The study of climate change has established retreating glaciers and

The study of climate change has established retreating glaciers and rising global temperatures from a number of data sources. Establishing the influence of mankind upon these effects has been more difficult, because the climate is subject to oscillations that are much longer in duration than our record of direct temperature measurements, which extends back only about 150 years.

By drilling and conducting chemical and physical studies of ice cores on six of the seven continents, scientists have developed a method of estimating climatic information that had previously been thought inaccessible. Ice cores removed from the earth's crust and studied in order to draw such inferences are termed paleo-proxies. The values of various climatic variables at a particular time and place can be inferred through some form of proxy analysis in a given ice core sample. For example, deuterium excess indicates humidity levels, electrical conductivity indicates volcanic activity, beryllium levels indicate solar activity, and particle size and concentration indicate wind speeds. Temperature, in particular, can be inferred from the ratios of water molecules composed of stable isotopes of oxygen and hydrogen, namely 1H2H16O and 1H218O. Because molecules consisting of these isotopes have slightly different weights than their more common counterparts, their concentration in the ice core in a given epoch depends on the condensation temperature prevailing at the time. This technique enables scientists to estimate the air temperature of condensation when the snow fell and establish variations in temperature over a series of multiple samples.

One advantage of using ice cores as a paleo-proxy is that ice core samples can be extracted from across the world using different drilling techniques, for analysis either on-site or in a laboratory, with results that can be compared to each other and stitched into a coherent global picture. The primary sources of ice cores are the ice sheets of Antarctica and Greenland, whose thickness allows scientists to extract long cores representing time spans of up to 100,000 or even 400,000 years. Nevertheless, samples representing spans of multiple centuries have been extracted more recently at low latitudes--for example, at Mt. Kilimanjaro, in the Andes Mountains, and on the Himalayan plateau. Depending on the objectives of the project and the nature of the ice core, scientists use a variety of types of drill ranging from hand-powered auger drill to electro-mechanical drills. A limitation of using ice cores is that they represent data for conditions during snowfall only. Periods bereft of snowfall will fail to leave a record in the ice and can even disrupt the essential step of dating the samples. To mitigate this problem, multiple cores are typically extracted from nearby locations. A more critical limitation of the ice core method, one indicative of the larger problem at hand, is that as ice fields continue to retreat, the ability to measure in some locations will disappear entirely.

1. In the passage, the author is primarily interested in

A. describing the data that supports a scientific theory
B. illustrating how a research method has generated results that challenge an accepted theory
C. arguing that data obtained from a particular research method are as useful as data obtained directly
D. describing a scientific challenge and a research technique to address that challenge
E. providing an overall evaluation of a research technique


2. The author of the passage would be most likely to agree with which of the following statements about using ice cores as paleo-proxies?

A. It is the only feasible method to collect climate data.
B. It yields data that are insufficient to determine the influence of mankind on retreating glaciers.
C. It should not be widely adopted, since it will be impossible in the near future.
D. It is one of multiple valid sources of data on the climate.
E. It yields unreliable data about global temperature but has advanced the state of our scientific knowledge.


3. It can be inferred from the passage that the technique of using ice cores to determine historical temperatures would be less advantageous if which of the following were true?

A. It indicated different temperatures at different times for a particular location, according to different isotope concentrations in the sample.
B. It indicated different results at the same location, according to differing extraction methods of the samples.
C. It yielded information dating back only 80,000 years in most locations.
D. It indicated that the ratios of oxygen isotopes in the air in a given location varied over time.
E. It indicated that ice sheets were not retreating.


4. According to the passage, which of the following is true of the ice cores extracted at low latitudes?

A. They indicate that sediments found during an ice age contain more calcium carbonate than sediments formed at other times.
B. They are less reliable than the evidence from rocks on land in determining the volume of land ice.
C. They can be used to deduce the relative volume of land ice that was present when the sediment was laid down.
D. They are more unpredictable during an ice age than in other climatic conditions.
E. They can be used to determine atmospheric conditions at various times in the past.


5. It can be inferred from the passage that the air temperature of condensation at a time in the past when snow fell

A. can be determined from the ratio of hydrogen and oxygen isotopes in the air
B. correlates with the average air temperature in that area at that time
C. correlates with the average air temperature in that area at the time of measurement
D. creates land ice of a higher density at higher temperatures
E. rises during periods in which glaciers are retreating


6. It can be inferred from the passage that snowfall at locations where ice cores are extracted

A. is generally heavier than at other land locations covered with ice
B. is invariably more common during colder periods
C. fails to leave a record in the ice at entirely unknown dates in time
D. becomes less common as ice fields continue to retreat
E. is consistent enough within an area to reduce dating errors