Countries in the tropics and Southern Hemisphere subtropics are projected to experience the largest impacts on economic growth due to climate change should global warming increase from 1.5°C to 2°C (medium confidence).
— Global Warming of 1.5°C SPM, 6 October 2018, p 12.
Climate Change 2014
Severe, Pervasive, and Irreversible Impacts
Climate change will amplify existing risks and create new risks for natural and human systems.
Risks are unevenly distributed and are generally greater for disadvantaged people and communities in countries at all levels of development.
Increasing magnitudes of warming increase the likelihood of severe, pervasive, and irreversible impacts for people, species and ecosystems.
Continued high emissions would lead to mostly negative impacts for biodiversity, ecosystem services, and economic development and amplify risks for livelihoods and for food and human security.
(p 24)
Observed Changes and Their Causes
Human influence on the climate system is clear, and recent anthropogenic emissions of greenhouse gases are the highest in history.
Recent climate changes have had widespread impacts on human and natural systems.
(p 5)
Observed Changes in the Climate System
Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia.
- The atmosphere and ocean have warmed,
- the amounts of snow and ice have diminished, and
- sea level has risen.
Past and recent drivers of climate change
Anthropogenic greenhouse gas emissions have increased since the pre-industrial era driven largely by economic and population growth.
From 2000 to 2010 emissions were the highest in history.
Historical emissions have driven atmospheric concentrations of carbon dioxide, methane and nitrous oxide, to levels that are unprecedented in at least the last 800,000 years, leading to an uptake of energy by the climate system.
(p 9)
[Since 2000, the increased] use of coal relative to other energy sources has reversed the long-standing trend in gradual decarbonisation … of the world’s energy supply.
(p 11, emphasis added)
Attribution of climate changes and impacts
The evidence for human influence on the climate system has grown since AR4.
Human influence has been detected
- in warming of the atmosphere and the ocean,
- in changes in the global water cycle,
- in reductions in snow and ice, and
- in global mean sea-level rise …
In recent decades, changes in climate have caused impacts on natural and human systems on all continents and across the oceans.
Impacts are due to observed climate change, irrespective of its cause, indicating the sensitivity of natural and human systems to changing climate.
(p 12)
Extreme Events
Changes in many extreme weather and climate events have been observed since about 1950.
Some of these changes have been linked to human influences, including
- a decrease in cold temperature extremes,
- an increase in warm temperature extremes,
- an increase in extreme high sea levels and
- an increase in the number of heavy precipitation events in a number of regions.
Exposure and Vulnerability
The character and severity of impacts from climate change and extreme events emerge from risk that depends not only on climate-related hazards but also on exposure (people and assets at risk) and vulnerability (susceptibility to harm) of human and natural systems.
(p 16)
Human Responses To Climate Change: Adaptation and Mitigation
Adaptation and mitigation experience is accumulating across regions and scales, even while global anthropogenic GHG emissions have continued to increase.
(p 17)
(AR5 Synthesis Report — Longer Report, 1 November, 2014)
The Reasons for Scientific Uncertainty
There are many uncertainties in our predictions [due to an] incomplete understanding of:
- sources and sinks of greenhouse gases [—] which affect predictions of future concentrations,
- clouds [—] which strongly influence the magnitude of climate change,
- oceans [—] which influence the timing and patterns of climate change [and]
- polar ice-sheets [—] which affect prediction of sea level rise.
However, the complexity of the system [is such] that we cannot rule out surprises.
(Climate Change: the Scientific Assessments, First Assessment Report, 1990, p 365)
Dangerous Anthropogenic Interference With The Climate System
The Parties to this Convention,
Acknowledging that change in the Earth's climate and its adverse effects are a common concern of humankind,
Concerned that human activities have been substantially increasing the atmospheric concentrations of greenhouse gases, that these increases enhance the natural greenhouse effect, and that this will result on average in an additional warming of the Earth's surface and atmosphere and may adversely affect natural ecosystems and humankind,
Noting that the largest share of historical and current global emissions of greenhouse gases has originated in developed countries, that per capita emissions in developing countries are still relatively low and that the share of global emissions originating in developing countries will grow to meet their social and development needs …
Recognizing that various actions to address climate change can be justified economically in their own right and can also help in solving other environmental problems …
Recognizing further that low-lying and other small island countries, countries with low-lying coastal, arid and semi-arid areas or areas liable to floods, drought and desertification, and developing countries with fragile mountainous ecosystems are particularly vulnerable to the adverse effects of climate change …
Affirming that responses to climate change should be coordinated with social and economic development in an integrated manner with a view to avoiding adverse impacts on the latter, taking into full account the legitimate priority needs of developing countries for the achievement of sustained economic growth and the eradication of poverty …
Determined to protect the climate system for present and future generations,
Have agreed …
Article 2: Objective(United Nations Framework Convention on Climate Change, 1992)
[To stabilize] greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system.
Such a level should be achieved within a time-frame sufficient to allow ecosystems to adapt naturally to climate change, to ensure that food production is not threatened and to enable economic development to proceed in a sustainable manner.
Article 3: Principles
- [To] protect the climate system for the benefit of present and future generations of humankind, on the basis of equity and in accordance with their common but differentiated responsibilities and respective capabilities.
Accordingly, the developed country Parties should take the lead in combating climate change and the adverse effects thereof. …
- [To] take precautionary measures to anticipate, prevent or minimize the causes of climate change and mitigate its adverse effects.
Where there are threats of serious or irreversible damage, lack of full scientific certainty should not be used as a reason for postponing such measures, taking into account that policies and measures to deal with climate change should be cost-effective so as to ensure global benefits at the lowest possible cost. …
Article 4: Commitments
- (a) [To] adopt national policies and take corresponding measures on the mitigation of climate change, by limiting its anthropogenic emissions of greenhouse gases and protecting and enhancing its greenhouse gas sinks and reservoirs.
These policies and measures will demonstrate that developed countries are taking the lead in modifying longer-term trends in anthropogenic emissions consistent with the objective of the Convention, recognizing that the return by the end of the present decade to earlier levels of anthropogenic emissions of carbon dioxide and other greenhouse gases not controlled by the Montreal Protocol would contribute to such modification …
(b) [To communicate] detailed information on its policies and measures referred to … above, as well as on its resulting projected anthropogenic emissions by sources and removals by sinks of greenhouse gases not controlled by the Montreal Protocol … with the aim of returning individually or jointly to their 1990 levels these anthropogenic emissions of … greenhouse gases …
The Organization
[The IPCC] was established [in 1988] by the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO) to provide the world with a clear scientific view on the current state of knowledge in climate change and its potential environmental and socio-economic impacts.
The UN General Assembly endorsed the action by WMO and UNEP in jointly establishing the IPCC.
The Secretariat [which] coordinates all the IPCC work and liaises with Governments [is] hosted at WMO headquarters in Geneva.
The IPCC is a scientific body.
It reviews and assesses the most recent scientific, technical and socio-economic information produced worldwide relevant to the understanding of climate change.
It does not conduct any research nor does it monitor climate related data or parameters.
Thousands of scientists from all over the world contribute to the work of the IPCC on a voluntary basis.
Review is an essential part of the IPCC process, to ensure an objective and complete assessment of current information.
IPCC aims to reflect a range of views and expertise.
The IPCC is an intergovernmental body. …
Currently 194 countries are members of the IPCC.
Governments participate in the review process and the plenary Sessions, where main decisions about the IPCC work programme are taken and reports are accepted, adopted and approved. …
Because of its scientific and intergovernmental nature, the IPCC embodies a unique opportunity to provide rigorous and balanced scientific information to decision makers. …
Contents
Climate Change 2014: Synthesis Report
Climate Change 2013: The Physical Science Basis
Carbon Capture and Storage
Renewable Energy and Mitigation
Managing the Risks of Extreme Events and Disasters
Climate Change 2007
Would you like to know more?
Intergovernmental Panel on Climate Change
- AR5 Synthesis Report — Longer Report, 1 November, 2014.
Core Writing Team members
Myles R Allen (United Kingdom), Vicente Ricardo Barros (Argentina), John Broome (United Kingdom), Wolfgang Cramer (Germany/France), Renate Christ (Austria/WMO), John A Church (Australia), Leon Clarke (USA), Qin Dahe (China), Purnamita Dasgupta (India), Navroz K Dubash (India), Ottmar Edenhofer (Germany), Ismail Elgizouli (Sudan), Christopher B Field (USA), Piers Forster (United Kingdom), Pierre Friedlingstein (United Kingdom), Jan Fuglestvedt (Norway), Luis Gomez-Echeverri (Colombia), Stephane Hallegatte (France/World Bank), Gabriele Hegerl (United Kingdom), Mark Howden (Australia), Kejun Jiang (China), Blanca Jimenez Cisneros (Mexico/UNESCO), Vladimir Kattsov (Russian Federation), Hoesung Lee (Republic of Korea), Katharine J Mach (USA), Jochem Marotzke (Germany), Michael D Mastrandrea (USA), Leo Meyer (The Netherlands), Jan Minx (Germany), Yacob Mulugetta (Ethiopia), Karen O'Brien (Norway), Michael Oppenheimer (USA), R K Pachauri (India), Joy J Pereira (Malaysia), Ramón Pichs-Madruga (Cuba), Gian-Kasper Plattner (Switzerland), Hans-Otto Pörtner (Germany), Scott B Power (Australia), Benjamin Preston (USA), NH Ravindranath (India), Andy Reisinger (New Zealand), Keywan Riahi (Austria), Matilde Rusticucci (Argentina), Robert Scholes (South Africa), Kristin Seyboth (USA), Youba Sokona (Mali), Robert Stavins (USA), Thomas F Stocker (Switzerland), Petra Tschakert (USA), Detlef van Vuuren (The Netherlands), Jean-Pascal van Ypersele (Belgium).
Extended Core Writing Team members
Gabriel Blanco (Argentina), Michael Eby (Canada), Jae Edmonds (USA), Marc Fleurbaey (France), Reyer Gerlagh (The Netherlands), Sivan Kartha (USA), Howard Kunreuther (USA), Joeri Rogelj (Belgium), Michiel Schaeffer (The Netherlands), Jan Sedlácek (Switzerland), Ralph Sims (New Zealand), Diana Ürge- Vorsatz (Hungary), David Victor (USA), Gary Yohe (USA).
Review Editors
Paulina Aldunce (Chile), Thomas Downing (United Kingdom), Sylvie Joussaume (France), Zbigniew Kundzewicz (Poland), Jean Palutikof (Australia), Jim Skea (United Kingdom), Kanako Tanaka (Japan), Fredolin Tangang (Malaysia), Chen Wenying (China), Zhang Xiao-Ye (China).
This report is dedicated to the memory of Stephen H Schneider 1945 – 2010.
(p 2)
Observed Changes And Their Causes
Observed changes in the climate system
Atmosphere
Each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850.
The period from 1983 to 2012 was … likely the warmest 30-year period of the last 1400 years [in the Northern Hemisphere] (medium confidence).
(p 5, emphasis added)
Ocean
Ocean warming dominates the increase in energy stored in the climate system, accounting for more than 90% of the energy accumulated between 1971 and 2010 (high confidence) with only about 1% stored in the atmosphere (Figure 1.2).
On a global scale, the ocean warming is largest near the surface, and the upper 75 m warmed by 0.11 [0.09 to 0.13] °C per decade over the period 1971 to 2010.
It is virtually certain that the upper ocean (0-700 m) warmed from 1971 to 2010, and it likely warmed between the 1870s and 1971.
It is likely that the ocean warmed from 700 m to 2000 m from 1957 to 2009 and from 3000 m to the bottom for the period 1992 to 2005.
Figure 1.2
(p 6)
Estimates are … given relative to 1971 …
Components included are- upper ocean (above 700 m),
- deep ocean (below 700 m; including below 2000 m estimates starting from 1992),
- ice melt (for glaciers and ice caps, Greenland and Antarctic ice sheet estimates starting from 1992, and Arctic sea ice estimate from 1979 to 2008),
- continental (land) warming, and
- atmospheric warming (estimate starting from 1979).
Cryosphere
Over the last two decades, the Greenland and Antarctic ice sheets have been losing mass (high confidence).
Glaciers have continued to shrink almost worldwide (high confidence).
Northern Hemisphere spring snow cover has continued to decrease in extent (high confidence).
There is high confidence that there are strong regional differences in the trend in Antarctic sea ice extent, with a very likely increase in total extent.
Sea level
Over the period 1901–2010, global mean sea level rose by 0.19 [0.17 to 0.21] m.
The rate of sea-level rise since the mid-19th century has been larger than the mean rate during the previous two millennia (high confidence). …
There is very high confidence that maximum global mean sea level during the last interglacial period (129,000 to 116,000 years ago) was … at least 5 m higher than present …
This change in sea level occurred in the context of different orbital forcing and with high-latitude surface temperature … at least 2°C warmer than present (high confidence).
(p 7)
Recent temperature trends and their implications
(p 8)
The observed reduction in surface warming trend over the period 1998 to 2012 as compared to the period 1951 to 2012, is due in roughly equal measure to- a reduced trend in radiative forcing and
- a cooling contribution from natural internal variability, which includes a possible redistribution of heat within the ocean
Past and recent drivers of climate change
Natural and anthropogenic radiative forcings
Atmospheric concentrations of greenhouse gases are at levels that are unprecedented in at least 800,000 years.
Concentrations of CO2 [40%], CH4 [150%] and N2O [20%] have all shown large increases since 1750 …
CO2 concentrations are increasing at the fastest observed decadal rate of change (2.0 ± 0.1 ppm yr^–1) for 2002-2011. …
The total anthropogenic [Radiative Forcing (RF)] over 1750-2011 is calculated to be a warming effect of 2.3 [1.1 to 3.3] W m^-2 (Figure 1.4) and it has increased more rapidly since 1970 than during prior decades.
Carbon dioxide is the largest single contributor to RF over 1750-2011 and its trend since 1970.
The total anthropogenic RF estimate for 2011 is substantially higher (43%) than the estimate reported in AR4 for the year 2005. …
The RF from aerosols, which includes cloud adjustments, is better understood and indicates a weaker cooling effect than in AR4.
The aerosol RF over 1750-2011 is estimated as –0.9 [–1.9 to -0.1] W m^-2 (medium confidence).
RF from aerosols has two competing components:- a dominant cooling effect from most aerosols and their cloud adjustments and
- a partially offsetting warming contribution from black carbon absorption of solar radiation.
Changes in solar irradiance and volcanic aerosols cause natural RF (Figure 1.4).
Changes in total solar irradiance are calculated to have contributed only around 2% of the total radiative forcing in 2011, relative to 1750.
Figure 1.4
(p 9, emphasis added)
Radiative forcing (RF) of climate change during the industrial era (1750–2011).
Bars show RF from- well-mixed greenhouse gases (WMGHG),
- other anthropogenic forcings,
- total anthropogenic forcings and
- natural forcings.
Other anthropogenic forcings include aerosol, land-use surface reflectance and ozone changes.
Natural forcings include solar and volcanic effects.
The total anthropogenic radiative forcing for 2011 relative to 1750 is 2.3 W m^-2 …
[A 44% increase over the total anthropogenic RF for 2005 of 1.6 W m^-2 (AR4, p 39)]
This corresponds to a CO2-equivalent concentration of 430 ppm …
Human activities affecting emission drivers
Since 1970- cumulative CO2 emissions from fossil fuel combustion, cement production and flaring have tripled and,
- cumulative CO2 emissions from forestry and other land use (FOLU) have increased by about 40% (Figure 1.5).
Figure 1.5
Annual global anthropogenic CO2 emissions (GtCO2 yr^-1) from fossil fuel combustion, cement production and flaring, and forestry and other land use (FOLU), 1750–2011. …
About 40% of these anthropogenic CO2 emissions have remained in the atmosphere … since 1750.
The ocean has absorbed about 30% of the emitted anthropogenic carbon dioxide, causing ocean acidification [and the remaining 30% has been taken up by vegetation with soils.]
Total annual anthropogenic GHG emissions have continued to increase over 1970 to 2010 with larger absolute increases between 2000 and 2010. (high confidence).
Despite a growing number of climate change mitigation policies, annual GHG emissions grew on average by 1.0 GtCO2eq (2.2%) per year, from 2000 to 2010, compared to 0.4 GtCO2eq (1.3%) per year, from 1970 to 2000.
Total anthropogenic GHG emissions from 2000 to 2010 were the highest in human history and reached 49 (±4.5) GtCO2eq yr^-1 in 2010. …
CO2 emissions from fossil fuel combustion and industrial processes contributed about 78% to the total GHG emission increase between 1970 and 2010, with a contribution of similar percentage over the 2000–2010 period (high confidence).
Fossil-fuel-related CO2 emissions [grew] by about 3% between 2010 and 2011, and by about 1% to 2% between 2011 and 2012.
[CO2 accounted] for 76% of total anthropogenic GHG emissions in 2010.
Of the total, 16% comes from methane (CH4), 6.2% from nitrous oxide (N2O), and 2.0% from fluorinated gases.
(p 10)
Total annual anthropogenic GHG emissions have increased by about 10 GtCO2eq between 2000 and 2010.
This increase directly came from the energy (47%), industry (30%), transport (11%) and building (3%) sectors (medium confidence). Accounting for indirect emissions raises the contributions by the building and industry sectors (high confidence). …
Globally, economic and population growth continue to be the most important drivers of increases in CO2 emissions from fossil fuel combustion.
The contribution of population growth between 2000 and 2010 remained roughly identical to that of the previous three decades, while the contribution of economic growth has risen sharply (high confidence).
(p 11)
Attribution of climate changes and impacts
Attribution of climate changes to human and natural influences on the climate system
It is extremely likely that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in greenhouse gas concentrations and other anthropogenic forcings together (Figure 1.9). …
It is very likely that anthropogenic influence, particularly greenhouse gases and stratospheric ozone depletion, has led to a detectable observed pattern of tropospheric warming and a corresponding cooling in the lower stratosphere since 1961.
Figure 1.9
Assessed likely ranges (whiskers) and their mid-points (bars) for warming trends over the 1951–2010 period from- well-mixed greenhouse gases,
- other anthropogenic forcings (including the cooling effect of aerosols and the effect of land use change),
- combined anthropogenic forcings,
- natural forcings, and
- natural internal climate variability (which is the element of climate variability that arises spontaneously within the climate system, even in the absence of forcings).
Over every continental region except Antarctica, anthropogenic forcings have likely made a substantial contribution to surface temperature increases since the mid-20th century.
(p 12)
Anthropogenic influences have very likely contributed to Arctic sea ice loss since 1979. …
Anthropogenic influences likely contributed to the retreat of glaciers since the 1960s and to the increased surface melting of the Greenland ice sheet since 1993. …
It is likely that anthropogenic influences have affected the global water cycle since 1960. …
It is very likely that anthropogenic forcings have made a substantial contribution to increases in global upper ocean heat content (0–700 m) observed since the 1970s.
Observed impacts attributed to climate change
In recent decades, changes in climate have caused impacts on natural and human systems on all continents and across the oceans.
Impacts are due to observed climate change, irrespective of its cause, indicating the sensitivity of natural and human systems to changing climate.
(p 13)
Figure 1.11
(A) Based on the available scientific literature since the AR4, there are substantially more impacts in recent decades now attributed to climate change. …
Numbers in ovals indicate regional totals of climate change publications from 2001 to 2010, based on the Scopus bibliographic database for publications in English with individual countries mentioned in title, abstract or key words (as of July 2011).
These numbers provide an overall measure of the available scientific literature on climate change across regions; they do not indicate the number of publications supporting attribution of climate change impacts in each region. …
(B) Average rates of change in distribution (km per decade) for marine taxonomic groups based on observations over 1900-2010.
Positive distribution changes are consistent with warming (moving into previously cooler waters, generally poleward).
The number of responses analysed is given for each category.
(C) Summary of estimated impacts of observed climate changes on yields over 1960-2013 for four major crops in temperate and tropical regions, with the number of data points analysed given within parentheses for each category. …
In many regions, changing precipitation or melting snow and ice are altering hydrological systems, affecting water resources in terms of quantity and quality (medium confidence). …
Many terrestrial, freshwater, and marine species have shifted their geographic ranges, seasonal activities, migration patterns, abundances, and species interactions in response to ongoing climate change (high confidence). …
Assessment of many studies covering a wide range of regions and crops shows that negative impacts of climate change on crop yields have been more common than positive impacts (high confidence). …
Climate change has negatively affected wheat and maize yields for many regions and in the global aggregate (medium confidence).
Effects on rice and soybean yield have been smaller in major production regions and globally, with a median change of zero across all available data …
(p 14)
At present the worldwide burden of human ill-health from climate change is relatively small compared with effects of other stressors and is not well quantified.
Extreme events
It is very likely that the number of cold days and nights has decreased and the number of warm days and nights has increased on the global scale.
It is likely that the frequency of heat waves has increased in large parts of Europe, Asia and Australia. …
It is likely that human influence has more than doubled the probability of occurrence of heat waves in some locations. …
There is medium confidence that the observed warming has increased heat-related human mortality and decreased cold-related human mortality in some regions. …
There are likely more land regions where the number of heavy precipitation events has increased than where it has decreased. …
There is low confidence that anthropogenic climate change has affected the frequency and magnitude of fluvial floods on a global scale.
(p 15, emphasis added)
There is low confidence in observed global-scale trends in droughts, due to lack of direct observations, dependencies of inferred trends on the choice of the definition for drought, and due to geographical inconsistencies in drought trends. …
There is low confidence that long-term changes in tropical cyclone activity are robust and there is low confidence in the attribution of global changes to any particular cause.
However, it is virtually certain that intense tropical cyclone activity has increased in the North Atlantic since 1970.
It is likely that extreme sea levels (for example, as experienced in storm surges) have increased since 1970, being mainly the result of mean sea-level rise. …
Impacts from recent climate-related extremes, such as heat waves, droughts, floods, cyclones, and wildfires, reveal significant vulnerability … to current climate variability (very high confidence).
Impacts of such climate-related extremes include- alteration of ecosystems,
- disruption of food production and water supply,
- damage to infrastructure and settlements,
- human morbidity and mortality, and
- consequences for mental health and human well-being.
Direct and insured losses from weather-related disasters have increased substantially in recent decades, both globally and regionally.
Exposure and vulnerability
Exposure and vulnerability are influenced by a wide range of social, economic, and cultural factors and processes that have been incompletely considered to date and that make quantitative assessments of their future trends difficult (high confidence). …
Differences in vulnerability and exposure arise from non-climatic factors and from multidimensional inequalities often produced by uneven development processes (very high confidence).
These differences shape differential risks from climate change.
People who are socially, economically, culturally, politically, institutionally or otherwise marginalized are especially vulnerable to climate change …
(p 16)
Climate-related hazards exacerbate other stressors, often with negative outcomes for livelihoods, especially for people living in poverty (high confidence).
Climate-related hazards affect poor people’s lives- directly through impacts on livelihoods, reductions in crop yields, or the destruction of homes, and
- indirectly through, for example, increased food prices and food insecurity. …
Violent conflict increases vulnerability to climate change (medium evidence, high agreement).
Human responses to climate change: adaptation and mitigation
Adaptation is becoming embedded in some planning processes, with more limited implementation of responses (high confidence). …
Governments at various levels have begun to develop adaptation plans and policies and integrate climate-change considerations into broader development plans. …
Global increases in anthropogenic emissions and climate impacts have occurred, even while mitigation activities have taken place in many parts of the world.
(p 17)
