12-14 November 2005 Vatican Water and the Environment The Pontificial Academy of Sciences Water...

12-14 November 2005 Vatican

Water and the EnvironmentThe Pontificial Academy of Sciences

Water cycle and climate change

Professor Lennart Bengtsson

Max-Planck –Institute for Meteorology, Hamburg, Germany

Environmental System Science Centre, Reading University, UK

How is the water distributed on the Earth?

The Heat Balance of the Atmosphere

Incoming energy from the Sun balances the outgoing energy

from the Earth

The Global Water Cycle

Solar forcing and atmospheric circulation are the drivers of the

water cycle

Annual precipitation

Precipitation in January

Precipitation in July

The role of the water cycle in the

climate system Precipitation is crucial for life on the planet

The largest warming factor of the atmosphere is through the relaease of latent heat amounting to 80-90 WM-2

The net transport of water from ocean to the land surfaces amounts to some 40000 km3/year

Precipitation over land is about 3 times as high

Water vapour is the dominating greenhouse gas. Removing the effect of water vapour in long wave radiation reduces climate warming at 2 x

CO2 by a factor of more than 3. (For the GFDL model from 3.38 K to 1.05 K).

Interannual variability in precipitation

El Nino and Southern Oscillation

El Nino changes precipitation patterns

Forest fires in Indonesia

Natural variability in precipitation patterns

The North Atlantic Oscillation

Negative phase

The North Atlantic OscillationPositive phase

The water cycle in a warmer climate

How will it change?

Integrated Water vapour 1978-1999

ECHAM5: T106/L31 using AMIP2 boundary conditions

Preliminary results:

Globally averaged results vary between 25.10 mm (1985) and 26.42 mm (1998)

Mean value for the 1990s is 1% higher than in the 1980s

Interannual variations are similar as in ERA-40

Variations follow broadly temperature observations from MSU (tropospheric channel) under unchanged relative humidity (1°C is

equivalent to some 6%).

How does the greenhouse warming work?

Greenhouse gas warming (early ideas)

Joseph Fourier (1827)„The atmosphere is relatively transparent to solar radiation, but highly absorbent to thermal radiation“

John Tyndall (1861)Water vapour and CO2 are dominant absorbers

Water vapour feedback and climate sensitivity

Svante Arrhenius (1896)„On the influence of carbonic acid in the air upon the temperature of the ground“

Thomas C. Chamberlin (1899) „An attempt to frame a working hypothesis of the cause of glacial periods on an atmospheric basis“

„Water vapor confessedly the greatest thermal absorbent in the atmosphere is dependent on temperature for its amount and if another agent, as CO2, not so dependent, raises the temperature of the surface, it calls into function a certain amount of water vapor which further absorbs heat, raises the temperature and calls forth more vapor....“

(in a letter to C. G. Abbott, 1905).

How does the greenhouse warming work?

Clausius-Clapeyron relation (1832)

The fractional change in es (de/e) resulting from a small changein temperature is proportionell to T-2

A 200K, a 1K increase results in a 15 % increase in water vapour; at 300Kt it causes a 6% increase

• The feedback problem

Annual mean global values of relative humidity f (in %) vertically averaged for 850-300 hPa and vertically integrated absolute humidity q (in kg/m2).

• Feedback results from different models

IPCC on water vapour feedback

1990: The best understood feedback mechanism is water vapor feedback, and this is intuitively easy to understand.

1992: There is no compelling evidence that water vapor feedback is anything other than positive - although there may be difficulties with upper tropospheric water vapor.

1995: Feedback from the redistribution of water vapor remains a substantial source of uncertainty in climate models - Much of the current debate has been addressing feedback from thetropical upper troposphere

Long Term Variations in the Water Cycle

Is the Weather more extreme Today than earlier?

Precipitation intensity Observations and Model Results

Railway Station in Dresden 17 August 2002

17. August 2002 939 7000?31. März 1845 877 57003. Februar 1862 824 44906. September 1890 827 446012. April 1865 748 348017. März 1940 778 336020. Februar 1876 776 329017. Januar 1920 772 319011. April 1900 773 31007. Mai 1896 732 307010. März 1881 726 3090

ELBE IN DRESDEN

cm m3/s

Quelle: Deutsches Hydrologisches Jahrbuch

Extreme flooding in Elbe

No upward trends in the occurence of extreme floods

in central Europe

Letter to Nature, 11 September 2003

Mudelsee, Börngen, Tetzlaff and Grünewald ( Uni. Leipzig, Techn Uni Cottbus)

No long term Trend in Extra-tropical Storms

• WASA, 1998: Changing Waves and Storms in the North Atlantic. Bull. Amer. Met. Soc.

• Weisse, von Storch und Feser, 2004

• Alexandersson, 2004

Transient eddies in ECHAMHamburg latest GCM

• Roeckner et al., (2003), MPI-Report 349

• Resolution used T63L31 (top at 10hPa)

• Water vapour, cloud liquid water and cloud ice in semi-Lagrangian flux form-scheme

How are transient eddies identified?

• Date sets are needed at least every 6 hour• We use a method proposed by Hodges

(Hodges, 1999, MWR)• We use the vorticity at 850hPa• A transient eddy must exist for >48hours and

be extended over at least1000km

Storm tracks DJF 2002/03 at 850 hPaERA 40

Validation using ERA40present climate

• 3 AMIP-type experiments 1979-1999 using observed SST and sea-ice ( with AMIP-2 protocol ( WGNE,1996)

• ERA40 1979-2002

ERA 40 storm track density and intensity

Storm tracks ERA40 (left)ECHAM5 ( right) NH(DJF)

Extra-Tropical and Tropical Storms

in a warmer climate

Changes in 2070-2100 (21C)

compared to 1970-2000 (20C)

Scenario A1B

Change in storm track density

Change in storm track intensity

Changes in storm tracks (21C-20C)north British isles (left), Mediterranean

area (right)

Tropical StormsHurricanes and Typhoons

Ranked by the number of lives throughout the world from 1947 to 1980, the 10 major types of disaster (not including droughts and other disasters affecting agriculture) were:

1. Tropical cyclones, hurricanes, typhoons 499,0002. Earthquakes 450,0003. Floods (other than associated with 1. above) 194,0004. Thunderstorms and tornadoes 29,0005. Snowstorms 10,0006. Volcanoes 9,0007. Heatwaves 7,0008. Avalanches 5,0009. Landslides 5,00010. Tidal waves (tsunamis) 5,000

Type of disaster Deaths (nearest thousand)

Hurricane Floyd approaching Florida

But now Hurricane Katrina

Exp cost: 200G$

Changes in storm track density (21C-20C) MJJASO

Change in storm tracks (21C-20C)

number( max intensity) Tropics

Extreme weather conditions

(What could we expect?)

Climate change experiment at MPI for Met,

Hamburg

Increase in intense precipitation

SummaryClimate observations so far

• There are no clear indication of an intensification of the global water cycle, but precipitation has increased over many parts of high and middle latitudes of the Northern Hemisphere.

• Water vapour has increased in the atmosphere which has enhanced the greenhouse effect.

• The severe floooding incidents in recent years are in all likelyhood due to natural processes and enhanced by increasing human exposure to events caused by severe weather.

SummaryWhat may happen?

• Extra-tropical storms have not intensified and are not expected to intensify in a warmer climate. In western Europe the storms at the end of the 19th century were as intense as those of the last decades.

• Intense winter storms depend on the temperatur difference between Arctic and middle latitudes. An increase warming in the Arctic (melting of sea-ice) will reduce the temperature gradient.

• Convective weather systems ( mainly in Summer) are expected to intensify as the higher concentration of water vapour will be able to release more latent heat, lead to more intense precipitaion and increase risk of flooding

Summary Changes in the water cycle

It is expected that the overall global precipitation will increase and be more dominated by intense

precipitation.

Modell experiments indicate changes in storm tracks and weather patterns also leading to reduced

precipitation in many areas.

The largest stress on Society is likely to occur in regions with systematic reduction in precipitation.

Particularly exposed regions could be the Mediterranian and Middle East, Southern Australia

and South Africa

SummaryWhat may happen in the tropics?

• Higher sea surface temperatures will enhance the tropical storms (hurricanes). At the same time expected increasing vertical wind shear will reduce the positive feedback between the convective elements of the storm and the main hurricane vortex and result in a weakening of the storm.

• Model calculations show that this feedback is very important and generally leads to a reduction in the number of hurricanes. However, when and where ideal conditions exist more intense hurricanes are likely to develop.

• It is expected that the overall global precipitation will increase and be more dominated by intense precipitation.

• Modell experiments indicate changes in storm tracks and weather patterns also leading to reduced precipitation in many areas.

Content of lecture

• The Global Water Cycle• Variations in the Water Cycle on different time scales• (Is the weather now more extreme than earlier?)

• Anthropogenic Climate change and expected Consequences for the Water Cycle

• Extra-tropial and tropical Storms• Extreme Weather conditions• (What could be expected?)

• Summary and concluding Remarkes

12-14 November 2005 Vatican Water and the Environment The Pontificial Academy of Sciences Water...

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