Nature: 指标季节性的分离揭示全球变暖已持续上万年
工业革命以来,人类活动引发的CO 2 度升高导致全球快速升温,显著影响着地球环境和人类 社会 。由于器测记录时限的有限性,通过地质记录定量重建过去温度,延长气候变化的 历史 ,对全面认识现代全球变暖在地球系统自然变率中的位置至关重要。
尽管古气候定量化目前已取得重要进展,但距我们最近的全新世(距今 11 700年以来),地质记录重建和古气候模拟的全球年均温变化存在显著差异。地质记录重建显示,温度在距今~10 000?6 000年处于峰值(“全新世大暖期”),其后逐渐下降,工业革命以来的全球变暖逆转了这一趋势(Marcott et al., 2013;Kaufman et al., 2020);然而,古气候模拟则显示,全新世年均温呈现整体上升趋势(Liu et al., 2014)(图1)。上述温度变化的巨大差异,被称为“全新世温度谜题(Holocene temperature conundrum)”(Liu et al., 2014),一直困扰着古气候学者。解开该谜团的关键在于厘清:气候代用指标是否存在季节性偏差?古气候模式的气候敏感性和反馈过程是否存在偏差?
图1 重建和模拟的全新世全球年均温度变化,蓝线为多指标重建结果,黑线为模拟的年均温,红线为模拟的夏季温度(改自Liu et al., 2014)
最近,美国罗格斯大学的Bova博士和合作者在Nature上发表论文,提出了一种有效分离季节性信号新方法(seasonal to mean annual transformation, SAT),更好地重建了季节和年均温度变化(图2)。
图2 SAT方法在IODP U1485钻孔末次间冰期和全新世时段温度重建中的应用(Bova et al., 2021)。(a、e)钻孔所在纬度(3 S)最相关季节(8月)和年均太阳辐射变化;(b、f)重建和模拟的季节性温度变化;(c、g)计算出的季节性偏差值(ΔSST);(d、h)校正后的年均海表温度变化
该方法的原理是:假设海表温度线性响应太阳辐射变化,重建温度变化(SST SN )与最相关的季节性太阳辐射的相关性,如高于其与年均太阳辐射的相关性,则认为重建温度存在季节性偏差;季节性偏差因子(ɑ s )由SST SN 与季节和年均太阳辐射的偏差值(ΔI)的线性回归获得(SST SN = ɑ s ΔI + ε s ),由此,得出重建温度的季节性偏差值(ΔSST = ɑ s ΔI ),进而获得校正后的年均温(MASST = SST SN - ΔSST)。季节性偏差因子的计算,基于末次间冰期(距今128 000-115 000年前)的海温重建数据,选择末次间冰期,原因在于该时期太阳辐射的季节性差异比全新世的大,而冰盖、温室气体等其他因素对温度的影响更弱,因此更易识别出温度的季节性信号。
首先,作者把这一方法应用到了位于巴布亚新几内亚东北部的海洋钻孔(IODP Site U1485)末次间冰期和全新世的温度重建(图2)。结果显示,重建温度与八月的太阳辐射变化最为相关,具有很好的季节性信号;校正后的年均海表温度变化在两个时段均呈现上升趋势,与同一地区的模拟结果基本一致(图2)。利用同样的方法,作者把模拟的季节性温度进行了校正,得到的年均温度变化趋势与模拟输出结果相一致,因此验证了方法的可靠性(图2)。
其次,作者进一步把SAT方法应用到40 S-40 N之间的海表温度重建(图3b)。结果显示,多数重建结果存在季节性偏差,且主要偏向于夏秋季,导致重建结果存在早中全新世大暖期(图3a、图3b);然而,校正后的年均温则显示,全新世呈持续升温趋势(图3b),与模拟结果基本一致(图3c);进而证实“全新世温度谜题”,可能主要源于气候代用指标的季节性偏差。
图3 全新世40 S-40 N海表温度重建、校正结果,以及温度变化机制(Bova et al., 2021)。(a)前人重建的全球年均温度变化(Marcott et al., 2013;Kaufman et al., 2020);(b)40 S-40 N海表温度重建结果(红线)和校正后的年均温度变化(蓝线);(c)模拟的年均温度变化及温室气体的贡献;(d)全球冰量变化和温室气体辐射强迫变化
在上述基础上,作者揭示出全新世年均海表温度长期增加的机理,全新世早中期(距今12 000-6 500年前)主要受冰盖、太阳辐射等驱动;而温室气体主导了包括工业革命以来,最近6 500年的全球变暖(图3c、图3d)。
主要参考文献
Bova S, Rosenthal Y. Liu Z. et al. Seasonal origin of the thermalmaxima at the Holocene and the last interglacial [J]. Nature, 2021, 589(7843):548–553.
Kaufman D, McKay N, Routson C, et al. A global database of Holocenepaleotemperature records [J]. Scientific Data, 2020, 7(1): 115.
Liu Z, Zhu J, Rosenthal Y, et al. The Holocene temperature conundrum[J]. Proceedings of the National Academy of Sciences, 2014, 111(34): E3501–E3505.
Marcott S A, Shakun J D, Clark P U, et al. A reconstruction ofregional and global temperature for the past 11,300 years [J]. Science, 2013,339(6124): 1198–1201.
(撰稿:张文超, 吴海斌 /新生代室)
校对:覃华清
全 球 变 暖
【前沿报道】Nature Geoscience:植被对早侏罗世全球变暖的响应
基于陆生植物孢粉及海洋浮游生物微体化石的研究显示,早侏罗世全球变暖事件(图阿尔期大洋缺氧事件)不仅破坏了海洋生态系统,也对陆地生态系统带来重大影响,且对陆地生态系统的影响明显早于海洋。
近期,瑞典自然 历史 博物馆古生物学系Slater等通过孢粉研究为回答上述问题提供了重要证据,成果发表于Nature Geoscience期刊(Slater et al., 2019)。孢粉是植物产生的孢子和花粉,因其数量大、抗腐蚀能力强,可以在古老地层中较好地保存下来。因此,沉积物中的孢粉组合已被广泛用于重建古植被演化及气候环境状况。Slater等在英国早侏罗世普林斯巴赫期及图阿尔期(Pliensbachian–Toarcian)浅海陆架沉积的页岩中获取了丰富的陆生植物孢粉和海洋浮游生物化石。结合沉积学及同位素研究,Slater与合作者重建了陆地生态系统对图阿尔期变暖事件的完整响应过程,发现此次变暖事件引发了陆地植物群的巨大转变。
在变暖事件初期,即普林斯巴赫期–图阿尔期界线至CIE之前(图1),陆地植物群即开始发生较大改变,由松柏类、种子蕨(产生双气囊花粉)及喜湿的蕨类和石松类为主的植物组合(图2a)转变为适应暖干环境的松柏类(主要为掌鳞杉科)和苏铁类(产生克拉梭粉及宽沟粉)为主的植物组合(图2b),孢粉丰度及多样性明显降低。相比而言,海洋中虽然发生了浮游生物组合的改变,但变化较小。
在变暖达到鼎盛的时候,即CIE期间,植物的丰度和多样性大幅度降低,植物组合以少量适应干热气候的松柏类(主要为掌鳞杉科)为主(图2c),并出现大量高温环境标志性花粉——脑形粉。同时,海洋生态系统也发生剧烈变化,鞭毛藻和多刺疑源类显著减少,球形亚类及青绿藻等藻类大量增加,并伴随着大量无定型有机物出现(图2c),指示了海水的富营养化。以上变化伴随着微球粒黄铁矿的出现,揭示了还原性的海洋环境。
变暖事件结束后,植物的丰度和多样性快速增加,恢复到事件之前的水平,但植物组合却发生了明显变化,掌鳞杉科、柏科及喜湿树种(产生周壁粉)占据主导地位(图2d、图2e)。海洋生态系统则基本恢复至事件前的面貌(图2e)。
图1 英国约克郡T-OAE期陆地植物和海洋生物记录。橘色条带为气候极热期;浅绿色及深绿色图谱分别为各类孢子和花粉丰度变化;蓝色及棕色图谱分别为各类海洋浮游生物及无定型有机物丰度变化; Mosses:苔藓;Club mosses:石松类;Ferns:蕨类;Bisaccate pollen:双气囊花粉;Classopollis:克拉梭粉;Cerebropollenites macroverrucosus:脑形粉;Perinopollenites:周壁粉;Chasmatosporites:宽沟粉;Cycadopites:苏铁粉;Dinoflagellate cysts:鞭毛藻囊泡;Sphaeromorphs:球形亚类;Tasmanites:一种青绿藻;Spiny acritarchs:多刺疑源类;Amorphous organic matter:无定型有机物
图2 T-OAE期海陆环境演变示意图,图例同图1。(a)普林斯巴赫期,气候湿润;(b)普林斯巴赫期/图阿尔期界线至CIE前,气候变暖具强季节性,陆地植被发生较大转变;(c)图阿尔期CIE时段,气候极暖具极端干/湿季,海陆生态系统发生剧烈变化;(d)图阿尔期CIE结束后藻类爆发阶段,陆地生态系统开始恢复,海洋生态系统恢复滞后;(e)图阿尔期藻类爆发后,海陆生态系统恢复,陆地植被组合已不同于事件前
该研究依据直观的孢粉证据重建的T-OAE时期气候暖干,并且具极端干/湿季(图2),与前人依据沉积特征推断的暖湿气候结论不同。海陆生态系统对比显示,全球变暖初期陆地植物群落即发生较大改变,而海洋生态系统变化较小;全球变暖鼎盛期海陆生态系统均发生剧烈变化。据此,作者认为由于海洋具有较高的热缓冲能力,全球变暖初期陆地生态系统受到的影响更为严重。该现象在地球更早的 历史 中也曾出现,如近期研究发现,由火山活动引发的二叠纪-三叠纪界线全球变暖使陆地植物先于海洋生物发生灭绝(Fielding et al., 2019)。
该论文作者接受了已有的“火山活动释放温室气体造成全球变暖进而引发生物灭绝”的观点,但亦有学者表示质疑。Nature Geoscience同时刊发针对该文章的评论,强调火山活动释放的汞对陆地植被的破坏不可忽视(Mander and McElwain, 2019)。目前,与二叠纪末生物灭绝(Wang et al., 2018)、白垩纪大洋缺氧事件(OAE 2)、白垩纪末生物灭绝(Percival et al., 2018)等事件相关的火山活动期均已获得汞同位素异常的证据。该研究虽获取了早侏罗世陆地生态系统演化的信息,但还需进一步研究全球范围内陆地生态系统演化过程及其机制。
参考文献:
C R, Frank T D, McLoughlin S, et al. Age and pattern of the southern high-latitude continental end-Permian extinction constrained by multiproxy analysis[J]. Nature Communications, 2019, 10(1): 385.
L, McElwain J C. Toarcian land vegetation loss[J]. Nature Geoscience, 2019, 12: 405-406.
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L M E, Jenkyns H C, Mather T A, et al. Does large igneous province volcanism always perturb the mercury cycle? Comparing the records of Oceanic Anoxic Event 2 and the end-Cretaceous to other Mesozoic events[J]. American Journal of Science, 2018, 318(8): 799-860.
S M, Twitchett R J, Danise S, et al. Substantial vegetation response to Early Jurassic global warming with impacts on oceanic anoxia[J]. Nature Geoscience, 2019, 12: 462-467.
X, Cawood P A, Zhao H, et al. Mercury anomalies across the end Permian mass extinction in South China from shallow and deep water depositional environments[J]. Earth and Planetary Science Letters, 2018, 496: 159-167.
(撰稿:王永达,杨石岭/新生代室)
美编:徐海潮
校对:李玉钤
The major reason of global warming is due to human activities, the green house gases such as carbon dioxide and nitrogen oxides produced by the industry traps the energy from the sun. If there is no such gas in the atmosphere, the earth will be too cold for any living organism to survive, it is natural to have some green house gases in the air and some people argue that even without human effect there are evidences show that the temperature of the earth increase and decrease in cycles, and now we are reaching another ice age. One of the concerns is that the green house gases increased so fast that it is now a big threat to all the species on the earth. The human activities that cause global warming are deforestation which means that less carbon dioxide can be converted back into oxygen, use of fossil fuels which releases the carbons that accumulated for many years and the consequences are the rising of sea level, melting of ice in the Antarctic and increase in temperature. Rising in sea level means that the space for the land organism decreases. Melting of ice mean the release of any harmful substances that may have been trapped thousand of years ago and also cause a further rise in sea level. The increase in temperature will also provide a better condition for bacteria and virus to grow which means more diseases.
这`` 你试着找下新加坡中学二年级快捷班的地理书 上面很详细的有写 包括各种污染只类的
Global warmingGlobal warming is an increase in the earth's temperature due to fossil fuels, industry, and agricultural processes caused by human, natural, and other gas emissions. This results in an increased emission of greenhouse gases. Short-wave solar radiation sinks into the Earth's atmosphere and warms its surface; while long wave infrared radiation emitted by earth's surface is absorbed, and then re-emitted by trace gases. Climate changes occur in our earth's atmosphere due to a buildup of greenhouse gases. Greenhouse gases can occur naturally as well as a result of human activities. Problems can occur when higher concentrations of greenhouse gases are present in our atmosphere because they have enhanced our earth's heat trapping capability. There are many misconceptions about global warming. Some believe that pollution causes global warming, but the fact is global warming is the result of burning fossil fuels, coal, and oil that release carbon dioxide. Another misconception is nuclear power causes climate change. Nuclear power actually reduces emissions of carbon dioxide when used in place of coal. Some believe that global warming means that it will become warmer all over. The name is misleading because in some places, it will actually become colder. The majority of scientists believe global warming is a process underway and that it is human-induced. The greenhouse gases are carbon dioxide, methane, and nitrous oxide. These gases occur naturally. The Earth uses those gases to warm its surface. Carbon dioxide is released into the atmosphere when solid waste, fossil fuels, wood, and wood products are burned. Each greenhouse gas absorbs heat differently. If natural gases did not occur, the temperatures would be degrees cooler than the current temperatures. These gases trap heat and cause the greenhouse effect, rising global temperatures. Human activities add to the levels of these gasses, causing more problems. The burning of solid waste, fossil fuels, and wood products are major causes. Automobiles, heat from homes and businesses, and factories are responsible for about 80% of today's carbon dioxide emissions, 25% of methane, and 20% of the nitrous oxide emissions. The increase in agriculture, deforestation, landfills, industrial production, and mining contribute a significant share of emissions too. The gases released into the atmosphere are tracked by emission inventories. An emission inventory counts the amount of air pollutants discharged into the atmosphere. These emission inventories are used by many organizations. The Centers for Disease Control have been involved in studying global warming's effect on human health. Global warming is a danger to a human's health. Its affect on climate can adversely affect humans. Plagues have been attributed to global warming. An increase in temperature can result in a longer life cycle for diseases or the agents spreading them. Living in a warm area makes egg production a quicker process. Global warming will lead to more precipitation, which enables infectious diseases to be more easily contracted and spread. Effects of global warming on human health might not be immediately detected. Global warming can affect our future ability to obtain food. As climates change, plants and animals will change, leading to a change in the eating patterns of humans. An increase in precipitation is one result of global warming that could have devastating effects. First, the quality of crops would be affected by an increase in precipitation. Second, increasing rain could lead to an increase in soil erosion. There are ways that you can help prevent global warming. Car pooling, auditing the energy in your home, buying fuel-efficient cars, and reducing the electricity in your home are ways to help prevent global warming. You can also write to your local congress representative or your local newspaper in response to stories, which say global warming, does not exist. Government authorities can help by passing laws to reduce emissions from factories. They can also form a treaty with other countries to legally bind limits on emissions of heat trapping gases. The future of emissions damage depends on several factors, demographics, economics, technology, policies and institutional developments. Future predictions do not look good for this planet if nothing is done. Without the help of emissions control policies, CO2 levels are projected to be 30 -150% higher in 2100. Our renewable resources will be very limited. With cooperation from citizens and government officials, we can slow the effect of global warming by reducing greenhouse gas emissions.
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