Rate Of Change

One important concept of paleoclimatology is to be able to track the changes in greenhouse gas concentrations by the heating or cooling of the Earth's surface. Scientists know that when the atmosphere warms up, carbon dioxide is released from the oceans. In addition, if the Earth's orbit changes and triggers a warming period, it can also increase greenhouse gases. When this happens, it triggers the greenhouse effect. This creates a positive feedback that encourages more warming. Conversely, when temperatures cool, CO2 is absorbed by the oceans, which contributes to additional cooling. According to the Intergovernmental Panel on Climate Change (IPCC) in their 2007 report, during the past 650,000 years, CO2 levels have been high, and during the cool glacial periods, CO2 levels have been low.

Because scientists can observe coinciding rates of change with temperatures and CO2 levels throughout the past several hundred thousand years and determine that there is a strong correlation, this also gives them a scientific basis and better understanding about the future. Through the correlation of temperatures and CO2 records, scientists can determine, through modeling, the types of effects that can be expected from various levels of CO2 in the atmosphere.

300,000 years ago

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300,000 years ago

200,000 years ago

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Fluctuations in temperature (red line) and in the amount of carbon dioxide concentrations in the atmosphere (blue line) over the past 350,000 years. The temperature and carbon dioxide concentrations at the South Pole run roughly parallel to each other, showing the strong correlation between the two.

Ocean currents are also affected by changes in the Earth's surface temperature. It has been proven that melting glaciers and ice caps can add enough freshwater to the northern oceans to slow or stop the flow of key currents such as the Gulf Stream. Because ocean currents have a significant effect on climates around the world, these changes can cause significant changes to world climate. For instance, if the Gulf Stream were to slow down or stop due to excess melting of glacial and ice cap ice in the Arctic, it could bring cold, ice age-like weather to normally moderate temperature regions in Europe. If ocean currents are altered, the global distribution of heat will be altered, which will cause major changes in climate from one area of the Earth to another.

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This graph shows how the recent warm temperatures and rising carbon dioxide levels relate to those of the past 1,000 years. Experts believe this sharp rise is due largely to how humans have enhanced the greenhouse effect.

Scientists have gathered information from records preserved in layers of ocean sediments of the fossils of marine life that show that this has happened several times throughout the Earth's history and that these changes have caused significant climate changes over large areas.

NOAA has completed several studies that show that the Earth's earlier climate had periods of stability interrupted by periods of rapid change. They believe this is because interglacial climates (such as the current climate) are more stable than cooler, glacial climates. Disruption of this stability can be caused by variations in the Earth's orbit through time and the associated variability of solar radiation received at

This rock landscape of the American Southwest was shaped over eons of geologic time by the multiple forces of wind, water, and ice.

(Nature's Images)

the Earth's surface. Glacial periods occur when summer solar radiation is reduced in the Northern Hemisphere. Throughout the Pleistocene epoch (the past 1.8 million years), these cycles have occurred with a frequency of about 100,000 years. Precession of the equinoxes also affects solar radiation in cycles of 23,000 years, which encourages glacial periods. Warming at the end of glacial periods also happens abruptly due to the ice-albedo feedback mechanism. With less ice to reflect incoming solar radiation, more heat is absorbed by the Earth's surface, causing temperatures to rise. Once ice begins to melt and expose the land and water, additional solar radiation can be absorbed by the Earth's surface, raising temperatures and causing even more ice to melt in a positive

Clues to past climate can be seen in present-day landscapes. The basin this alpine lake is contained within was originally carved out by a glacier during the last ice age. The lake is in the Uinta Mountains in northern Utah, part of the Rocky Mountains. (Nature's Images)

feedback. Abrupt, rapid climate changes often accompany the transitions between glacial and interglacial periods. Most current civilizations came into existence during relatively stable periods of climate.

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