One of the most difficult aspects of deciding whethercurrentclimaticeventsrevealevidenceof theimpactof human activities is that it is hard to get ameasureof what constitutes the naturalvariabilityof theclimate. We know that over the pastmillenniatheclimatehas undergonemajorchanges without anysignificanthuman intervention. We also know that the globalclimatesystem is immenselycomplicatedand that everything is in some way connected, and so the system iscapableof fluctuating in unexpected ways. We needthereforeto know how much theclimatecanvaryof its ownaccordin order tointerpretwithconfidencetheextentto which recent changes are natural asopposedto being the result of human activities.

Instrumentalrecords do not go back far enough to provide us withreliablemeasurements of globalclimaticvariabilityon timescales longer than acentury. What we do know is that as we include longer time intervals, therecordshows increasingevidenceof slow swings inclimatebetween different regimes. To build up a better picture of fluctuationsappreciablyfurther back in time requires us to use proxy records.

Over long periods of time, substances whosephysicaland chemical properties change with theambientclimateat the time can be deposited in asystematicway to provide acontinuousrecordof changes in those propertiesovertime, sometimes for hundreds or thousands of years. Generally, the layering occurs on anannualbasis, hence the observed changes in the records can bedated. Information ontemperature,rainfall, and other aspects of theclimatethat can be inferred from thesystematicchanges in properties is usually referred to as proxydata. Proxytemperaturerecords have been reconstructed from icecoredrilled out of the central Greenland ice cap, calcite shells embedded in layered lake sediments in Western Europe, ocean floorsedimentcores from thetropicalAtlantic Ocean, ice cores fromPeruvianglaciers, and ice cores from easternAntarctica. While these records provide broadlyconsistentindications thattemperaturevariations canoccuron a globalscale, there arenonethelesssomeintriguingdifferences, which suggest that thepatternoftemperaturevariations in regional climates can also differsignificantlyfrom each other.

What the proxy records make abundantlyclearis that there have beensignificantnatural changes in theclimateover timescales longer than a few thousand years. Equallystriking, however, is therelativestabilityof theclimatein the past 10.000 years (the Holocene period).

To theextentthat thecoverageof the globalclimatefrom these records can provide ameasureof its truevariability, it should atleastindicatehow all the natural causes ofclimatechange have combined. These include thechaoticfluctuations of theatmosphere, the slower but equallyerraticbehaviorof the oceans, changes in the land surfaces, and theextentof ice and snow. Also included will be any variations that have arisen fromvolcanicactivity,solaractivity, and, possibly, human activities.

One way toestimatehow all the various processesleadingtoclimatevariabilitywillcombineis by using computer models of the globalclimate. They can do only so much torepresentthe fullcomplexityof the globalclimateand hence may give only limited information about naturalvariability. Studies suggest that todatethevariabilityin computer simulations isconsiderablysmaller than indataobtained from the proxy records.

Inadditionto theinternalvariabilityof the globalclimatesystem itself, there is the addedfactorofexternalinfluences, such as volcanoes andsolaractivity. There is a growing body of opinion that both thesephysicalvariations have a measurableimpacton theclimate. Thus we need to be able to include these in our deliberations. Somecurrentanalysesconcludethat volcanoes andsolaractivityexplain quite aconsiderableamountof the observedvariabilityin the period from the seventeenth to the early twentieth centuries, but that they cannot be invoked to explain the rapid warming in recent decades.

Questions:
question_stem: According to paragraph 1, which of the following must we find out in order to determine the impact of human activities upon climate?
choices: tag: A
text: The major changes in climate over the past millennia

tag: B
text: The degree to which the climate varies naturally

tag: C
text: The best method for measuring climatic change

tag: D
text: The millennium when humans began to interfere with the climate
answer_key: B
explanation: B 以 human activities 做关键词定位至第一句，说在判断人类对气候的影响之前必须断定自然的影响，所以 B 正确。A 和 D 都提到了 millenium，这是这句话没说到的，所以两个都错；C 的 best method 也没说。

question_stem: According to paragraph 2, an advantage of proxy records over instrumental records is that
choices: tag: A
text: they are more-reliable measures of climatic variability in the past century

tag: B
text: they provide more-accurate measures of local temperatures

tag: C
text: they provide information on climate fluctuations further back in time

tag: D
text: they reveal information about the human impact on the climate
answer_key: C
explanation: C 以 proxy records 做关键词定位至最后一句，a better picture of fluctuations further back in time，指的是时间更久远，所以答案是 C，这个比较简单，跟文章说的完全一样。

question_stem: Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
choices: tag: A
text: Because physical and chemical properties of substances are unchanging, they are useful records of climate fluctuations over time.

tag: B
text: For hundreds or thousands of years, people have been observing changes in the chemical and physical properties of substances in order to infer climate change.

tag: C
text: Because it takes long periods of time for the climate to change, systematic changes in the properties of substances are difficult to observe.

tag: D
text: Changes in systematically deposited substances that are affected by climate can indicate climate variations over time.
answer_key: D
explanation: D, 去掉定语从句后，原文变成 substance can be deposited to record blabla，A 和 C 的因果关系是硬造出来的，原文没有，错；而且 A 说 unchanging，原文是变化，A 说反；B 原文是 record，不是 infer，B 错；而且 C 说 difficult to observe，原文没说，错；D 正确。

question_stem: According to paragraph 3, scientists are able to reconstruct proxy temperature records by
choices: tag: A
text: studying regional differences in temperature variations

tag: B
text: studying and dating changes in the properties of substances

tag: C
text: observing changes in present day climate conditions

tag: D
text: inferring past climate shifts from observations of current climatic changes
answer_key: B
explanation: B 以 peoxy temperature records 做关键词定位至第四句，本句说了很多重建温度的很多方法，无论是冰川，沉积物还是碳酸盐，都属于 substance，所以 B 正确，其他都没说。

question_stem: The word “striking” in the passage is closest in meaning to
choices: tag: A
text: noticeable

tag: B
text: confusing

tag: C
text: true

tag: D
text: unlikely
answer_key: A
explanation: striking: 显著的，吸引人的。A 是显著的，值得注意的；B 是令人困惑的；C 是正确的；D 是不可能的。所以 noticeable 引人注意的正确。对应原文：Equally striking, however, is the relative stability of the climate in the past 10,000 years (the Holocene period).句子一开始就说同样 striking 的是，说明之前一定有一个很 striking 的东西。前一句说有 significant natural changes，所以 significant 的同义词就是 striking。

question_stem: According to paragraphs 3 and 4, proxy data have suggested all of the following about the climate EXCEPT:
choices: tag: A
text: Regional climates may change overtime.

tag: B
text: The climate has changed very little in the past 10,000 years.

tag: C
text: Global temperatures vary more than regional temperatures.

tag: D
text: Important natural changes in climate have occurred over large timescales.
answer_key: C
explanation: 第四段很短，快速读完。A 和 D 对应第四段第一句：What the proxy records make abundantly clear is that there have been significant natural changes in the climate over timescales longer than a few thousand years.说气候在一段时间内会变化；第二句里的 stability 对应 B 中的 changed little：Equally striking, however, is the relative stability of the climate in the past 10.000 years (the Holocene period).所以这 B 选项都正确，不选；只有 C 的比较关系在原文没说，所以 C 是答案。

question_stem: The word “erratic” in the passage is closest in meaning to
choices: tag: A
text: dramatic

tag: B
text: important

tag: C
text: unpredictable

tag: D
text: common
answer_key: C
explanation: erratic: 古怪的，不稳定的，飘忽不定的。A 是戏剧的，引人注意的；B 是重要的；C 是不可预测的；D 是常见的，普通的。所以 C，unpredictable 正确。对应原文：These include the chaotic fluctuations of the atmosphere, the slower but equally erratic behavior of the oceans, changes in the land surfaces, and the extent of ice and snow.原句说 equally erratic，所以之前一定得有一个跟 erratic 意思差不多的词，之前有 chaotic fluctuation，所以 erratic 和 chaotic 是同义词，chaotic 混乱的，备选项中只 unpredictable 跟这个意思靠谱，ABD 都不对。

question_stem: All of the following are mentioned in paragraph 5 as natural causes of climate change EXCEPT
choices: tag: A
text: atmospheric changes

tag: B
text: the slow movement of landmasses

tag: C
text: fluctuations in the amount of ice and snow

tag: D
text: changes in ocean activity
answer_key: B
explanation: B  EXCEPT 题，排除法。A 对应第二句的 fluctuation of the atmosphere，正确，不选；B 与原文的 changes in land surface 有明显区别，错，选；C 对应原文的 extent of ice and snow，正确，不选；D 对应原文的 erratic behavior of the ocean，正确，不选。

question_stem: According to paragraph 6, which of the following is true of computer models of the global climate?
choices: tag: A
text: The information they produce is still limited.

tag: B
text: They are currently most useful in understanding past climatic behaviors.

tag: C
text: They allow researchers to interpret the data obtained from proxy records.

tag: D
text: They do not provide information about regional climates.
answer_key: A
explanation: A 以 computer models 做关键词定位至第一句，但这句只是在单纯重复问题，所以往下看。说 computer model 能给出气候的 complexity，并且给出 limited info，只有 A 答案说到 limited info，所以 A 正确。其他都没说。

question_stem: The word “deliberations” in the passage is closest in meaning to
choices: tag: A
text: records

tag: B
text: discussions

tag: C
text: results

tag: D
text: variations
answer_key: B
explanation: deliberation: 深思熟虑，审议。A 是记录；B 是讨论；C 是结果；D 是变化。所以 B 的 discussions 正确。对应原文：Thus we need to be able to include these in our deliberations.本句以 thus 开头，说明这句话是一个结果，造成结果的原因是越来越多的人认为这些物理上的变化对气候的影响是可计算的，因此在我们的什么当中必须包含这些，A 记录和 C 结果都没法被主观的东西包含的，所以错；我们的变化完全不靠谱。

question_stem: The word “invoked” in the passage is closest in meaning to
choices: tag: A
text: demonstrated

tag: B
text: called upon

tag: C
text: supported

tag: D
text: expected
answer_key: B
explanation: invoke: 引起，求助。in 表示内部，voke 表示声音，所以 B 的 call upon 引起正确。A 是展示；C 是支持；D 是期盼。对应原文：Some current analyses conclude that volcanoes and solar activity explain quite a considerable amount of the observed variability in the period from the seventeenth to the early twentieth centuries, but that they cannot be invoked to explain the rapid warming in recent decades.说现在的分析能够得出一些结论，但这些结论不能什么解释气候快速变暖。demonstrate 和 support 错，即使支持解释和展示解释是对的，也不能用被动态；expect 代入是对的，所以只能靠认识了。

question_stem: What is the author's purpose in presenting the information in paragraph 7?
choices: tag: A
text: To compare the influence of volcanoes and solar activity on climate variability with the influence of factors external to the global climate system

tag: B
text: To indicate that there are other types of influences on climate variability in addition to those previously discussed

tag: C
text: To explain how external influences on climate variability differ from internal influences

tag: D
text: To argue that the rapid warming of Earth in recent decades cannot be explained
answer_key: B
explanation: B，问整段的关注第一句，这句说除了 internal 之外，还有 external，是一个典型的承上启下的句子，启下的才是这段要说的，也就是 external 的部分，所以答案是 B。A 和 C 都说比较，而原文根本没有比较；D 错因为原文没有 argue。