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Climate Change 2014
Synthesis Report
Summary for Policymakers
Chapter
Climate Change 2014
Synthesis Report
Summary for Policymakers
Chapter
Summary for Policymakers
Introduction
This Synthesis Report is based on the reports of the three Working Groups of the Intergovernmental Panel on Climate Change
(IPCC), including relevant Special Reports. It provides an integrated view of climate change as the final part of the IPCC’s
Fifth Assessment Report (AR5).
This summary follows the structure of the longer report which addresses the following topics: Observed changes and their
SPM
causes; Future climate change, risks and impacts; Future pathways for adaptation, mitigation and sustainable development;
Adaptation and mitigation.
In the Synthesis Report, the certainty in key assessment findings is communicated as in the Working Group Reports and
Special Reports. It is based on the author teams’ evaluations of underlying scientific understanding and is expressed as a
qualitative level of confidence (from very low to very high) and, when possible, probabilistically with a quantified likelihood
(from exceptionally unlikely to virtually certain)
. Where appropriate, findings are also formulated as statements of fact with-
1
out using uncertainty qualifiers.
This report includes information relevant to Article 2 of the United Nations Framework Convention on Climate Change
(UNFCCC).
SPM 1.
Observed Changes and their Causes
Human influence on the climate system is clear, and recent anthropogenic emissions of green-
house gases are the highest in history. Recent climate changes have had widespread impacts
on human and natural systems.
{1}
SPM 1.1
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.
{1.1}
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, where
such assessment is possible (medium confidence). The globally averaged combined land and ocean surface temperature
data as calculated by a linear trend show a warming of 0.85 [0.65 to 1.06] °C
over the period 1880 to 2012, when multiple
2
independently produced datasets exist (Figure SPM.1a). {1.1.1, Figure 1.1}
In addition to robust multi-decadal warming, the globally averaged surface temperature exhibits substantial decadal and
interannual variability (Figure SPM.1a). Due to this natural variability, trends based on short records are very sensitive to the
beginning and end dates and do not in general reflect long-term climate trends. As one example, the rate of warming over
Each finding is grounded in an evaluation of underlying evidence and agreement. In many cases, a synthesis of evidence and agreement supports an
1
assignment of confidence. The summary terms for evidence are: limited, medium or robust. For agreement, they are low, medium or high. A level of
confidence is expressed using five qualifiers: very low, low, medium, high and very high, and typeset in italics, e.g., medium confidence. The follow-
ing terms have been used to indicate the assessed likelihood of an outcome or a result: virtually certain 99–100% probability, very likely 90–100%,
likely 66–100%, about as likely as not 33–66%, unlikely 0–33%, very unlikely 0–10%, exceptionally unlikely 0–1%. Additional terms (extremely
likely 95–100%, more likely than not >50–100%, more unlikely than likely 0–<50%, extremely unlikely 0–5%) may also be used when appropriate.
Assessed likelihood is typeset in italics, e.g., very likely. See for more details: Mastrandrea, M.D., C.B. Field, T.F. Stocker, O. Edenhofer, K.L. Ebi, D.J. Frame,
H. Held, E. Kriegler, K.J. Mach, P.R. Matschoss, G.-K. Plattner, G.W. Yohe and F.W. Zwiers, 2010: Guidance Note for Lead Authors of the IPCC Fifth Assess-
ment Report on Consistent Treatment of Uncertainties, Intergovernmental Panel on Climate Change (IPCC), Geneva, Switzerland, 4 pp.
Ranges in square brackets or following ‘±’ are expected to have a 90% likelihood of including the value that is being estimated, unless otherwise
2
stated.
2
Summary for Policymakers
(a)
Globally averaged combined land and ocean surface temperature anomaly
0.4
0.2
0
−0.2
−0.4
−0.6
−0.8
SPM
−1
1850
1900
1950
2000
Year
(b)
Globally averaged sea level change
0.1
0.05
0
−0.05
−0.1
−0.15
−0.2
1850
1900
1950
2000
Year
(c)
Globally averaged greenhouse gas concentrations
400
380
360
1800
330
340
1600
320
1400
310
320
300
1200
290
300
1000
280
800
280
270
1850
1900
1950
2000
Year
Cumulative CO
Global anthropogenic CO
emissions
2
2
(d)
emissions
Quantitative information of CH
and N
O emission time series from 1850 to 1970 is limited
4
2
40
Fossil fuels, cement and flaring
2000
35
Forestry and other land use
30
1500
25
20
1000
15
10
500
5
0
0
1850
1900
1950
2000
1750
1750
Year
1970
2011
Figure SPM.1 |
The complex relationship between the observations (panels a, b, c, yellow background) and the emissions (panel d,
light blue background) is addressed in Section 1.2 and Topic 1. Observations and other indicators of a changing global climate system. Observa-
tions: (a) Annually and globally averaged combined land and ocean surface temperature anomalies relative to the average over the period 1986 to 2005.
Colours indicate different data sets. (b) Annually and globally averaged sea level change relative to the average over the period 1986 to 2005 in the
longest-running dataset. Colours indicate different data sets. All datasets are aligned to have the same value in 1993, the first year of satellite altimetry
data (red). Where assessed, uncertainties are indicated by coloured shading. (c) Atmospheric concentrations of the greenhouse gases carbon dioxide
(CO
, green), methane (CH
, orange) and nitrous oxide (N
O, red) determined from ice core data (dots) and from direct atmospheric measurements (lines).
2
4
2
Indicators: (d) Global anthropogenic CO
emissions from forestry and other land use as well as from burning of fossil fuel, cement production and flaring.
2
Cumulative emissions of CO
from these sources and their uncertainties are shown as bars and whiskers, respectively, on the right hand side. The global
2
effects of the accumulation of CH
and N
O emissions are shown in panel c. Greenhouse gas emission data from 1970 to 2010 are shown in Figure SPM.2.
4
2
{Figures 1.1, 1.3, 1.5}
3
Summary for Policymakers
the past 15 years (1998–2012; 0.05 [–0.05 to 0.15] °C per decade), which begins with a strong El Niño, is smaller than the
rate calculated since 1951 (1951–2012; 0.12 [0.08 to 0.14] °C per decade). {1.1.1, Box 1.1}
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. 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
SPM
between the 1870s and 1971. {1.1.2, Figure 1.2}
Averaged over the mid-latitude land areas of the Northern Hemisphere, precipitation has increased since 1901 (medium
confidence before and high confidence after 1951). For other latitudes, area-averaged long-term positive or negative trends
have low confidence. Observations of changes in ocean surface salinity also provide indirect evidence for changes in the
global water cycle over the ocean (medium confidence). It is very likely that regions of high salinity, where evaporation dom-
inates, have become more saline, while regions of low salinity, where precipitation dominates, have become fresher since
the 1950s. {1.1.1, 1.1.2}
Since the beginning of the industrial era, oceanic uptake of CO
has resulted in acidification of the ocean; the pH of ocean
2
surface water has decreased by 0.1 (high confidence), corresponding to a 26% increase in acidity, measured as hydrogen ion
concentration. {1.1.2}
Over the period 1992 to 2011, the Greenland and Antarctic ice sheets have been losing mass (high confidence), likely at a
larger rate over 2002 to 2011. 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 permafrost tempera-
tures have increased in most regions since the early 1980s in response to increased surface temperature and changing snow
cover. {1.1.3}
The annual mean Arctic sea-ice extent decreased over the period 1979 to 2012, with a rate that was very likely in the range
3.5 to 4.1% per decade. Arctic sea-ice extent has decreased in every season and in every successive decade since 1979, with
the most rapid decrease in decadal mean extent in summer (high confidence). It is very likely that the annual mean Antarctic
sea-ice extent increased in the range of 1.2 to 1.8% per decade between 1979 and 2012. However, there is high confidence
that there are strong regional differences in Antarctica, with extent increasing in some regions and decreasing in others.
{1.1.3, Figure 1.1}
Over the period 1901 to 2010, global mean sea level rose by 0.19 [0.17 to 0.21] m (Figure SPM.1b). 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). {1.1.4,
Figure 1.1}
SPM 1.2
Causes of climate change
Anthropogenic greenhouse gas emissions have increased since the pre-industrial era, driven
largely by economic and population growth, and are now higher than ever. This has led to atmo-
spheric concentrations of carbon dioxide, methane and nitrous oxide that are unprecedented in
at least the last 800,000 years. Their effects, together with those of other anthropogenic driv-
ers, have been detected throughout the climate system and are extremely likely to have been
the dominant cause of the observed warming since the mid-20th century.
{1.2, 1.3.1}
Anthropogenic greenhouse gas (GHG) emissions since the pre-industrial era have driven large increases in the atmospheric
concentrations of carbon dioxide (CO
), methane (CH
) and nitrous oxide (N
O) (Figure SPM.1c). Between 1750 and 2011,
2
4
2
cumulative anthropogenic CO
emissions to the atmosphere were 2040 ± 310 GtCO
. About 40% of these emissions have
2
2
remained in the atmosphere (880 ± 35 GtCO
); the rest was removed from the atmosphere and stored on land (in plants and
2
soils) and in the ocean. The ocean has absorbed about 30% of the emitted anthropogenic CO
, causing ocean acidification.
2
About half of the anthropogenic CO
emissions between 1750 and 2011 have occurred in the last 40 years (high confidence)
2
(Figure SPM.1d). {1.2.1, 1.2.2}
4
Summary for Policymakers
Total annual anthropogenic GHG emissions by gases 1970–2010
+2.2%/yr
2000–2010
52 Gt
49 Gt
2.2%
50
2.0%
5.0%
+1.3%/yr
6.2%
1970–2000
16%
20%
40
38 Gt
SPM
0.81%
7.4%
11%
10%
18%
30
27 Gt
0.44%
16%
7.9%
19%
20
17%
Gas
65%
62%
F-Gases
N
O
59%
2
10
CH
4
55%
CO
FOLU
2
CO
Fossil fuel and
2
industrial processes
0
1980
1985
1990
1995
2000
2005
2010
1970
1975
2010
2010
Year
(GWP
SAR)
(GWP
AR5)
100
100
Figure SPM.2 |
Total annual anthropogenic greenhouse gas (GHG) emissions (gigatonne of CO
-equivalent per year, GtCO
-eq/yr) for the period 1970
2
2
to 2010 by gases: CO
from fossil fuel combustion and industrial processes; CO
from Forestry and Other Land Use (FOLU); methane (CH
); nitrous oxide
2
2
4
(N
O); fluorinated gases covered under the Kyoto Protocol (F-gases). Right hand side shows 2010 emissions, using alternatively CO
-equivalent emission
2
2
weightings based on IPCC Second Assessment Report (SAR) and AR5 values. Unless otherwise stated, CO
-equivalent emissions in this report include the
2
basket of Kyoto gases (CO
, CH
, N
O as well as F-gases) calculated based on 100-year Global Warming Potential (GWP
) values from the SAR (see Glos-
2
4
2
100
sary). Using the most recent GWP
values from the AR5 (right-hand bars) would result in higher total annual GHG emissions (52 GtCO
-eq/yr) from an
100
2
increased contribution of methane, but does not change the long-term trend significantly. {Figure 1.6, Box 3.2}
Total anthropogenic GHG emissions have continued to increase over 1970 to 2010 with larger absolute increases between
2000 and 2010, despite a growing number of climate change mitigation policies. Anthropogenic GHG emissions in 2010 have
reached 49 ± 4.5 GtCO
-eq/yr
. Emissions of CO
from fossil fuel combustion and industrial processes contributed about 78%
3
2
2
of the total GHG emissions increase from 1970 to 2010, with a similar percentage contribution for the increase during the
period 2000 to 2010 (high confidence) (Figure SPM.2). Globally, economic and population growth continued to be the most
important drivers of increases in CO
emissions from fossil fuel combustion. The contribution of population growth between
2
2000 and 2010 remained roughly identical to the previous three decades, while the contribution of economic growth has
risen sharply. Increased use of coal has reversed the long-standing trend of gradual decarbonization (i.e., reducing the carbon
intensity of energy) of the world’s energy supply (high confidence). {1.2.2}
The evidence for human influence on the climate system has grown since the IPCC Fourth Assessment Report (AR4). 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 GHG concentrations and other anthropogenic forcings together. The best estimate
of the human-induced contribution to warming is similar to the observed warming over this period (Figure SPM.3). Anthro-
pogenic forcings have likely made a substantial contribution to surface temperature increases since the mid-20th century
over every continental region except Antarctica
. Anthropogenic influences have likely affected the global water cycle since
4
1960 and contributed to the retreat of glaciers since the 1960s and to the increased surface melting of the Greenland ice
sheet since 1993. Anthropogenic influences have very likely contributed to Arctic sea-ice loss since 1979 and have very likely
made a substantial contribution to increases in global upper ocean heat content (0–700 m) and to global mean sea level rise
observed since the 1970s. {1.3, Figure 1.10}
3
Greenhouse gas emissions are quantified as CO
-equivalent (GtCO
-eq) emissions using weightings based on the 100-year Global Warming Potentials,
2
2
using IPCC Second Assessment Report values unless otherwise stated. {Box 3.2}
For Antarctica, large observational uncertainties result in low confidence that anthropogenic forcings have contributed to the observed warming aver-
4
aged over available stations.
5