In the late 1960s, paleoclimatologists shifted their attention from marine sediment cores to the isotopic composition of glacial ice, inaugurating a methodological revolution in historical climatology. Prior to this, analyzing the ratios of oxygen isotopes in fossilized foraminifera from deep-sea mud had been the gold standard for reconstructing Pleistocene temperatures. However, this marine record, while offering a vast chronological sweep, was inherently smoothed; the slow accumulation and biological mixing of seafloor sediments erased short-term climatic fluctuations, blurring decadal variations into millennial averages.
Ice cores extracted from the Greenland and Antarctic ice sheets promised significantly higher resolution. Because polar snow accumulates in discrete annual layers that trap ambient air bubbles, scientists theorized that they could extract uncontaminated samples of the ancient atmosphere. The initial drilling project at Camp Century in Greenland provided a continuous ice core stretching back over 100,000 years. Isotopic analysis of this core fundamentally disrupted the prevailing gradualist paradigm of climate change. Rather than slow, predictable transitions between glacial and interglacial periods, the ice record revealed abrupt temperature shifts, sometimes occurring within a single human lifetime.
Yet, extracting these insights was fraught with interpretive challenges. Early researchers struggled to distinguish whether the isotopic variations in the ice were caused by global temperature shifts or localized changes in precipitation patterns. Furthermore, while the trapped air bubbles offered a direct archive of greenhouse gas concentrations, the gas age is always younger than the surrounding ice because air circulates through the porous firn before sealing off entirely—a lag that complicated efforts to establish precise causal sequences between carbon dioxide levels and temperature spikes. Despite these hurdles, the success of the Camp Century core established ice as the premier medium for investigating the velocity of past climate change.
The passage most strongly supports which one of the following statements regarding the air bubbles trapped in polar ice?
- AThey provide an absolutely precise chronological record that definitively establishes the causal sequence between carbon dioxide levels and historical temperature spikes.
- BBecause they circulate through the porous firn before sealing off entirely, they inevitably blur short-term decadal variations into millennial averages.
- CEarly researchers initially argued that the bubbles primarily reflected localized changes in precipitation patterns rather than global shifts in greenhouse gas concentrations.
- The atmospheric gases found within a specific layer of an ice core became isolated from the ambient atmosphere more recently than the frozen precipitation constituting that layer.Answer
- EThey reveal that the abrupt temperature transitions recorded in the Pleistocene epoch were triggered primarily by fluctuations in human-generated carbon emissions.