Reasons for concern
Encyclopedia
The Intergovernmental Panel on Climate Change
(IPCC) has organized many of the risks of climate change
into five "reasons for concern." The reasons for concern show that these risks increase with increases in the Earth's global mean temperature (i.e., global warming
). The IPCC's five reasons for concern are: threats to endangered species and unique systems, damages from extreme climate events, effects that fall most heavily on developing countries and the poor within countries, global aggregate impacts (i.e., various measurements of total social, economic and ecological impacts), and large-scale high-impact events. The five reasons for concern are described in more detail below. The following descriptions are based on information from the IPCC's Third (TAR)
and Fourth Assessment Reports (AR4)
, published in 2001 and 2007, respectively.
s), biological (e.g., coral reef
s), or human (e.g., indigenous communities
). IPCC (2007) pointed to evidence of observed impacts on unique and vulnerable systems, with impacts projected to be greater at higher levels of warming. Examples of projected impacts included the risk of species extinctions, coral bleaching
and mortality, and increased vulnerability of indigenous communities in the Arctic and on small island
s.
s, soil moisture deficits, tropical and other storm
s, anomalous temperatures, and fire
s. IPCC (2007) pointed to evidence of greater vulnerability to extreme events than had previously been estimated in the TAR.
The most common aggregate measure of impacts is money
. Monetizing impacts is well-suited to climate change impacts that have an effect on economic markets, e.g., impacts on agriculture, but is less well-suited to impacts that do not clearly have a market value, i.e., "non-market" impacts (Smith et al., 2001). Examples of non-market impacts include the effects of climate change on ecosystem
s and human health
. Alternative measures of aggregate impacts include the number of people affected, change in net primary productivity, and the number of systems undergoing change.
With medium confidence, Smith et al. (2001) concluded that world gross domestic product
(GDP) would change by plus or minus a few percent for a small increase in global mean temperature (up to around 2 °C above the 1990 temperature level).
With low confidence, aggregate non-market impacts were estimated to be negative for a small temperature increase. In the view of Smith et al. (2001), most people in the world would be negatively affected by a small to medium increase in temperature (up to around 2-3 °C above the 1990 temperature level). Most studies assessed by Smith et al. (2001) projected increasing net losses in world GDP for higher temperatures. More recent studies assessed by Schneider et al. (2007) were consistent with these findings.
(IPCC, 2001d:93). Other changes may be intrinsically irreversible, for example, the extinction of species.
Sometimes the word "singularity
" is used to describe a system that behaves in an irregular and unpredictable way. Singularities could lead to rapid, large, and unexpected climate change impacts on local, regional, and global scales (Smith et al., 2001).
Anticipating and adapting to such events and their impacts would be much more difficult than responding to "smooth" climate change. Examples of large-scale singularities include:
Based on the "vague" evidence they had assessed, Smith et al. (2001) concluded that large-scale, discontinuous climate change impacts were unlikely below 2 °C warming (above 1990 levels). It was judged that large-scale discontinuities might be "relatively plausible" for a sustained warming of 8-10 °C (above 1990 levels). Based on the relatively small set of investigations they had assessed, warming of 4-5 °C was judged to be temperature range where large-scale discontinuities might start to emerge. The rate of warming was also viewed as being important in determining such a temperature range. IPCC (2001d) noted that the risk of these events was largely unquantified. Risk was defined as the product of the probabilities of these events and the magnitude of their consequences.
The diagram opposite, sometimes called the "burning embers" diagram, is adapted from the TAR. The burning embers diagram is based on the five reasons for concern. AR4 provided a written update for each of the reasons for concern, but did not update the burning embers diagram. An update of the burning embers diagram was later provided by a group of IPCC authors (Smith et al., 2009). These authors were responsible for writing the chapter in AR4 which contains the written update of the reasons for concern. Their revision of the burning embers diagram was published independently of the IPCC process, and appeared in the Proceedings of the National Academy of Sciences of the United States of America scientific journal
. The revision shows increased risks in all five reasons for concern.
Intergovernmental Panel on Climate Change
The Intergovernmental Panel on Climate Change is a scientific intergovernmental body which provides comprehensive assessments of current scientific, technical and socio-economic information worldwide about the risk of climate change caused by human activity, its potential environmental and...
(IPCC) has organized many of the risks of climate change
Climate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...
into five "reasons for concern." The reasons for concern show that these risks increase with increases in the Earth's global mean temperature (i.e., global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...
). The IPCC's five reasons for concern are: threats to endangered species and unique systems, damages from extreme climate events, effects that fall most heavily on developing countries and the poor within countries, global aggregate impacts (i.e., various measurements of total social, economic and ecological impacts), and large-scale high-impact events. The five reasons for concern are described in more detail below. The following descriptions are based on information from the IPCC's Third (TAR)
IPCC Third Assessment Report
The IPCC Third Assessment Report, Climate Change 2001, is an assessment of available scientific and socio-economic information on climate change by the IPCC. The IPCC was established in 1988 by the United Nations Environment Programme and the UN's World Meteorological Organization ".....
and Fourth Assessment Reports (AR4)
IPCC Fourth Assessment Report
Climate Change 2007, the Fourth Assessment Report of the United Nations Intergovernmental Panel on Climate Change , is the fourth in a series of reports intended to assess scientific, technical and socio-economic information concerning climate change, its potential effects, and options for...
, published in 2001 and 2007, respectively.
Unique and threatened systems
Unique systems are restricted to a relatively narrow geographical range but can affect other entities beyond their range (Smith et al., 2001). Unique systems may be physical (e.g., tropical glacierGlacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
s), biological (e.g., coral reef
Coral reef
Coral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...
s), or human (e.g., indigenous communities
Indigenous peoples
Indigenous peoples are ethnic groups that are defined as indigenous according to one of the various definitions of the term, there is no universally accepted definition but most of which carry connotations of being the "original inhabitants" of a territory....
). IPCC (2007) pointed to evidence of observed impacts on unique and vulnerable systems, with impacts projected to be greater at higher levels of warming. Examples of projected impacts included the risk of species extinctions, coral bleaching
Coral bleaching
Coral bleaching is the loss of intracellular endosymbionts through either expulsion or loss of algal pigmentation.The corals that form the structure of the great reef ecosystems of tropical seas depend upon a symbiotic relationship with unicellular flagellate protozoa, called zooxanthellae, that...
and mortality, and increased vulnerability of indigenous communities in the Arctic and on small island
Island
An island or isle is any piece of sub-continental land that is surrounded by water. Very small islands such as emergent land features on atolls can be called islets, cays or keys. An island in a river or lake may be called an eyot , or holm...
s.
Frequency and severity of extreme climate events
With high confidence (see footnote), Smith et al. (2001) concluded that a small increase in global mean temperature (up to 2 °C above the 1990 global mean temperature level) would result in an increase in the frequency and magnitude of many extreme climate events. Higher levels of warming would be associated with further increases in the frequency and magnitude of extreme events. Examples of extreme events include floodFlood
A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water...
s, soil moisture deficits, tropical and other storm
Storm
A storm is any disturbed state of an astronomical body's atmosphere, especially affecting its surface, and strongly implying severe weather...
s, anomalous temperatures, and fire
Fire
Fire is the rapid oxidation of a material in the chemical process of combustion, releasing heat, light, and various reaction products. Slower oxidative processes like rusting or digestion are not included by this definition....
s. IPCC (2007) pointed to evidence of greater vulnerability to extreme events than had previously been estimated in the TAR.
Global distribution and balance of impacts
The impacts of climate change will not affect everyone equally (Smith et al., 2001). Some individuals, sectors, systems, and regions will be less affected, or may even benefit. In general, developing countries are at greater risk of adverse impacts from climate change than are developed countries (IPCC, 2001d). IPCC (2007) found increased evidence that some groups, such as the poor and elderly, were more vulnerable to climate change than others. This conclusion applied to those living in both developed and developing countries.Total economic and ecological impact
This reason for concern attempts to reflect the overall (or aggregate) economic and ecological effect of climate change (Smith et al., 2001). Aggregating impacts requires value judgements made by the author of the study regarding the importance of different climate change impacts occurring in different regions and at different times. Depending on these choices, aggregation may be viewed as controversial (Banuri et al., 1996:98-99). Another example of possible controversy is the aggregation of beneficial climate impacts in one region offsetting adverse climate impacts in another region (Smith et al., 2001).The most common aggregate measure of impacts is money
Money
Money is any object or record that is generally accepted as payment for goods and services and repayment of debts in a given country or socio-economic context. The main functions of money are distinguished as: a medium of exchange; a unit of account; a store of value; and, occasionally in the past,...
. Monetizing impacts is well-suited to climate change impacts that have an effect on economic markets, e.g., impacts on agriculture, but is less well-suited to impacts that do not clearly have a market value, i.e., "non-market" impacts (Smith et al., 2001). Examples of non-market impacts include the effects of climate change on ecosystem
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
s and human health
Health
Health is the level of functional or metabolic efficiency of a living being. In humans, it is the general condition of a person's mind, body and spirit, usually meaning to be free from illness, injury or pain...
. Alternative measures of aggregate impacts include the number of people affected, change in net primary productivity, and the number of systems undergoing change.
With medium confidence, Smith et al. (2001) concluded that world gross domestic product
Gross domestic product
Gross domestic product refers to the market value of all final goods and services produced within a country in a given period. GDP per capita is often considered an indicator of a country's standard of living....
(GDP) would change by plus or minus a few percent for a small increase in global mean temperature (up to around 2 °C above the 1990 temperature level).
With low confidence, aggregate non-market impacts were estimated to be negative for a small temperature increase. In the view of Smith et al. (2001), most people in the world would be negatively affected by a small to medium increase in temperature (up to around 2-3 °C above the 1990 temperature level). Most studies assessed by Smith et al. (2001) projected increasing net losses in world GDP for higher temperatures. More recent studies assessed by Schneider et al. (2007) were consistent with these findings.
Risk of irreversible large-scale and abrupt transitions
Systems may respond in an irregular, discontinuous, abrupt, and unpredictable way to climate change (Smith et al., 2001). This may apply to physical, biological and human systems. Available records of climate variability, for example, reveal sudden fluctuations of key variables at all time scales. Some changes in systems may be "irreversible." Some irreversible changes may be reversible over long time periods, for example, the partial melting of the Greenland ice sheetGreenland ice sheet
The Greenland ice sheet is a vast body of ice covering , roughly 80% of the surface of Greenland. It is the second largest ice body in the world, after the Antarctic Ice Sheet. The ice sheet is almost long in a north-south direction, and its greatest width is at a latitude of 77°N, near its...
(IPCC, 2001d:93). Other changes may be intrinsically irreversible, for example, the extinction of species.
Sometimes the word "singularity
Mathematical singularity
In mathematics, a singularity is in general a point at which a given mathematical object is not defined, or a point of an exceptional set where it fails to be well-behaved in some particular way, such as differentiability...
" is used to describe a system that behaves in an irregular and unpredictable way. Singularities could lead to rapid, large, and unexpected climate change impacts on local, regional, and global scales (Smith et al., 2001).
Anticipating and adapting to such events and their impacts would be much more difficult than responding to "smooth" climate change. Examples of large-scale singularities include:
- the possible abrupt shutdown of the Atlantic Meridional Overturning Circulation,
- a large, rapid release of methane into the atmosphere
- the melting of the Greenland and West Antarctic Ice Sheets.
Based on the "vague" evidence they had assessed, Smith et al. (2001) concluded that large-scale, discontinuous climate change impacts were unlikely below 2 °C warming (above 1990 levels). It was judged that large-scale discontinuities might be "relatively plausible" for a sustained warming of 8-10 °C (above 1990 levels). Based on the relatively small set of investigations they had assessed, warming of 4-5 °C was judged to be temperature range where large-scale discontinuities might start to emerge. The rate of warming was also viewed as being important in determining such a temperature range. IPCC (2001d) noted that the risk of these events was largely unquantified. Risk was defined as the product of the probabilities of these events and the magnitude of their consequences.
"Burning embers" diagram
Scientific journal
In academic publishing, a scientific journal is a periodical publication intended to further the progress of science, usually by reporting new research. There are thousands of scientific journals in publication, and many more have been published at various points in the past...
. The revision shows increased risks in all five reasons for concern.
Footnotes
Confidence levels are given for some of the conclusions of the TAR. These confidence levels represented the degree of belief among the authors of the TAR in the validity of a particular conclusion. Confidence levels were assigned based on the authors' collective expert judgment of observational evidence, modeling results, and theory that they had examined. Five confidence levels are used in the TAR (White et al., 2001):- Very High = 95% or greater
- High = 67-95%
- Medium = 33-67%
- Low = 5-33%
- Very Low = 5% or less