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

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

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)

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!

Global warming: Some facts

Global warming: Keeling curve

CO2 concentration over past 1000 years

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

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

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

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)

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!

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!)

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

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

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

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 …)

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

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

Global Warming: Risks Sea level rise: Even small changes in global temperature can cause huge sea level rise or fall: E.g. 120000 years ago (last warm period), temperatures were only 1°C higher Sea level was 2 to 6 meters higher than today 20.000 years ago (last ice age): Temperature was 4 to 7°C below nowadays average Sea level was 120 m lower than today

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)

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: 20.000 to 30.000 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

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

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