Download Assessing the Physical Science of Climate Change

Assessing the Physical Science
of Climate Change:
IPCC Working Group 1 (2007)
From Material Presented by
Susan Solomon, co-chair WG I
at the Royal Society London, March, 2007
and Norwegian Academy Of Sciences
Oslo, Norway April 2007
1.
Introduction and Background
2.
IPCC Process
3.
Key Findings
INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE (IPCC)
Working Group I
The World Has Warmed
Globally averaged, the planet is about 0.75°C warmer than it was in 1860, based
upon dozens of high-quality long records using thermometers worldwide, including
land and ocean.
Eleven of the last 12 years are among 12 warmest since 1850 in the global
average.
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Intergovernmental Panel on Climate Change
Governments require information on
climate change for negotiations
The IPCC formed in 1988 under auspices
of the United Nations
Function is to provide assessments of the
science of climate change
Scientific community contributes widely
and on a voluntary basis
75% of the authors in WG1 IPCC (2007)
did not work on WG1 IPCC (2001)
Substance of IPCC WG1 report in the
hands of scientists
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Preparation and Review of the WG1 AR4
•
Each report is an assessment of the state of understanding based upon peerreviewed published work. IPCC assesses published research but does not do
research. Each assessment goes through multiple reviews and revision and rereview over a period of years.
•
Informal draft prepared, comments sought from 6-12 outside experts for each
chapter (Oct 2004 - Mar 2005).
•
Formal first order draft (FOD) reviewed by about 600 reviewers worldwide (Sept
-Nov 2005).
•
Formal second order draft (SOD) re-reviewed by about 600 experts worldwide
and by dozens of governments (April-May 2006).
•
Govt comments on revised Summary for Policy Makers (Oct-Nov 2006).
•
WG1 received and considered over 30000 comments in total.
•
The assessment conclusions are not the views of any single scientist, but
reflect a much broader process.
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The Working Group I Report
•
•
•
•
•
•
Started 2004
Completed February 2007
152 Authors
~450 contributors
~600 expert reviewers
30,000+ review comments
Contents
• Summary for Policymakers
You can get it at:
• Technical Summary
http://ipcc-wg1.ucar.edu/
• 11 Chapters
Includes supplementary material.
• Frequently Asked Questions
All figures available in PowerPoint
format.
• ~5000
literature references
• ~1000 pages
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Industrial revolution and the atmosphere
The current concentrations of key greenhouse gases,
and their rates of change, are unprecedented.
Carbon dioxide
Methane
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Nitrous Oxide
(ppmv)
350
Last Interglacial
Last Ice Age
Carbon Dioxide
300
250
200
[Adapted from Figure 6.3, ©IPCC 2007: WG1-AR4]
600
500
400
300
200
100
0
Thousands of Years Before Present
Humans are ‘forcing’ the system in a new way. CO2 increases are
mainly due to fossil fuel burning. CO2 has not been this high in
more than half a million years.
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Ice ages
are not
random.
They are
'forced'
(by
earth’s
orbital
clock….
changes
in the
sunlight
received).
Better and longer satellite data about the Sun
Improved assessment:
a) no observed trend in solar irradiance since 1978 using high
quality inter-calibrated data; b) spectral information c) solar
magnetic flux model rather than proxy data; d) re-evaluation of
variations in Sun-like stars.
No observed trend in this data. Solar forcing much less than
greenhouse gases.
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Human and Natural Drivers of Climate Change
Carbon dioxide is
causing the bulk
of the forcing.
On average, it
lives more than a
hundred years in
the atmosphere
and therefore
affects climate
over long time
scales.
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Water Vapor Feedback
Water vapor responds to
changes in climate, but it
doesn’t drive changes in
climate. It’s a major
feedback that amplifies
global climate change.
New in IPCC (2007):
Observed trends that
demonstrate the trend, in
both the upper
troposphere and at the
surface.
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Explosive Volcanic
Eruptions: Proof of
Fast-Response Climate
Change Due to Forcing
Changing forcing
changes the
temperature (and
water vapor, etc.).
If volcanoes can cool,
then GHG must
warm….
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Ice Age Forcing and Response
Last
interglacial
[After Figure 6.3, ©IPCC 2007: WG1-AR4]
Last
Ice
age
Warming is
Unequivocal
Rising
atmospheric
temperature
Rising sea
level
Reductions in NH
snow cover
And oceans..
And upper
atmosphere….
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Paleoclimate: New and Independent
Evidence From Many Types of Past Data
eg., changes in
glaciers, indicating
a global average
temperature
change in the 20th
century consistent
with the
thermometers.
And the corals.
And the tree rings.
And the boreholes.
And the ice cores.
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A different world in the Arctic: present and future
The Arctic was also warm in the period
1925-1940, but the extent of warmth was
not global at that time.
Large future changes in Arctic sea ice are
very likely.
Changes in sea ice don’t significantly affect
sea level because this ice is already
floating. Changes in land ice (glaciers, ice
caps, and ice sheets) do affect sea level.
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Clear decreases in Arctic
sea ice extent.
Global distribution of
temperature change
for June/July/Aug
since 1880
http://www.ncdc.noaa.gov/gcag/gcag.html
• There are some
exceptions to the
general trends (land
use?), and local ups
and downs in
individual years
• Global warming
more likely than not
contributed to the
2003 European heat
wave. Future?
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Land Precipitation is changing significantly over broad areas
Smoothed annual anomalies for precipitation (%) over land from 1900 to
2005; other regions are dominated by variability.
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A World of Drought
Many dry areas are getting drier as soils dry
out.
Observed sea surface temperature (SST)
and links to the pattern of rain in Africa?
SSTs and Sahelian rainfall have varied in the
past.
Some studies suggest links now to the
widespread ocean SST trends and global
warming.
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Sahelian rainfall decline is
reproduced in many
models
Attribution
•
Asks whether observed
changes are consistent with
 expected responses to
forcings
 inconsistent with alternative
explanations
Most of the observed
increase in globally
averaged temperatures
since the mid-20th
century is very likely
(>90% certainty) due to
the observed increase
in anthropogenic
greenhouse gas
concentrations
Anthro+ Nat forcing
TS-23
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Understanding and Attributing Climate Change
Anthropogenic
warming is
likely
discernible on
all inhabited
continents
Observed
Expected for all
forcings
Natural forcing
only
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Solar
Attribution studies
• Separate time-space
patterns of response.
•
Solar response has very
different behavior to GHG,
especially with altitude.
The upper atmosphere
would be expected to be
much warmer than it is if
solar irradiance were the
cause of current surface
climate change.
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“All” forcings
Changing winds, temperatures
and storm tracks
• Anthropogenic
forcing has likely
contributed to
circulation changes
(storm tracks, winds
and temperature
patterns)
• Warmer, wetter
winters in Norway;
drier in Spain (and
North Africa)
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What’s in the pipeline and what could come
Warming will increase if GHG increase. If GHG were kept fixed at
current levels, a committed 0.6°C of further warming would be
expected by 2100. More warming would accompany more emission.
CO2 Eq
3.4oC = 6.1oF
850
2.8oC = 5.0oF
600
1.8oC = 3.2oF
0.6oC = 1.0oF
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400
A1B is a typical “business as usual” (2090-2099)
scenario: Global mean warming 2.8oC;
Much of land area warms by ~3.5oC
Arctic warms by ~7oC; would be less for less emission
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Projections of Future Changes in Climate
New in AR4: Drying in much of the subtropics, more rain in
higher latitudes, continuing the broad pattern of rainfall
changes already observed.
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What else happens in a hotter world?
Observations of sea level rise from
satellites, 1993-2003.
The global average SLR for the 20th
century was about 6 inches (0.17m),
mostly from expansion of the hot ocean,
and with contributions from glacier melt
(Alaska, Patagonia, Europe….).
Future changes just from these
processes could be up to 1.5 feet
(0.5 m) by 2100, and up to 3 feet (1
meter) within about 2-3 centuries,
depending on how much GHGs are
emitted.
But what about other processes?
Rapid ice flow?
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Ice shelves influence glacier flow
The break up of the
Larsen B ice shelf off the
Antarctic Peninsula in
February 2002 is
illustrative of the speed up
of glaciers after the
blocking of the ice shelf is
removed.
Glaciers
lost ice
shelf and
sped up
Other examples, such
as Jakobshavn Glacier
(Greenland), show
speed up in flow after
collapse of the floating Glacier still has
ice shelf and did
glacier tongue.
not speed up
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[Image courtesy of
http://nsidc.org/iceshelves/larsenb2002/]
Sea level rise and the ice
sheets
7m of SL equivalent is on Greenland. This is
expected to melt slowly, and raise sea level
on a time scale of millennia, for warming
>2-5°C.
BUT rapid ice flow has been observed - and is
not in current models. Could sea level rise
be much faster than thought? Some
glaciological studies suggest this is
transient and will stop. Others suggest it
may increase.
Future?
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Past Change in The Greenland Ice Sheet
The last time polar regions were
significantly warmer (by 3-5°C)
than present for an extended
period (about 125,000 years
ago), reductions in polar ice
volume led to 4 to 6 m of sea
level rise.
White and black dots show drill
sites where ice older than
125,000 years is and is not
found.
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The IPCC Sequence of Key Findings……
IPCC (1990) Broad overview of climate change science,
discussion of uncertainties and evidence for warming.
IPCC (1995) “The balance of evidence suggests a
discernible human influence on global climate.”
IPCC (2001) “Most of the warming of the past 50 years is
likely (>66%) to be attributable to human activities.”
IPCC (2007) “Warming is unequivocal, and most of the
warming of the past 50 years is very likely (90%) due to
increases in greenhouse gases.”
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And More….
• Forcing: Greenhouse gases are at unprecedented levels,
and are forcing the climate to change.
• Beyond global warming: Discernible human influences on
other aspects of climate including heat waves, wind patterns,
drought, and more…this is the first ‘earth system’ IPCC report.
• Commitment: Already committed to more warming (next few
decades), with choices about emissions affecting the longer
term more and more.
• Expected future earth system changes: likely to virtually
certain: more extremes, wet in some places, dry in others, etc...
• Long term: Sea level rise is inexorable and will continue, and
the face of the planet will change. By how much? How fast?
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