Lean Encyclopedia and Wholesome Articles for the Hungry Mind.
Category: Global warming
Global warming is the consequence of the inevitable climate change the world is facing due to years and years of not paying attention to the signs nature is sending us. It is the observed century-scale rise in the average temperature of the Earth’s climate system and its related effects.
Sea level rise is already redrawing coastlines around the world. What happens when the coast retreats through a major city? We look at how the world map will change in the year 2100, and what coastal cities can do to defend themselves. Infographic: Sea Level Rise and Global Warming, Sea level is rising—and at an accelerating rate—especially along the U.S. East Coast and Gulf of Mexico.
Why are the East Coast and Gulf of Mexico hotspots of sea level rise? Global average sea level has increased 8 inches since 1880. Several locations along the East Coast and Gulf of Mexico have experienced more than 8 inches of local sea level rise in only the past 50 years.
The rate of local sea level rise is affected by global, regional, and local factors. Along the East Coast and Gulf of Mexico, changes in the path and strength of ocean currents are contributing to faster-than-average sea level rise. In parts of the East Coast and Gulf regions, land is subsiding, which allows the ocean to penetrate farther inland.
How quickly is land ice melting? Shrinking land ice — glaciers, ice caps, and ice sheets — contributed about half of the total global sea level rise between 1972 and 2008, but its contribution has been increasing since the early 1990s as the pace of ice loss has accelerated. Recent studies suggest that land ice loss added nearly half an inch to global sea level from 2003 to 2007, contributing 75 to 80 percent of the total increase during that period.
Why is there such a large range in sea level rise projections? The long-term rate of global sea level rise will depend on the amount of future heat-trapping emissions and on how quickly land ice responds to rising temperatures. Scientists have developed a range of scenarios for future sea level rise based on estimates of growth in heat-trapping emissions and the potential responses of oceans and ice. The estimates used for these two variables result in the wide range of potential sea level rise scenarios.
How high and how quickly will sea level rise in the future? Our past emissions of heat-trapping gases will largely dictate sea level rise through 2050, but our present and future emissions will have great bearing on sea level rise from 2050 to 2100 and beyond.
Even if global warming emissions were to drop to zero by 2016, sea level will continue to rise in the coming decades as oceans and land ice adjust to the changes we have already made to the atmosphere.
The greatest effect on long-term sea level rise will be the rate and magnitude of the loss of ice sheets, primarily in Greenland and West Antarctica, as they respond to rising temperatures caused by heat-trapping emissions in the atmosphere.
The frozen continent of Antarctica contains the vast majority of all freshwater on Earth. Now that ice is melting at an accelerating rate, in part because of climate change. What does this transformation mean for coastal communities across the globe? William Brangham reports from Antarctica on the troubling trend of ice loss and how glaciers can serve as a climate record from the past
A damning report from the the Intergovernmental Panel on Climate Change has put the world on the path to a ‘climate catastrophe’ as global warming nears 3C. As scientists say global warming must be limited to 1.5 C, we investigate if it’s too late to turn back. Newsnight is the BBC’s flagship news and current affairs TV programme – with analysis, debate, exclusives, and robust interviews.
Infographic: Reduced climate impacts from the Paris Agreement Image Credit: “Paris” by Pug Girl (Flickr) is licensed under CC BY 2.0 January 1, 2018
Infographic: Western Wildfires and Climate Change Rising temperatures are increasing wildfire risk throughout the Western U.S.
Panel 1: Wildfires and Wildfire Season The number of large wildfires — defined as those covering more than 1,000 acres — is increasing throughout the region. Over the past 12 years, every state in the Western U.S. has experienced an increase in the average number of large wildfires per year compared to the annual average from 1980 to 2000. Wildfire season is generally defined as the time period between the year’s first and last large wildfires. This infographic highlights the length of the wildfire season for the Western U.S. as a region. Local wildfire seasons vary by location, but have almost universally become longer over the past 40 years. Panel 2: Rising Temperatures and Earlier Snowmelt Temperatures are increasing much faster in the Western U.S. than for the planet as a whole. Since 1970, average annual temperatures in the Western U.S. have increased by 1.9° F, about twice the pace of the global average warming. Scientists are able to gauge the onset of spring snowmelt by evaluating streamflow gauges throughout the Western U.S. Depending on location, the onset of spring snowmelt is occurring 1-4 weeks earlier today than it did in the late 1940s. Panel 3: Future Projections The projected increase in annual burn area varies depending on the type of ecosystem. Higher temperatures are expected to affect certain ecosystems, such as the Southern Rocky Mountain Steppe-Forest of central Colorado, more than others, such as the semi-desert and desert of southern Arizona and California. Every ecosystem type, however, is projected to experience an increase in average annual burn area. The range of projected temperature increases in the Western U.S. by mid-century (2040 – 2070) represents a choice of two possible futures — from one in which we drastically reduce heat-trapping emissions (the projected low end of a lower emissions pathway) to a future in which we continue with “business as usual” (the projected high end of a higher emissions pathway).
Climate change is the greatest global threat to coral reef ecosystems, and scientific evidence now clearly indicates that the Earth’s atmosphere and ocean are warming. A changing climate is affecting coral reef ecosystems through sea level rise, changes to the frequency and intensity of tropical storms, and altered ocean circulation patterns. When combined, all of these impacts dramatically alter ecosystem function, as well as the goods and services coral reef ecosystems provide to people around the globe. Our infographic explains the process, from sea-level rise to ocean acidificiation. Source: https://www.noaa.gov/multimedia/infographic/infographic-how-does-climate-change-affect-coral-reefs
” The Intergovernmental Panel on Climate Change (IPCC) is a scientific and intergovernmental body under the auspices of the United Nations, set up at the request of member governments, dedicated to the task of providing the world with an objective, scientific view of climate change and its political and economic impacts. It was first established in 1988 by two United Nations organizations, the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP), and later endorsed by the United Nations General Assembly through Resolution 43/53. Membership of the IPCC is open to all members of the WMO and UNEP. The IPCC produces reports that support the United Nations Framework Convention on Climate Change (UNFCCC), which is the main international treaty on climate change. The ultimate objective of the UNFCCC is to “stabilize greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic [i.e., human-induced] interference with the climate system”. IPCC reports cover “the scientific, technical and socio-economic information relevant to understanding the scientific basis of risk of human-induced climate change, its potential impacts and options for adaptation and mitigation.”
The IPCC does not carry out its own original research, nor does it do the work of monitoring climate or related phenomena itself. The IPCC bases its assessment on the published literature, which includes peer-reviewed and non-peer-reviewed sources.
Thousands of scientists and other experts contribute (on a voluntary basis, without payment from the IPCC) to writing and reviewing reports, which are then reviewed by governments. IPCC reports contain a “Summary for Policymakers”, which is subject to line-by-line approval by delegates from all participating governments. Typically this involves the governments of more than 120 countries.
The IPCC provides an internationally accepted authority on climate change,[10] producing reports which have the agreement of leading climate scientists and the consensus of participating governments. The 2007 Nobel Peace Prize was shared, in equal parts, between the IPCC and Al Gore.” https://en.wikipedia.org/wiki/Intergovernmental_Panel_on_Climate_Change.
One of the worst ecological human disasters happened in the Aral Sea (Sea of Islands) located in the far western Asia, in the east of the Caspian Sea located in the countries of Kazakhstan and Uzbekistan. It once had 68,000 square km. Today the sea is almost completely gone it is evaporating day by day, contaminated by fertilizer residues, biological weapons tested by the Soviet Union for the Cold War. Source: https://www.worldatlas.com/aatlas/infopage/aralsea.htm. This magnificent sea was the 4th largest in 1960 until the high demand of cotton killed it. The Sea paid with its life for the production of entire fields of cotton, (white gold) at the very high price.
Location of The Aral Sea
“There is not enough cotton”- that is what the authorities said. Cotton needed to be planted everywhere to provide all Russia even though the Aral had to die in the process and so it was made. Over 40 years ago two rivers that ran into the Aral, were deviated those were the Amu Daria and Sir Daria in order to irrigate field full of cotton. The tubes and material used to take this waters were not good quality and most of the flow was lost in its way. During years and years, the Sea received no water from its tributaries, the consequence was it began to dry day by day. Today it is only 75% of what it was in its good times. It was not only it was drying up but its waters were polluted with all the fertilizers used for cotton plantations. Its waters started affecting people around cases as malformations, high infant mortality, and linfatic cancer appeared.
The Aral Sea in 1989 (left) and 2014 (right).
Symposiums are held in order to generate ideas to bring the Aral back. Salinity is so high flora and fauna die, pesticides in the sand left are being carried to the population in forms of dust storms. The Soviet Union had secret laboratories installed in the Aral, they were abandoned as the sea dried out with no care of biosecurity rules. The multiple virus present in them were free into the environment. The Aral´s sand contains boats all around its body, the ones that make the settlers feel nostalgic of this immense and beautiful sea in its good times. Temperatures have turned extreme in the place and authorities say it is because of climate change.
Settlers say there is an old legend that tells that The Aral has gone three times and three times it has come back. They hoped some time it will come back. Fisherman remembers the good and tasty fish they used to capture in the Sea. Thet said those fish ate Seagrass that made them tastier. Their diet was based on fish, every meal they had food prepared with fish. The great factory of fish established on the place processed thousands of tons of fish and approximately 600 men worked in here they sent their products mostly to the Soviet Union. The factory had to close when the water level went down and the fish could no longer live in its waters.Source: Documentary by We are Water Foundation (Isabel Coixet) “Aral the Lost Sea”.
The Aral is all over, no more fish no more water to sail on………
Climate change is taking a serious toll on planet earth, and whether is man-made or as a result of natural causes, there’s no denying that it’s worse then ever.
WatchMojo presents the top 10 signs that climate change is worse than ever.
Greenland is the singing canary for this:
Severe wildfires, melting glaciers and extreme weather rank amongst the top of these foreboding signs.
So, an important playlist on Climate change basics. Climate change occurs when changes in Earth’s climate system result in new weather patterns that last for at least a few decades, and maybe for millions of years. The climate system is comprised of five interacting parts, the atmosphere (air), hydrosphere (water), cryosphere (ice and permafrost), biosphere (living things), and lithosphere(earth’s crust and upper mantle). The climate system receives nearly all of its energy from the sun, with a relatively tiny amount from earth’s interior. The climate system also gives off energy to outer space. The balance of incoming and outgoing energy, and the passage of the energy through the climate system, determines Earth’s energy budget. When the incoming energy is greater than the outgoing energy, earth’s energy budget is positive and the climate system is warming. If more energy goes out, the energy budget is negative and earth experiences cooling.
This is a complete course on the matter:
And here is another fairly well extended playlist on climate change
On the broadest scale, the rate at which energy is received from the Sun and the rate at which it is lost to space determine the equilibrium temperature and climate of Earth. This energy is distributed around the globe by winds, ocean currents,[9][10] and other mechanisms to affect the climates of different regions.[11]
Factors that can shape climate are called climate forcings or “forcing mechanisms”.[12] These include processes such as variations in solar radiation, variations in the Earth’s orbit, variations in the albedo or reflectivity of the continents, atmosphere, and oceans, 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 more slowly in reaction to climate forcings, while others respond more quickly. There are also key threshold factors which when exceeded can produce rapid change.
Forcing mechanisms can be either “internal” or “external”. Internal forcing mechanisms are natural processes within the climate system itself (e.g., the thermohaline circulation). External forcing mechanisms can be either anthropogenic (e.g. increased emissions of greenhouse gases and dust) or natural (e.g., changes in solar output, the earth’s orbit, volcano eruptions).
Whether the initial forcing mechanism is internal or external, the response of the climate system might be fast (e.g., a sudden cooling due to airborne volcanic ash reflecting sunlight), slow (e.g. thermal expansion of warming ocean water), or a combination (e.g., sudden loss of albedo in the Arctic Ocean as sea ice melts, followed by more gradual thermal expansion of the water). Therefore, the climate system can respond abruptly, but the full response to forcing mechanisms might not be fully developed for centuries or even longer.
Internal forcing mechanisms
Scientists generally define the five components of earth’s climate system to include atmosphere, hydrosphere, cryosphere, lithosphere (restricted to the surface soils, rocks, and sediments), and biosphere.[13] Natural changes in the climate system (“internal forcings”) result in internal “climate variability”.[14] Examples include the type and distribution of species, and changes in ocean-atmosphere circulations.
The ocean and atmosphere can work together to spontaneously generate internal climate variability that can persist for years to decades at a time.[15][16] Examples of this type of variability include the El Niño–Southern Oscillation, the Pacific decadal oscillation, and the Atlantic Multidecadal Oscillation. These variations can affect global average surface temperature by redistributing heat between the deep ocean and the atmosphere[17][18] and/or by altering the cloud/water vapor/sea ice distribution which can affect the total energy budget of the earth.[19][20]
The oceanic aspects of these circulations can generate variability on centennial timescales due to the ocean having hundreds of times more mass than in the atmosphere, and thus very high thermal inertia. For example, alterations to ocean processes such as thermohaline circulation play a key role in redistributing heat in the world’s oceans. Due to the long timescales of this circulation, ocean temperature at depth is still adjusting to effects of the Little Ice Age[21] which occurred between the 1600 and 1800s.
A schematic of modern thermohaline circulation. Tens of millions of years ago, continental-plate movement formed a land-free gap around Antarctica, allowing the formation of the ACC, which keeps warm waters away from Antarctica.
glaciation 2.3 billion years ago triggered by the evolution of oxygenic photosynthesis, which depleted the atmosphere of the greenhouse gas carbon dioxide and introduced free oxygen.[25][26]
In the context of climate variation, anthropogenic factors are human activities which affect the climate. The scientific consensus on climate change is “that climate is changing and that these changes are in large part caused by human activities”,[35] and it “is largely irreversible”.[36]
… there is a strong, credible body of evidence, based on multiple lines of research, documenting that climate is changing and that these changes are in large part caused by human activities. While much remains to be learned, the core phenomenon, scientific questions, and hypotheses have been examined thoroughly and have stood firm in the face of serious scientific debate and careful evaluation of alternative explanations.
Of most concern in these anthropogenic factors is the increase in CO2 levels. This is due to emissions from fossil fuelcombustion, followed by aerosols (particulate matter in the atmosphere), and the CO2 released by cementmanufacture.[37] Other factors, including land use, ozone depletion, animal husbandry (ruminant animals such as cattleproduce methane,[38] as do termites), 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.[39]
Slight variations in Earth’s motion 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 kinematic change 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 affect climate and are notable for their correlation to glacialand interglacial periods,[40] their correlation with the advance and retreat of the Sahara,[40] and for their appearance in the stratigraphic record.[41][42]
The IPCC notes that Milankovitch cycles drove the ice age cycles, CO2 followed temperature change “with a lag of some hundreds of years”, and that as a feedback amplified temperature change.[43] The depths of the ocean have a lag time in changing temperature (thermal inertia on such scale). Upon seawater temperature change, the solubility of CO2 in the oceans changed, as well as other factors affecting air-sea CO2 exchange.[44]
Variations in solar activity during the last several centuries based on observations of sunspots and berylliumisotopes. The period of extraordinarily few sunspots in the late 17th century was the Maunder minimum.
The Sun is the predominant source of energy input to the Earth. Other sources include geothermal energy from the Earth’s core, tidal energy from the Moon and heat from the decay of radioactive compounds. Both long- and short-term variations in solar intensity are known to affect global climate.
Three to four billion years ago, the Sun emitted only 75% as much power as it does today.[45] If the atmospheric composition had been the same as today, liquid water should not have existed on Earth. However, there is evidence for the presence of water on the early Earth, in the Hadean[46][47] and Archean[48][46] eons, leading to what is known as the faint young Sun paradox.[49] Hypothesized solutions to this paradox include a vastly different atmosphere, with much higher concentrations of greenhouse gases than currently exist.[50] Over the following approximately 4 billion years, the energy output of the Sun increased and atmospheric composition changed. The Great Oxygenation Event—oxygenation of the atmosphere around 2.4 billion years ago—was the most notable alteration. Over the next five billion years from the present, 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 any life on Earth that survives until that time.[51]
Solar activity events recorded in radiocarbon. Values since 1950 not shown.
Solar output varies on shorter time scales, including the 11-year solar cycle[52] and longer-term modulations.[53] Solar intensity variations, possibly as a result of the Wolf, Spörer, and the Maunder Minima, are considered to have been influential in triggering the Little Ice Age.[54]This event extended from 1550 to 1850 AD and was marked by relative cooling and greater glacier extent than the centuries before and afterward.[55][56] Solar variation may also have affected 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.
Some studies point toward solar radiation increases from cyclical sunspot activity affecting global warming, and climate may be influenced by the sum of all effects (solar variation, anthropogenic radiative forcings, etc.).[57][58]
A 2010 study suggests “that the effects of solar variability on temperature throughout the atmosphere may be contrary to current expectations”.[59]
In 2011, CERN announced the initial results from its CLOUD experiment in the Nature journal.[60] The results indicate that ionisation from cosmic rays significantly enhances aerosol formation in the presence of sulfuric acid and water, but in the lower atmosphere where ammonia is also required, this is insufficient to account for aerosol formation and additional trace vapours must be involved. The next step is to find more about these trace vapours, including whether they are of natural or human origin.
Volcanism
In atmospheric temperature from 1979 to 2010, determined by MSUNASA satellites, effects appear from aerosols released by major volcanic eruptions (El Chichón and Pinatubo). El Niño is a separate event, from ocean variability.
The eruptions considered to be large enough to affect the Earth’s climate on a scale of more than 1 year are the ones that inject over 100,000 tons of SO2 into the stratosphere.[61] This is due to the optical properties of SO2 and sulfate aerosols, which strongly absorb or scatter solar radiation, creating a global layer of sulfuric acid haze.[62] On average, such eruptions occur several times per century, and cause cooling (by partially blocking the transmission of solar radiation to the Earth’s surface) for a period of several years.
The eruption of Mount Pinatubo in 1991, the second largest terrestrial eruption of the 20th century, affected the climate substantially, subsequently global temperatures decreased by about 0.5 °C (0.9 °F) for up to three years.[63][64] Thus, the cooling over large parts of the Earth reduced surface temperatures in 1991–93, the equivalent to a reduction in net radiation of 4 watts per square meter.[65] The Mount Tambora eruption in 1815 caused the Year Without a Summer.[66]Much larger eruptions, known as large igneous provinces, occur only a few times every fifty – one hundred million years – through flood basalt, and caused in Earth past global warming and mass extinctions.[67]
Small eruptions, with injections of less than 0.1 Mt of sulfur dioxide into the stratosphere, affect the atmosphere only subtly, as temperature changes are comparable with natural variability. However, because smaller eruptions occur at a much higher frequency, they too significantly affect Earth’s atmosphere.[61][68]
Seismic monitoring maps current and future trends in volcanic activities, and tries to develop early warning systems. In climate modelling the aim is to study the physical mechanisms and feedbacks of volcanic forcing.[69]
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. The US Geological Survey estimates are that volcanic emissions are at a much lower level than the effects of current human activities, which generate 100–300 times the amount of carbon dioxide emitted by volcanoes.[70] A review of published studies indicates that annual volcanic emissions of carbon dioxide, including amounts released from mid-ocean ridges, volcanic arcs, and hot spot volcanoes, are only the equivalent of 3 to 5 days of human-caused output. The annual amount put out by human activities may be greater than the amount released by supererruptions, the most recent of which was the Toba eruption in Indonesia 74,000 years ago.[71]
Although volcanoes are technically part of the lithosphere, which itself is part of the climate system, the IPCC explicitly defines volcanism as an external forcing agent.[72]
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.[73]
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.[74][75] During the Carboniferousperiod, about 300 to 360 million years ago, plate tectonics may have triggered large-scale storage of carbon and increased glaciation.[76] Geologic evidence points to a “megamonsoonal” circulation pattern during the time of the supercontinentPangaea, and climate modeling suggests that the existence of the supercontinent was conducive to the establishment of monsoons.[77]
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 or islands.
Other mechanisms
The Earth receives an influx of ionized particles known as cosmic rays from a variety of external sources, including the Sun. A hypothesis holds that an increase in the cosmic ray flux would increase the ionization in the atmosphere, leading to greater cloud cover. This, in turn, would tend to cool the surface. The non-solar cosmic ray flux may vary as a result of a nearby supernova event, the solar system passing through a dense interstellar cloud, or the oscillatory movement of the Sun’s position with respect to the galactic plane. The latter can increase the flux of high-energy cosmic rays coming from the Virgo cluster.[78]
Evidence exists that the Chicxulub impact some 66 million years ago had severely affected the Earth’s climate. Large quantities of sulfate aerosols were kicked up into the atmosphere, decreasing global temperatures by up to 26 °C and producing sub-freezing temperatures for a period of 3−16 years. The recovery time for this event took more than 30 years.[79]
Study of past climates
A number of disciplines throw light on past climates.
Climate change in the recent past may be detected by corresponding changes in settlement and agricultural patterns.[80]Archaeological evidence, oral historyand historical documents can offer insights into past changes in the climate. Climate change effects have been linked to the rise[81] and also the collapse of various civilizations.[80]
Decline in thickness of glaciers worldwide over the past half-century
Physical evidence and effects
Global temperature anomalies for 2015 compared to the 1951–1980 baseline. 2015 was the warmest year in the NASA/NOAAtemperature record, which starts in 1880. It has since been superseded by 2016 (NASA/NOAA; 20 January 2016).[82]
Comparisons between Asian Monsoonsfrom 200 AD to 2000 AD (staying in the background on other plots), Northern Hemisphere temperature, Alpine glacier extent (vertically inverted as marked), and human history as noted by the U.S. NSF.
Arctic temperature anomalies over a 100-year period as estimated by NASA. Typical high monthly variance can be seen, while longer-term averages highlight trends.
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 19th century. 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,[3]dendrochronology, sea level change, and glacial geology.
Temperature (surface and oceans)
The instrumental temperature record from surface stations was supplemented by radiosonde balloons, extensive atmospheric monitoring by the mid-20th century, and, from the 1970s on, with global satellite data as well. Taking the record as a whole, most of the 20th century had been unprecedentedly warm, while the 19th and 17th centuries were quite cool.[83]
The 18O/16O ratio in calcite and ice core samples used to deduce ocean temperature in the distant past is an example of a temperature proxy method, as are other climate metrics noted in subsequent categories.
Glaciers
Glaciers are considered among the most sensitive indicators of climate change.[84] Their size is determined by a mass balance between snow input and melt output. As temperatures warm, glaciers retreat unless snow precipitation increases to make up for the additional melt; the converse is also true.
Glaciers grow and shrink due both to natural variability and external forcings. Variability in temperature, precipitation, and englacial and subglacial hydrology can strongly determine the evolution of a glacier in a particular season. Therefore, one must average over a decadal or longer time-scale and/or over many individual glaciers to smooth out the local short-term variability and obtain a glacier history that is related to climate.
A world glacier inventory has been compiled since the 1970s, initially based mainly on aerial photographs and maps but now relying more on satellites. This compilation tracks more than 100,000 glaciers covering a total area of approximately 240,000 km², and preliminary estimates indicate that the remaining ice cover is 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 the present.[85][86]
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.[87] 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 orbital forcing.
Glaciers leave behind moraines that contain a wealth of material—including organic matter, quartz, and potassium that may be 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 ascertained.
Data from NASA‘s Grace satellites show that the land ice sheets in both Antarctica (upper chart) and Greenland (lower) have been losing mass since 2002. Both ice sheets have seen an acceleration of ice mass loss since 2009.[88]
The decline in Arctic sea ice, both in extent and thickness, over the last several decades is further evidence for rapid climate change.[89] Sea ice is frozen seawater that floats on the ocean surface. It covers millions of square kilometers in the polar regions, varying with the seasons. In the Arctic, some sea ice remains year after year, whereas almost all Southern Ocean or Antarctic sea ice melts away and reforms annually. Satellite observations show that Arctic sea ice is now declining at a rate of 13.2 percent per decade, relative to the 1981 to 2010 average.[90] The 2007 Arctic summer sea ice retreat was unprecedented. Decades of shrinking and thinning in a warm climate has put the Arctic sea ice in a precarious position, it is now vulnerable to atmospheric anomalies.[91] “Both extent and volume anomaly fluctuate little from January to July and then decrease steeply in August and September”.[91] This decrease is because of lessened ice production as a result of the unusually high SAT. During the Arctic summer, a slower rate of sea ice production is the same as a faster rate of sea ice melting.
This video summarizes how climate change, associated with increased carbon dioxide levels, has affected plant growth.
The estimated change in sea level caused by carbon dioxide emissions.
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.[92] To measure sea levels prior to instrumental measurements, scientists have dated coral reefs that grow near the surface of the ocean, coastal sediments, marine terraces, ooids in limestones, and nearshore archaeological remains. The predominant dating methods used are uranium series and radiocarbon, with cosmogenic radionuclides being sometimes used to date terraces that have experienced relative sea level fall. In the early Pliocene, global temperatures were 1–2˚C warmer than the present temperature, yet sea level was 15–25 meters higher than today.[93][94][95]
According to recent studies, global-mean sea level rose by 195 mm during the period from 1870 to 2004.[96] Since 2004, satellite-based records indicate that there has been a further 43 mm of global-mean sea levels rise, as of July 2017.[97]
Ice cores
The Antarctic temperature changes during the last several glacial and interglacial cycles of the present ice age, according to δ18O ratios.
Analysis of ice in a core drilled from an 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.
Past precipitation can be estimated in the modern era with the global network of precipitation gauges. Surface coverage over oceans and remote areas is relatively sparse, but, reducing reliance on interpolation, satellite clouds and precipitation data has been available since the 1970s.[98] Quantification of climatological variation of precipitation in prior centuries and epochs is less complete but approximated using proxies such as marine sediments, ice cores, cave stalagmites, and tree rings.[99] In July 2016 scientists published evidence of increased cloud cover over polar regions,[100] as predicted by climate models.[101]
Climatological temperatures substantially affect cloud cover and precipitation. For instance, during the Last Glacial Maximum of 18,000 years ago, thermal-driven evaporation from the oceans onto continental landmasses was low, causing large areas of extreme desert, including polar deserts (cold but with low rates of cloud cover and precipitation).[102] In contrast, the world’s climate was cloudier and wetter than today near the start of the warm Atlantic Period of 8000 years ago.[102]
Estimated global land precipitation increased by approximately 2% over the course of the 20th century, though the calculated trend varies if different time endpoints are chosen, complicated by ENSO and other oscillations, including greater global land cloud cover precipitation in the 1950s and 1970s than the later 1980s and 1990s despite the positive trend over the century overall.[98][103][104] Similar slight overall increase in global river runoff and in average soil moisture has been perceived.[103]
Vegetation
A change in the type, distribution and coverage of vegetation may occur given a change in the climate. Some changes in climate may result in increased precipitation and warmth, resulting in improved plant growth and the subsequent sequestration of airborne CO2. A gradual increase in warmth in a region will lead to earlier flowering and fruiting times, driving a change in the timing of life cycles of dependent organisms. Conversely, cold will cause plant bio-cycles to lag.[105] Larger, faster or more radical changes, however, may result in vegetation stress, rapid plant loss and desertification in certain circumstances.[106][107] An example of this occurred during the Carboniferous Rainforest Collapse (CRC), an extinction event 300 million years ago. At this time vast rainforests covered the equatorial region of Europe and America. Climate change devastated these tropical rainforests, abruptly fragmenting the habitat into isolated ‘islands’ and causing the extinction of many plant and animal species.[106] Such stress can alter the growth rate of trees, which allows scientists to infer climate trends by analyzing the growth rate of tree rings. This branch of climate science is called dendroclimatology, and is one of the many ways they research climate trends prior to written records.[108]
Forest genetic resources
Even though this is a field with many uncertainties, it is expected that over the next 50 years climate changes will have an effect on the diversity of forest genetic resources and thereby on the distribution of forest tree species and the composition of forests. Diversity of forest genetic resources enables the potential for a species (or a population) to adapt to climatic changes and related future challenges such as temperature changes, drought, pests, diseases and forest fire. However, species are not naturally capable to adapt in the pace of which the climate is changing and the increasing temperatures will most likely facilitate the spread of pests and diseases, creating an additional threat to forest trees and their populations.[109] To inhibit these problems human interventions, such as transfer of forest reproductive material, may be needed.[110]
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 layers of sediment in lakes, bogs, or river deltas indicate changes in plant communities. These changes are often a sign of a changing climate.[111][112] As an example, palynological studies have been used to track changing vegetation patterns throughout the Quaternary glaciations[113] and especially since the last glacial maximum.[114]
Bottom: Potential vegetation in climate now if not for human effects like agriculture.[102]
Animals
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.[115] The studies of the impact in vertebrates are few mainly from developing countries, where there are the fewest studies; between 1970 and 2012, vertebrates declined by 58 percent, with freshwater, marine, and terrestrial populations declining by 81, 36, and 35 percent, respectively.[116]
Similarly, the historical abundance of various fish species has been found to have a substantial relationship with observed climatic conditions.[117] Changes in the primary productivity of autotrophs in the oceans can affect marine food webs.[118]
Human impacts
According to the IPCC, human-caused global warming is driving climate changes impacting both human and natural systems on all continents and across the oceans. Human-caused global warming results from the increased use of fossil fuels in transportation, manufacturing and communications. Internet induced climate change is newest contributor to human-induced climate change.[119] Some of the impacts include the altering of ecosystems (with a few extinctions), threat to food production and water supplies due to extreme weather, and the dislocation of human communities due to sea level rise and other climate factors. Taken together these hazards also exacerbate other stressors such as poverty.[120] Possible societal responses include efforts to prevent additional climate change, adapting to unavoidable climate change, and possible future climate engineering.
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