Paleoclimatology: A Window to Past and Future
Paleoclimatology, the study of past climate patterns, is urgently being pursued in order to unravel the mysteries of current climate upheavals, such as droughts, floods, and global warming. Instrumental temperature records do not go back beyond the mid-1800s, but paleoclimatologists can investigate climate changes over past decades, centuries, and millennia. Through the study of tree rings, coral reefs, ice cores, and sediments in lakes and oceans, paleoclimatologists can help to determine what amount of climate variability is normal or natural for the earth.
One of the most pressing questions scientists hope to answer through paleoclimatology is whether the increase in global temperature, which was the highest on record during the last ten years of the 20th century, is an unprecedented occurrence induced by humans or whether the record warmth is consistent with climate fluctuations in the past.
An extensive climate history has been preserved in nature. Tree rings have been the most familiar and reliable source of past climate records, with wide rings representing rainy seasons and thin rings indicative of dry seasons. The rings begin forming each spring with a layer of thin, light-colored cells, called the cambium, that grows between the bark and old wood. During the fall the growth rate slows and the cells become small and dense, indicating the end of another year. Scientists count the years by counting the rings, and they match ring patterns in living trees with those in older trees in order to date the older trees. By matching ring patterns in older trees, scientists have dated climate conditions back 10,000 years. This dating process, called dendrochronology, does not work in areas with year-round growth, because trees there do not develop rings, but in climates with limited growing seasons, the rings reveal secrets of past forest fires, floods, insect attacks, volcanic eruptions, and glacier movement.
Coral reefs also form rings that represent their growth rates. Coral reef growth, which has occurred on earth for 450 million years, depends on ideal water temperature and sunlight. Thin rings indicate that the water was too warm (a common consequence of El Nino) or too cold. Most of the coral reef is dead skeleton under the top layer of growth, but paleoclimatologists can figure out the water temperature in which the previous coral grew by measuring the ratio of light to heavy oxygen isotopes in the coral. Scientists can also determine how much light was available during the growth period by measuring the levels of a specific carbon isotope.
Daring extractions of ice cores are being undertaken worldwide, and, like coral reef samples, these cores are analyzed chemically to reveal the climate thousands of years ago. Ice cores are composed of snow and elements of the air that were trapped in the snow as it fell to the earth. Over time the snow was compacted into ice. By measuring the oxygen isotopes in each layer of ice, researchers calculate the ambient air temperature in effect at the time that the ice was formed. They also measure carbon dioxide and methane, found in air bubbles in the ice core, to track greenhouse gases and to understand how much of the current greenhouse effect may be a typical fluctuation on the planet and how much is the result of human interference. Volcanic ash and sulfate found in ice cores reveal past volcanic activity, and some ice cores contain fossilized pollen and insects.
Ice cores from Kilimanjaro in eastern Africa provide over 11,000 years of climate history, including three sudden climate changes; one such change, about 4,000 years ago, coincides with the greatest historically recorded drought in the African tropics. In Antarctica's Dyer Plateau, ice cores produced a 480-year paleoclimatic history, with the last two decades showing pronounced warming. Paleoclimatologists expect to uncover climate secrets spanning several thousand years through the study of ice core extractions from China's Qinghai-Tibetan Plateau, the highest plateau in the world, and from Bolivia's highest peak, Sajama, which is topped by a glacier.
Scientists feel an urgent drive to extract and analyze ice cores before further ice melts destroy the rich history stored in their layers. Recent ice melts in the Alps and in Canada uncovered, respectively, two men from the Ice Age and caribou dung and spears from the Stone Age.
Sediment in the bottom of lakes and oceans also holds climate history. Globally, billions of tons of sediment are buried each year in these bodies of water, embedding pollen and small fossils. Researchers extract sediment cores from the sediments and study the pollen to learn what plants grew in the area and what the climate must have been like to sustain such vegetation. They also conduct chemical analyses.
Through these endeavors paleoclimatologists have begun to realize that the earth undergoes dramatic climate "surprises" from time to time and that some of these changes occur only regionally for a few decades rather than globally for centuries, as was previously thought. Scientists have not yet figured out what causes these surprise episodes, but they hope through continued international collaboration to remove some of the mystery surrounding climate changes, particularly regarding global warming. The more thoroughly paleoclimatologists are able to unravel the past, the more accurately they will be able to determine the causes of climate fluctuations, predict and plan for future weather shifts, and develop persuasive global strategies to counter human-induced climate changes.
One of the most pressing questions scientists hope to answer through paleoclimatology is whether the increase in global temperature, which was the highest on record during the last ten years of the 20th century, is an unprecedented occurrence induced by humans or whether the record warmth is consistent with climate fluctuations in the past.
An extensive climate history has been preserved in nature. Tree rings have been the most familiar and reliable source of past climate records, with wide rings representing rainy seasons and thin rings indicative of dry seasons. The rings begin forming each spring with a layer of thin, light-colored cells, called the cambium, that grows between the bark and old wood. During the fall the growth rate slows and the cells become small and dense, indicating the end of another year. Scientists count the years by counting the rings, and they match ring patterns in living trees with those in older trees in order to date the older trees. By matching ring patterns in older trees, scientists have dated climate conditions back 10,000 years. This dating process, called dendrochronology, does not work in areas with year-round growth, because trees there do not develop rings, but in climates with limited growing seasons, the rings reveal secrets of past forest fires, floods, insect attacks, volcanic eruptions, and glacier movement.
Coral reefs also form rings that represent their growth rates. Coral reef growth, which has occurred on earth for 450 million years, depends on ideal water temperature and sunlight. Thin rings indicate that the water was too warm (a common consequence of El Nino) or too cold. Most of the coral reef is dead skeleton under the top layer of growth, but paleoclimatologists can figure out the water temperature in which the previous coral grew by measuring the ratio of light to heavy oxygen isotopes in the coral. Scientists can also determine how much light was available during the growth period by measuring the levels of a specific carbon isotope.
Daring extractions of ice cores are being undertaken worldwide, and, like coral reef samples, these cores are analyzed chemically to reveal the climate thousands of years ago. Ice cores are composed of snow and elements of the air that were trapped in the snow as it fell to the earth. Over time the snow was compacted into ice. By measuring the oxygen isotopes in each layer of ice, researchers calculate the ambient air temperature in effect at the time that the ice was formed. They also measure carbon dioxide and methane, found in air bubbles in the ice core, to track greenhouse gases and to understand how much of the current greenhouse effect may be a typical fluctuation on the planet and how much is the result of human interference. Volcanic ash and sulfate found in ice cores reveal past volcanic activity, and some ice cores contain fossilized pollen and insects.
Ice cores from Kilimanjaro in eastern Africa provide over 11,000 years of climate history, including three sudden climate changes; one such change, about 4,000 years ago, coincides with the greatest historically recorded drought in the African tropics. In Antarctica's Dyer Plateau, ice cores produced a 480-year paleoclimatic history, with the last two decades showing pronounced warming. Paleoclimatologists expect to uncover climate secrets spanning several thousand years through the study of ice core extractions from China's Qinghai-Tibetan Plateau, the highest plateau in the world, and from Bolivia's highest peak, Sajama, which is topped by a glacier.
Scientists feel an urgent drive to extract and analyze ice cores before further ice melts destroy the rich history stored in their layers. Recent ice melts in the Alps and in Canada uncovered, respectively, two men from the Ice Age and caribou dung and spears from the Stone Age.
Sediment in the bottom of lakes and oceans also holds climate history. Globally, billions of tons of sediment are buried each year in these bodies of water, embedding pollen and small fossils. Researchers extract sediment cores from the sediments and study the pollen to learn what plants grew in the area and what the climate must have been like to sustain such vegetation. They also conduct chemical analyses.
Through these endeavors paleoclimatologists have begun to realize that the earth undergoes dramatic climate "surprises" from time to time and that some of these changes occur only regionally for a few decades rather than globally for centuries, as was previously thought. Scientists have not yet figured out what causes these surprise episodes, but they hope through continued international collaboration to remove some of the mystery surrounding climate changes, particularly regarding global warming. The more thoroughly paleoclimatologists are able to unravel the past, the more accurately they will be able to determine the causes of climate fluctuations, predict and plan for future weather shifts, and develop persuasive global strategies to counter human-induced climate changes.
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