Climate Change Facts and Impacts

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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
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Outline
Current evidence - trends in temperature and
greenhouse gases - observed impacts Future
climate - Trends - Impacts Dangerous
anthropogenic interference
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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
gt 90 likelihood
IPCC AR4
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Current evidence Global mean surface
temperatures keep warming

• Global temperatures have increased by some 0.7C
  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
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Current Evidence All continental regions have
warmed except Antarctica
MODELS
All drivers
Natural drivers only
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Current evidence New Zealand temperatures have
warmed

• New Zealand temperatures have increased by some
  0.9C since the 20th century
• 1998 and 1999 were the two warmest years on
  record

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Current evidence Unequivocal warming

• - Atmosphere, oceans, ice, land
• - Richer more compelling story
• 100-yr temperature trend 0.74C/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

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Current evidence Greenhouse gases far exceed
pre-industrial going back 650,000 yrs
1780ppb
380ppm
Source Petit et al., Nature, 1999, Berger
Loutre, QSR, 1991
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Current evidence Human activities dominant cause
of increases

• 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

Carbon dioxide, ppm
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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
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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
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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)
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Current evidence Species shift polewards

• Species ranges have shifted polewards and to
  higher elevations in the last 25 years
• 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
• Observed changes in many physical and biological
  systems consistent with a warming world
• The majority (gt85 of the gt29,000 datasets
  respond in the expected direction

km
Source Hickling et al 2006
Source Root et al 2005
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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

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Current evidence Species shift polewards

• Observed changes in many physical and biological
  systems consistent with a warming world
• The majority (gt85 of the gt29,000 datasets
  respond in the expected direction expected as a
  response to warming
• This shows a discernible influence on changes in
  many natural systems

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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

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Future Climate Global

• Globally averaged surface temperature
  sensitivity is projected to be 2 4.5C with
  the most likely value of about 3C
• 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
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Future Climate Global
Projected range of global mean annual temperature
change by 2025, 2055 and 2085 for 6 scenarios and
5 CO2 stabilisation profiles
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Future Climate New Zealand

• 1.5 2C warmer
• Decrease in frosts
• Increase in number of days above 25C
• 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
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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
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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
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Dangerous anthropogenic interference Thresholds
From Schneider, in Avoiding Dangerous Climate
Change, 2006
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Dangerous anthropogenic interference Climate
Uncertainties

• Climate Sensitivity
• How strongly climate responds to increased CO2
  levels
• IPCC AR4 puts this in the range 2 to 4.5C

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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 - 6C 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

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Dangerous anthropogenic interference Melting
icecaps

• Greenland Central thickening more than offset by
  increased melting near coast.
• 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)

• New issues
• Breakoff of ice-shelves might regionally
  destabilise ice-sheet
• Surface meltwater ? crevasse ? base lubrication
  ? speedup of ice stream
• 2-4C gives a commitment to widespread ice-sheet
  deglaciation and potential for sea level rise of
  several metres

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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
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Dangerous anthropogenic interference Ocean
acidification
Less acidic
More acidic

• Potential deleterious effects on coral reefs and
  their ecosystems
• Marine ecosystems become less robust especially
  plankton species, and particularly in the
  Southern Oceans

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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)
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