1. Dan Hodson d.l.r.hodson@reading.ac.uk
EC110 Economics of Climate Change
What is Climate Change?
Dan Hodson

2. Economics of Climate Change: 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?

3. What is Climate?

4. Economics of Climate Change: What is Climate Change?
“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?

5. What is the Climate System?
Ice
Atmosphere
Atmosphere
Land
Vegetation
Ocean
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Economics of Climate Change: What is Climate Change?

6. 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
PLUS Water vapour (variable amounts ~1%)
Greenhouse Gases
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Economics of Climate Change: What is Climate Change?

7. Can Climate change?

8. Economics of Climate Change: What is Climate Change?
Ice Ages
Climate has varied in the past.
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Economics of Climate Change: What is Climate Change?

9. Economics of Climate Change: What is Climate Change?
Sun
Earth:
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Economics of Climate Change: What is Climate Change?

10. Economics of Climate Change: What is Climate Change?
The Greenhouse Effect
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Economics of Climate Change: What is Climate Change?

11. Economics of Climate Change: What is Climate Change?
Greenhouse Gases
Greenhouse Gases
The remaining 0.1%
Carbon Dioxide (CO2)
Methane (CH4)
Nitrous Oxide (N2O)
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?

12. 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
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Economics of Climate Change: What is Climate Change?

13. Is the Climate changing?

14. Economics of Climate Change: What is Climate Change?
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?

15. Economics of Climate Change: What is Climate Change?
CET
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Economics of Climate Change: What is Climate Change?

16. Global Observing Network
Locations of land, ship and buoy observations across the world at 6am 14 January 2008
1970
Land observations concentrated in inhabited areas and mainly in the Northern Hemisphere
Locations of land, ship and buoy observations across the world at 6am 14 January 2008
Distribution of measurements not uniform - Land observations concentrated in inhabited areas and mainly in the Northern Hemisphere
In addition to dedicated weather stations, amateurs and commercial ships and airplanes contribute
Many locations release weather balloons which measure most of the troposphere
Satellites have been used since the 70s and provide a global view
For climate monitoring purposes a long record of observations are needed
Only short satellite record
Good coverage of all oceans only happened in the last 5 years
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Economics of Climate Change: What is Climate Change?

17. Has the Earth Surface Warmed?
Average across all months in the year, all measurements across the globe – sea and land.
Corrected for non-uniform distribution of measurements across the globe
Coloured curves are four different estimates (from different research groups) of the global average temperature change – they have been smoothed to remove some of the year-to-year (noisy) variations.
“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. “
IPCC AR5 WGI
IPCC AR5
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Economics of Climate Change: What is Climate Change?

18. Economics of Climate Change: What is Climate Change?
Global Trends
Temperature trends at each point on the Earth
More warming over land than oceans
IPCC AR5 WGI
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Economics of Climate Change: What is Climate Change?

19. 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?

20. 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?

21. Estimates of past Northern Hemisphere Temperature
Recent warming unprecedented
IPCC AR4
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Economics of Climate Change: What is Climate Change?

22. Have other things changed?
Arctic Sea Ice Area
Glaciers
Sea level height
IPCC AR5 WGI
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Economics of Climate Change: What is Climate Change?

23. 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?

24. Can we predict future changes in climate?

25. Climate System Components
Ice
Atmosphere
Land
Vegetation
Ocean
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Economics of Climate Change: What is Climate Change?

26. 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.
Can then use model Earth climate to predict future changes in climate.
Physics
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Economics of Climate Change: What is Climate Change?

27. 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
Model
Annual Rainfall
IPCC AR4
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Economics of Climate Change: What is Climate Change?

28. 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
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Economics of Climate Change: What is Climate Change?

29. 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

30. 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.
The A2 scenario represents mixed world with mainly a regional focus, high population growth and fragmented economic growth, heating is projected to be 3.4ºC (range 2.0—5.4)
The A1B scenario is more globally focussed with low population growth, rapid economic growth and a balance between fossil fuels and non-fossil fuels, projection is 2.8ºC (1.7—4.4)
The B1 scenario is similar to A1B, but with the introduction of more clean and resource-efficient technologies, projection is 1.8ºC (1.1—2.9)
Even if we stop all emissions right now, we are still committed to some warming due to latency in the climate system and the long lifetimes of some greenhouse gases
Note that all scenarios are very similar until about 2030
Higher values of warming cannot be ruled out
IPCC AR5 WG1
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Economics of Climate Change: What is Climate Change?

31. Projected regional temperature changes 2090-2099
Northern latitudes warm more.
Melting sea ice – feedbacks
Land warms more than oceans.
High latitudes warm faster than low latitudes, especially in the Northern Hemisphere
Temperatures increase faster over land than over the ocean
When the average temperature increases, so do extreme temperatures
Heat waves will be more intense, more frequent and longer lasting
Cold episodes are projected to decrease
Daily minimum temperatures are projected to increase faster than daily maximum temperatures
Reduced frost days are projected for in middle to high latitudes
IPCC AR4
IPCC AR5 WG1
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Economics of Climate Change: What is Climate Change?

32. 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
Drier, more droughts.
Dotted regions are where we are confident.
Summer
Precipitation generally increases in the areas of regional tropical precipitation maxima (such as monsoon regimes)
There is a general decrease in precipitation in the subtropics
There is an increase in precipitation in high latitudes due to an intensification of the hydrological cycle
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Economics of Climate Change: What is Climate Change?

33. Can we Fix it?

34. Economics of Climate Change: What is Climate Change?
Geoengineering
Can we control the impact of our CO2 emissions with a technological fix?
Either:
Remove CO2 from the atmosphere (Carbon Dioxide Removal, CDR).
Probably expensive
Does address root cause of the problem
Reduce the amount of sunlight reaching the surface of the Earth (Solar Radiation Management , SRM).
Probably cheaper than (I)
Unwanted side effects
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Economics of Climate Change: What is Climate Change?

35. 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?

36. 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
4/10/2016
Economics of Climate Change: What is Climate Change?

37. Economics of Climate Change: What is Climate Change?
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Economics of Climate Change: What is Climate Change?

38. The ten warmest years on record
2014
2010
2005
1998
2003
2009
2006
2002
2013
2007
Seven of these are from the last decade
All are from the last 18 years
1998
2005
2003
2002
2009
2004
2006
2007
2001
1997
Eight of these are from the last decade
All are from the last 13 years
(Data taken from the Hadley Centre)
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Economics of Climate Change: What is Climate Change?