雷表明,这些壳的化学成分(见下一节for more on isotopes) varied depending on the temperature of the water. Extracting this information, thus provided information on the climate when the organisms were alive – going back many millions of years.

Urey described his discovery as “suddenly [finding] myself with a地质温度计in my hands”, explains Pearson.

找到了世界上的代理数据?

从南极洲的冰盖和海底of the Atlantic, to the boreal forests of Europe and corals of southeast Asia, proxy data is found across the Earth’s land and ocean.

NOAA持有档案超过10,000个代理数据集covering more than a dozen categories. With its permission, Carbon Brief has mapped this data.

使用左侧图例中的类别选择特定的代理或存档类型,以及右上角的按钮可放大和缩小。单击单独的数据点将显示数据,站点名称和NOAA参考网页的链接以获取更多信息的句点。

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What information do proxies capture?

代理数据可以提供关于一系列气候相关变化的见解。这些包括突然事件 - 例如volcanic eruptionsor洪水-and gradual, long-term trends – such as变暖和冷却droughtchanging sea levels旋风图案季风季节波动大气二氧化碳orthinning ice sheets

Proxies generally falls into one of three categories – physical, biological or chemical – explains Prof Pearson:

“Proxies can be something physical like the amount of silt in sea floor mud which can be a proxy for the speed of the current, something biological like the width of a tree-ring or growth band in a marine shell, or something chemical like the elemental or isotopic composition of a substance that we can measure in the lab.”

这些不同类型的代理已被一系列古社会捕获“档案“,如沉积物,冰芯和洞穴形成。这些是“媒体,即[代理]数据被记录在”中,解释说明Allison Cluett.那a PhD candidate at the大学在布法罗

例如,Cluett的研究分析了海洋沉积物(档案)中的叶蜡(代理)以重建格陵兰南部的气候。

每种类型的代理都反映了条件的变化,但它们不仅仅是捕获温度或降雨或其他单个变量。相反,他们经常反映几个。因此,古教物程学领域涉及“解开”具体的气候信息,说,罗哈斯博士说。

生物

采取树木,提供一棵树随着时间的推移在一棵树上增加了新的木材的生物学记录。每个环包括光和暗的部分 - 苍白的部分,表示春季和初夏的快速生长以及暗部,表明夏季晚期和秋季增长较慢。一起携带,每个戒指都表明了树的一年。

Scientists can ““一棵树通过其行李箱提取横截面。这允许他们分析其戒指而不会损坏树。

这rate of tree growth can “respond to both precipitation and temperature – and will depend on the tree and where it is located”, explains Rojas. Rings will be wider in warm, wet years where the tree is getting sufficient sunshine and rainfall to support growth, and rings will be narrower during a drought or if the tree is hit by pests, disease or fire.

树戒指。信用:克里斯梨/ alamy股票照片。
树戒指。信用:克里斯梨/ alamy股票照片。

It is, therefore, the job of scientists to draw out the climate data from the information the proxy provides. In the case of tree-rings, this will first involve “交叉约会” rings between a number of trees to identify the correct year for each ring.

这n, using records of local weather data, scientists can calibrate the rings against an observed climate record. Simpler relationships can be calibrated using a straightforward equation, but scientists use models for those that are more complex.

如果两个数据源,这棵树-rings can be used to cast further back – before the observed record began – to analyse the climate during the tree’s full lifetime. (Seelater section更多关于校准代理数据。)

树木戒指记录可以回到很长的路上,注意到臭名药物:

“这longest continuous tree-ring record – that includes a measurement for each year – is the German oak-pine chronology that dates back to 10,461BC…But for palaeoclimate purposes, tree-rings are mostly used to study the past ~500 to 2,000 years.”

And there are subtleties around which locations are best suited to certain analyses, explains Trouet:

“Trees grow a lot – and form wide rings – under favorable climate conditions. These can be wet conditions in dry regions, such as the American southwest, or warm conditions in cold regions, such as the European Alps or Scandinavia…To reconstruct past temperature, we use tree-rings from cold regions. To reconstruct past drought conditions, we use tree-rings from dry regions.”

当然还有其他并发症。戒指在树上最突出的树木全年经历明确界定的季节。这意味着“中间人的树木对气候比热带树木的氛围更敏感”,Rojas说:

“所以欧洲是良好的,北美,北亚,南美洲以及沿着安第斯山脉,有很多树木可以使用。”

In contrast, tropical trees are more of a challenge for dendrochronology, although some species do still form annual rings.

这可以在上面的地图中看到 - 大多数树木数据来自北半球的温带和北方林。在热带地带中,树圈数据不是不可能的,增加了臭味 - 有数百个记录可用,有“肯定潜力”。

化学

Moving onto chemical proxies, one example is同位素。这提供了谈论最着名的古古典气候档案馆之一 - 冰芯的机会。

这些冰气缸钻出冰盖和冰川,可以跑到几公里。地球的冰盖和冰川从数千年的降雪中建立了一大千年,每层都会随着时间的推移而压实 - 捕获微小的空气气泡。通过冰仔细采用横截面,因此提供了这些气泡的时间表。

在美国科罗拉多州国家冰核实验室储存在-36C的冰芯的一米米。信用:吉姆西部/ alamy股票照片。
在美国科罗拉多州国家冰核实验室储存在-36C的冰芯的一米米。信用:吉姆西部/ alamy股票照片。

气泡通过冰盖或冰川的寿命是大气的微小样本。

While scientists can analyse the bubbles directly to ascertain the makeup of the atmosphere in the distant past, they also contain a proxy to估计过去的温度- 氧同位素“18O“。

同位素是与不同数量相同的相同元件的形式neutrons在原子的核内。最丰富的氧同位素是16O那which has eight neutrons, giving it an overall atomic mass of 16 (eight neutrons plus eight质子)。

18O has an extra two neutrons, giving it an atomic mass of 18. As a result, atoms of 18O are very slightly heavier than 16O. This weight difference has implications when water is evaporated from the oceans and falls as snow at the Earth’s poles, explainsDr Robert Mulvaney那a glaciologist at theBritish Antarctic Survey,在一篇文章中Scientific American

“简单地说,从海洋表面蒸发含有沉重同位素的水分子需要更多的能量,并且随着潮湿的空气被输送并冷却,含有较重同位素的水分子优先损失沉淀。”

Both of these processes are temperature dependent, says Mulvaney, which means that measurements of 18O in ice cores can tell scientists how warm the climate was at that time in the past.

研究氧同位素 - 大部分involving marine sediments-“was fundamental to a great discovery of 20th century science that the冰夜Pearson说,是由地球的轨道变量的偏心,轴向倾斜和PREASION“。

这些轨道变量 - 被称为“米兰科赫循环” after Serbian scientist Milutin Milankovitch who developed the theory – describe how a collection of variations in the Earth’s position relative to the sun can trigger both the beginning and end of ice ages.

身体的

Finally, for the last of the three categories, an example of a physical proxy is marine and lake sediments.

每年,数十亿吨沉积物被冲入世界各地的湖泊和海洋中。这些沉积物随着时间的推移积累,每年都会在层上添加层。因此,钻孔钻孔通过海或湖泊的床,可以提供沉积物的时间表 - 而且,气候变化。

来自德国不来梅大学海洋环境科学中心的墨西哥湾的沉积物核心。乐动体育 英超信用:DPA图片联盟/ Alamy股票照片。
来自德国不来梅大学海洋环境科学中心的墨西哥湾的沉积物核心。乐动体育 英超信用:DPA图片联盟/ Alamy股票照片。

这些沉积物的尺寸,形状,结构和颜色都可以提供关于时间气候的线索。例如,解释了US Geological Survey website

“科学家使用沉积物粒子的尺寸和形状来确定沉积物是否被运输,运输有多远,以及运输环境的有多高能量(例如,海浪在海滩上撞到粗砂颗粒后面的海浪,而且非常小谷物在非常静止的条件下沉积。“

但沉积物也是其他代理的非常重要的档案。与科学家们可以分析的各种化石埋藏着埋藏。“Foraminifera“是一个经典的例子,解释了Pearson:

“Foraminifera是 - 大多数 - 由单细胞生物分泌的微观壳,其生活在浮游生物或海上床上。在正确的埋葬条件下,他们的壳可以无限期地在几乎完善的条件下存活。这些贝壳在海底上慢慢地积聚,生产或多或少连续的代理记录。“

Foraminifera从海水中提取的碳酸钙构建它们的壳。同位素分析可以揭乐动体育app苹果j示海洋中的条件 - 而且,在那些生物体活着时,气候变化。

硅藻.。Credit: The Natural History Museum / Alamy Stock Photo.
硅藻.。Credit: The Natural History Museum / Alamy Stock Photo.

硅藻.是另一个微生物 - 这次用二氧化硅制成的壳。虽然foraminifera是restricted to marine and coastal environments,硅藻也被发现在内陆湖泊中。沉积物是一个重建干旱历史的主要自然档案它们含有的硅藻已经被使用,例如,一起拼接美国中西部极端干旱记录

Leaf waxes found in the marine sediments are also a useful climate proxy, adds Cluett:

“Leaf waxes are a group of simple organic molecules that are widely produced by vegetation, both on the terrestrial landscape and within lakes… [They] are useful biomarkers because plants incorporate hydrogen atoms into the structure of these molecules from the water – generally derived from precipitation – in which they use to grow.”

叶蜡的同位素分析乐动体育app苹果j“提供类似于冰芯中稳定水同位素的稳定水同位素的陆地气候记录”。例如,这种方法已被使用,例如,在11,000-5,000年前的“绿色撒哈拉”期间重建降雨模式,当时该区域支持不同植被,永久湖泊和人口

由于代理数据自然累计,其记录可以延伸到该介质存在。因此,对于冰芯中的同位素,例如,只要冰盖或冰川已经到位即可。海洋沉积纪录可以是数百万年,一路走回白垩纪时期100米年 - 恐龙的时间。这反映了海底比树木,珊瑚甚至冰盖所存在的事实。

探讨地球历史的最古老的部分,古生物性研究员必须使用岩层,解释杰西卡蒂德尼博士,亚利桑那大学的副教授和一个副教授lead author关于IPCC的第六次评估报告。她讲碳简短:乐动体育下载app

“在大约100亿年前学习气候变化,我们必须在陆地上工作,其中包含已被思维的海洋或陆地沉积物。”

锂化是沉积物在压力下压实的过程,形成固体岩石。这可能自然地“露出”景观,Tierney或科学家可能会钻入他们来获得核心。她补充说:

“In these ancient archives, we find evidence of truly extreme climate changes, like theend-Permian global warming和大众灭绝,和'雪球地球’ – a time when the Earth was totally covered in ice.”
在孟菲普山,萨默塞特,英国的石灰石露头。信用:克雷格木匠摄影/ alamy股票照片。
在孟菲普山,萨默塞特,英国的石灰石露头。信用:克雷格木匠摄影/ alamy股票照片。

虽然海洋沉积物的潜在记录长,但可以衍生的采样“间隔”更有限。这些数据可能只能将气候变化从一个世纪显示到下一个世纪,而树圈和石笋的数据可以显示在一年到下一个的变化。(有关不同类型的代理和档案,请参阅下面的部分。)

代理数据可以帮助深入了解人类对其环境变化的方式。例如,一个乐动体育 英超科学推进来自今年早些时候的纸张从17个沉积物核心使用的花粉和木炭数据 - 以及考古学调查以及如何在英国南部的西南南部的斯普利群岛的居民适应在4-5,000年龄约4-5,000岁的青铜时期改变海平面几年前。

Finally, it is worth highlighting another form of palaeoclimate archive – historical documents. These can be diaries, logbooks, photographs andeven paintings携带直接和间接的气候信息。

For example, English manorial accounts from the Middle Ages – financial and farming records kept by rural estates – provide detailed information on harvests and milk production. Scientists have used these records to团结在一起的干旱记录that hit England hundreds of years ago.

(Left): Brenva glacier, Italy, 1897. (Right): Historical meteorological recordings from the UK colonial registers, 1830.
(Left): Brenva glacier, Italy, 1897. (Right): Historical meteorological recordings from the UK colonial registers, 1830. Carbon Brief composite. (Click to expand).

另一个例子是如何历史照片和速写地图可用于重建冰川长度的变化 - 以及气候波动。

其他形式包括天气描述个人日记,记录葡萄收获日期那and descriptions of wind, weather and sea ice coverin ship logbooks

回到顶部

代理数据的不同来源是什么?

这table below summarises the key archives of climate proxies, the data they provide and the typical intervals and time spans that they cover.

代理档案 测量类型 典型的间隔 典型的时间跨度 Description
钻孔 温度 世纪 数百年 钻孔are narrow shafts drilled into the Earth, typically to extract substances such as water or oil. As heat at the surface slowly diffuses vertically down into the Earth, temperature readings taken a different depths through the borehold can indicate past temperatures at the surface. While borehole measurements are taken directly, they are classed as a proxy as they are used to indirectly measure past temperatures.
Corals and sponges 同位素,化学性质,生长速率 Centuries Corals build their hard skeletons from calcium carbonate they extract from seawater. The density of those skeletons changes from season to season and year to year with fluctuations in sea temperature, water clarity and available nutrients. These variations are revealed in annual growth rings similar to those in trees. Scientists take small samples from the corals to analyse these rings, which sometimes need x⁠–rays to identify. Isotope analysis of the oxygen atoms contained in the skeleton can also signal changes in variables such as ocean temperature. Although sponges do not build hard exoskeletons like corals, they grow by putting on layers of calcium carbonate or silicon dioxide, which also produces growth rings.
Glaciers Glacier extent 数百年 Mountain glaciers grow and retreat over time in response to the climatic conditions and so records of their length can be used as a climate proxy. Records ⁠– in the form of measurements, photos and paintings ⁠– often go back several hundred years. Carbon dating of plants and other organic material that is uncovered by a retreating glacier can also indicate past glacier extent.
历史documents 历史 小时到日 数百年 Direct and indirect information about the climate can be gleaned from historical documents. These include accounts of weather in newspapers, ship logs, personal diaries and church records, while documented harvest dates ⁠– for grapes and other crops, for example ⁠– can also indicate climatic conditions of the past. Photos, maps, charts and paintings can all be sources of data too.
冰核 同位素,灰尘,积累速度,温室气体浓度 Hundreds of thousands of years Ice sheets and glaciers form from the accumulation and compaction of snow over thousands of years. Drilling down through the layers of ice to retrieve a "core" provides a cross⁠–section of that accumulation and hence a timeline of snow build⁠–up. The information contained in the ice includes dust from volcanic eruptions, air bubbles that provide sample of past atmospheres, and isotopes that offer evidence of past climates.
Lake sediments 身体的and chemical properties, shells, pollen, insects, molecular fossils, isotopes 几十年到几个世纪 数百万年 沉积物被洗净到湖泊中并通过时间积累。像海洋沉积物一样,湖泊沉积物提供各种气候代理。叶片蜡等分子化石的碳和氢同位素分析(来自植物叶片上的保护乐动体育app苹果j涂层)可用于推断出景观和水循环的变化。昆虫的僵化遗体可用于推断过去的气候。从开花植物的花粉颗粒保存在湖泊沉积物中,可用于推断植被和气候的变化。湖泊沉积物中的木炭量可用于推断出射频和强度的变化。
黄土 粉尘积累,物理和化学性质,分子化石 几个世纪到千年 数百万年 风吹淤泥的形成,运输和沉积称为“黄土”和“Eolian粉尘”⁠-与气候变化密切相关。当冰盖和冰川覆盖大部分土地时,在干燥时期⁠ - 例如,在干燥期间记录大型除尘沉积物。土地上的灰尘沉积物可以达到数十或数百米厚。
Marine sediments 物理和化学性质,贝壳,花粉,分子化石,同位素 几个世纪到千年 Tens of millions of years 每年都会看到数十亿吨沉积物积聚在世界各地的海洋床上。这些沉积物捕获了时间的气氛⁠-包括微生物的气氛,例如Foraminifera壳,以及分子化石,如叶蜡。这些线索的同位素乐动体育app苹果j分析可以透露有关气候的信息。沉积物本身的性质⁠ - 如其尺寸,形状,结构和颜色⁠-也可以随着气候改变。
Pack rat middens Pollen, insects, plant remnants, bones, teeth, isotopes Decades Tens of thousands of years 包装大鼠,也称为Woodrats,构建可以随着时间的推移结晶的碎片堆,这些含量在尿液中保持内容数千年。这些“Middens”含有植物,骨骼,牙齿,昆虫,壳种和种子的残余物,可用于其同位素含量,提供气候信息。
岩石露头 物理和化学性质,贝壳,花粉,昆虫,牙齿,植物化石,分子化石,同位素 千禧年 Hundreds of millions of years 古代沉积岩提供了地球气候最古老的档案。与海洋和湖泊沉积物一样,可以在其中测量许多不同的代理。通过对口气的分析,工厂化石提供了重建二氧化碳水平的机会。乐动体育app苹果j化石哺乳动物的牙齿的形状和状况可以提供有关过去的气候条件的信息。例如,食草动物牙齿上的磨损表面可以指示植被⁠-,因此,过去的气候⁠。
Seal pelts Isotopes Decades 几个世纪到千年 密封毛皮/皮肤已经使用了数千年来制造温暖和防水衣服和鞋类。这些皮肤含有各种元素,如碳和氮,即累积的碳和氮气累积了它们所消耗的猎物。因此,不同同位素的浓度可以表明过去的食物链的结构,因此的环境条件。
speleothems. Isotopes, chemical properties 几十年到几个世纪 Tens of thousands of years Speleothems是洞穴形成,如钟乳石(悬挂在洞穴天花板)和石笋(从地板上升)。它们是由矿物沉积物的构建形成,主要是碳酸钙通过岩石渗透地进行地下水携带。同位素和微量元素的变化可用于确定过去的气候。
Tree rings Ring width, wood density, isotopes 几千年来 树的年增长率通常通过行李箱记录在戒指中。每一圈都有一个灯光部分(春夏/初夏的快速增长)以及每年增长的夜晚(晚夏/秋季缓慢增长)。增长量⁠-,因此环的宽度⁠-反映了时间的气候条件。例如,树木在温暖,潮湿的条件下越来越快地生长,冷干燥和干燥。树木可以是“核心”,以去除行李箱的小横梁部分,以便在不损坏树的情况下进入环。还可以分析木材内的同位素,以普遍存在的气候信息。

测量类型:温度

典型的间隔:世纪

典型的时间跨度:数百年

描述:钻孔是钻孔进入地球的窄轴,通常用于提取水或油等物质。随着表面的热量缓慢地扩散到地球中,温度读数通过堆部的不同深度拍摄可以指示表面的过去温度。虽然直接采集钻孔测量,但它们被归类为代理,因为它们用于间接测量过去的温度。

测量类型:同位素,化学性质,生长速率

典型的间隔:年

典型的时间跨度:几个世纪

描述:珊瑚从海水中提取的碳酸钙构建它们的硬质骨架。这些骷髅的密度从季节和一年的季节和年度发生变化,在海水温度,水清晰度和可用营养中的波动。这些变化在年生长戒指中揭示了与树木中的每年增长环。科学家从珊瑚采取小型样品来分析这些戒指,有时需要X¼射线来识别。骨架中包含的氧原乐动体育app苹果j子的同位素分析还可以在诸如海洋温度的变量中发出变化。虽然海绵不像珊瑚这样的硬脑膜,但它们通过放置碳酸钙或二氧化硅层而生长,这也产生了生长环。

测量类型:冰川范围

典型的间隔:年

典型的时间跨度:数百年

描述:山地冰川在响应气候条件下,随着时间的推移,它们的长度记录可以用作气候代理。记录⁠-以测量,照片和绘画的形式⁠-经常回到几百年。由退缩冰川未覆盖的植物和其他有机材料的碳约会也可以表明过去的冰川范围。

测量类型:历史

典型的间隔:小时至日

典型的时间跨度:数百年

描述:可以从历史文件中收集有关气候的直接和间接信息。其中包括报纸,船舶日志,个人日记和教堂记录的天气账户,而记录的收获日期⁠-葡萄和其他作物,例如⁠-也可以表明过去的气候条件。照片,地图,图表和绘画也可以是数据的来源。

测量类型:同位素,灰尘,累积率,温室气体浓度

典型的间隔:年

典型的时间跨度:数十万年

Description: Ice sheets and glaciers form from the accumulation and compaction of snow over thousands of years. Drilling down through the layers of ice to retrieve a "core" provides a cross⁠–section of that accumulation and hence a timeline of snow build⁠–up. The information contained in the ice includes dust from volcanic eruptions, air bubbles that provide sample of past atmospheres, and isotopes that offer evidence of past climates.

测量类型:物理和化学性质,贝壳,花粉,昆虫,分子化石,同位素

典型的间隔:数十年到几个世纪

典型时间范围:数百万年

Description: Sediments are washed into lakes and accumulate through time. Like marine sediments, lake sediments offer a variety of climate proxies. Carbon and hydrogen isotope analysis of molecular fossils like leaf waxes (coming from the protective coat on the leaves of plants) can be used to infer changes in the landscape and the water cycle. The fossilised remains of insects can be used to infer past climate. Grains of pollen from flowering plants are preserved in lake sediments, and can be used to infer changes in both vegetation and climate. The amount of charcoal in lake sediments can be used to infer changes in fire frequency and intensity.

测量类型:粉尘积累,物理和化学性质,分子化石

典型的间隔:几个世纪到千年

典型时间范围:数百万年

描述:风吹淤泥的形成,运输和沉积为“黄土”和“Eolian粉尘”⁠-与气候变化密切相关。当冰盖和冰川覆盖大部分土地时,在干燥时期⁠ - 例如,在干燥期间记录大型除尘沉积物。土地上的灰尘沉积物可以达到数十或数百米厚。

测量类型:物理和化学性质,贝壳,花粉,分子化石,同位素

典型的间隔:几个世纪到千年

典型时间跨度:数百万年

描述:每年看到数十亿吨沉积物积累在世界各地的海洋床上。这些沉积物捕获了时间的气氛⁠-包括微生物的气氛,例如Foraminifera壳,以及分子化石,如叶蜡。这些线索的同位素乐动体育app苹果j分析可以透露有关气候的信息。沉积物本身的性质⁠ - 如其尺寸,形状,结构和颜色⁠-也可以随着气候改变。

测量类型:Pollen, insects, plant remnants, bones, teeth, isotopes

典型的间隔:几十年

典型的时间跨度:数千年

描述:包装大鼠,也称为Woodrats,构建可随时间结晶的碎片桩,其尿液会保持内容数千年。这些“Middens”含有植物,骨骼,牙齿,昆虫,壳种和种子的残余物,可用于其同位素含量,提供气候信息。

测量类型:物理和化学性质,贝壳,花粉,昆虫,牙齿,植物化石,分子化石,同位素

典型的间隔:千年

典型时间范围:数亿年

描述:古代沉积岩提供最古老的地球气候档案。与海洋和湖泊沉积物一样,可以在其中测量许多不同的代理。通过对口气的分析,工厂化石提供了重建二氧化碳水平的机会。乐动体育app苹果j化石哺乳动物的牙齿的形状和状况可以提供有关过去的气候条件的信息。例如,食草动物牙齿上的磨损表面可以指示植被⁠-,因此,过去的气候⁠。

测量类型:Isotopes

典型的间隔:几十年

典型的时间跨度:几个世纪到千年

描述:密封毛皮/皮肤已经使用了数千年来制造温暖和防水衣服和鞋类。这些皮肤含有各种元素,如碳和氮,即累积的碳和氮气累积了它们所消耗的猎物。因此,不同同位素的浓度可以表明过去的食物链的结构,因此的环境条件。

测量类型:Isotopes, chemical properties

典型的间隔:数十年到几个世纪

典型的时间跨度:数千年

描述:Speleothems是洞穴形成,如钟乳石(悬挂从洞穴天花板)和石笋(从地板上升)。它们是由矿物沉积物的构建形成,主要是碳酸钙通过岩石渗透地进行地下水携带。同位素和微量元素的变化可用于确定过去的气候。

测量类型:环宽,木质密度,同位素

典型的间隔:年

典型的时间跨度:千年

Description: The annual growth of a tree is typically recorded in rings through the trunk. Each ring has a light part (fast growth in spring/early summer) and a dark part (slow growth in late summer/autumn) for each year of growth. The amount of growth ⁠– and, thus, the width of the rings ⁠– reflects the climatic conditions of the time. For example, trees tend to grow faster in warm, wet conditions, and slower in cold and dry. Trees can be "cored" to remove a small cross⁠–section of the trunk in order to access the rings without damaging the tree. Isotopes within the wood can also be analysed to provde climate information.

Table produced with the help of Dr Jessica Tierney.

如何校准和使用代理数据?

由于代理没有直接测量气候变量,因此需要转换以将氧同位素值,树木宽度或其他代理测量变成气候变量,例如温度或降雨。转换被称为“校准” and usually takes one of two forms.

最近近期的高分辨率代理可以是“校准时间“。This is where researchers look to see what the relationship is between the proxy values and direct observations during the recent period in which climate observations exist, and use that relationship to infer values in the more distant past.

For example, if tree-ring width is closely related to temperature during the 1850-2000 period, scientists can use the tree-ring record before 1850 – say, from 1500 to 1850 – to reconstruct the temperature of that period.

第二种方法是“校准空间“。这涉及测量跨越空间范围的现代环境的代理,其中控制因素 - 例如温度 - 是众所周知的。当无法与观察记录的直接比较时使用该技术。

例如,可以在现代湖泊沉积物中测量不同种类的花粉,以跨越一系列温度以产生校准。在某些情况下,通过在不同温度下培养生物 - 例如Foraminifera或藻类,也可以在实验室中进行校准。

Foraminifera. Credit: Scenics & Science / Alamy Stock Photo.
Foraminifera. Credit: Scenics & Science / Alamy Stock Photo.

然而,在某些情况下,超过一个因素会影响代理估计。例如,树木宽度可能取决于降雨和温度的位置,研究人员希望确保它们不会在低温下误解干旱。研究人员可以利用复杂的统计模型来区分影响代理测量的不同因素。

除此之外relationship between the proxy value and the climate variable may not hold steady over time. For example, if a changing climate makes tree-ring width – and associated tree growth – more rainfall-dependent than temperature-dependent, the proxy may cease being useful. This has occurred in一些刷毛松树记录

An example of this is the “发散问题“ - 某种树木木质密度记录的趋势”脱钩“从1950年之后的观察到的温度。虽然世界上一些地区的木质密度和树木宽度在1950年之前的观察到的温度良好,但一些 - 虽然不是全部 - 树木记录未能在该点之后捕获快速观察的变暖。

然而,这些事件存在问题,因为研究人员必须尝试并确保在观察记录的可用性之前的其他时段期间没有发生在代理值和气候变量之间的关系中的相似分歧。

In some cases, limited historical observations prior to the advent of modern climate monitoring networks可以使用for providing a cross-check on reconstructions based on other proxy records and for validating past model simulations.

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How does proxy data inform climate science?

如上所述,观察到的全球温度记录只回到1850年,在许多地区,温度记录甚至更短。其他气候记录 - 如地球大气,流出,飓风,野火或太阳能输出的组成 - 可能有更短的历史观测记录。

To understand changes across different aspects of the Earth system prior to the start of instrumental records, scientists, therefore, have to rely on proxy measurements.

代理人在许多方面都是有助于发展现代气候科学的方式。乐动体育 英超例如,过去80万年的温室浓度和温度的代理记录有助于科学家了解冰河年龄循环的驱动因素 - 包括二氧化碳的关键作用进行中。

While many studies have examined individual proxy types and locations – such as a specific coral reef or cave – over the past few decades there has been a focus on using a number of different proxies in conjunction to get a better understanding of regional or global changes.

This is important, as a single location such as Antarctica may exhibit much larger swings in temperature or other climate variables over time than the globe as a whole. These “多分歧气候重建“在其他因素中检查了空气温度,干旱,降水,海面温度,海平面,海冰和植被的变化。

例如,最近Naturestudy pulled together “a large collection of geochemical proxies for sea surface temperature” in an effort to reconstruct global temperatures during the most recent ice age, known as theLast Glacial Maximum。然后,研究人员对其产生的结果验证了衍生自Ice Cores和Speleothems的180同位素记录。

最大的多分X重建之一是从过去的全局变化(PAGES) project, a collaboration between thousands of palaeoclimatologists from 125 different countries that began back in 1991.

2019年,他们published彻底分析了过去2000乐动体育app苹果j年的全球表面温度 - 称为PAGES 2K项目。下图显示了在团队审查的所有不同方法上的结果重建。黄线显示​​他们检查的所有古古怪的代理重建的中位数,而黄色阴影区域显示了代理重建的不确定性范围(2.5%至97.5百分位数)。红线显示1850年后观察到的全局表面温度。

全球平均地表温度重建(你们llow line) and uncertainties (yellow range) for the years 0-2000 period from the第2K联盟页面随着来自COWTAN的观察以及从1850-2017开始的观察。可用的数据NOAA Paleoclimate Archive

研究人员还在全新的全新世 - 过去12,000年跨越的现代地质时代制作了古怪的地位重建。下图显示了一系列重建(灰度)以及全局平均温度的中值估计(黄线)。

全球平均地表温度重建(你们llow line) and uncertainties (grey range) for the period from 10,050BC to AD1950 from the温度12K数据库。Recent observations are not shown due to the low temporal resolution of the underlying data. Data available in theNOAA Paleoclimate Archive

(It is worth noting that there is some disagreement between different methods of Holocene temperature reconstructions, with最近的一篇论文suggesting that the holocene maximum temperatures may have been considerably lower than other proxy reconstructions have estimated.)

这further back in time reconstructions go, the较低的时间分辨率they tend to have. In other words, records from 10,000 years ago might only represent an average temperature value over a 100-year period or more, while more recent proxy data tends to be closer to 20-year averages.

这有点限制了科学家将早期代理重建的能力与现代温度记录进行比较,而无需应用类似的长期平均,虽然研究人员已经发现some ways to get around this problem.

除了了解过去的温度和其他气候变量的改变之外,代理数据还为科学家提供了如何在未来改变的内容。代理数据提供三个中的一个关键证据that scientists have used to better estimate the range of气候敏感性-which determines how much the Earth will warm in the future if CO2 concentrations double.

For example, explainsProf Dan Lunt那professor of climate science at theUniversity of Bristol那“50m years ago, CO2 concentrations were greater than today and the planet was substantially warmer. Proxies for CO2 allow us to quantify the former and proxies for temperature allow us to estimate the latter”. Scientists can use this information to estimate climate sensitivity.

然而,他补充说,与这些估计有相当大的不确定性。这是因为“我们没有完整的全球的地理覆盖,因为代理和气候之间的相关性并不完美”。除此之外气候的“敏感性”(当地球在不同的状态下,当大气中的CO2增加或减少时,地球的温度会发生多大的变化) - 如冰河时代 - 未来可能不是“可靠的指标”,因为它在未来的敏感性,Lunt说。

Proxy data can also help determine changes to海levelice coverand植被在过去的温暖时期。一个例子是前一个205,000年前的中间峡地期间 - 叫做eemian这可能比今天温暖或温暖 - 这可以提供关于所有这些因素如何随着世界变暖而变化的证据。

Another way that proxies inform climate science is through modelling. Proxy records can be used to help evaluate气候模型。Scientists run “环球” simulations of models to see how well they reproduce the past climate and proxy data is needed to test against the climate of the distant past.

这是两倍的好处,解释说:

“A model that agrees well with the proxy data can then be used with confidence to improve our understanding of that time period…[and] if a model agrees well with proxy evidence of the past, then in some cases this can give increased confidence in its simulation of the future.”

Lunt领导一个叫做国际建模项目DeepMIP(深度模型互通项目)。该项目旨在承认气候模型通常对地球相对近期评估的事实,而全球温度可能正在达到数百万年(“深度”)的水平,他解释道。

DeepMip使用代理数据评估模型并了解过去的气候系统,Lunt说 - “特别是超温早期的初级期限最佳(EECO,〜50米年前)和古世茂 - 何人热最大(PETM,〜55米前)”。

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What are the limitations of proxy data?

As the sections above highlight, the process of identifying, extracting, interpreting and calibrating proxy data to produce climate records is anything but straightforward. Such complicated techniques, therefore, have their pitfalls and limitations.

Cluett说,代理数据是间接的,所以Cluett说。因此,虽然代理正在记录环境的变化,但科学家需要考虑到当地条件和任何可能在游戏的范围内的任何更广泛的影响。

例如,在本地规模上,“代理与其环境之间的关系可能在不同的系统中不同,因此了解您所做的系统在准确地解释代理数据时至关重要”。

例如,Pearson,世界海洋中同位素的总体量随时间而变化。这影响了对个人记录的分析,他解释说乐动体育app苹果j:

“世界冰盖的大小的变化会改变整个海洋同位素比,因此对[代理]记录感到印记。”

Not all proxy records are made equal, points outDr Justin Martin那an ecologist at theUS Geological Survey。An ideal record is typically “long, accurately dated and of sufficiently high resolution over time to provide useful information”, he tells Carbon Brief. However, this is not always what scientists get, he says:

“一些代理不得perio封面很长时间d, or may only provide a relative estimate of climate variability over time that lacks certain dates. Others may only provide very coarse estimates of variability measured in decades, centuries or longer.”

所有代理人“受到一种方式的虚拟化的失败者”,添加了Pearson。

例如,通过历史文档,旧记录通常不太有用。一本关于温度重建的书US National Research Council注意到,在第一个千年广告中,有“在爱尔兰和挪威人中保留的天气记录”,但“他们的约会是不精确的,天气和气候的描述通常被夸大”。

所有这些并发症都意味着“可能存在相当大的错误栏,这不仅仅是我们的分析精度,而且校准了代理的程度是或者可以到目标的目标变量”,Pearson说。他补充说:

“For these reasons, there is a lot of technical literature on the subject and, in general, we like to use multiple proxies together, if we can.”

这些障碍也使古怪的气门成为“有点疯狂的科学”,Pearson笔记和“关于过去的某些了解是非常困难的”。乐动体育 英超尽管如此,他说:

“It is also very exciting because the timescales are potentially huge and the proxies we use are limited only by our scientific imagination and ability to measure things of interest.”

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