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Climate Change Facts and Impacts
Dr Jim Salinger
National Institute of Water & Atmospheric Research, Auckland, NZ
Talking,Walking Sustainability Conference, 20-23 February 2007
Outline
Current evidence
- trends in temperature and greenhouse gases
- observed impacts
Future climate
- Trends
- Impacts
Dangerous anthropogenic interference
Current evidence: The warming of the
climate system is unequivocal
Warming of the climate system is unequivocal, as is now
evident from observations of increases in global average
air temperatures, widespread melting of snow and ice,
and rising global mean sea level
Most of the observed increase in globally averaged
temperatures since the mid-20th century is very likely due
to the increase in greenhouse gas concentrations
Very likely
=>
90% likelihood
IPCC AR4
Current evidence: Global mean surface
temperatures keep warming
• Global temperatures have increased by some 0.7°C over the 20th century
• 19 out of 20 warmest years on record occurred since 1980
• 1998 and 2005 were the two warmest years on record
UK Met Office, Hadley Centre, 2006
Current Evidence: All continental regions
have warmed except Antarctica
MODELS
All drivers
Natural
drivers only
Current evidence: New Zealand
temperatures have warmed
Departure (°C) from 1971-2000
Annual Temperature
1.0
0.5
0.0
-0.5
-1.0
-1.5
Global
New Zealand
-2.0
1853
1873
1893
1913
1933
1953
1973
1993
• New Zealand temperatures have increased by some 0.9°C since the 20th
century
• 1998 and 1999 were the two warmest years on record
Current evidence:
Unequivocal
warming
- Atmosphere, oceans,
ice, land
- Richer more
compelling story
• 100-yr temperature trend
+0.74°C/century
- Last 50 years is
double that
- 11 of last 12 years
warmest on record
- Heat island effect
negligible
- Satellite record
reconciled with
balloons & surface
measurements
Current evidence: Greenhouse gases far
exceed pre-industrial going back 650,000 yrs
1780ppb
Civilisation
4
Temperature
o
C
0
-4
800
-8
Methane
ppb
600
380ppm
400
ppm
280
CO2
240
200
400k
300k
200k
100k
Age (years)
Source: Petit et al., Nature, 1999, Berger & Loutre, QSR, 1991
0
Current evidence: Human activities dominant
cause of increases
•
Carbon dioxide, ppm
Since 1750
-
carbon dioxide increase 35%, now 380 ppm
-
methane increase 150%, now 1780 ppb
-
Nitrous oxide increase 18%, now 319 ppb
•
Human activities now emit annually
~7,000,000,000 tonnes (7 ppm) of carbon
dioxide - about half of this stays in the
atmosphere
•
About ¾ anthropogenic CO2 emissions in last
20 years from fossil fuel burning
•
It is virtually certain that human activities have
been the dominant cause of increases in
greenhouse gases and aerosols in the past 250
years
Current evidence: Human activities are
effecting climate
“There is very high confidence that
the globally averaged net effect of
human activities since 1750 has been
one of warming
IPCC AR4 (Assessment Report 4) 2007
• To explain early 20th century
warming requires:
- solar changes,
- less volcanic activity
• To explain warming in the late 20th
century requires:
- greenhouse gases
• Solar and volcanic effects explain
much of the variability prior to 1850
Source: www.wikipedia.org, based on
Meehl et al. (2004). J. Climate
Current evidence: The amount of ice on
Earth is decreasing
• There has been widespread loss
of mountain glaciers since the end
of the 19th century
• The rate of mass loss from
glaciers and the Greenland ice
sheet is increasing
• The recession of glaciers during
last century is larger than at any
time over the last 5,000 years, being
particularly fast in the 1930s, 1940s
and after 1990
• Arctic and Antarctic ice shelves
several thousand years old have
started to collapse due to warming
Mt Kilimanjaro
Current evidence: Arctic sea ice is declining
• Arctic sea ice extent has declined from 7.2
to 5.2 million sq km since 1979
• Annual averaged Arctic sea ice has shrunk
by 2.7% per decade since 1978, with summer
minimum by 7.4% per decade
Source: U.S. National Snow & Ice Data
Center (NSIDC)
Current evidence: Species shift polewards
• Altered timing of spring events (earlier)
have been reported for a broad
multitude of species for budding,
flowering, egg laying, early migration,
etc., advancing by 10 days in the last 30
years
km
• Species ranges have shifted
polewards and to higher elevations in
the last 25 years
Source: Hickling et al 2006
• Observed changes in many physical
and biological systems consistent with
a warming world
• The majority (>85% of the >29,000
datasets respond in the expected
direction
Source: Root et al 2005
Current evidence: European heat wave 2003
Comparison with Swiss summer temperatures (JJA), 1864 - 2000
Schär et al, Nature, Jan 2004
• 35000 deaths are directly attributable to the 2003
European heat wave
• As this may not have occurred without anthropogenic
climate change, these may be the first casualties of
climate change
Current evidence: Species shift polewards
• Observed changes in many physical
and biological systems consistent
with a warming world
• The majority (>85% of the >29,000
datasets respond in the expected
direction expected as a response to
warming
• This shows a discernible influence
on changes in many natural systems
Future climate: projections
If current climate
science is even only
roughly correct, then
the projected rate of
warming during the
21st century is very
likely to be without
precedent during at
least the last 10,000
years
IPCC, 2001
• 1000 to 1861, N.
Hemisphere, proxy data;
• 1861 to 2000 Global,
Instrumental;
• 2000 to 2100, SRES
projections
Future Climate: Global
• Globally averaged surface
temperature sensitivity is
projected to be 2 – 4.5°C – with
the most likely value of about 3°C
• The middle and upper end of the
projections are without precedent
in at least the last 10,000 years
Carbon dioxide, temperature and
sea level continue to rise after
carbon dioxide emissions
reduced
Future Climate: Global
Projected range of global mean annual temperature change
by 2025, 2055 and 2085 for 6 scenarios and 5 CO2
stabilisation profiles
Future Climate: New Zealand
• 1.5 – 2°C warmer
• Decrease in frosts
• Increase in number of days
above 25°C
• More evaporation
• More frequent westerly
winds
• Heavy rain more frequent
• More El Niño-like ?
• Sea Level ~+30 cm (5 - 70)
• More droughts in eastern
New Zealand
• Increased rural fire risk
Average recurrence interval (years) for drought
Climate impacts : Coral bleaching
• Loss of corals due to bleaching
are very likely over the next 50
years, especially for the Great
Barrier Reef and Caribbean Reefs
• Corals could become rare on
tropical and subtropical reefs due
to increasing concentrations of
carbon dioxide, and increasing
frequency of bleaching events by
2050
USGRP, 2000
Climate impacts : Human mortality
• By 2030, droughts will
increase hunger and
malnutrition, especially
in Africa
• By 2030 coastal
flooding is projected to
result in a large
proportional mortality
increase. Overall a 2 to 3
fold increase of
population to be flooded
is expected by 2080
• Significant increases
of people at risk of
deaths from heating are
estimated for this
century
Paris Deaths, summer 2003
Dangerous anthropogenic interference :
Thresholds
From Schneider, in “Avoiding Dangerous Climate Change”, 2006
Dangerous anthropogenic interference :
Climate Uncertainties
Climate Sensitivity
• How strongly climate
responds to increased CO2
levels
• IPCC AR4 puts this in the
range 2 to 4.5°C
Dangerous anthropogenic interference :
Thermohaline circulation
• THC (Thermohaline Circulation) / MOC (Meridional Overturning Circulation) driven by
formation & sinking of denser water primarily in N Atlantic and around Antarctic coast.
Enhances some wind-driven surface currents e.g. Gulf Stream.
• Younger Dryas (~13-11 ky ago): Probable cause freshwater from outburst flood of Lake
Aggasiz + deglaciation -- temporarily slowed or shut down Atlantic THC, with a 2 - 6°C
cooling of the North Atlantic region. Rapid onset.
• Most climate models predict weakening of the MOC over the next 100 years
• For this period modelled local cooling is outweighed by “global warming” - Temperatures
over the North Atlantic and Europe still projected to increase
Dangerous anthropogenic interference :
Melting icecaps
•
Greenland: Central thickening more than
offset by increased melting near coast.
•
•
•
•
•
New issues:
• Breakoff of ice-shelves might
regionally destabilise ice-sheet
• Surface meltwater ⇒ crevasse ⇒
base lubrication ⇒ speedup of ice
stream
•2-4°C gives a commitment to
widespread ice-sheet deglaciation
and potential for sea level rise of
several metres
Ice loss has accelerated (1993-2003 cf
1961-2003)
Nett loss ~ 240 km3 in 2005 (Chen et
al,2006)
1993 to 2003: 50 to 100Gt loss/y (=0.14 to
0.28 mm sea level equiv)
Some outlet glaciers accelerating
Antarctica:
•
•
•
Some outlet glaciers accelerating
Ice sheet mass-balance +50 to -200 Gt/y for
1993-2003 (= -0.14 to +0.55 SLE)
Ice loss might have accelerated. (Not
certain. If so less than Greenland)
Dangerous anthropogenic interference :
Further ocean acidification likely
• Surface ocean pH has decreased by
0.1 since 1750
• Further 0.3-0.4 pH reduction projected
by end 21st C under IS92a scenario
• Carbonate ion concentrations
projected to decrease too
Scientific American March 2006
More acidic
Less acidic
Dangerous anthropogenic interference :
Ocean acidification
• Potential deleterious effects on coral reefs and their ecosystems
• Marine ecosystems become less robust especially plankton species, and particularly in
the Southern Oceans
Summary
Evidence is overwhelming if widespread warming in the climate system
The principal cause is increasing greenhouse gases from human activities
Abundant evidence of observed impacts already – widespread melting of
ice, biota shifting polewards and increased deaths from heatwaves
Future climate expected to warm 2-4.5 °C with more floods and droughts
Future impacts will be widespread – e.g coral bleaching, heatwave deaths
Some suggest a target of no more than 2 °C global temperature rise above
19th century values to prevent dangerous anthropogenic interference
Critical uncertainties exist for the climate sensitivity, melting of Greenland
and Antarctic ice sheets and ocean acidification impacts
Prevention of the 2 °C global temperature rise threshold requires very large
reductions in emissions (~70%)