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

IPCC AR4

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

Current evidence: Global mean surface temperatures keep warming

UK Met Office, Hadley Centre, 2006

• 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

Current Evidence: All continental regions have warmed except Antarctica

All drivers

Natural drivers only

MODELS

Current evidence: New Zealand temperatures have warmed

• New Zealand temperatures have increased by some 0.9°C since the 20th century

• 1998 and 1999 were the two warmest years on record

Annual Temperature

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1853 1873 1893 1913 1933 1953 1973 1993

Dep

artu

re

(°C) fr

om

19

71-2

00

0

GlobalNew Zealand

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

400k 300k 200k 100k 0

200

240

280

Age (years)

ppm

400

600

800

ppb

-8

-4

0

4

Temperature

Methane

CO2

o C

400k 300k 200k 100k 0

200

240

280

Age (years)

ppm

400

600

800

ppb

Source: Petit et al., Nature, 1999, Berger & Loutre, QSR, 1991

Civilisation

380ppm

1780ppb

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

Current evidence: Human activities are effecting climate

Source: www.wikipedia.org, based on Meehl et al. (2004). J. 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

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

Source: U.S. National Snow & Ice Data Center (NSIDC)

• 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

Current evidence: Species shift polewards

Source: Hickling et al 2006

Source: Root et al 2005

• 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 (>85% of the >29,000 datasets respond in the expected direction

km

Schär et al, Nature, Jan 2004

Current evidence: European heat wave 2003

Comparison with Swiss summer temperatures (JJA), 1864 - 2000

• 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

• 1000 to 1861, N. Hemisphere, proxy data;

• 1861 to 2000 Global, Instrumental;

• 2000 to 2100, SRES 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

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

USGRP, 2000

• 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

Climate impacts : Human mortality

Paris Deaths, summer 2003

• 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

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.

• 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•2-4°C gives a commitment to widespread ice-sheet deglaciation and potential for sea level rise of several metres

Dangerous anthropogenic interference : Further ocean acidification likely

Scientific American March 2006

• 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

Les

s ac

idic

Mo

re a

cid

ic

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

SummaryEvidence 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%)