Thursday, March 11, 2010

Global Warming-vs- Climate Change (Causes and Effects)

Global warming

Global annual surface temperatures relative to 1951-1980 mean temperatures from GISS. Analysis summarizes satellite measurements 1982 onward, and ship-based analysis from years earlier. Estimated error 95% confidence resulting from incomplete spatial coverage.[1]
Comparison of ground based (blue) and satellite based (red: UAH; green: RSS) records of temperature variations since 1979. Trends plotted since January 1982.
Mean surface temperature change for the period 2000 to 2009 relative to the average temperatures from 1951 to 1980.

Global warming is the increase in the average temperature of Earth's near-surface air and oceans since the mid-20th century and its projected continuation. Global surface temperature increased 0.74 ± 0.18 °C (1.33 ± 0.32 °F) between the start and the end of the 20th century.[3][A] The Intergovernmental Panel on Climate Change (IPCC) concludes that most of the observed temperature increase since the middle of the 20th century was very likely caused by increasing concentrations of greenhouse gases resulting from human activity such as fossil fuel burning and deforestation.[3] The IPCC also concludes that variations in natural phenomena such as solar radiation and volcanic eruptions had a small cooling effect after 1950.[4][5] These basic conclusions have been endorsed by more than 40 scientific societies and academies of science,[B] including all of the national academies of science of the major industrialized countries.[6]

Climate model projections summarized in the latest IPCC report indicate that the global surface temperature is likely to rise a further 1.1 to 6.4 °C (2.0 to 11.5 °F) during the 21st century. The uncertainty in this estimate arises from the use of models with differing sensitivity to greenhouse gas concentrations and the use of differing estimates of future greenhouse gas emissions. Most studies focus on the period leading up to the year 2100. However, warming is expected to continue beyond 2100 even if emissions stop, because of the large heat capacity of the oceans and the long lifetime of carbon dioxide in the atmosphere.

An increase in global temperature will cause sea levels to rise and will change the amount and pattern of precipitation, probably including expansion of subtropical deserts.Warming is expected to be strongest in the Arctic and would be associated with continuing retreat of glaciers, permafrost and sea ice. Other likely effects include changes in the frequency and intensity of extreme weather events, species extinctions, and changes in agricultural yields. Warming and related changes will vary from region to region around the globe, though the nature of these regional variations are uncertain.

Political and public debate continues regarding global warming, and what actions to take in response. The available options are mitigation to reduce further emissions; adaptation to reduce the damage caused by warming; and, more speculatively, geoengineering to reverse global warming. Most national governments have signed and ratified the Kyoto Protocol aimed at reducing greenhouse gas emissions.

Temperature changes


Two millennia of mean surface temperatures according to different reconstructions, each smoothed on a decadal scale. The instrumental record and the unsmoothed annual value for 2004 are shown in black.

The most common measure of global warming is the trend in globally averaged temperature near the Earth's surface. Expressed as a linear trend, this temperature rose by 0.74 ± 0.18 °C over the period 1906–2005. The rate of warming over the last half of that period was almost double that for the period as a whole (0.13 ± 0.03 °C per decade, versus 0.07 °C ± 0.02 °C per decade). The urban heat island effect is estimated to account for about 0.002 °C of warming per decade since 1900.Temperatures in the lower troposphere have increased between 0.13 and 0.22 °C (0.22 and 0.4 °F) per decade since 1979, according to satellite temperature measurements. Temperature is believed to have been relatively stable over the one or two thousand years before 1850, with regionally varying fluctuations such as the Medieval Warm Period and the Little Ice Age.

Estimates by NASA's Goddard Institute for Space Studies and the National Climatic Data Center show that 2005 was the warmest year since reliable, widespread instrumental measurements became available in the late 1800s, exceeding the previous record set in 1998 by a few hundredths of a degree. Estimates prepared by the World Meteorological Organization and the Climatic Research Unit show 2005 as the second warmest year, behind 1998. Temperatures in 1998 were unusually warm because the strongest El Niño in the past century occurred during that year.Global temperature is subject to short-term fluctuations that overlay long term trends and can temporarily mask them. The relative stability in temperature from 2002 to 2009 is consistent with such an episode.

Temperature changes vary over the globe. Since 1979, land temperatures have increased about twice as fast as ocean temperatures (0.25 °C per decade against 0.13 °C per decade).Ocean temperatures increase more slowly than land temperatures because of the larger effective heat capacity of the oceans and because the ocean loses more heat by evaporation. The Northern Hemisphere warms faster than the Southern Hemisphere because it has more land and because it has extensive areas of seasonal snow and sea-ice cover subject to ice-albedo feedback. Although more greenhouse gases are emitted in the Northern than Southern Hemisphere this does not contribute to the difference in warming because the major greenhouse gases persist long enough to mix between hemispheres.

The thermal inertia of the oceans and slow responses of other indirect effects mean that climate can take centuries or longer to adjust to changes in forcing. Climate commitment studies indicate that even if greenhouse gases were stabilized at 2000 levels, a further warming of about 0.5 °C (0.9 °F) would still occur.


What Is The Greenhouse Effect?

Seen from space, our atmosphere is but a tiny layer of gas around a huge bulky planet. But it is this gaseous outer ring and its misleadingly called greenhouse effect that makes life on Earth possible – and that could destroy life as we know it.

What Is The Greenhouse Effect?

The Greenhouse Effect (click image to download graphic)

Global warming causes and effects at a glance

The sun is the Earth’s primary energy source, a burning star so hot that we can feel its heat from over 150 million kilometers away. Its rays enter our atmosphere and shower upon on our planet. About one third of this solar energy is reflected back into the universe by shimmering glaciers, water and other bright surfaces. Two thirds, however, are absorbed by the Earth, thus warming land, oceans, and atmosphere.

Much of this heat radiates back out into space, but some of it is stored in the atmosphere. This process is called the greenhouse effect. Without it, the Earth’s average temperature would be a chilling -18 degrees Celsius, even despite the sun’s constant energy supply.

In a world like this, life on Earth would probably have never emerged from the sea. Thanks to the greenhouse effect, however, heat emitted from the Earth is trapped in the atmosphere, providing us with a comfortable average temperature of 14 degrees.

What Is The Greenhouse Effect?

Picture Gallery (click the image to start)

Arctic Meltdown: See how global warming is changing the North Pole

So, how does it work? Sunrays enter the glass roof and walls of a greenhouse. But once they heat up the ground, which, in turn, heats up the air inside the greenhouse, the glass panels trap that warm air and temperatures increase.

Our planet, however, has no glass walls; the only thing that comes close to acting as such is our atmosphere. But in here, processes are way more complicated than in a real greenhouse.

Like a radiator in space

Only about half of all solar energy that reaches the Earth is infrared radiation and causes immediate warming when passing the atmosphere. The other half is of a higher frequency, and only translates into heat once it hits Earth and is later reflected back into space as waves of infrared radiation.

This transformation of solar radiation in to infrared radiation is crucial, because infrared radiation can be absorbed by the atmosphere. So, on a cold and clear night for example, parts of this infrared radiation that would normally dissipate into space get caught up in the Earth’s atmosphere. And like a radiator in the middle of a room, our atmosphere radiates this heat into all directions.

Parts of this heat are finally sent out in the frozen nothingness of space, parts of it are sent back to Earth where they step up global temperatures. Just how much warmer it gets down here depends on how much energy is absorbed up there– and this, in turn, depends on the atmosphere’s composition.


The switch from carbon dioxide to oxygen

Nitrogen, oxygen, and argon make up 98 percent of the Earth’s atmosphere. But they do not absorb significant amounts of infrared radiation, and thus do not contribute to the greenhouse effect. It is the more exotic components like water vapour, carbon dioxide, ozone, methane, nitrous oxide, and chlorofluorocarbons that absorb heat and thus increase atmospheric temperatures.

Studies indicate that until some 2.7 billion years ago, there was so much carbon dioxide (CO2) and methane in our atmosphere that average temperatures on Earth were as high as 70 degrees. But bacteria and plants slowly turned CO2 into oxygen and the concentration of CO2 in our current atmosphere dropped to just about 0.038 percent or 383 parts per million (ppm), a unit of measurement used for very low concentrations of gases that has become a kind of currency in climate change debates.


Minuscule changes – global impact

But while we are still far from seeing major concentrations of CO2 in our atmosphere, slight changes already alter the way our celestial heating system works. Measurements of carbon dioxide amounts from Mauna Loa Observatory in Hawaii show that CO2 has increased from about 313 ppm in 1960 to about 375 ppm in 2005.

That means for every million particles in our atmosphere, there are now 62 CO2-particles more than in 1960. Even if this does not seem like much, scientists say this increase – most probably caused by human activities – is mainly responsible for rising global temperatures throughout the last decades.

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Even if the term “greenhouse effect” is somewhat of a misnomer, it still might be a useful handle from which the public can grasp an otherwise intricate natural process. Most people can relate to how hot and stuffy a greenhouse can get. Now that the Earth has started to heat up, we realize that our own global greenhouse has no window that we can open to catch some fresh air.


The UN Global Warming Report
Facts and Predictions

The latest report from the Intergovernmental Panel on Climate Change delivered a huge blow to global warming skeptics. Leading climate scientists are now 90 percent sure that human activity is heating up the planet. They present various scenarios that show where global warming could take us by the end of the century. The choice is ours.

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Global and Continental Temperature Change

Global temperature changes during the 20th century. The blue line depictures only changes due to natural forcings triggered by solar activity and volcanoes. The red lines is made up of changes induced by natural and anthropogenic sources (Graphic: IPCC)

First, the facts as outlined by the report. Global warming is a reality and “very likely” human-induced. Although the term “very likely” may seem vague, it is as close as 700 scientists, 2,500 reviewers and countless government officials can get to consensus about if humanity is to blame.

Greenhouse gases in our atmosphere have increased since 1750 due to the consumption of fossil fuels, new forms of land use, and agriculture. While atmospheric pollution has had a cooling effect during the last centuries, the massive increase in greenhouse gases has lead to a rise of average temperatures by 0.74 degrees Celsius since 1901. Scientists are 90 percent sure that the last half of the 20th century has been the hottest period in the Northern Hemisphere since 500 years.

"Numerous long-term changes in climate have been observed. These include changes in Arctic temperatures and ice, widespread changes in precipitation amounts, ocean salinity, wind patterns and aspects of extreme weather including droughts, heavy precipitation, heat waves and the intensity of tropical cyclones." [IPCC: Summary for Policymakers, p.8]

Scientists have refined their simulations and now have a fairly good idea of the effects of carbon dioxide emissions. A doubling of carbon dioxide levels in the atmosphere, relates to a surface warming of some 3 degrees Celsius plus-minus one degree. Even if we manage to reduce carbon emissions to year 2000 levels such a doubling of carbon dioxide is unpreventable. Warming, the report reads, will not be equally distributed. Effects will be more pronounced in the northern latitudes.

Critics often referred to changes in the sun’s radiation to account for global warming. Although scientists have found fluctuations in the sun's radiation, its effects are nearly 20 times weaker than human-induced warming.

Meanwhile glaciers all over the world are declining, an effect that is also perceivable at the fringes of the vast Antarctica ice shield. Scientists say that sea levels have already risen 17 centimeters during the 20th century, most of it due to the simple fact that warm water has a larger volume than cold water.

With the melting of icecaps and glaciers, the annual rise has nearly doubled since 1993 to a rate of about 3.1 mm. Even if carbon dioxide emissions can be stabilized, sea levels will keep on rising for centuries until the temperature gain will have reached the deep oceans.

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Picture Gallery (click on the image to start)

Find out more about the UN climate change scenarios

Findings also show that the atmosphere now holds more water vapor, one of the driving forces of tropical storms and floods. Since the 1960, Westerly winds have gained in strength all over the planet. The Atlantic was particularly effected by more frequent and severe tropical cyclones, a phenomenon in line with rising surface water temperatures. The report says that there is a chance of six out of ten that recent severe storms were boosted by global warming.

Arctic temperatures have increased twice as fast as global average temperatures. Summer ice in the Arctic Ocean is decreasing by 7.4 percent per decade. By the end of the century, the Arctic might well be ice-free in summer. Meanwhile permafrost is on the retreat. Since 1900, the seasonally frozen ground in the Northern Hemisphere has shrunken by some 7 percent. This has freed large amounts of methane, another potent greenhouse gas. To which extent such side-effects amplify ongoing global warming is not yet properly understood. The IPCC’s scenarios, therefore, do not account for eventual runaway effects that would speed up global warming.

Precipitation patterns, too, changed over the last century. There is significantly more rain in the eastern parts of North and South America, northern Europe and northern and central Asia. On the other hand, dry spells are more frequent in the Sahel, the Mediterranean, southern Africa and parts of southern Asia.

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The IPCC Scenarios

The world’s leading scientists have put together data and expertise available and devised seven climate scenarios for the 21st century. It all depends – they say – on the level of demographic and economic development, and how serious we are about the fight against global warming.

Level 2000: If we manage to stabilize our greenhouse gas emissions to the levels attained in the year 2000, we will still feel the heat, but the increase will be less than a degree over the next hundred years. Unfortunately, this option is not even considered a real scenario but rather a benchmark to compare with more realistic models.

Global Service Economy: Scenario B1 presents the most optimistic outlook: by mid-century, global population will hit a peak and decline thereafter. Rapid economic changes will bring about a service and information economy based on clean and efficient technologies. The international community will unite around policy solutions - such as the Kyoto Protocol - for the reduction of greenhouse gases. While all this sounds promising, global warming will still occur, albeit not beyond a range of 1.1 to 2.9 degrees Celsius. Sea level rise between 18 and 38 centimeters until the end of the century.

Population Growth: Scenario B2 is less rosy: global population will constantly grow while climate change mitigation efforts have a regional focus. This translates into a temperature rise of some 1.4 to 3.8 degree Celsius. Sea levels increase some 20 to 40 centimeters by 2100.

Rapid Economic Growth: The A1 scenario has been split up in three sub-divisions. Each of them is based on rapidly growing economies and a growing number of people, albeit populations will decline towards the second half of the century.

A1FI represents “business-as-usual” - a world that still runs on coal and gas. It is here that predictions are most shocking: temperature gains of some 2.4 to 6.4 degrees are within reach. The sea would rise some 26 to 50 centimeters until the end of the century flooding large coastal cities and numerous islands.

A1B, the most probable scenario given current trends, is also alarming. While fossil fuels are still widely used, they are part of a more balanced energy mix. Still, by the end of the century, temperatures will have risen some 1.7 to 4.4 degrees Celsius, with the oceans gaining some 21 to 48 centimeters. Rainfall is likely to decrease by some 20 percent in the subtropics, while more rain will fall in the northern and southern latitudes. The Gulf Stream will not stop, but it will lose about a quarter of its force.

Finally, A1T is a world that has lived through a third industrial revolution - a widespread conversion to “green” energy sources. It is similar to B1 in the sense that temperatures and oceans will rise, but to an extent that experts such as Hans Joachim Schellnhuber call “manageable".


Climate change

Climate change is a change in the statistical distribution of weather over periods of time that range from decades to millions of years. It can be a change in the average weather or a change in the distribution of weather events around an average (for example, greater or fewer extreme weather events). Climate change may be limited to a specific region, or may occur across the whole Earth. It can be caused by recurring, often cyclical climate patterns such as El Niño-Southern Oscillation, or come in the form of more singular events such as the Dust Bowl.[1]

In recent usage, especially in the context of environmental policy, climate change usually refers to changes in modern climate. It may be qualified as anthropogenic climate change, more generally known as "global warming" or "anthropogenic global warming" (AGW).

For information on temperature measurements over various periods, and the data sources available, see temperature record. For attribution of climate change over the past century, see attribution of recent climate change.

Causes

Factors that can shape climate are climate forcings. These include such processes as variations in solar radiation, deviations in the Earth's orbit, mountain-building and continental drift, and changes in greenhouse gas concentrations. There are a variety of climate change feedbacks that can either amplify or diminish the initial forcing. Some parts of the climate system, such as the oceans and ice caps, respond slowly in reaction to climate forcing because of their large mass. Therefore, the climate system can take centuries or longer to fully respond to new external forcings.

Plate tectonics

Over the course of millions of years, the motion of tectonic plates reconfigures global land and ocean areas and generates topography. This can affect both global and local patterns of climate and atmosphere-ocean circulation.[2]

The position of the continents determines the geometry of the oceans and therefore influences patterns of ocean circulation. The locations of the seas are important in controlling the transfer of heat and moisture across the globe, and therefore, in determining global climate. A recent example of tectonic control on ocean circulation is the formation of the Isthmus of Panama about 5 million years ago, which shut off direct mixing between the Atlantic and Pacific Oceans. This strongly affected the ocean dynamics of what is now the Gulf Stream and may have led to Northern Hemisphere ice cover.[3][4] Earlier, during the Carboniferous period, plate tectonics may have triggered the large-scale storage of carbon and increased glaciation.[5] Geologic evidence points to a "megamonsoonal" circulation pattern during the time of the supercontinent Pangaea, and climate modeling suggests that the existence of the supercontinent was conducive to the establishment of monsoons.[6]

More locally, topography can influence climate. The existence of mountains (as a product of plate tectonics through mountain-building) can cause orographic precipitation. Humidity generally decreases and diurnal temperature swings generally increase with increasing elevation. Mean temperature and the length of the growing season also decrease with increasing elevation. This, along with orographic precipitation, is important for the existence of low-latitude alpine glaciers and the varied flora and fauna along at different elevations in montane ecosystems.

The size of continents is also important. Because of the stabilizing effect of the oceans on temperature, yearly temperature variations are generally lower in coastal areas than they are inland. A larger supercontinent will therefore have more area in which climate is strongly seasonal than will several smaller continents and/or island arcs.

Solar output

Main article: Solar variation
Variations in solar activity during the last several centuries based on observations of sunspots and beryllium isotopes.

The sun is the predominant source for energy input to the Earth. Both long- and short-term variations in solar intensity are known to affect global climate.

Early in Earth's history the sun emitted only 70% as much power as it does today. With the same atmospheric composition as exists today, liquid water should not have existed on Earth. However, there is evidence for the presence of water on the early Earth, in the Hadeanand Archean eons, leading to what is known as the faint young sun paradox. Hypothesized solutions to this paradox include a vastly different atmosphere, with much higher concentrations of greenhouse gases than currently exist Over the following approximately 4 billion years, the energy output of the sun increased and atmospheric composition changed, with the oxygenation of the atmosphere being the most notable alteration. The luminosity of the sun will continue to increase as it follows the main sequence. These changes in luminosity, and the sun's ultimate death as it becomes a red giant and then a white dwarf, will have large effects on climate, with the red giant phase possibly ending life on Earth.

Solar output also varies on shorter time scales, including the 11-year solar cycle and longer-term modulations. The 11-year sunspot cycle produces low-latitude warming and high-latitude cooling over limited areas of statistical significance in the stratosphere with an amplitude of approximately 1.5°C. But although "variability associated with the 11-yr solar cycle has a significant influence on stratospheric temperatures. ...there is still no consensus on the exact magnitude and spatial structure".[14] These stratospheric variations are consistent with the idea that excess equatorial heating can drive thermal winds. In the near-surface troposphere, there is only a small change in temperature (on the order of a tenth of a degree, and only statistically significant in limited areas underneath the peaks in stratospheric zonal wind speed) due to the 11-year solar cycle. Solar intensity variations are considered to have been influential in triggering the Little Ice Age,[15] and for some of the warming observed from 1900 to 1950. The cyclical nature of the sun's energy output is not yet fully understood; it differs from the very slow change that is happening within the sun as it ages and evolves, with some studies pointing toward solar radiation increases from cyclical sunspot activity affecting global warming.

Orbital variations

Main article: Milankovitch cycles

Slight variations in Earth's orbit lead to changes in the seasonal distribution of sunlight reaching the Earth's surface and how it is distributed across the globe. There is very little change to the area-averaged annually-averaged sunshine; but there can be strong changes in the geographical and seasonal distribution. The three types of orbital variations are variations in Earth's eccentricity, changes in the tilt angle of Earth's axis of rotation, and precession of Earth's axis. Combined together, these produce Milankovitch cycles which have a large impact on climate and are notable for their correlation to glacial and interglacial periods,[18] their correlation with the advance and retreat of the Sahara,[18] and for their appearance in the stratigraphic record.[19]

Volcanism

Volcanism is a process of conveying material from the crust and mantle of the Earth to its surface. Volcanic eruptions, geysers, and hot springs, are examples of volcanic processes which release gases and/or particulates into the atmosphere.

Eruptions large enough to affect climate occur on average several times per century, and cause cooling (by partially blocking the transmission of solar radiation to the Earth's surface) for a period of a few years. The eruption of Mount Pinatubo in 1991, the second largest terrestrial eruption of the 20th century (after the 1912 eruption of Novarupta) affected the climate substantially. Global temperatures decreased by about 0.5 °C (0.9 °F). The eruption of Mount Tambora in 1815 caused the Year Without a Summer.Much larger eruptions, known as large igneous provinces, occur only a few times every hundred million years, but may cause global warming and mass extinctions.

Volcanoes are also part of the extended carbon cycle. Over very long (geological) time periods, they release carbon dioxide from the Earth's crust and mantle, counteracting the uptake by sedimentary rocks and other geological carbon dioxide sinks. According to the US Geological Survey, however, estimates are that human activities generate more than 130 times the amount of carbon dioxide emitted by volcanoes.

Ocean variability

Main article: Thermohaline circulation
A schematic of modern thermohaline circulation

The ocean is a fundamental part of the climate system. Short-term fluctuations (years to a few decades) such as the El Niño–Southern Oscillation, the Pacific decadal oscillation, the North Atlantic oscillation, and the Arctic oscillation, represent climate variability rather than climate change. On longer time scales, alterations to ocean processes such as thermohaline circulation play a key role in redistributing heat by carrying out a very slow and extremely deep movement of water, and the long-term redistribution of heat in the world's oceans.

Human influences

Main article: Global warming

Anthropogenic factors are human activities that change the environment. In some cases the chain of causality of human influence on the climate is direct and unambiguous (for example, the effects of irrigation on local humidity), while in other instances it is less clear. Various hypotheses for human-induced climate change have been argued for many years. Presently the scientific consensus on climate change is that human activity is very likely the cause for the rapid increase in global average temperatures over the past several decades.Consequently, the debate has largely shifted onto ways to reduce further human impact and to find ways to adapt to change that has already occurred.

Of most concern in these anthropogenic factors is the increase in CO2 levels due to emissions from fossil fuel combustion, followed by aerosols (particulate matter in the atmosphere) and cement manufacture. Other factors, including land use, ozone depletion, animal agriculture and deforestation, are also of concern in the roles they play - both separately and in conjunction with other factors - in affecting climate, microclimate, and measures of climate variables.

Physical evidence for climatic change

Evidence for climatic change is taken from a variety of sources that can be used to reconstruct past climates. Reasonably complete global records of surface temperature are available beginning from the mid-late 1800s. For earlier periods, most of the evidence is indirect—climatic changes are inferred from changes in proxies, indicators that reflect climate, such as vegetation, ice cores,[28] dendrochronology, sea level change, and glacial geology.

Historical and archaeological evidence

Main article: Historical impacts of climate change

Climate change in the recent past may be detected by corresponding changes in settlement and agricultural patterns.Archaeological evidence, oral history and historical documents can offer insights into past changes in the climate. Climate change effects have been linked to the collapse of various civilisations.

Glaciers

Variations in CO2, temperature and dust from the Vostok ice core over the last 450,000 years

Glaciers are considered among the most sensitive indicators of climate change,advancing when climate cools (for example, during the period known as the Little Ice Age) and retreating when climate warms. Glaciers grow and shrink, both contributing to natural variability and amplifying externally forced changes. A world glacier inventory has been compiled since the 1970s. Initially based mainly on aerial photographs and maps, this compilation has resulted in a detailed inventory of more than 100,000 glaciers covering a total area of approximately 240,000 km2 and, in preliminary estimates, for the recording of the remaining ice cover estimated to be around 445,000 km2. The World Glacier Monitoring Service collects data annually on glacier retreat and glacier mass balance From this data, glaciers worldwide have been found to be shrinking significantly, with strong glacier retreats in the 1940s, stable or growing conditions during the 1920s and 1970s, and again retreating from the mid 1980s to present.Mass balance data indicate 17 consecutive years of negative glacier mass balance.

Percentage of advancing glaciers in the Alps in the last 80 years

The most significant climate processes since the middle to late Pliocene (approximately 3 million years ago) are the glacial and interglacial cycles. The present interglacial period (the Holocene) has lasted about 11,700 years.Shaped by orbital variations, responses such as the rise and fall of continental ice sheets and significant sea-level changes helped create the climate. Other changes, including Heinrich events, Dansgaard–Oeschger events and the Younger Dryas, however, illustrate how glacial variations may also influence climate without the forcing effect of orbital changes.

Glaciers leave behind moraines that contain a wealth of material - including organic matter that may be accurately dated - recording the periods in which a glacier advanced and retreated. Similarly, by tephrochronological techniques, the lack of glacier cover can be identified by the presence of soil or volcanic tephra horizons whose date of deposit may also be precisely ascertained.

Vegetation

A change in the type, distribution and coverage of vegetation may occur given a change in the climate; this much is obvious. In any given scenario, a mild change in climate may result in increased precipitation and warmth, resulting in improved plant growth and the subsequent sequestration of airborne CO2. Larger, faster or more radical changes, however, may well[weasel words] result in vegetation stress, rapid plant loss and desertification in certain circumstances.

Ice cores

Analysis of ice in a core drilled from a ice sheet such as the Antarctic ice sheet, can be used to show a link between temperature and global sea level variations. The air trapped in bubbles in the ice can also reveal the CO2 variations of the atmosphere from the distant past, well before modern environmental influences. The study of these ice cores has been a significant indicator of the changes in CO2 over many millennia, and continues to provide valuable information about the differences between ancient and modern atmospheric conditions.

Dendroclimatology

Dendroclimatology is the analysis of tree ring growth patterns to determine past climate variations. Wide and thick rings indicate a fertile, well-watered growing period, whilst thin, narrow rings indicate a time of lower rainfall and less-than-ideal growing conditions.

Pollen analysis

Palynology is the study of contemporary and fossil palynomorphs, including pollen. Palynology is used to infer the geographical distribution of plant species, which vary under different climate conditions. Different groups of plants have pollen with distinctive shapes and surface textures, and since the outer surface of pollen is composed of a very resilient material, they resist decay. Changes in the type of pollen found in different sedimentation levels in lakes, bogs or river deltas indicate changes in plant communities; which are dependent on climate conditions.

Insects

Remains of beetles are common in freshwater and land sediments. Different species of beetles tend to be found under different climatic conditions. Given the extensive lineage of beetles whose genetic makeup has not altered significantly over the millennia, knowledge of the present climatic range of the different species, and the age of the sediments in which remains are found, past climatic conditions may be inferred.

Sea level change

Main article: Current sea level rise
Global sea level change for much of the last century has generally been estimated using tide gauge measurements collated over long periods of time to give a long-term average. More recently, altimeter measurements — in combination with accurately determined satellite orbits — have provided an improved measurement of global sea level change.


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