Climate Change 2007: IPCC Fourth Assessment Report

Climate Change is Real

and Here!

Lučka Kajfež Bogataj

University of Ljubljana IPCC WG2 vicechair through AR4

The 21st Century changes

Four distinctive characteristics:

• They are cumulative

• The effects are irreversible

• Large time lags – today’s actions are

tomorrow’s problems

• They are global

Observed

Raupach et al 2007, PNAS

World

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

1980 1985 1990 1995 2000 2005

Fac

tor (relative to 199

0)

Emissions

Population

Wealth = per capita GDP

Drivers of Anthropogenic Emissions

The atmospheric concentration of CO2 and CH4 in 2005 exceeds by far the natural range of the last 650,000 years

CO2

CH4

Direct Observations of Recent Climate Change

Gobal mean

temperature

Global average

sea level

Northern hemisphere

Snow cover

It is warmer on average across the globe than it was a century ago

Globally averaged, the planet is ~0.75°C warmer than it was in 1860

8

Observed temperature change during the last 50 years

Annual

Winter Summer

The most important spatial pattern of the monthly Palmer Drought Severity Index (PDSI) for 1900 to 2002.

Drought is increasing most places

Regions of disproportionate changes in heavy (95th) and very heavy (99th) precipitation

Proportion of heavy rainfalls: increasing in most land areas

Snow cover and Arctic sea ice are decreasing

Arctic sea ice area decreased by 2.7% per decade

Summer: -7.4%/decade

Muir Glacier, Alaska, August 13, 1941, photo by W.O. Field

Muir Glacier, Alaska, August 31, 2004, photo by B.F. Molnia

Leaf unfolding dates in EuropeLeaf unfolding dates in Europe

Human and natural drivers of climate change

• Annual fossil CO2 emissions increased from an

average of 6.4 GtCper year in the 1990s, to 7.2 GtCper year in 2000-2005

• CO2 radiative forcing increased by 20% from 1995 to 2005, the largest in any decade in at least the last

200 years

----------------------------------------------------------------------

• Changes in solar irradiance since 1750 are

exstimated to have caused a radiative forcing of +0.12 [+0.06 to +0.30] Wm-2

GlobalGlobal--average radiative forcing estimatesaverage radiative forcing estimates

Observed

Projections of Future Changes in Climate

Best estimate for low scenario (B1) is 1.8°C (likely

range is 1.1°C to 2.9°C),

and

for high scenario (A1FI) is 4.0°C (likely range is 2.4°C to 6.4°C).

Currently at 430 ppm, rising at 2.5 ppm p.a. and

this rate of increase is increasing

Probabilities (in %) of exceeding a temperature

increase at equilibrium

Source: Hadley Centre: From Murphy et al. 2004

127246999550

49245894100650

922478299100750

00131878450

7°C6°C5°C4°C3°C2°CStabilisation level (in

ppm CO2e)

Projected warming

in 21st century expected to be

greatest over land

and at most high

northern latitudes

and least over the Southern Ocean

and parts of the

North Atlantic Ocean

Projections of Future Changes in Climate

IPCC 4AR: Precipitation Projections

December-February

June-August

Observed temperature change during the last 50 years.

Annual Winter Summer

http://eca.knmi.nl/download/)

Modelled change in T from the period 1980-1999 and 2080-2099 for the IPCC-SRES A1B scenario (IPCC, 2007).

24

Europe: Geographic ChangesEurope: Geographic Changes

+10

-1

+50%

-50%

20802080--20992099 Minus Minus 19801980--19991999 (A1B)(A1B)

Projections of Future Changes in Climate

Best estimate for low scenario (B1) is 1.8°C (likely

range is 1.1°C to 2.9°C),

and

for high scenario (A1FI) is 4.0°C (likely range is 2.4°C to 6.4°C).

Climate Change: Faster than expected in 1990s

IPCC 4 (2007) was limited to science published by early 2006

Subsequent research shows increasing rates of:

Global GHG emissions

3.3% p.a. in 2000s, vs 1.3% p.a. in 1990s

Temperature rise

especially in polar regions

Ice melt (Arctic: 40% loss since

1980, accelerating 2006-07)

CO2 Concentration

Av Surface Temp

Sea Level Rise (cm)

Dashed lines =

1990s projections

Rahmstorf, Church, et

al., Science 2007

Solid lines =

observed

1975 1985 1995 2005

A global shift southward

European climate in 2080 according to Arpège-Climat in Scenario SRES/A2

SUMMARY

• CO2 conc. = unprecedented in the last 650,000 years

• Warming of the climate system = unequivocal

• Most of the global warming of the past half-century

is due to increases in greenhouse gases

• Already committed to more warming (next few

decades), with choices affecting the longer term

more and more.

• Future climate changes include: more extremes,

wetter in high latitudes, drier in subtropics.

CONCLUSIONS

• Most of the global warming

of the past half-century is due to increases in

greenhouse gases

• Climate change is here to stay

• Humans now control the

mechanisms for global

climate change, for betteror worse