How do scientists study the past climate of the Earth?

Question

and also how has the Earths temperature changed over the last 800,00 years?

Answer 1

They just make it up. If it sounds good, it must be true.

Answer 2

Changes in the Earth's orbit: Changes in the shape of the Earth's orbit (or eccentricity) as well as the Earth's tilt and precession affect the amount of sunlight received on the Earth's surface. These orbital processes -- which function in cycles of 100,000 (eccentricity), 41,000 (tilt), and 19,000 to 23,000 (precession) years -- are thought to be the most significant drivers of ice ages according to the theory of Mulitin Milankovitch, a Serbian mathematician (1879-1958). The National Aeronautics and Space Administration's (NASA) Earth Observatory offers additional information about orbital variations and the Milankovitch Theory.

Changes in the sun's intensity: Changes occurring within (or inside) the sun can affect the intensity of the sunlight that reaches the Earth's surface. The intensity of the sunlight can cause either warming (for stronger solar intensity) or cooling (for weaker solar intensity). According to NASA research, reduced solar activity from the 1400s to the 1700s was likely a key factor in the “Little Ice Age” which resulted in a slight cooling of North America, Europe and probably other areas around the globe. (See additional discussion under The Last 2,000 Years.)

Volcanic eruptions: Volcanoes can affect the climate because they can emit aerosols and carbon dioxide into the atmosphere.

Aerosol emissions: Volcanic aerosols tend to block sunlight and contribute to short term cooling. Aerosols do not produce long-term change because they leave the atmosphere not long after they are emitted. According to the United States Geological Survey (USGS), the eruption of the Tambora Volcano in Indonesia in 1815 lowered global temperatures by as much as 5ºF and historical accounts in New England describe 1816 as “the year without a summer.”

Carbon dioxide emissions: Volcanoes also emit carbon dioxide (CO2), a greenhouse gas, which has a warming effect. For about two-thirds of the last 400 million years, geologic evidence suggests CO2 levels and temperatures were considerably higher than present. One theory is that volcanic eruptions from rapid sea floor spreading elevated CO2 concentrations, enhancing the greenhouse effect and raising temperatures. However, the evidence for this theory is not conclusive and there are alternative explanations for historic CO2 levels (NRC, 2005). While volcanoes may have raised pre-historic CO2 levels and temperatures, according to the USGS Volcano Hazards Program, human activities now emit 130 times as much CO2 as volcanoes (whose emissions are relatively modest compared to some earlier times).

These climate change “drivers” often trigger additional changes or “feedbacks” within the climate system that can amplify or dampen the climate's initial response to them (whether the response is warming or cooling). For example:

Changes in greenhouse gas concentrations: The heating or cooling of the Earth's surface can cause changes in greenhouse gas concentrations. For example, when global temperatures become warmer, carbon dioxide is released from the oceans. When changes in the Earth's orbit trigger a warm (or interglacial) period, increasing concentrations of carbon dioxide may amplify the warming by enhancing the greenhouse effect. When temperatures become cooler, CO2 enters the ocean and contributes to additional cooling. During at least the last 650,000 years, CO2 levels have tended to track the glacial cycles (IPCC, 2007). That is, during warm interglacial periods, CO2 levels have been high and during cool glacial periods, CO2 levels have been low (see Figure 1).



Figure 1: Fluctuations in temperature (red line) and in the atmospheric concentration of carbon dioxide (yellow) over the past 649,000 years. The vertical red bar at the end is the increase in atmospheric carbon dioxide levels over the past two centuries and before 2007. Click on thumbnail for a full-size image and references.

Changes in ocean currents: The heating or cooling of the Earth's surface can cause changes in ocean currents. Because ocean currents play a significant role in distributing heat around the Earth, changes in these currents can bring about significant changes in climate from region to region.

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Rates of Change

Studies of the Earth's previous climate suggest periods of stability as well as periods of rapid change. Recent climate research suggests:

Interglacial climates (such as the present) tend to be more stable than cooler, glacial climates. For example, the climate during the current and previous interglacials (known as the Holocene and Eemian interglacials) has been more stable than the most recent glacial period (known as the Last Glacial Maximum). This glacial period was characterized by a long string of widespread, large and abrupt climate changes (NRC, 2002).

Abrupt or rapid climate changes tend to frequently accompany transitions between glacial and interglacial periods (and vice versa). For example, a significant part of the Northern Hemisphere (particularly around Greenland) may have experienced warming ratesof 14-28ºF over several decades during and after the most recent ice age (IPCC, 2007).

While abrupt climate changes have occurred throughout the Earth's history, human civilization arose during a period of relative climate stability.

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The Last 2,000 Years

During the last 2,000 years, the climate has been relatively stable. Scientists have identified three departures from this stability, known as the Medieval Climate Anomaly (also referred to as the Medieval Warm Period), the Little Ice Age and the Industrial Era:

The Medieval Climate Anomaly: Between roughly 900 and 1300 AD, evidence suggests Europe, Greenland and Asia experienced relative warmth. While historical accounts and other evidence document the warmth that occurred in some regions, the geographical extent, magnitude and timing of the warmth during this period is uncertain (NRC, 2006). The American West experienced very dry conditions around this time.

The Little Ice Age: A wide variety of evidence supports the global existence of a "Little Ice Age" (this was not a true "ice age" since major ice sheets did not develop) between about 1500 and 1850 (NRC, 2006). Average temperatures were possibly up to 2ºF colder than today, but varied by region.

The Industrial Era: An additional warm period has emerged in the last 100 years, coinciding with substantially increasing emissions of greenhouse gases from human activities (see Recent Climate Change for more information).

Prior to the Industrial Era,  the Medieval Climate Anomaly and Little Ice Age had defined the upper and lower boundaries of the climate's recent natural variability and are a reflection of changes in climate drivers (the sun's variability and volcanic activity) and the climate's internal variability (referring to random changes in the circulation of the atmosphere and oceans).

The issue of whether the temperature rise of last 100 years crossed over the warm limit of the boundary defined by the Medieval Climate Anomaly has been a controversial topic in the science community. The National Academy of Sciences recently completed a study to assess the efforts to reconstruct temperatures of the past one to two millennia (see Figure 2) and place the Earth's current warming in historical context (NRC, 2006).



Figure 2: Reconstructions of (Northern Hemisphere average or global average) surface temperature variations from six research teams (in different color shades) along with the instrumental record of global average surface temperature (in black). Each curve illustrates a somewhat different history of temperature changes, with a range of uncertainties that tend to increase backward in time (as indicated by the shading). Reference: NRC, 2006. (Figure reprinted with permission from Surface Temperature Reconstructions© (2006) by the National Academy of Sciences, Courtesy of the National Academies Press , Washington, D.C.)

According to the study  (NRC, 2006):

There is a high level of confidence that the global average temperature during the last few decades was warmer than any comparable period during the last 400 years.

Present evidence suggests that temperatures at many, but not all, individual locations were higher during the past 25 years than any period of comparable length since A.D. 900. However, uncertainties associated with this statement increase substantially backward in time.

Very little confidence can be assigned to estimates of hemisphere average or global average temperature prior to A.D. 900 due to limited data coverage and challenges in analyzing older data.

Answer 3

A number of ways, but most are forms of what are known as “proxies.” This means in the absence of direct measurement we can find indicators that compare to known values; for example how wide a tree ring is (indicating its growth) compared to a period where we could directly measure temperature and precipitation.

Proxies include tree rings, ice cores, records of growing seasons, harvest dates, weather records, etc.

Answer 4

There are many ways. Ice core, tree rings, sediment studies.

This passage comes from the website, "Loehle gathered as many non-tree ring reconstructions as possible for places throughout the world (Figure 1). There are dozens of very interesting ways to peer into the climatic past of a location, and Loehle included borehore temperature measurements, pollen remains, Mg/Ca ratios, oxygen isotope data from deep cores or from stalagmites, diatoms deposited on lake bottoms, reconstructed sea surface temperatures, and so on. Basically, he grabbed everything available, so long as it did not rely on trees."

http://www.worldclimatereport.com/index....

Answer 5

They use Ice Core data and tree rings. I know it sounds like a fortune teller reading tea leaves, but it's true.

As for Earths Temperature oer the last 800,000 years - Well we had at least two major ice ages known as Glaciation periods and at least one other interglaciation period - this is what we are in right now. The hard part is to figure out when another glaciation period will happen or if it will ever happen again. And we may never know in our life time or even or great grand kids life time.

Answer 6

Read it from the National Academy of Science...

http://dels.nas.edu/dels/rpt_briefs/clim...

Answer 7

They study ice cross sections and tree rings (palaeontology). For example: ice traps carbon dioxide and can show increases which can be related to the change in industrialization over the years.

Earthe's temp, has increased. it is normal over era's but anthropogenic activity is increaseing the temperature since carbon dioxide and other gases are being emitted into the atmosphere

Answer 8

The climate of the past climate is a concern of a science called paleoclimatology. It is the study of the climate before the use of measurement tools: thermometers, barometers etc.

To study the past climate they use what is called proxy data. they use some climate markers that contains some evidence of the climate variation and use them to deduce the climate parameters. Among them we have:

- earth sediments: lake sediments, marine sediments, fossils.

- tree rings

-historical archives: pictures, chronicles etc.

- ice cores

-etc.

From a Quaternary geology and global change student