Transcript Global Warming - Walker Institute

Global Warming
The heat is on!
What do you know about global
warming?
• Did you know:
– the earth on average has warmed up?
– some places have got colder in the past 250
years?
– Temperature, rainfall, storms, drought, sea
level, sea ice and glaciers are all changing due
to global warming?
– We think that human activities are partly
responsible.
Proof: The Earth is getting warmer
And the northern hemisphere is probably the
warmest it’s been for at least 1000 years…
Mann et al., Science 1999 (Northern Hemisphere only)
Global average temperature is one way of measuring the climate
of the Earth
What is climate?
• “Global warming” is a popular term for
climate change
• Climate is the average weather
– “ Climate is what we expect, weather is what
we get”
• Reading climate?
• Climate is easier to predict than weather!
To CD!
What affects the climate system?
What can affect climate?
• Climate is a balance between the Earth
being heated by the Sun, and cooling by
sending out heat itself
Changing the solar
radiation that we
get
•Clouds
•Particles like dust
•Changes to snow
and ice
•Volcanoes
Changing the infrared radiation the
Earth sends to
space
•“Greenhouse”
gases
• Clouds
THE GREENHOUSE EFFECT: identified in 1896!
..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.
Arrhenius 1896
Infra-red radiation
is given off by the earth...
“Human” Global warming
• Without some natural
greenhouse effect the
Earth would be at -15
degrees C (Brr….)
• We get this from the
natural amounts of water
vapour and carbon
dioxide in the atmosphere
• But human activities add
carbon dioxide and other
greenhouse gases to the
atmosphere
• More greenhouse effect
• “Global warming”
More greenhouse gases leads to more
trapping of IR and a warmer surface
SUN
More energy is
absorbed by the
Earth than it emits
CO2
Sunlight
passes
through the
atmosphere..
..and warms the earth.
CO2
CO2
Infra-red radiation
is given off by the earth...
Arrhenius 1896
Other human effects on climate?
• Particles (or aerosols) in the atmosphere
reflect sunlight back to space and can
cause cooling in local areas (and also
gives us air quality problems). But small
changes compared to greenhouse effect.
• Large scale agriculture changes the Earth’s
surface which affects the radiation
reflected back
Climate lucky dip!
The future of climate change?
By 2100:
• Increase in global mean temperature of
1.4°C - 5.8°C.
• Sea level rise by a further 0.09m – 0.88m.
Climate changes over the next few decades are
predicted to be much larger than we have seen
so far, but there is quite a range of
“uncertainty” in the predictions…
IPCC (2001)
Global change
• Changing the temperature patterns
around the globe
• Changing wind and rainfall patterns
• Global climate change
And in the UK?
2080
temperature
change (K)
2080
precipitation
change (%)
Source: Mat Collins, Hadley Centre
Impacts of climate change may be disastrous…….
ANNUAL NUMBER OF PEOPLE FLOODED
Change from the present day to the 2080s
(unmitigated emissions)
UK Climate
Impacts
Programme
Water Supply
Water availability
will be the major
issue in the coming
century.
Pressure on water
supplies comes not
only from climate
change but also
human use.
Countries shown
currently use more
than 20% of water
resources
Food supplies
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
How do we predict climate change?
• We only have one real Earth to experiment with
•
so.. We build artificial ones… inside a computer
This involves equations that describe things like
• How the air moves
• How the ocean currents work
• How water freezes and melts and evaporates and condenses
(forming clouds!)
• We have to divide the earth up into squares and
calculate these things only every few 100kms
The Met Office
The earth is represented
by a grid of squares,
typically of length 250 km,
and by a stack of layers.
This gives us a 3-D picture
of the circulation of the
atmosphere and oceans
Probability forecasts?
• We need to know what is most likely to
happen, not just what can theoretically
happen!
High
Likelihood
Low
Temperature change
To CD
Summary
• Climate change is real.
• Global warming is most likely to happen,
•
•
although different parts of the globe will warm
by different amounts
At least over the past 50 years, human activities
have contributed to climate change
Future changes will be larger than those we
have seen already
To CD