1. The IPCC Fourth Assessment Working Group Reports: Key findings
WMO
UNEP
Dr R K Pachauri
Chairman, IPCC
Director-General, TERI
United Nations Headquarters
New York City
24th September 2007

2. Human contribution to climate change
Changes in CO2 from ice core and modern data
Radiative Forcing (Wm ) -2
Carbon Dioxide (ppm)
Global atmospheric concentrations of greenhouse gases increased markedly as result of human activities
In 2005 concentration of CO2 exceeded by far the natural range over the last 650,000 years
Figure SPM.1. Changes in greenhouse gases from ice core and modern data. Atmospheric concentrations of carbon dioxide over the last 10,000 years and since
1750. Measurements are shown from ice cores (symbols with different colours for different studies)
and atmospheric samples (red lines). The corresponding radiative forcings are shown on the right
hand axes of the large panels. WG1 {Figure 6.4} (SPM p. 3)
Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations. WG1 {9.4, 9.5} (SPM p.10)
Global atmospheric concentrations of carbon dioxide, methane and nitrous oxide have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values determined from ice cores spanning many thousands of years. WG1 {2.3, 6.4, 7.3} (SPM p. 2)
Carbon dioxide is the most important anthropogenic greenhouse gas. The atmospheric concentration of carbon dioxide in 2005 exceeds by far the natural range over the last 650,000 years (180 to 300 ppm) as determined from ice cores. The global atmospheric concentration of carbon dioxide has increased from a pre-industrial value of about 280 ppm to 379 ppm in WG1 {2.3, 7.3} (SPM p. 2)
Time (before 2005)

3. Direct observations of recent climate change
Changes in temperature, sea level and
northern hemisphere snow cover
Global average temperature
Global average sea level
Direct observations of recent climate change. GW1 SPM p.5.
Figure SPM.3. Observed changes in (a) global average surface temperature, (b) global average sea level from tide gauge (blue) and satellite data (red) and (c) Northern Hemisphere snow cover for March-April.
All changes are relative to corresponding averages for the period 1961–1990. Smoothed curves represent decadal average values while circles show yearly values. The shaded areas are the uncertainty intervals. WG1 {FAQ 3.1, Figure 1, Figure 4.2, Figure 5.13} (SPM p.6)
Eleven of the last twelve years (1995–2006) rank among the 12 warmest years in the instrumental record of global surface temperature (since 1850). The total temperature increase from 1850–1899 to 2001–2005 is 0.76°C. WG1 {3.2} (SPM p.6)
Mountain glaciers and snow cover have declined on average in both hemispheres. Widespread decreases in glaciers and ice caps have contributed to sea level rise. WG1 {4.6, 4.7, 4.8, 5.5} (SPM p.6)
Northern hemisphere
snow cover

4. of glacier mass in some regions
Glacier mass balance
Cumulative balance
of glacier mass in some regions
During the 20th century, glaciers and ice caps have experienced widespread mass losses and have contributed to sea level rise
Further decline of mountain glaciers projected to reduce water availability in many regions
Widespread decreases in glaciers and ice caps have contributed to sea level rise. WG1 {4.6, 4.7, 4.8, 5.5} (SPM p.6)
In the course of the century, water supplies stored in glaciers and snow cover are projected to decline, reducing water availability in regions supplied by meltwater from major mountain ranges, where more than one-sixth of the world population currently lives. WG2 [3.4] SPM p.5

5. Heavier precipitation, more intense and longer droughts….
More intense and longer droughts have been observed over wider areas since the 1970s, particularly in the tropics and subtropics. {3.3} The frequency of heavy precipitation events has increased over most land areas. WG1 {3.8, 3.9} (SPM p.8)
It is very likely that hot extremes, heat waves and heavy precipitation events will continue to become more frequent {10.3} and that future tropical cyclones (typhoons and hurricanes) will become more intense. WG1 {9.5, 10.3, 3.8} (SPM p.15)

6. Key vulnerabilities to climate change
Some regions will be more affected than others:
The Arctic (ice sheet loss, ecosystem changes)
Sub-Saharan Africa (water stress, reduced crops)
Small islands (coastal erosion, inundation)
Asian mega-deltas (flooding from sea and rivers)
Some ecosystems are highly vulnerable:
Coral reefs, marine shell organisms
Tundra, boreal forests, mountain and Mediterranean regions
20-30% of plant and animal species at risk of extinction
Depending on circumstances, some of these impacts could be associated with ‘key vulnerabilities’,
based on a number of criteria in the literature (magnitude, timing, persistence/reversibility, the
potential for adaptation, distributional aspects, likelihood and “importance” of the impacts). WG2 [19.ES, 19.1].
SPM p.13.
The numbers affected will be largest in the mega-deltas of Asia and Africa while small islands are
especially vulnerable. WG2 [6.4] p.7
Average arctic temperatures increased at almost twice the global average rate in the past 100 years. WG1 {3.2}, SPM p.7. In the Polar Regions, the main projected biophysical effects are reductions in thickness and extent of
glaciers and ice sheets, and changes in natural ecosystems with detrimental effects on many organisms
including migratory birds, mammals and higher predators. WG2 [15.3, 15.4, 15.2] SPM p.11
In seasonally dry and tropical regions, crop productivity is projected to decrease for even small local temperature increases (1-2°C), which would increase risk of hunger. WG2 [5.4] SPM p.6. In Africa, by 2020, between 75 and 250 million people are projected to be exposed to an increase of water stress due to climate change. If coupled with increased demand, this will adversely affect livelihoods and exacerbate water-related problems. WG2 [9.4, 3.4, 8.2, 8.4], SPM p.8.
Agricultural production, including access to food, in many African countries and regions is projected
to be severely compromised by climate variability and change. This would further adversely affect food security and exacerbate malnutrition in the continent.
Small islands, whether located in the tropics or higher latitudes, have characteristics which make them
especially vulnerable to the effects of climate change, sea level rise and extreme events. WG2 [16.1,
16.5]
Deterioration in coastal conditions, for example through erosion of beaches and coral bleaching, is
expected to affect local resources, e.g., fisheries, and reduce the value of these destinations for tourism.
WG2 [16.4]
Sea-level rise is expected to exacerbate inundation, storm surge, erosion and other coastal hazards,
thus threatening vital infrastructure, settlements and facilities that support the livelihood of island
communities. WG2 [16.4] SPM p.11
Coastal areas, especially heavily-populated mega-delta regions in South, East and Southeast Asia, will
be at greatest risk due to increased flooding from the sea and, in some mega-deltas, flooding from the
rivers. WG2 [10.4], SPM p.8.
The resilience of many ecosystems is likely to be exceeded this century by an unprecedented
combination of climate change, associated disturbances (e.g., flooding, drought, wildfire, insects,
ocean acidification), and other global change drivers (e.g., land use change, pollution, overexploitation
of resources). WG2 [4.1 to 4.6], SPM p.5.
Corals are vulnerable to thermal stress and have low adaptive capacity. WG2 [B6.1, 6.4] p.6
The progressive acidification of oceans due to increasing atmospheric carbon dioxide is expected to
have negative impacts on marine shell forming organisms (e.g., corals) and their dependent species. WG2 [B4.4, 6.4], SPM p.6.
Approximately 20-30% of plant and animal species assessed so far are likely to be at increased risk of
extinction if increases in global average temperature exceed C. N [4.4, T4.1] (SPM p.6)

7. Coastal settlements most at risk

8. Ranges for predicted surface warming
Multi-model averages and assessed ranges for surface warming
Figure SPM.5. Multi-model averages and assessed ranges for surface warming. Solid lines are multi-model global averages of surface warming (relative to 1980–1999) for the scenarios A2, A1B and B1, shown as continuations of the 20th century simulations. Shading denotes the ±1 standard deviation range of individual model annual averages. The orange line is for the experiment where concentrations were held constant at year 2000 values. The grey bars at right indicate the best estimate (solid line within each bar) and the likely range assessed for the six SRES marker scenarios. The assessment of the best estimate and likely ranges in the grey bars includes the AOGCMs in the left part of the figure, as well as results from a hierarchy of independent models and observational constraints. {Figures 10.4 and 10.29}
Continued greenhouse gas emissions at or above current rates would cause further
warming and induce many changes in the global climate system during the 21st century that
would very likely be larger than those observed during the 20th century. The best estimate for the
low scenario, among those projected by IPCC, is 1.8°C, and the best estimate for the high scenario
is 4.0°C. WG1 {10.3} (SPM p.15)
Model experiments show that even if all radiative forcing agents were held constant at year
2000 levels, a further warming trend would occur in the next two decades at a rate of about 0.1°C
per decade, due mainly to the slow response of the oceans. WG1 {9.4, 10.3, 10.5, 11.2} (SPM
p.12)
Both past and future anthropogenic carbon dioxide emissions will continue to contribute to
warming and sea level rise for more than a millennium, due to the time scales required for
removal of this gas from the atmosphere and to the slow response of the oceans. WG1 {7.3, 10.3,
10.7} (SPM p.12,17)

9. Mitigation urgently needed
Continued GHG emissions at or above current rate would induce larger climatic changes than those observed in 20th century
Emissions of the greenhouse gases covered by the Kyoto Protocol increased by about 70% from 1970–2004
Mitigation needs to start in short term, even when benefits may only arise in a few decades
Adaptation is essential, particularly in addressing near-term impacts.
However, adaptation alone is not expected to cope with all the projected effects of climate change, and especially not over the long run as most impacts increase in magnitude WG2 [Table SPM-1] (SPM p.17)
Impacts of climate change are very likely to impose net annual costs which will increase over
time as global temperatures increase. WG2 [F20.3] (SPM p.16)
This suggests the value of a portfolio or mix of strategies that includes adaptation,
technological development (to enhance both adaptation and mitigation), research (on climate
science, impacts, adaptation and mitigation) and mitigation of GHG. WG2 SPM p.18

10. Beyond adaptation
Adaptation to climate change is necessary to address impacts resulting from the warming which is already unavoidable due to past emissions
However:
Adaptation alone cannot cope with all the projected impacts
of climate change
The costs of adaptation and impacts will increase as global
temperatures increase
Making development more sustainable can enhance both mitigative and adaptive capacity, and reduce emissions and vulnerability to climate change
Adaptation is essential, particularly in addressing near-term impacts.
However, adaptation alone is not expected to cope with all the projected effects of climate change, and especially not over the long run as most impacts increase in magnitude WG2 [Table SPM-1] (SPM p.17)
Impacts of climate change are very likely to impose net annual costs which will increase over
time as global temperatures increase. WG2 [F20.3] (SPM p.16)
Making development more sustainable can enhance both mitigative and adaptive capacity, and reduce emissions and vulnerability to climate change. WG3 [2.5, 3.5, 4.5, 6.9, 7.8, 8.5, 9.5, 11.9, 12.1] SPM p.34

11. Pathways towards stabilization
Characteristics of stabilization scenarios
Stabilization
level
(ppm CO2-eq)
Global mean temp. increase
at equilibrium (ºC)
Year CO2 needs to peak
Year CO2 emissions back at 2000 level
Reduction in 2050 CO2 emissions compared to 2000
445 – 490
2.0 – 2.4
-85 to -50
490 – 535
2.4 – 2.8
-60 to -30
535 – 590
2.8 – 3.2
-30 to +5
590 – 710
3.2 – 4.0
+10 to +60
710 – 855
4.0 – 4.9
+25 to +85
855 – 1130
4.9 – 6.1
+90 to +140
Table SPM.5: Characteristics of post-TAR stabilization scenarios WG3 [Table TS 2, 3.10], SPM p.23
In order to stabilize the concentration of GHGs in the atmosphere, emissions would
need to peak and decline thereafter. The lower the stabilization level, the more
quickly this peak and decline would would need to occur. Mitigation efforts over the next
two to three decades will have a large impact on opportunities to achieve lower
stabilization levels WG3 (3.3), SPM p.22.
Mitigation efforts over the next two to three decades
will have a large impact on opportunities to achieve lower stabilization levels
[1] The best estimate of climate sensitivity is 3ºC [WG 1 SPM].
[2] Note that global mean temperature at equilibrium is different from expected global mean temperature at the time of stabilization of GHG concentrations due to the inertia of the climate system. For the majority of scenarios assessed, stabilisation of GHG concentrations occurs between 2100 and 2150.
[3] Ranges correspond to the 15th to 85th percentile of the post-TAR scenario distribution. CO2 emissions are shown so multi-gas scenarios can be compared with CO2-only scenarios.

12. Mitigation costs in 2030 0.6% gain to 3% decrease of GDP < 0.12
Estimated global macro-economic costs in 2030 for least-cost trajectories towards different long-term stabilization levels
< 0.12
< 3
Not available
<0.1
0.2 – 2.5
0.6
< 0.06
-0.6 – 1.2
0.2
Reduction of average annual GDP growth rates
(percentage points)
Range of GDP reduction
(%)
Median
GDP reduction
Trajectories towards stabilization levels
(ppm CO2-eq)
Table SPM.4: Estimated global macro-economic costs in 2030 for least-cost trajectories
towards different long-term stabilization levels.
Results based on studies using various baselines.
The calculation of the reduction of the annual growth rate is based on the average reduction during the period till 2030 that would result in the indicated GDP decrease in 2030.
Some show GDP gains because they assume that baselines are non-optimal and mitigation policies improve market efficiencies, or they assume that more technological change may be induced by
mitigation policies. WG3 SPM p.16
In 2030 macro-economic costs for multi-gas mitigation, consistent with emissions trajectories towards stabilization between 445 and 710 ppm CO2-eq, are estimated at between a 3% decrease of global GDP and a small increase, compared to the baseline. However, regional costs may differ significantly from global averages. WG3 SPM p.16
The reduction of GDP relative to the GDP baseline increases with the stringency of the stabilization target. WG3 SPM p.16
As regard long term mitigation, in 2050 global average macro-economic costs for multi-gas mitigation towards stabilization between 710 and 445 ppm CO2-eq, are between a 1% gain to a 5.5% decrease of global GDP. For specific countries and sectors, costs vary considerably from the global average.
WG3 SPM p.27
0.6% gain to 3% decrease of GDP

13. Illustration of cost numbers
GDP
GDP without mitigation
80%
GDP with stringent mitigation
77%
Time
Current
~1 Year
2030

14. Key technologies to reduce emissions
Key mitigation technologies and practices currently commercially available
Energy
Supply
Efficiency; fuel switching; renewable (hydropower, solar, wind, geothermal and bioenergy); combined heat and power; nuclear power; early applications of CO2 capture and storage
Transport
More fuel efficient vehicles; hybrid vehicles; biofuels;
modal shifts from road transport to rail and public
transport systems; cycling, walking; land-use planning
Buildings
Table SPM 3: Key mitigation technologies and practices by sector. Sectors and technologies are listed in no particular order. Non-technological practices, such as lifestyle changes, which are cross-cutting, are not included in this table (but are addressed in paragraph 7 in this SPM).
Efficient lighting; efficient appliances and aircodition;
improved insulation ; solar heating and cooling;
alternatives for fluorinated gases in insulation and
appliances

15. Key policies to reduce emissions
Appropriate incentives for
development of technologies
Effective carbon price signal to
create incentives to invest in low-GHG
products, technologies and processes
Appropriate energy infrastructure
investment decisions, which have
long term effects on emissions
Changes in lifestyle and behavior
patterns, especially in building,
transport and industrial sectors
The actual implementation of these technological solutions assumes that appropriate and effective incentives are in place for development, acquisition, deployment and diffusion of technologies and for addressing related barriers.
Policies that provide a real or implicit price of carbon could create incentives for producers and consumers to significantly invest in low-GHG products, technologies and processes. Such policies could include economic instruments, government funding and regulation
For stabilisation at around 550 ppm CO2eq carbon prices should reach US$/tCO2eq by 2030 (5-65 if “induced technological change” happens)
Costs may be substantially lower under the assumption that revenues from carbon taxes or auctioned
permits under an emission trading system are used to promote low-carbon technologies or reform of
existing taxes. WG3 [11.4] (SPM p.16)
Future energy infrastructure investment decisions, expected to total over 20 trillion US$19 between now and 2030, will have long term impacts on GHG emissions, because of the long life-times of energy plants and other infrastructure capital stock. Initial estimates show that returning global energy-related CO2 emissions to 2005 levels by 2030 would require a large shift in the pattern of investment, although the net additional investment required ranges from negligible to 5-10% GW3 [4.1, 4.4, 11.6] (SPM p.18)
In addition to this, changes in lifestyle and behaviour patterns can contribute to climate change mitigation across all sectors. For instance, changes in occupant behaviour can result in considerable reduction in CO2 emissions related to energy use in buildings [6.7]. Education and training programmes can help overcome barriers to the market acceptance of energy efficiency. WG3 SPM p.17

16. A technological society has two choices
A technological society has two choices. First it can wait until catastrophic failures expose systemic deficiencies, distortion and self-deceptions…
Secondly, a culture can provide social checks and balances to correct for systemic distortion prior to catastrophic failures.