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How do ice cores provide evidence about temperatures during the Little Ice Age?

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Line graph showing estimated temperature variations from 1000 to 2000 CE for the Northern Hemisphere and central England, with three lines representing different data sources. The chart highlights the medieval warm period around 1100-1300 and the Little Ice Age from about 1500 to 1850, followed by a sharp temperature rise in the late 20th century. Temperature is shown as deviations from the 1961-1990 average. — Little Ice Age Estimates of temperature variations for the Northern Hemisphere and central England from 1000 to 2000 ce.

Ice cores serve as vital "proxy" records that allow scientists to reconstruct past climate conditions, including those during the Little Ice Age (roughly 1300–1850 CE).12

The primary method for determining temperature involves analyzing the isotopic composition of the ice. Because the air temperature at the time moisture condenses to fall as snow influences the ratio of oxygen and hydrogen isotopes within that snow, researchers can study these ratios to estimate historical temperature variations.34

Additionally, ice cores provide context for the climate of that era through other indicators:
* Atmospheric Composition: Air bubbles trapped in the ice preserve samples of the ancient atmosphere, allowing scientists to measure concentrations of gases like carbon dioxide and methane.34
* Volcanic Activity: By measuring sulfate concentrations, researchers can identify major volcanic eruptions that occurred during the period, which may have influenced global cooling by reflecting solar radiation.14
* Dust Content: Measuring microparticles in the ice helps reveal information about atmospheric circulation patterns and wind intensity during the interval.34