Climate variability and change

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Atmospheric sciences

Climate variability includes all the variations in the climate that last longer than individual weather events, whereas the term climate change only refers to those variations that persist for a longer period of time, typically decades or more. Climate change may refer to any time in Earth's history, but the term is now commonly used to describe contemporary climate change, often popularly referred to as global warming. Since the Industrial Revolution, the climate has increasingly been affected by human activities.

The climate system receives nearly all of its energy from the sun and radiates energy to outer space. The balance of incoming and outgoing energy and the passage of the energy through the climate system is 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.

The energy moving through Earth's climate system finds expression in weather, varying on geographic scales and time. Long-term averages and variability of weather in a region constitute the region's climate. Such changes can be the result of "internal variability", when natural processes inherent to the various parts of the climate system alter the distribution of energy. Examples include variability in ocean basins such as the Pacific decadal oscillation and Atlantic multidecadal oscillation. Climate variability can also result from external forcing, when events outside of the climate system's components produce changes within the system. Examples include changes in solar output and volcanism.

Climate variability has consequences for sea level changes, plant life, and mass extinctions; it also affects human societies.

Terminology

Climate variability is the term to describe variations in the mean state and other characteristics of climate (such as chances or possibility of extreme weather, etc.) "on all spatial and temporal scales beyond that of individual weather events." Some of the variability does not appear to be caused by known systems and occurs at seemingly random times. Such variability is called random variability or noise. On the other hand, periodic variability occurs relatively regularly and in distinct modes of variability or climate patterns.

The term climate change is often used to refer specifically to anthropogenic climate change. Anthropogenic climate change is caused by human activity, as opposed to changes in climate that may have resulted as part of Earth's natural processes. Global warming became the dominant popular term in 1988, but within scientific journals global warming refers to surface temperature increases while climate change includes global warming and everything else that increasing greenhouse gas levels affect.

A related term, climatic change, was proposed by the World Meteorological Organization (WMO) in 1966 to encompass all forms of climatic variability on time-scales longer than 10 years, but regardless of cause. During the 1970s, the term climate change replaced climatic change to focus on anthropogenic causes, as it became clear that human activities had a potential to drastically alter the climate. Climate change was incorporated in the title of the Intergovernmental Panel on Climate Change (IPCC) and the UN Framework Convention on Climate Change (UNFCCC). Climate change is now used as both a technical description of the process, as well as a noun used to describe the problem.

Causes

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, and other mechanisms to affect the climates of different regions.

Factors that can shape climate are called climate forcings or "forcing mechanisms". 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. External forcing 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). There are a variety of climate change feedbacks that can either amplify or diminish the initial forcing. There are also key thresholds which when exceeded can produce rapid or irreversible change.

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. An example of fast change is the atmospheric cooling after a volcanic eruption, when volcanic ash reflects sunlight. Thermal expansion of ocean water after atmospheric warming is slow, and can take thousands of years. A combination is also possible, e.g., sudden loss of albedo in the Arctic Ocean as sea ice melts, followed by more gradual thermal expansion of the water.

Climate variability can also occur due to internal processes. Internal unforced processes often involve changes in the distribution of energy in the ocean and atmosphere, for instance, changes in the thermohaline circulation.

Internal variability

There is seasonal variability in how new high temperature records have outpaced new low temperature records.

Climatic changes due to internal variability sometimes occur in cycles or oscillations. For other types of natural climatic change, we cannot predict when it happens; the change is called random or stochastic. From a climate perspective, the weather can be considered random. If there are little clouds in a particular year, there is an energy imbalance and extra heat can be absorbed by the oceans. Due to climate inertia, this signal can be 'stored' in the ocean and be expressed as variability on longer time scales than the original weather disturbances. If the weather disturbances are completely random, occurring as white noise, the inertia of glaciers or oceans can transform this into climate changes where longer-duration oscillations are also larger oscillations, a phenomenon called red noise. Many climate changes have a random aspect and a cyclical aspect. This behavior is dubbed stochastic resonance. Half of the 2021 Nobel prize on physics was awarded for this work to Klaus Hasselmann jointly with Syukuro Manabe for related work on climate modelling. While Giorgio Parisi who with collaborators introduced the concept of stochastic resonance was awarded the other half but mainly for work on theoretical physics.

Ocean-atmosphere variability

The ocean and atmosphere can work together to spontaneously generate internal climate variability that can persist for years to decades at a time. These variations can affect global average surface temperature by redistributing heat between the deep ocean and the atmosphere and/or by altering the cloud/water vapor/sea ice distribution which can affect the total energy budget of the Earth.

Oscillations and cycles

Colored bars show how El Niño years (red, regional warming) and La Niña years (blue, regional cooling) relate to overall global warming. The El Niño–Southern Oscillation has been linked to variability in longer-term global average temperature increase.

A climate oscillation or climate cycle is any recurring cyclical oscillation within global or regional climate. They are quasiperiodic (not perfectly periodic), so a Fourier analysis of the data does not have sharp peaks in the spectrum. Many oscillations on different time-scales have been found or hypothesized:

• the El Niño–Southern Oscillation (ENSO) – A large scale pattern of warmer (El Niño) and colder (La Niña) tropical sea surface temperatures in the Pacific Ocean with worldwide effects. It is a self-sustaining oscillation, whose mechanisms are well-studied. ENSO is the most prominent known source of inter-annual variability in weather and climate around the world. The cycle occurs every two to seven years, with El Niño lasting nine months to two years within the longer term cycle. The cold tongue of the equatorial Pacific Ocean is not warming as fast as the rest of the ocean, due to increased upwelling of cold waters off the west coast of South America.
• the Madden–Julian oscillation (MJO) – An eastward moving pattern of increased rainfall over the tropics with a period of 30 to 60 days, observed mainly over the Indian and Pacific Oceans.
• the North Atlantic oscillation (NAO) – Indices of the NAO are based on the difference of normalized sea-level pressure (SLP) between Ponta Delgada, Azores and Stykkishólmur/Reykjavík, Iceland. Positive values of the index indicate stronger-than-average westerlies over the middle latitudes.
• the Quasi-biennial oscillation – a well-understood oscillation in wind patterns in the stratosphere around the equator. Over a period of 28 months the dominant wind changes from easterly to westerly and back.
• Pacific Centennial Oscillation - a climate oscillation predicted by some climate models
• the Pacific decadal oscillation – The dominant pattern of sea surface variability in the North Pacific on a decadal scale. During a "warm", or "positive", phase, the west Pacific becomes cool and part of the eastern ocean warms; during a "cool" or "negative" phase, the opposite pattern occurs. It is thought not as a single phenomenon, but instead a combination of different physical processes.
• the Interdecadal Pacific oscillation (IPO) – Basin wide variability in the Pacific Ocean with a period between 20 and 30 years.
• the Atlantic multidecadal oscillation – A pattern of variability in the North Atlantic of about 55 to 70 years, with effects on rainfall, droughts and hurricane frequency and intensity.
• North African climate cycles – climate variation driven by the North African Monsoon, with a period of tens of thousands of years.
• the Arctic oscillation (AO) and Antarctic oscillation (AAO) – The annular modes are naturally occurring, hemispheric-wide patterns of climate variability. On timescales of weeks to months they explain 20–30% of the variability in their respective hemispheres. The Northern Annular Mode or Arctic oscillation (AO) in the Northern Hemisphere, and the Southern Annular Mode or Antarctic oscillation (AAO) in the southern hemisphere. The annular modes have a strong influence on the temperature and precipitation of mid-to-high latitude land masses, such as Europe and Australia, by altering the average paths of storms. The NAO can be considered a regional index of the AO/NAM. They are defined as the first EOF of sea level pressure or geopotential height from 20°N to 90°N (NAM) or 20°S to 90°S (SAM).
• Dansgaard–Oeschger cycles – occurring on roughly 1,500-year cycles during the Last Glacial Maximum

Ocean current changes

See also: Thermohaline circulation

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.

The oceanic aspects of climate variability 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.

Ocean currents transport a lot of energy from the warm tropical regions to the colder polar regions. Changes occurring around the last ice age (in technical terms, the last glacial period) show that the circulation in the North Atlantic can change suddenly and substantially, leading to global climate changes, even though the total amount of energy coming into the climate system did not change much. These large changes may have come from so called Heinrich events where internal instability of ice sheets caused huge ice bergs to be released into the ocean. When the ice sheet melts, the resulting water is very low in salt and cold, driving changes in circulation.

Life

Life affects climate through its role in the carbon and water cycles and through such mechanisms as albedo, evapotranspiration, cloud formation, and weathering. Examples of how life may have affected past climate include:

• 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
• another glaciation 300 million years ago ushered in by long-term burial of decomposition-resistant detritus of vascular land-plants (creating a carbon sink and forming coal)
• termination of the Paleocene–Eocene Thermal Maximum 55 million years ago by flourishing marine phytoplankton
• reversal of global warming 49 million years ago by 800,000 years of arctic azolla blooms
• global cooling over the past 40 million years driven by the expansion of grass-grazer ecosystems

External climate forcing

Greenhouse gases

Main article: Greenhouse gas

CO₂ concentrations over the last 800,000 years as measured from ice cores (blue/green) and directly (black)

Whereas greenhouse gases released by the biosphere is often seen as a feedback or internal climate process, greenhouse gases emitted from volcanoes are typically classified as external by climatologists. Greenhouse gases, such as CO₂, methane and nitrous oxide, heat the climate system by trapping infrared light. 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.

Since the Industrial Revolution, humanity has been adding to greenhouse gases by emitting CO₂ from fossil fuel combustion, changing land use through deforestation, and has further altered the climate with aerosols (particulate matter in the atmosphere), release of trace gases (e.g. nitrogen oxides, carbon monoxide, or methane). Other factors, including land use, ozone depletion, animal husbandry (ruminant animals such as cattle produce methane), and deforestation, also play a role.

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. The annual amount put out by human activities may be greater than the amount released by supereruptions, the most recent of which was the Toba eruption in Indonesia 74,000 years ago.

Orbital variations

Milankovitch cycles from 800,000 years ago in the past to 800,000 years in the future.

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, these produce Milankovitch cycles which affect climate and are notable for their correlation to glacial and interglacial periods, their correlation with the advance and retreat of the Sahara, and for their appearance in the stratigraphic record.

During the glacial cycles, there was a high correlation between CO₂ concentrations and temperatures. Early studies indicated that CO₂ concentrations lagged temperatures, but it has become clear that this is not always the case. When ocean temperatures increase, the solubility of CO₂ decreases so that it is released from the ocean. The exchange of CO₂ between the air and the ocean can also be impacted by further aspects of climatic change. These and other self-reinforcing processes allow small changes in Earth's motion to have a large effect on climate.

Solar output

Variations in solar activity during the last several centuries based on observations of sunspots and beryllium isotopes. 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's climate system. 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 term variations in solar intensity are known to affect global climate. Solar output varies on shorter time scales, including the 11-year solar cycle and longer-term modulations. Correlation between sunspots and climate and tenuous at best.

Three to four billion years ago, the Sun emitted only 75% as much power as it does today. If the atmospheric composition had been the same as today, liquid water should not have existed on the Earth's surface. However, there is evidence for the presence of water on the early Earth, in the Hadean and 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. Over the next five billion years, 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.

Volcanism

In atmospheric temperature from 1979 to 2010, determined by MSU NASA satellites, effects appear from aerosols released by major volcanic eruptions (El Chichón and Pinatubo). El Niño is a separate event, from ocean variability.

The volcanic 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. 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. 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. 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.

Notable eruptions in the historical records are the 1991 eruption of Mount Pinatubo which lowered global temperatures by about 0.5 °C (0.9 °F) for up to three years, and the 1815 eruption of Mount Tambora causing the Year Without a Summer.

At a larger scale—a few times every 50 million to 100 million years—the eruption of large igneous provinces brings large quantities of igneous rock from the mantle and lithosphere to the Earth's surface. Carbon dioxide in the rock is then released into the atmosphere. 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.

Plate tectonics

Main article: 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.

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. During the Carboniferous period, about 300 to 360 million years ago, plate tectonics may have triggered large-scale storage of carbon and increased glaciation. 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.

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

It has been postulated that ionized particles known as cosmic rays could impact cloud cover and thereby the climate. As the sun shields the Earth from these particles, changes in solar activity were hypothesized to influence climate indirectly as well. To test the hypothesis, CERN designed the CLOUD experiment, which showed the effect of cosmic rays is too weak to influence climate noticeably.

Evidence exists that the Chicxulub asteroid 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. The large-scale use of nuclear weapons has also been investigated for its impact on the climate. The hypothesis is that soot released by large-scale fires blocks a significant fraction of sunlight for as much as a year, leading to a sharp drop in temperatures for a few years. This possible event is described as nuclear winter.

Humans' use of land impact how much sunlight the surface reflects and the concentration of dust. Cloud formation is not only influenced by how much water is in the air and the temperature, but also by the amount of aerosols in the air such as dust. Globally, more dust is available if there are many regions with dry soils, little vegetation and strong winds.

Evidence and measurement of climate changes

Paleoclimatology is the study of changes in climate through the entire history of Earth. It uses a variety of proxy methods from the Earth and life sciences to obtain data preserved within things such as rocks, sediments, ice sheets, tree rings, corals, shells, and microfossils. It then uses the records to determine the past states of the Earth's various climate regions and its atmospheric system. Direct measurements give a more complete overview of climate variability.

Direct measurements

Climate changes that occurred after the widespread deployment of measuring devices can be observed directly. Reasonably complete global records of surface temperature are available beginning from the mid-late 19th century. Further observations are derived indirectly from historical documents. Satellite cloud and precipitation data has been available since the 1970s.

Historical climatology is the study of historical changes in climate and their effect on human history and development. The primary sources include written records such as sagas, chronicles, maps and local history literature as well as pictorial representations such as paintings, drawings and even rock art. Climate variability in the recent past may be derived from changes in settlement and agricultural patterns. Archaeological evidence, oral history and historical documents can offer insights into past changes in the climate. Changes in climate have been linked to the rise and the collapse of various civilizations.

Proxy measurements

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

Various archives of past climate are present in rocks, trees and fossils. From these archives, indirect measures of climate, so-called proxies, can be derived. 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. Stress, too little precipitation or unsuitable temperatures, 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 science studying this called dendroclimatology. 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.

Analysis of ice in cores 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. 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.

The remnants of plants, and specifically pollen, are also used to study climatic change. Plant distributions 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 indicate changes in plant communities. These changes are often a sign of a changing climate. As an example, pollen studies have been used to track changing vegetation patterns throughout the Quaternary glaciations and especially since the last glacial maximum. 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.

Analysis and uncertainties

One difficulty in detecting climate cycles is that the Earth's climate has been changing in non-cyclic ways over most paleoclimatological timescales. Currently we are in a period of anthropogenic global warming. In a larger timeframe, the Earth is emerging from the latest ice age, cooling from the Holocene climatic optimum and warming from the "Little Ice Age", which means that climate has been constantly changing over the last 15,000 years or so. During warm periods, temperature fluctuations are often of a lesser amplitude. The Pleistocene period, dominated by repeated glaciations, developed out of more stable conditions in the Miocene and Pliocene climate. Holocene climate has been relatively stable. All of these changes complicate the task of looking for cyclical behavior in the climate.

Positive feedback, negative feedback, and ecological inertia from the land-ocean-atmosphere system often attenuate or reverse smaller effects, whether from orbital forcings, solar variations or changes in concentrations of greenhouse gases. Certain feedbacks involving processes such as clouds are also uncertain; for contrails, natural cirrus clouds, oceanic dimethyl sulfide and a land-based equivalent, competing theories exist concerning effects on climatic temperatures, for example contrasting the Iris hypothesis and CLAW hypothesis.

Impacts

Life

Top: Arid ice age climate

Middle: Atlantic Period, warm and wet

Bottom: Potential vegetation in climate now if not for human effects like agriculture.

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. Though an increase in CO₂ may benefit plants, some factors can diminish this increase. If there is an environmental change such as drought, increased CO₂ concentrations will not benefit the plant. So even though climate change does increase CO₂ emissions, plants will often not use this increase as other environmental stresses put pressure on them. However, sequestration of CO₂ is expected to affect the rate of many natural cycles like plant litter decomposition rates. 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.

Larger, faster or more radical changes, however, may result in vegetation stress, rapid plant loss and desertification in certain circumstances. 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.

Wildlife

One of the most important ways animals can deal with climatic change is migration to warmer or colder regions. On a longer timescale, evolution makes ecosystems including animals better adapted to a new climate. Rapid or large climate change can cause mass extinctions when creatures are stretched too far to be able to adapt.

Humanity

Collapses of past civilizations such as the Maya may be related to cycles of precipitation, especially drought, that in this example also correlates to the Western Hemisphere Warm Pool. Around 70 000 years ago the Toba supervolcano eruption created an especially cold period during the ice age, leading to a possible genetic bottleneck in human populations.

Changes in the cryosphere

Glaciers and ice sheets

Glaciers are considered among the most sensitive indicators of a changing climate. Their size is determined by a mass balance between snow input and melt output. As temperatures increase, glaciers retreat unless snow precipitation increases to make up for the additional melt. Glaciers grow and shrink due both to natural variability and external forcings. Variability in temperature, precipitation and hydrology can strongly determine the evolution of a glacier in a particular season.

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 orbital forcing.

Sea level change

During the Last Glacial Maximum, some 25,000 years ago, sea levels were roughly 130 m lower than today. The deglaciation afterwards was characterized by rapid sea level change. 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.

Sea ice

Sea ice plays an important role in Earth's climate as it affects the total amount of sunlight that is reflected away from the Earth. In the past, the Earth's oceans have been almost entirely covered by sea ice on a number of occasions, when the Earth was in a so-called Snowball Earth state, and completely ice-free in periods of warm climate. When there is a lot of sea ice present globally, especially in the tropics and subtropics, the climate is more sensitive to forcings as the ice–albedo feedback is very strong.

Climate history

See also: List of periods and events in climate history and Paleoclimatology

Various climate forcings are typically in flux throughout geologic time, and some processes of the Earth's temperature may be self-regulating. For example, during the Snowball Earth period, large glacial ice sheets spanned to Earth's equator, covering nearly its entire surface, and very high albedo created extremely low temperatures, while the accumulation of snow and ice likely removed carbon dioxide through atmospheric deposition. However, the absence of plant cover to absorb atmospheric CO₂ emitted by volcanoes meant that the greenhouse gas could accumulate in the atmosphere. There was also an absence of exposed silicate rocks, which use CO₂ when they undergo weathering. This created a warming that later melted the ice and brought Earth's temperature back up.

Paleo-eocene thermal maximum

Climate changes over the past 65 million years, using proxy data including Oxygen-18 ratios from foraminifera.

The Paleocene–Eocene Thermal Maximum (PETM) was a time period with more than 5–8 °C global average temperature rise across the event. This climate event occurred at the time boundary of the Paleocene and Eocene geological epochs. During the event large amounts of methane was released, a potent greenhouse gas. The PETM represents a "case study" for modern climate change as in the greenhouse gases were released in a geologically relatively short amount of time. During the PETM, a mass extinction of organisms in the deep ocean took place.

The Cenozoic

Throughout the Cenozoic, multiple climate forcings led to warming and cooling of the atmosphere, which led to the early formation of the Antarctic ice sheet, subsequent melting, and its later reglaciation. The temperature changes occurred somewhat suddenly, at carbon dioxide concentrations of about 600–760 ppm and temperatures approximately 4 °C warmer than today. During the Pleistocene, cycles of glaciations and interglacials occurred on cycles of roughly 100,000 years, but may stay longer within an interglacial when orbital eccentricity approaches zero, as during the current interglacial. Previous interglacials such as the Eemian phase created temperatures higher than today, higher sea levels, and some partial melting of the West Antarctic ice sheet.

Climatological temperatures substantially affect cloud cover and precipitation. At lower temperatures, air can hold less water vapour, which can lead to decreased precipitation. 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). In contrast, the world's climate was cloudier and wetter than today near the start of the warm Atlantic Period of 8000 years ago.

The Holocene

Temperature change over the past 12 000 years, from various sources. The thick black curve is an average.

The Holocene is characterized by a long-term cooling starting after the Holocene Optimum, when temperatures were probably only just below current temperatures (second decade of the 21st century), and a strong African Monsoon created grassland conditions in the Sahara during the Neolithic Subpluvial. Since that time, several cooling events have occurred, including:

• the Piora Oscillation
• the Middle Bronze Age Cold Epoch
• the Iron Age Cold Epoch
• the Little Ice Age
• the phase of cooling c. 1940–1970, which led to global cooling hypothesis

In contrast, several warm periods have also taken place, and they include but are not limited to:

• a warm period during the apex of the Minoan civilization
• the Roman Warm Period
• the Medieval Warm Period
• Modern warming during the 20th century

Certain effects have occurred during these cycles. For example, during the Medieval Warm Period, the American Midwest was in drought, including the Sand Hills of Nebraska which were active sand dunes. The black death plague of Yersinia pestis also occurred during Medieval temperature fluctuations, and may be related to changing climates.

Solar activity may have contributed to part of the modern warming that peaked in the 1930s. However, solar cycles fail to account for warming observed since the 1980s to the present day. Events such as the opening of the Northwest Passage and recent record low ice minima of the modern Arctic shrinkage have not taken place for at least several centuries, as early explorers were all unable to make an Arctic crossing, even in summer. Shifts in biomes and habitat ranges are also unprecedented, occurring at rates that do not coincide with known climate oscillations.

Modern climate change and global warming

Main article: Climate change

As a consequence of humans emitting greenhouse gases, global surface temperatures have started rising. Global warming is an aspect of modern climate change, a term that also includes the observed changes in precipitation, storm tracks and cloudiness. As a consequence, glaciers worldwide have been found to be shrinking significantly. Land ice sheets in both Antarctica and Greenland have been losing mass since 2002 and have seen an acceleration of ice mass loss since 2009. Global sea levels have been rising as a consequence of thermal expansion and ice melt. The decline in Arctic sea ice, both in extent and thickness, over the last several decades is further evidence for rapid climate change.

Variability between regions

Examples of regional climate variability

• 
  Land-ocean. Surface air temperatures over land masses have been increasing faster than those over the ocean, the ocean absorbing about 90% of excess heat.
   
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  Hemispheres. The Hemispheres' average temperature changes have diverged because of the North's greater percentage of landmass, and due to global ocean currents.
  
  
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  Latitude bands. Three latitude bands that respectively cover 30, 40 and 30 percent of the global surface area show mutually distinct temperature growth patterns in recent decades.
   
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  Altitude. A warming stripes graphic (blues denote cool, reds denote warm) shows how the greenhouse effect traps heat in the lower atmosphere so that the upper atmosphere, receiving less reflected energy, cools. Volcanos cause upper-atmosphere temperature spikes.
  
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  Global versus regional. For geographical and statistical reasons, larger year-to-year variations are expected for localized geographic regions (e.g., the Caribbean) than for global averages.
  
• 
  Relative deviation. Though northern America has warmed more than its tropics, the tropics have more clearly departed from normal historical variability (colored bands: 1σ, 2σ standard deviations).

In addition to global climate variability and global climate change over time, numerous climatic variations occur contemporaneously across different physical regions.

The oceans' absorption of about 90% of excess heat has helped to cause land surface temperatures to grow more rapidly than sea surface temperatures. The Northern Hemisphere, having a larger landmass-to-ocean ratio than the Southern Hemisphere, shows greater average temperature increases. Variations across different latitude bands also reflect this divergence in average temperature increase, with the temperature increase of northern extratropics exceeding that of the tropics, which in turn exceeds that of the southern extratropics.

Upper regions of the atmosphere have been cooling contemporaneously with a warming in the lower atmosphere, confirming the action of the greenhouse effect and ozone depletion.

Observed regional climatic variations confirm predictions concerning ongoing changes, for example, by contrasting (smoother) year-to-year global variations with (more volatile) year-to-year variations in localized regions. Conversely, comparing different regions' warming patterns to their respective historical variabilities, allows the raw magnitudes of temperature changes to be placed in the perspective of what is normal variability for each region.

Regional variability observations permit study of regionalized climate tipping points such as rainforest loss, ice sheet and sea ice melt, and permafrost thawing. Such distinctions underlie research into a possible global cascade of tipping points.

Climate change and poverty

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Climate_change_and_poverty

Demonstration against climate poverty (2007)

Climate change and poverty are deeply intertwined because climate change disproportionally affects poor people in low-income communities and developing countries around the world. The impoverished have a higher chance of experiencing the ill-effects of climate change due to the increased exposure and vulnerability. Vulnerability represents the degree to which a system is susceptible to, or unable to cope with, adverse effects of climate change including climate variability and extremes.

Climate change highly exacerbates existing inequalities through its effects on health, the economy, and human rights. The Intergovernmental Panel on Climate Change's (IPCC) Fourth National Climate Assessment Report found that low-income individuals and communities are more exposed to environmental hazards and pollution and have a harder time recovering from the impacts of climate change. For example, it takes longer for low-income communities to be rebuilt after natural disasters. According to the United Nations Development Programme, developing countries suffer 99% of the casualties attributable to climate change.

Different countries' impact on climate change also varies based on their stage of development; the 50 least developed countries of the world account for a 1% contribution to the worldwide emissions of greenhouse gasses, which are a byproduct of global warming. Additionally, 92% of accumulated greenhouse gas emissions can be attributed to countries from the Global North, which comprise 19% of the global population, while 8% of emissions are attributed to countries from the Global South, who bear the heaviest consequences of increasing global temperature.

Climate and distributive justice questions are central to climate change policy options. Many policy tools can be employed to solve environmental problems such as cost-benefit analysis; however, such tools usually do not deal with such issues because they often ignore questions of just distribution and the environmental effects on human rights.

Poverty Percentage World Map

Connection to poverty

A 2020 World Bank paper estimated that between 32 million and 132 million additional people will be pushed into extreme poverty by 2030 due to climate change. The cycle of poverty exacerbates the potential negative impacts of climate change. This phenomenon is defined when poor families become trapped in poverty for at least three generations, have limited to no resources access, and are disadvantaged in means of breaking the cycle. While in rich countries, coping with climate change has largely been a matter of dealing with longer, hotter summers, and observing seasonal shifts; for those in poverty, weather-related disasters, bad harvest, or even a family member falling ill can provide crippling economic shocks.

Besides these economic shocks, the widespread famine, drought, and potential humanistic shocks could affect the entire nation. High levels of poverty and low levels of human development limit the capacity of poor households to manage climate risks. With limited access to formal insurance, low incomes, and meager assets, poor households have to deal with climate-related shocks under highly constrained conditions. In addition, poorer households are heavily impacted by environmental shocks due to the lack of post-shock support from friends and family, the financial system, and social safety nets.

Relationship to environmental racism

As global climate has changed progressively over the past several decades, it has collided with environmental racism. The overlap of these two phenomena, has disproportionately affected different communities and populations throughout the world due to disparities in socio-economic status. This is especially evident in the Global South where, for example, byproducts of global climate change such as increasingly frequent and severe landslides resulting from more heavy rainfall events in Quito, Ecuador force people to also deal with profound socio-economic ramifications like the destruction of their homes and death. Countries such as Ecuador often contribute relatively little to climate change in terms of carbon dioxide emissions but have far fewer resources to ward off the negative localized impacts of climate change. This issue occurs globally, where nations in the global south bear the burden of natural disasters and weather extremes despite contributing little to the global carbon footprint.

While people living in the Global South have typically been impacted most by the effects of climate change, people of color in the Global North also face similar situations in several areas. The issues of climate change and communities that are in a danger zone are not limited to North America or the United States either. Environmental racism and climate change coincide with one another. Rising seas affect poor areas such as Kivalina, Alaska, and Thibodaux, Louisiana, and countless other places around the globe.

Impacts of environmental racism due to climate change become particularly evident during climate disasters. Following the 1995 Chicago heat wave, scholars analyzed the effects of environmental racism on the unequal death rate between races during this crisis. Direct impacts of this phenomenon can be observed through the lack of adequate warning and the failure to utilize pre-existing cooling centers which disadvantaged impoverished groups, and caused particularly devastating effects in Chicago's poorest areas. Poorer individuals are more susceptible to harm from climate change because they have less access to resources to help them recover from natural disasters. With the number of climate disasters increasing dramatically over the past 50 years, the impacts of environmental racism has increased, and social movements calling for environmental justice have grown in turn.

Atmospheric colonization

The concept of 'atmospheric colonization' refers to the observation that 92% of accumulated greenhouse gas emissions are attributable to countries from the Global North, comprising 19% of global population, while only 8% of emissions are attributable to countries from the Global South that will bear the heaviest consequences of increasing global temperatures.

A 2020 World Bank paper estimated that between 32 million and 132 million additional people will be pushed into extreme poverty by 2030 due to climate change.

Reversing development

Climate change is globally encompassing and can reverse development in some areas in the following ways.

Agricultural production and food security

Microorganisms and Climate Change

There has been considerable research comparing the interrelated processes of climate change on agriculture. Climate change affects rainfall, temperature, and water availability for agriculture in vulnerable areas. It also affects agriculture in several ways including productivity, agricultural practices, environmental effects, and distribution of rural space. Extreme events such as droughts, disease, and pests will be heavily impacted resulting in an increase of food prices from 3-84% by the year 2050. Additional numbers affected by malnutrition could rise to 600 million by 2080. Climate change could worsen the prevalence of hunger through direct negative effects on production and indirect impacts on purchasing powers.

Water insecurity

Of the 3 billion growth in population projected worldwide by the mid-21st century, the majority will be born in countries already experiencing water shortages. As the overall climate of the earth warms, changes in the nature of global rainfall, evaporation, snow, and runoff flows will be affected. Safe water sources are essential for survival within a community. Manifestations of the projected water crisis include inadequate access to safe drinking water for about 884 million people as well as inadequate access to water for sanitation and water disposal for 2.5 billion people. As waters become warmer, hazardous algae and other bacteria growth increase, not only contaminating the water that we drink but also the seafood that we consume. With a population ranging between 198 and 210 million people in Nigeria, existing sanitation and water infrastructural facilities remain inadequate with 2.2billion people lacking access to safe water and 4.2 billion lacking safe sanitations both in the rural and urban areas.

Rising sea levels and exposure to climate disasters

Sea levels could rise rapidly with accelerated ice sheet disintegration. Global temperature increases of 3–4 degrees C could result in 330 million people being permanently or temporarily displaced through flooding Warming seas will also fuel more intense tropical storms. The destruction of coastal landscapes exacerbates the damage done by this increase in storms. Wetlands, forests, and mangroves have been removed for land development. These features usually slow runoff, storm surges, and prevent debris from being carried by flooding. Developing over these areas has increased the destructive power of floods and makes homeowners more susceptible to extreme weather events. Flooding causes the risk of submersion of lands in coastal areas in densely populated poverty areas, such as Alexandria and Port Said in Egypt, Lagos and Port Harcourt in Nigeria, and Cotonou in Benin. In some areas, such as coastal properties, real estate prices go up because of ocean access and housing scarcity, in part caused by homes being destroyed during storms. Wealthy homeowners have more resources to rebuild their homes and have better job security, which encourages them to stay in their communities following extreme weather events. Highly unstable areas, such as slopes and delta regions, are sold to lower-income families at a cheaper price point. After extreme weather events, Impoverished people have a difficult time finding or maintaining a job and rebuilding their homes. These challenges force many to relocate in search of job opportunities and housing.

Ecosystems and biodiversity

Coral Bleaching of Coral Reefs in Hawaii

Climate change is already transforming ecological systems. Around one-half of the world's coral reef systems have suffered bleaching as a result of warming seas. In addition, the direct human pressures that might be experienced include overfishing which could lead to resource depletion, nutrient, and chemical pollution and poor land-use practices such as deforestation and dredging. Also, climate change may increase the number of arable land in high-latitude regions by reduction of the number of frozen lands. A 2005 study reports that temperature in Siberia has increased three degrees Celsius on average since 1960, which is reportedly more than in other areas of the world.

Human health

Main article: Effects of global warming on human health

A direct effect is an increase in temperature-related illnesses and deaths related to prolonged heat waves and humidity. Climate change could also change the geographic range of vector-borne, specifically mosquito-borne diseases such as malaria dengue fever exposing new populations to the disease. Because a changing climate affects the essential ingredients of maintaining good health: clean air and water, sufficient food, and adequate shelter, the effects could be widespread and pervasive. The report of the WHO Commission on Social Determinants of Health points out that disadvantaged communities are likely to shoulder a disproportionate share of the burden of climate change because of their increased exposure and vulnerability to health threats. Over 90 percent of malaria and diarrhea deaths are borne by children aged 5 years or younger, mostly in developing countries. Other severely affected population groups include women, the elderly, and people living in small island developing states and other coastal regions, mega-cities, or mountainous areas.

Aspects of Climate Change on Human Health

Likely Relative Impact on Health Outcomes of the Components of Climate Change

Health Outcome	change in mean, temperature...	extreme events	rate of change of climate variable	day-night difference
Heat-related deaths and illness		+++		+
Physical and psychological trauma due to disasters		++++
Vector-borne diseases	+++	++	+	++
Non-vector-borne infectious diseases	+	+
Food availability and hunger	++	+	++
Consequences of sea level rise	++	++	+
Respiratory effects: -air pollutants -pollens, humidity	+ ++	++		+
Population displacement	++	+	+

++++= great effect; += small effect; empty cells indicate no known relationship.

Human rights and democracy

Further information: Human Rights and Climate Change

In June 2019, United Nations Special Rapporteur Philip Alston warned of a "climate apartheid" where the rich pay to escape the effects of climate change while the rest of the world suffers, potentially undermining basic human rights, democracy, and the rule of law. When Superstorm Sandy struck in 2012, he recounts, most people in New York City were left without power, while the Goldman Sachs headquarters had a private generator and protection by "tens of thousands of its own sandbags".

An approach that is currently trying to be established by combining human rights with the effects of climate change is an HBRA law. An HBRA law is the adoption of a human rights-based approach (HRBA) to address climate change, from both a legal and a policy perspective. This approach is an advocacy created by younger generations that are preparing for future climate change incidents that could potentially affect future generations.

Security impacts

The concept of human security and the effects that climate change may have on it will become increasingly important as the affects become more apparent. Some effects are already evident and will become very clear in the human and climatic short-run (2007–2020). They will increase and others will manifest themselves in the medium term (2021–2050); whilst in the long run (2051–2100), they will all be active and interacting strongly with other major trends. There is the potential for the end of the petroleum economy for many producing and consuming nations, possible financial and economic crisis, a larger population of humans, and a much more urbanized humanity – far in excess of the 50% now living in small to very large cities. All these processes will be accompanied by the redistribution of the population nationally and internationally. Such redistributions typically have significant gender dimensions; for example, extreme event impacts can lead to male out migration in search of work, culminating in an increase in women-headed households – a group often considered particularly vulnerable. Indeed, the effects of climate change on impoverished women and children is crucial in that women and children, in particular, have unequal human capabilities. An example of a predicted trend called "The Great Migration" is estimated to affect millions of Americans in the year 2070. Due to the impacts of climate change millions will be forced to relocate. To accommodate TGM, the U.S. will need 25–30 million new housing units. Failure to build these new units will increase material deprivation and poverty.

Infrastructure impacts

The potential effects of climate change and the security of infrastructure will have the most direct effect on the poverty cycle. Areas of infrastructure effects will include water systems, housing and settlements, transport networks, utilities, and industry. Infrastructure designers can contribute in three areas for improving the living environment for the poor, in building design, in settlement planning and design as well as in urban planning.

The National Research Council has identified five climate changes of particular importance to infrastructure and factors that should be taken into consideration when designing future structures. These factors include increases in very hot days and heat waves, increases in Arctic temperatures, rising sea levels, increases in intense precipitation events, and increases in hurricane intensity. Heat waves affect communities that live in traditionally cooler areas because many of the homes are not equipped with air conditioning units. Rising sea levels can be devastating for poor countries situated near the ocean and in delta regions, which experience increasingly overwhelming storm damage. In parts of eastern Caribbean nations, almost 60 percent of the homes were constructed without any building regulations. Many of these endangered populations are also affected by an increase in flooding in locations that lack adequate drainage. In 1998, close to 200 million people were affected by flooding in China's Yangtze River Valley; and in 2010, flooding in Pakistan affected 20 million people. These issues are made worse for people living in lower income areas and force them to relocate at a higher rate than other economic groups.

In areas where poverty is prevalent and infrastructure is underdeveloped, climate change produces a critical threat to the future development of that country. Reports of a study done on ten geographically and economically diverse countries show how nine out of ten countries revealed an inability to develop infrastructures and its expensive maintenance due to the influence of climate change and cost.

Proposed policy solutions

Mitigation efforts

Climate change mitigation (or decarbonisation) is action to limit the greenhouse gases in the atmosphere that cause climate change. Climate change mitigation actions include conserving energy and replacing fossil fuels with clean energy sources. Secondary mitigation strategies include changes to land use and removing carbon dioxide (CO₂) from the atmosphere. Current climate change mitigation policies are insufficient as they would still result in global warming of about 2.7 °C by 2100, significantly above the 2015 Paris Agreement's goal of limiting global warming to below 2 °C.

Adaptation efforts

Adaptation to global warming involves actions to tolerate the effects of global warming. Collaborative research from the Institute of Development Studies draws links between adaptation and poverty to help develop an agenda for pro-poor adaptation that can inform climate-resilient poverty reduction. Adaptation to climate change will be "ineffective and inequitable if it fails to learn and build upon an understanding of the multidimensional and differentiated nature of poverty and vulnerability". Poorer countries tend to be more seriously affected by climate change, yet have reduced assets and capacities with which to adapt. One can see this effect by comparing outcomes between Bangladesh and the United States following two severe storms. In the United States, Hurricane Andrew killed 23 people when it made landfall in 1992; however, one year before, in Bangladesh, a tropical cyclone killed approximately 100,000 people. Bangladesh, having a poorer population, was less prepared for the storm; and the country lacked sufficient weather forecasting systems needed to predict meteorological events. After the storm, Bangladesh required assistance from the international community because it didn't possess the funds needed to recover. As events like these increase in their frequency and severity, a more proactive approach is needed. This has led to more activities to integrate adaptation within development and poverty reduction programs. The rise of adaptation as a development issue has been influenced by concerns around minimizing threats to progress on poverty reduction, notably the Millennium Development Goals, and by the injustice of impacts that are felt hardest by those who have done least to contribute to the problem, framing adaptation as an equity and human rights issue.

Other solutions include increasing access to quality health care for poor people and people of color, preparedness planning for urban heat island effects, identifying neighborhoods that are most likely to be impacted, investing in alternative fuel and energy research, and measuring the results of policy impacts.

Regional effects

Regional effects from global climate change varies from country to country. Many countries have different approaches to how they adapt to global climate change versus others. Bigger countries with more resources do not react the same as a country with less resources to use. Urgency to fix the problem is not present until the effect of global climate change is felt directly. Bangladesh is just one of the many examples of people being affected because they are not properly prepared to face global climate. Workers in the agriculture field in these countries specifically are effected more than others but the extent to how much each agriculture worker is effected varies from region to region.

A country that exemplifies the inequality that is created due to varying affects in different regions by climate change is Nigeria. Nigeria is a country that mainly relies on oil as its main money generator, but is being affected by climate change and affecting the lower class workers such as farmers in their everyday life. Lack of climate change information along with overprice land cost and government irresponsibleness towards climate change adaption continues to constrain farmers in Nigeria. A country supported by agricultural would take more action in order to combat climate change. Its economic value would be too high not to put more effort into fighting climate change. Since it's not a priority for the wealthier class in Nigeria, lower-class people directly suffer the effects of climate change in Nigeria more.

Nigeria along with the rest of Africa is in danger of being affected by climate change the most. According to author Ignatius A. Madu research, the IPCC has declared Africa a high vulnerable area based on its high exposure, and lack of adaptability to global climate change.(IPCC 2007) It will effect the economy as well as social system in Africa if it is not addressed the way it should be. A country with so many natural resources such as Africa will lose those resources over time and will be effected harder than most regions of the world if climate change is not addressed with urgency.

Lower class workers feel the effects differently region to region of climate change but the effects in some of these countries are not as devastating due to better adaption methods than others in different countries and regions. Located in South Asia is the country Sri Lanka that struggles with global climate change, but is doing more to combat it than others. The country Sri Lanka has now started to investigate farm level adaptation to climate change by observing smaller farming communities in Sri Lanka. These farmers use their personal experiences and gained knowledge to fight global climate change. They have emphasized managing non-climatic elements which they have no control over and this has helped them adapt faster than most farming communities to climate change. Climate change has caused these farmers efficiency to increase. This increase gives them a greater chance of not being effected by climate change too much. It also shows how social networks can effect adaption efforts. When more people take an issue seriously the response will be greater. Sri Lanka depends on agriculture goods to keep their economy stable and many people depend on it. Adaption efforts in Sri Lanka shows how the response from society can dictate the level of importance that people see in an issue.

Understanding of the way people process information is just as important as knowing the information needed to combat socio-economic, cognitive and normative aspects with in communities. Unlike Nigeria, studies have been run and tested by the Sri Lanka government on how to adapt to climate change which is helping them not be completely defenseless against global climate change. Countries like Sri Lanka who have a government who depend on agricultural exports to sustain part of the government sure completely different response to combating climate change unlike places like Nigeria. When the issue affects those of the top adaption will happen with the urgency. This war cause approaches the climate change to look different until we are all affected equally. Adaption efforts have to be collective or we will not fix the worldwide problem or climate change in poverty.

Proposed policy challenges

The main difficulties involved with climate change policy are the timetable of return on investment and the disparate costs on countries. To control the price of carbon, richer countries would have to make large loans to poorer countries, with the potential return on investment taking generations.