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‘Unequivocal’ global
warming
The 2013 IPCC report
Simon Oakes
‘Unequivocal’ global warming
What this presentation covers
1
What is the IPCC?
2
What are the key findings of the 2013 IPCC report?
3
What is happening to sea level?
4
Why is there still uncertainty about the severity of future change?
5
What can be done about climate change?
‘Unequivocal’ global warming
The data show a warming world
Earlier data
show some
natural
Insert
graphic
variability,
but
suggest
a fairly
see
his orig
steady longterm trend
In the last
100 years
there is a
strong
upwards
movement
away from the
established
trend
‘Unequivocal’ global warming
How does warming vary
•
Look at the world map on pages 20–21 of Geography Review
•
Watch the NASA video of changing global temperature anomalies, 1880–2012 at:
http://www.nasa.gov/topics/earth/features/2012-temps.html
•
How does warming vary with:
(a) latitude?
(b) continentality?
‘Unequivocal’ global warming
How far will temperatures rise?
•
The latest report states that it
is‘likely’ we will see a global
temperature rise of at least 1.5ºC
by 2100, assuming a doubling of
GHG.
•
Temperature could rise by as much
as 4.8ºC or as little as 0.3ºC
according to different projections.
•
As exam practice, compare the two
projected trends shown in the
diagram.
‘Unequivocal’ global warming
Evidence of a warmer world
•
Major ice sheets have lost
mass.
•
Land-based glaciers
continue to shrink.
•
Arctic sea-ice cover has
fallen since 1979.
•
The IPCC is ‘virtually
certain’ of further
permafrost melting
‘Unequivocal’ global warming
Sea-level rise
Sea level is rising. The world has recorded a
20 cm rise since 1900. A warming climate
affects the oceans in two ways to bring this
eustatic rise:
1Thermal expansion – as water warms it
expands, like liquid in a thermometer.
2Large amounts of water are locked on land
in glaciers and permafrost. When this
melts water pours into oceans.
Local isostatic changes – such as land
subsidence in delta regions – increase sealevel rise further in some places.
‘Unequivocal’ global warming
Summary of sea-level rise
Thermal
expansion
Melting
land ice
Eustatic
sea level
rise
• The equation looks simple: so why is there such uncertainty over just how
much sea-level rise will actually take place (the latest IPCC estimates range
from 26 to 82 cm)?
• The answer lies with the complexity of positive feedback effects taking
place in the Earth–atmosphere system (see next slide).
‘Unequivocal’ global warming
Climate-change uncertainty
Arctic
albedo
change
Positive
feedback and
accelerated
global
warming
Permafrost
melting
• Loss of snow and ice
cover in the Arctic means
less sunlight is reflected.
Warming accelerates.
• The release of
methane, a potent
greenhouse gas, from the
melting of the Arctic
tundra increases GHG in
the atmosphere,
triggering a second
feedback loop.
‘Unequivocal’ global warming
Climate change uncertainty
There are other causes of uncertainty for climate-change modelling and extreme
weather event attribution.
El Niño and La Niña
events naturally last for
a few years and cause
weather changes
Scientists do not fully
understand the role that
oceans play in
absorbing warming
Sunspot activity brings
change in average
temperatures, although not
a sustained rise
The North Atlantic
Oscillation is another
climate phenomenon
that may be linked with
the recent extreme
weather in the UK
‘Unequivocal’ global warming
What can be done?
Adaptation
Mitigation
Carbon intensity
• This means dealing
with the impacts of
climate change, for
instance by
strengthening flood
defences
• The long-term costs
of adaptation to a
much warmer world
may be greater than
spending money on
mitigation in the
short-term
• This means slowing
global warming by
tackling the
underlying problem
of the build-up of
GHG, for instance,
by switching to
renewable energy
sources
• The global economic
slowdown has
hampered mitigation
efforts
• This is a measure of
how much carbon
dioxide is produced
in relation to GDP
• A country like China
whose GDP is rising
can partially mitigate
by decreasing the
carbon intensity of
its GDP as that
figure rises
• But total emissions
will still rise