Table 1 Robust findings and key uncertainties? [from Summary for Policymakers (SPM) of Climate Change 2001,
Synthesis Report, part of the Third Assessment Report (TAR) of the IPCC, published by Cambridge University Press
2001]
Robust findings
Key uncertainties
Observations show Earth’s surface is warming.
Globally, 1990s very likely warmest decade in
instrumental record (Figure 4)
Atmospheric concentrations of main anthropogenic
greenhouse gases [CO
(Figure 3), CH
, N
O, and
tropospheric O
] increased substantially since 1750
Climate change and
attribution
Magnitude and character of climate
variability
Climate forcings due to anthropogenic
aerosols (particularly indirect effects)
Relating regional trends to anthropogenic
climate change
Some greenhouse gases have long lifetimes (e.g. CO
,
N
O and PFCs)
Most of observed warming over last 50 years likely due
to increases in greenhouse gas concentrations due to
human activities (Figure 5)
CO
concentrations increasing over 21st century
virtually certain to be mainly due to fossil-fuel
emissions (Figure 3)
Stabilization of atmospheric CO
concentrations at 450,
650 or 1000 ppm would require global anthropogenic
CO
emissions to drop below year 1990 levels, within a
few decades, about a century, or about 2 centuries,
respectively, and continue to decrease steadily thereafter
to a small fraction of current emissions. Emissions
would peak in about 1—2 decades (450 ppm) and
roughly a century (1000 ppm) from the present
For most SRES scenarios, SO
emissions (precursor for
sulfate aerosols) are lower in the year 2100 compared
with year 2000
Future emissions and
concentrations of
greenhouse gases
and aerosols based
on models and
projections with the
SRES
† and
stabilization
scenarios
†
Assumptions underlying the wide range@
of SRES emissions scenarios relating to
economic growth, technological progress,
population growth, and governance
structures (lead to largest uncertainties in
projections). Inadequate emission
scenarios for ozone and aerosol
precursors
Factors in modelling of carbon cycle
including effects of climate feedbacks@
Global average surface temperature during 21st century
rising at rates very likely without precedent during last
10 000 years (Figure 4)
Nearly all land areas very likely to warm more than
global average, with more hot days and heat waves and
fewer cold days and cold waves
Rise in sea level during 21st century that will continue
for further centuries
Hydrological cycle more intense. Increase in globally
averaged precipitation and more intense precipitation
events very likely over many areas
Increased summer drying and associated risk of
drought likely over most mid-latitude continental
interiors
Future changes in
global and regional
climate based on
model projections
with SRES scenarios
Assumptions associated with a wide
rangeA of SRES scenarios, as above
Factors associated with model
projections,A in particular climate
sensitivity, climate forcing, and feedback
processes, especially those involving water
vapour, clouds, and aerosols (including
aerosol indirect effects)
Understanding the probability
distribution associated with temperature
and sea-level projections
The mechanisms, quantification, time
scales, and likelihoods associated with
large-scale abrupt/non-linear changes (e.g.
ocean thermohaline circulation)
Capabilities of models on regional scales
(especially regarding precipitation) leading
to inconsistencies in model projections
and difficulties in quantification on local
and regional scales
J. Houghton
16
Synthesis Report, part of the Third Assessment Report (TAR) of the IPCC, published by Cambridge University Press
2001]
Robust findings
Key uncertainties
Observations show Earth’s surface is warming.
Globally, 1990s very likely warmest decade in
instrumental record (Figure 4)
Atmospheric concentrations of main anthropogenic
greenhouse gases [CO
(Figure 3), CH
, N
O, and
tropospheric O
] increased substantially since 1750
Climate change and
attribution
Magnitude and character of climate
variability
Climate forcings due to anthropogenic
aerosols (particularly indirect effects)
Relating regional trends to anthropogenic
climate change
Some greenhouse gases have long lifetimes (e.g. CO
,
N
O and PFCs)
Most of observed warming over last 50 years likely due
to increases in greenhouse gas concentrations due to
human activities (Figure 5)
CO
concentrations increasing over 21st century
virtually certain to be mainly due to fossil-fuel
emissions (Figure 3)
Stabilization of atmospheric CO
concentrations at 450,
650 or 1000 ppm would require global anthropogenic
CO
emissions to drop below year 1990 levels, within a
few decades, about a century, or about 2 centuries,
respectively, and continue to decrease steadily thereafter
to a small fraction of current emissions. Emissions
would peak in about 1—2 decades (450 ppm) and
roughly a century (1000 ppm) from the present
For most SRES scenarios, SO
emissions (precursor for
sulfate aerosols) are lower in the year 2100 compared
with year 2000
Future emissions and
concentrations of
greenhouse gases
and aerosols based
on models and
projections with the
SRES
† and
stabilization
scenarios
†
Assumptions underlying the wide range@
of SRES emissions scenarios relating to
economic growth, technological progress,
population growth, and governance
structures (lead to largest uncertainties in
projections). Inadequate emission
scenarios for ozone and aerosol
precursors
Factors in modelling of carbon cycle
including effects of climate feedbacks@
Global average surface temperature during 21st century
rising at rates very likely without precedent during last
10 000 years (Figure 4)
Nearly all land areas very likely to warm more than
global average, with more hot days and heat waves and
fewer cold days and cold waves
Rise in sea level during 21st century that will continue
for further centuries
Hydrological cycle more intense. Increase in globally
averaged precipitation and more intense precipitation
events very likely over many areas
Increased summer drying and associated risk of
drought likely over most mid-latitude continental
interiors
Future changes in
global and regional
climate based on
model projections
with SRES scenarios
Assumptions associated with a wide
rangeA of SRES scenarios, as above
Factors associated with model
projections,A in particular climate
sensitivity, climate forcing, and feedback
processes, especially those involving water
vapour, clouds, and aerosols (including
aerosol indirect effects)
Understanding the probability
distribution associated with temperature
and sea-level projections
The mechanisms, quantification, time
scales, and likelihoods associated with
large-scale abrupt/non-linear changes (e.g.
ocean thermohaline circulation)
Capabilities of models on regional scales
(especially regarding precipitation) leading
to inconsistencies in model projections
and difficulties in quantification on local
and regional scales
J. Houghton
16