Download The climate and climate change

EC110 Economics of Climate Change
What is Climate Change?
Dan Hodson
[email protected]
What is Climate Change?
In this lecture we will discuss:
 What is Climate?
 Can it Change?
 Is the Climate Changing?
 Can we predict future changes in climate?
 Can we Fix it?
4/10/2016
Economics of Climate Change: What is Climate Change?
What is Climate?
What is Climate?
 “Climate is what you expect, Weather is what you
get”.
 Climate is the statistics of weather, e.g. the average
of weather conditions over some period of time.
 Expect :
Maldives to
be Warm
Antarctica
to be Cold
Atacama
Desert Dry
Bergen
Wet
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Economics of Climate Change: What is Climate Change?
What is the Climate System?
Ice
Atmosphere
Land
Vegetation
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Economics of Climate Change: What is Climate Change?
Ocean
Atmospheric Composition
The Atmosphere is a mixture of gases:
–
–
–
–
Nitrogen 78% by volume
Oxygen 21% by volume
Argon 0.9%
The remaining 0.1%
•
•
•
•
Carbon Dioxide (CO2)
Methane (CH4)
Nitrous Oxide (N20)
+ other trace gases
Greenhouse Gases
PLUS Water vapour (variable amounts ~1%)
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Economics of Climate Change: What is Climate Change?
Can Climate change?
Ice Ages
 Climate has varied in the
past.
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Economics of Climate Change: What is Climate Change?
Sun
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Economics of Climate Change: What is Climate Change?
The Greenhouse Effect
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Economics of Climate Change: What is Climate Change?
Greenhouse Gases
The remaining 0.1%
Carbon Dioxide (CO2)
Methane (CH4)
Nitrous Oxide (N2O)
Greenhouse Gases
Water vapour
 Although small fraction of Atmosphere, large impact.
 Greenhouses gases are transparent to Sunlight, but opaque to
Infrared light/radiation from the Earth.
 Greenhouse gases trap Infrared light/radiation -> Warming.
 No Greenhouse gases, the average temperature on Earth
would be -19ºC , Actually 14ºC.
 If the 0.1% was 0.2% -> A warmer climate
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Economics of Climate Change: What is Climate Change?
Greenhouse Gases: Are they increasing?
 Carbon Dioxide
– Burning of Fossil Fuel
– Deforestation
– Manufacture of Cement (~5% global)
 Methane
– Agriculture
– Natural Gas
– Landfill decomposition
 Nitrous Oxide
– Artificial fertilizers
– Burning of Fossil Fuel
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Economics of Climate Change: What is Climate Change?
Is the Climate changing?
Measuring Climate
 To know if Climate is Changing – need to measure
climate over time.
 Measure e.g.:
– Temperature
– Rainfall
– Sea surface height
 Over what time?
– Centuries?
 And where?
– Everywhere!
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Economics of Climate Change: What is Climate Change?
CET
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Economics of Climate Change: What is Climate Change?
Global Observing Network
Locations of land, ship and buoy observations across
the world at 6am 14 January 2008
1970
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Land observations concentrated
in inhabited areas and mainly in
the Northern Hemisphere
Economics of Climate Change: What is Climate Change?
Has the Earth Surface Warmed?
~ 0.8ºC
IPCC AR5
4/10/2016
“It is certain that Global Mean Surface Temperature
has increased since the late 19th century. …. The
globally averaged combined land and ocean surface
temperature data …, show a warming of 0.85 [0.65
to 1.06] °C, over the period 1880–2012. “
Economics of Climate
What is Climate Change?
IPCCChange:
AR5 WGI
Global Trends
Temperature trends at each point on the Earth
IPCC AR5 WGI
 More warming over land than oceans
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Economics of Climate Change: What is Climate Change?
Is it unusual?
 Global average temperature rose in the
20th Century
 Is this unusual?
 Have temperatures changed like this in
the past?
 Problem: Very few temperature
measurements before 1900.
 How can we measure temperatures
before the invention of the
thermometer?
 Natural Thermometers!
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Economics of Climate Change: What is Climate Change?
Tree Rings
 Trees grow outwards and lay
down a new ring of wood every
year.
 More vigorous growth = thicker
ring.
 Growth dependent on
temperature, rainfall etc.
 Can estimate past temperature
from the width of rings.
 ~1000 years.
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Economics of Climate Change: What is Climate Change?
Estimates of past Northern Hemisphere Temperature
IPCC AR4
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Recent warming
unprecedented
Economics of Climate Change: What is Climate Change?
Have other things changed?
 Arctic Sea Ice Area
 Glaciers
 Sea level height
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Economics of Climate Change: What is Climate Change?
IPCC AR5 WGI
Have other things changed?
 Oceans are Warming:
Estimates of the Amount of heat in the upper ocean.
IPCC AR5 WGI
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Economics of Climate Change: What is Climate Change?
Can we predict future changes in
climate?
Climate System Components
Ice
Atmosphere
Land
Vegetation
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Economics of Climate Change: What is Climate Change?
Ocean
Modelling the Climate System
 Do experiments to find out how Climate components
(e.g. water) behave.
 Write down a mathematical description of this
behaviour.
 Convert this into a form for use in a computer.
Physics
 Can then use model Earth climate to predict future
changes in climate.
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Economics of Climate Change: What is Climate Change?
Is the model Correct?
 If we use our Climate Model to simulate 20th Century
climate we can compare to our past measurements
of the real 20th Century climate.
– Model Validation
Real World
Annual Rainfall
Model
IPCC AR4
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Economics of Climate Change: What is Climate Change?
Two Experiments
 EXPT1: Use our climate models to simulate 20th
Century climate as it was.
– Known Increases in Greenhouse gases
– Known changes in Natural Forcings
• Volcanoes
• The slight variations of light from the Sun.
 EXPT2: Use our climate models to simulate 20th
Century climate as it might have been
– No changes in Greenhouse gases
– Known changes in Natural Forcings
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Economics of Climate Change: What is Climate Change?
Results
 EXPT1: Greenhouse
gases + Natural Forcings.
– Black line: measured 20th
Century Global average
Temperature.
– Red and Blue: Average of
same experiment with many
different climate models.
 EXPT2: Natural Forcings
Only.
 Implication: Increases in
Global average
Temperature due to
increases in Greenhouse
gas emissions.
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Economics of Climate Change: What is Climate Change?
IPCC AR5 WG1
Projected global temperatures
 RCP – different estimates of
future GHG emissions.
– RCP 8.5 = High Emissions
– RCP 2.6 = Low Emissions
 Large range by
end of century
 Can reverse
warming with
sufficient
mitigation.
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Economics of Climate Change: What is Climate Change?
IPCC AR5 WG1
Projected regional temperature changes
2090-2099
 Northern latitudes warm
more.
– Melting sea ice –
feedbacks
 Land warms more than
oceans.
IPCC AR4
IPCC AR5 WG1
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Economics of Climate Change: What is Climate Change?
Projected regional Rainfall Changes
2081-2100
Winter
 Different regions show
different rainfall changes.
 Northern high latitudes:
increased rainfall in N.
Hemisphere winter.
– Wetter, more flooding.
 Southern Africa &
Mediterranean reduced
rainfall in N. Hem. Summer
Summer
– Drier, more droughts.
 Dotted regions are where
we are confident.
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Economics of Climate Change: What is Climate Change?
Can we Fix it?
Geoengineering
 Can we control the impact of our CO2 emissions with
a technological fix?
 Either:
I.
Remove CO2 from the atmosphere (Carbon Dioxide
Removal, CDR).
•
•
II.
Reduce the amount of sunlight reaching the surface of
the Earth (Solar Radiation Management , SRM).
•
•
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Probably expensive
Does address root cause of the problem
Probably cheaper than (I)
Unwanted side effects
Economics of Climate Change: What is Climate Change?
Stratospheric aerosols
 Feed reflective particles into the upper
atmosphere
 Reduces sunlight at the surface
– Less heating
 But:
–
–
–
–
–
–
–
Particles fall to Earth, need to keep doing it.
CO2 still rising, if you stop -> rapid warming.
Governance – who is in charge?.
May change patterns of rainfall – more drought?
Oceans will still become more acidic.
Other Unknown impacts!
Moral Hazard.
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Economics of Climate Change: What is Climate Change?
Summary
In this lecture we have discussed:
 What we mean by ‘Climate’.
 How climate can change – The Greenhouse effect.
 The evidence that Climate is changing.
 How Projections of future Climate are made and what they
tell us.
 Technical fixes and the side effects.
Dan Hodson
[email protected]
4/10/2016
Economics of Climate Change: What is Climate Change?
4/10/2016
Economics of Climate Change: What is Climate Change?
The ten warmest years on record
1. 1998
2014
2. 2005
2010
3. 2003
2005
4. 2002
1998
5. 2009
2003
6. 2004
2009
7. 2006
8. 2007
2002
9. 2001
2013
10.2007
10.1997
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 Seven
theseare
arefrom
from
Eight ofofthese
the last decade
 All are from the last 18
13
years
(Data taken from the Hadley Centre)
Economics of Climate Change: What is Climate Change?