Transcript Is our climate changing?

Is our climate changing?
What does the future hold?
JULIA SLINGO
NERC Centre for Global Atmospheric Modelling
The University of Reading
OUTLINE
• Observational evidence
• Scientific basis for climate change
• How we predict the future climate and
assess the impacts of climate change
• Why we are still uncertain about the
magnitude and effects of future climate
change
• What can we do about climate change?
Climate has always changed, so what’s different now?
Holocene – period of climate stability – coincides with birth of civilisation
Natural causes of climate change
Variation’s in the Sun’s output
Volcanoes
Long term natural climate changes are likely driven by
Earth's orbit changes
The northern hemisphere is probably the
warmest it’s been for at least 1000 years
Mann et al., Science 1999
(Northern Hemisphere only)
For the past 10 years, the planet
has been very warm ...
Evidence for Climate Change is
stacking up!
INCREASE
• Length of freeze free
season
• Length of growing
season
• More frequent heat
waves
• Wetter winters/Drier
summers
• Sea level rise
DECREASE
• Extent of mountain
glaciers
• Sea-ice amounts
and thickness
• Fewer Frosts
What is different now is that humans are changing the
chemical composition of the atmosphere in
unprecedented ways….
The NATURAL Greenhouse Effect
..most escapes to outer space
and cools the earth...
SUN
…but some IR is trapped by
some gases, in the air, thus
reducing the cooling….
Sunlight
passes
through the
atmosphere..
..and warms the earth.
Infra-red radiation
is given off by the earth...
Arrhenius 1896
The NATURAL Greenhouse Effect
The ENHANCED Greenhouse Effect
..most escapes to outer space
and cools the earth...
SUN
More CO2 traps more IR,
thus reducing the cooling
further
Most sunlight
passes
through the
atmosphere..
..and warms the earth.
CO2
CO2
Infra-red radiation
is given off by the earth...
Arrhenius 1896
The ENHANCED Greenhouse Effect
Major Players in the Greenhouse Effect
Water Vapour:
The natural greenhouse gas which makes our planet habitable
Human influences on
the greenhouse effect
Climate Change
Carbon dioxide Fossil fuels, deforestation
100 years
Methane
10 years
Agriculture, natural gas
Other gases (nitrous oxide, CFCs, ground-level ozone..)
Aerosols
Power generation, transport
Fundamentally a cooling effect
2 weeks
Concentrations are now higher than for the
past thousand years………
IPCC (2001)
And the present
trends in CO2 and
methane are
outside those
experienced on
earth for at least
the last 400,000
years…..
Earth’s major systems are changing more rapidly than
at any time in the last half million years at least.
Many of these changes are pushing the planet into
hitherto uncharted territory – we have never been here
before and it’s because of us…..
So…..
What
does
the
future
hold?
…..To answer that question we must use
CLIMATE PREDICTION MODELS
Models are our laboratory.
We use them to explore forcing and feedbacks in the
earth system, to test hypotheses, to understand
past changes and to predict the future.
Image: BMRC
Climate Models are huge computer codes
based on fundamental mathematical
equations of motion, thermodynamics and
radiative transfer
These govern:
 Flow of air and water - winds in the atmosphere,
currents in the ocean.
 Exchange of heat between the atmosphere and
the earth’s surface
 Release of latent heat by condensation during the
formation of clouds and raindrops
 Absorption of sunshine and emission of thermal
(infra-red) radiation
Climate models are extensions of weather forecast models
To solve these equations we represent the earth by a grid of
squares, typically of length 150 km or smaller.
The atmosphere and oceans are divided into vertical slices of
varying depths.
This gives us a 3-dimensional picture of the circulation of the
atmosphere and oceans.
UK in typical climate models
Models must contain all the components
of the climate system and consider all
the possible influences on climate
……..And they must consider human behaviour and
our response to climate change.
Development of climate models over the last 30 years
Climate Modelling and Prediction
requires huge supercomputers
Inside the Earth Simulator
Capable of performing 35x109 sums per second
Electric Cables Connecting Cabinets
Weather in NUGAM
Land snow + ice
twin typhoons
Precipitation (colour scale)
Shallow (warm) clouds
Deep (cold) clouds
Land snow + ice
Sea ice
Stages in predicting climate change
Scenarios from
population, energy,
economics models
EMISSIONS
CONCENTRATIONS
Carbon cycle and
chemistry models
HEATING EFFECT
‘Climate Forcing’.
CLIMATE CHANGE
feedbacks
CO2, methane, etc.
Gas properties
Temp, rain, sea level, etc.
Coupled climate
models
IMPACTS
Impacts models
Flooding, food supply, etc.
Human influences will continue to
change atmospheric composition
throughout the 21st century
How quickly the climate will change in the
future depends on:
• How much greenhouse gas emissions grow
–depends on population growth, energy use, new
technologies, etc
• How sensitive the climate system is to
emissions
–how clouds, ice, oceans etc respond to the extra
heating
Predicted changes in global mean temperatures
IPCC (2001)
Far outside
anything we
have
experienced
over the last
1000 years
And possibly close to those last experienced in the
age of the dinosaurs!
Land areas are projected to warm more than the oceans
with the greatest warming at high latitudes
Annual mean temperature change, 2071 to 2100 relative to 1990:
Global Average in 2085 = 3.1oC
ANNUAL NUMBER OF PEOPLE FLOODED
Change from the present day to the 2080s
(unmitigated emissions)
UK Climate
Impacts
Programme
Change in water
stress, due to
climate change, in
countries using more
than 20% of their
potential water
resources.
Water availability will
be the major issue in
the coming century.
Pressure on water
supplies comes not
only from climate
change but also from
human use.
Percentage change in
average crop yields
for staple crops:
wheat, maize and rice.
Yellow, brown and red
areas denote lower
yields
But note increased
yields in some
northern latitudes due
to more favourable
climate
UK TEMPERATURE RISE
Medium-high emissions scenario, 2080s
Winter
Summer
°C
CHANGE IN PRECIPITATION
Medium-high emissions scenario, 2080s
Winter
Summer
%
Changes in Extremes
Schematic of probabilities of daily temperatures
Caveat: Assumes that statistics of weather stay the same
Percentage of years experiencing ‘extreme’
seasonal anomalies across southern UK
MEDIUM-HIGH EMISSIONS
2020s
2050s 2080s
‘Hot’ August 1995
1
20
63
‘Warm’ year 1999
28
73
100
10
Hot summer 2003
‘Dry’ summer 1995
‘Wet’ winter 1994/95
10
29
50
1
3
7
CLIMATE ‘TIPPING POINTS’
Delicate thresholds where a slight
change in the Earth's temperature
can cause a dramatic change in the
environment that itself triggers a far
greater change in global
temperatures.
The earth has been capable of abrupt changes in the past
Examples of potential ‘Tipping
Points’ from global warming
• Loss of Arctic sea-ice, major ice sheets – shut-down of
thermohaline circulation, massive sea level rise.
• Melting of permafrost - release of billions of tonnes of
methane, a greenhouse gas 20 times more potent than carbon
dioxide.
• Loss of tropical rainforests, increasing soil temperatures –
terrestrial biosphere becomes carbon source rather than
carbon sink
• Acidification of the oceans - reduction in carbon sequestration
leading to further increases in carbon dioxide levels.
• …………………..????
UK emits more than its “fair
share” of carbon dioxide
HOW CAN WE REDUCE CO2 EMISSIONS?
• Use less energy
–insulate homes, businesses and factories
–less polluting transport; travel less
–Combined Heat and Power generation
• Generate energy without emissions of CO2
–renewable energy (wind, solar..)
–nuclear power
Multi-faceted approach to reducing emissions: ‘Wedges’
Emissions (MtCO 2 per year)
90,000
Conservation
and Energy
Efficiency
MiniCAM
80,000
Renewable
Energy
70,000
60,000
Nuclear
50,000
40,000
30,000
Coal to Gas
Substitution
Emissions to the atmosphere
20,000
10,000
CCS
2005
2020 2035
2050
2065 2080
2095
Allowable
Emissions for
WRE 550
Innovative solutions: CO2 capture and storage systems
Fuels
Processes
Storage options
INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE (IPCC)
CLIMATE CHANGE IS HAPPENING…….
…..AND ITS EFFECTS ARE LIKELY TO BE VERY PROFOUND