1. Bochum University of Applied Sciences
Global Warming
Prof. Dr. Carsten Vogt
Bochum University of Applied Sciences
Summer term 2013

2. Global warming: Some facts
Average global surface temperature:
Depends on two things:
Amount of incoming solar radiation
Amount of reflected energy (reflection by surface and clouds)
Depends on concentration of certain gases in the atmosphere
Some gases let incoming short wave radiation pass through
But absorb the reflected long wave radiation (wave length is altered by reflection – remember your physics courses!)
So called natural greenhouse effect

3. Global warming: Some facts
main effect: global average surface temperature of 15°C
Without greenhouse gases: -18°C!
Simple positive relation: The higher the concentration of greenhouse gases, the higher the average temperature!
Most important gases: water vapour, carbon dioxide (CO2), methane (CH4)

4. Global warming: Some facts
Main problem: concentration of CO2 and CH4 increases due to human activities
CO2: burning of fossil fuels
CH4: emerges in agriculture (ranching, rice cultivation)
 so called anthropogenic greenhouse effect
How strong?
Measure: radiative forcing
Natural greenhouse effect: 324 W/m2
Anthropogenic effect: 2.7 W/m2
60% due to CO2!

5. Global warming: Some facts

6. Global warming: Keeling curve

7. CO2 concentration over past 1000 years

8. Global temperature (°C) since 1850 (deviation from long run average)

9. Climate Sensitivity
Definition: temperature increase resulting from a doubling of CO2 concentration
Can be directly measured (in experiment): 1,2°C
Problem: Different additional effects in the field
 several feedback loops
Positive feedbacks:
e.g. water vapour

10. Climate Sensitivity. Positive feedbacks
Atmospheric content of water vapour increases T
Temp. increase + +

11. Climate Sensitivity: Feedbacks
Another positive feedback: melting of arctic ice
Reduced ‚albedo‘ (ability to reflect sunlight)
Leads to further warming
Example for a negative feedback loop:
Increased temperature leads to more clouds
Clouds can have a cooling effect (more sunlight is reflected)

12. Climate Sensitivity
One important difficulty in climatology: quantifying these feedbacks
Taking feedbacks into account, climatologists end up with a measure of CS of 2°C up to 4,5°C (best guess at 3°C)
Note: if we have a meaure for CS AND if we know development of future CO2-emissions we can predict future temperature increase!

13. Future temperature Depends on several variables like, e.g.
Level of economic activity (economic growth)
Population growth
energy policy
Technical progress
impossible to predict the future, but:
We can calculate scenarios (this is much different from a forecast!)

14. Future temperature increase
Economists have developed 40 plausible scenarios for IPCC (Intergovernmental Panel on Climate Change) (SRES scenarios)
Most optimistic scenario
Low population growth
High speed of technical progress
Fast substitution of fossil fuel based energy generation to renewables
CO2 concentration increases up to 540 ppm
Leading to a temperature increase of 1,1°C

15. Future temperature increase (until 2100)
Most pessimistic scenario (high economic growth, high population growth, low speed of energy substitution…)
CO2 increases to 970 ppm
Temperature increases by 6,4°C

16. What do we know about Global Warming for sure ?
Atmospheric concentration of CO2 has increased from 280 ppm (1850) up to 379 ppm (2005)
Without doubt due to anthropogenic causes (burning of fossils)
Climate sensitivity lies in a range from 2,0 to 4,5 °C
Global warming since 1850: +0,8°C

17. Global Warming: Risks Melt down of glaciers worldwide
E.g. in the Alpes, glaciers have lost half of their original volume
May cause water stress in different areas of the world
Melting of arctic ice
Loss of habitat for animal species and Inuit
Positive feedback loop: less reflection of sunlight in the polar region stimulates the greenhouse effect
Melting of permafrost
Loss of infrastructure (buildings, streets, plants …)

18. Global Warming: Risks
Melting of inland iceshelfs (Greenland, Antarctica)
Greenland: Meltdown of iceshelf already expected for a global temperature increase by 2°C
Caution: Melting process will last several hundreds years
However: Complete meltdown lets the sealevel rise by 7m!
Problems for low lying coastal areas
Many big cities are located at coastal lines

19. Global Warming: Risks Antarctica: contains 57 m sea level rise !
Temperatures in Antarctica very low
Global warming will not directly affect the iceshelf
Indirect: Warmer incoming water lets shelfs melt down
This process has accelerated during the past years

20. Global Warming: Risks
Sea level rise: Even small changes in global temperature can cause huge sea level rise or fall:
E.g years ago (last warm period), temperatures were only 1°C higher
Sea level was 2 to 6 meters higher than today
years ago (last ice age): Temperature was 4 to 7°C below nowadays average
Sea level was 120 m lower than today

21. Global Warming: Risks
Break down (partial or total) of thermohaline circulation
Atlantic ocean: water transport from southern areas to northern areas
Cold water sinks down in the Labrador sea, creating a gigantic flow of water and heat (15 mio cubicmeters of water every second, 2000 times energy generated in all europan power plants)
Warming of northern sea may cause to break down this flow
Warm water is less dense than cold water
In addition: melting of Greenland ice contributes (sweet water flow in the ocean, reducing salt concentration in the sea water and thus the density)

22. Global Warming: Risks
Total breakdown of northern atlantic circulation: decrease of temperatures in northern and western Europe by several degrees
Most models predict at worst a 50% weakening of thermohaline circulation
Higher probability of extreme weather events
Droughts and heating waves (Europe 2003: to lives lost in addition)
More destructive hurricanes (e.g. 2005: estimated loss of 160 Billion US-Dollars and 3900 lives lost)
More intense rainfalls and floodings

23. Global Warming: Benefits
Less lives lost due to cold weather in winter
Increased crop yields in northern areas (Canada, northern parts of US, northern Europe)
New sea routes available in arctic sea (northwest and north-eastern passage)  decrease in transportation costs
Increased availability of natural resources, e.g. in the arctic sea

24. Global Warming: Summary
Clearly, costs of global warming more than outweigh benefits
Central question: What should we do against global warming?
How much action is needed ?
How strongly should CO2-emissions be decreased?
And: how fast?
 question of OPTIMAL CLIMATE POLICY