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Climate change Topic 4.4.

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Presentation on theme: "Climate change Topic 4.4."— Presentation transcript:

1 Climate change Topic 4.4

2 U: CO2 and H2O vapor are the most significant greenhouse gases
Glass in a greenhouse retains heat Gases in atmosphere retain heat on earth CO2 & H2O (“greenhouse gases”) have largest warming effect How CO2 is formed: cell resp, combustion of biomass & fossil fuels How CO2 is removed: photosyn, dissolving in oceans How H2O(g) is formed: evaporation & transpiration How H2O(g) is removed: rain & snow H2O retains heat as droplets of water in clouds, so air temp drops more quickly at night with clear skies than on cloudy night.

3 U: Other gases including CH4 & NOx have less impact
CH4 = 3rd most significant greenhouse gas How it’s released: marshed, landfills, extractions of fossil fuels, melting polar ice caps Nitrous oxide How it’s released: by bacteria in some habitats, agriculture, vehicle exhausts Atmosphere: 78% N not greenhouse gases (they don’t absorb longer-wave radiation) 21 % O2 1 % greenhouse gases

4 U: The impact of a gas depends on its ability to absorb long-wave radiation as well as on its concentration in the atmosphere Two factors that determine warming impact of greenhouse gas: How readily it absorbs long-wave radiation Concentration of the gas in the atmosphere e.g. CH4 causes more warming per molecule than CO2, but it’s at much lower concentration, so impact on global warming is less. Concentration in air depends on rate of release & and how long it stays there. H2O remains 9 days CH4 remains 12 yrs Nox remains 114 years CO2 remains 20 – 200 yrs

5 U: The warmed Earth emits longer-wave radiation

6 U: Longer-wave radiation is reabsorbed by greenhouse gases which retains the heat in the atmosphere
This is the naturally occurring “Greenhouse Effect” and is necessary to maintain warm temps on the Earth (otherwise Earth’s mean temp would be -18 ⁰C)

7 Global warming = enhanced greenhouse effect

8 Greenhouse gases Greenhouse gas = absorbs longer wavelengths (infrared) H2O CO2 CH4 Nitrous oxide

9 Wavelengths absorbed by individual gases

10 U: Correlations between global temps & CO2 concentrations on Earth
Hypothesis: rises in CO2 conc increase the greenhouse effect Correlation does not prove causation! What is known: CO2 is a greenhouse gas Data has been gathered from the European Project for Ice Coring in the Antarctic (EPICA) Dome C ice core, from ice dating 800,000 ya Bubbles of trapped air measured for CO2 Temps deduced from ratios of H isotopes in the ice 2 ice cores reveal 800,000 yrs of climate history!

11 EPICA data shows repeating pattern of warming followed by cooling, correlation between CO2 & temp Conclusion: at least some of temp variation over past 800,000 yrs due to rise and fall of CO2

12 U: Global temps & climate patterns are influenced by concentrations of greenhouse gases
Global avg temps are not directly proportional to greenhouse gas concentrations, but they do influence. Other factors that influence global avg temp: Milankovitch cycles in Earth’s orbit Variation in sunspot activity Effects of higher global avg temps: More frequent & intense heat waves More frequent & increased amount of rain (more evaporation) Higher ocean temp cause more frequent & more powerful tropical storms & hurricanes Temps not evenly spread (not all areas become warmer, some become colder) Changed distribution of rainfall, some more with flooding, some droughts Just a few degrees of warming would cause very profound changes to Earth’s climate patterns!

13 U: There is a correlation between rising atmospheric conc of CO2 since the start of the industrial revolution 200 years ago & avg global temp History of CO2 conc (in ppm) During glaciations – 180 During warm interglacial periods – 300 Late 18th century (Industrial Revolution) – 1950 (modern global industrialization) – when rapid rising started Current – 400 (unprecedented)

14 U: Recent increases in atmospheric CO2 are largely due to increases in the combustion of fossilized organic matter Industrial revolution – burning of coal for heat & power 19th century – combustion of oil & natural gas (& coal) 1950’s to current – increased combustion of fossil fuels AND steepest rise in atmospheric CO2 Conclusion: burning of fossil fuels has been major contributing factor in rise of atmospheric CO2 conc to higher levels than experience don Earth for more than 800,000 years

15 Precautionary Principle
When an activity raises threats of harm to the environment or human health, precautionary measures should be taken even if some cause and effect relationships are not fully established scientifically  taking preventive action in the face of uncertainty; shifting the burden of proof to the proponents of an activity; exploring a wide range of alternatives to possibly harmful actions; and increasing public participation in decision making. 

16 NOS: Assessing claims: Assessment of the claims that human activities are not causing climate change
Why the controversy? When scientists publish their uncertainties, giving impression to public that evidence is weak Predictions of global climate patterns is complex and difficult Consequences can be severe for humans & other species, so many believe there’s an immediate need for action even if uncertainties remain Companies make huge profits from coal, oil, natural gas State of Fear by Michael Crichton – scientists as eco-terrorists

17 App: Evaluating claims that human activities are not causing climate change
In science, we should base our evaluations on reliable evidence. There is evidence about emissions of greenhouse gases by humans, effects of these gases, & climate change. Not all sources on internet are trustworthy. Distinguish between websites with objective assessments based on reliable evidence and others showing bias.

18 App: Threats to coral reefs from increasing concentrations of dissolved CO2
Increased CO2 has effects on the ocean too! Over 500 billion tons of CO2 released by humans since industrial revolution have dissolved in oceans, causing acidification of water, reducing numbers of coral, sea urchins, others that make skeletons from CaCO3 If carbonate ion conc drops, it is more difficult for reef-building corals to absorb them to make their skeletons. If seawater stops being a saturated solution of carbonate ions, CaCO3 tends to dissolve, threatening existing coral skeletons

19 Marine animals with CaCO3 exoskeletons
Reef-building coral Sea urchin

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