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Climate Change

Climate Change. – New Science – Old Arguments. Overview. Some old science The big experiment … The Earth’s climate Is the Earth warming? Does it matter? What can we do about it ?. So what is the - ‘Greenhouse effect’ ?. So what is the (Earth’s) ‘Greenhouse effect’ ?.

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Climate Change

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  1. Climate Change – New Science– Old Arguments

  2. Overview • Some old science • The big experiment … • The Earth’s climate • Is the Earth warming? • Does it matter? • What can we do about it?

  3. So what is the - ‘Greenhouse effect’ ?

  4. So what is the (Earth’s)‘Greenhouse effect’ ? It’s all just a bit of physics! Actually it started with Joseph Fourier (1820’s) John Tyndall (1860’s) Svante Arrhenius (1890’s)

  5. Climate Science 101 • “The Earth should be a lot colder than it is” Joseph Fourier ~1820

  6. Climate Science 101 • Fourier used basic physics to calculate that the Earth ought to be a frozen snowball!

  7. Climate Science 101 • He realised that somehow the atmosphere must be trapping heat

  8. Climate Science 101 • Tyndall found it was the water vapour and carbon dioxide gases in the air John Tyndall ~ 1860

  9. Climate Science 101 • Earth’s energy balance • Svante August Arrhenius worked it out in 1896

  10. Climate Science 101 ? • Earth’s energy balance • Svante August Arrhenius worked it out in 1896 “The Earth’s average temperature should be about –18oC”

  11. Climate Science 101 • Earth’s energy balance • Svante August Arrhenius worked it out in 1896 “CO2 and H2O absorb heat and send enough back to Earth to raise the temperature by +33 degrees!”

  12. Climate Science 101 ? • Earth’s energy balance • Svante August Arrhenius worked it out in 1896 “So what will all the CO2 we are putting in the atmosphere do?”

  13. Climate Science 101 • Earth’s energy balance • Svante August Arrhenius worked it out in 1896 “If we double the CO2 it could raise the temperature by about 5 degrees!” That’s not all that far off modern IPCC estimates of 2°C – 5°C “That will make Sweden warmer – good !”

  14. Climate Science 101 • The Earth’s temperature is determined by the balance between incoming solar radiation from the Sun…

  15. Climate Science 101 • The Earth’s temperature is determined by the balance between incoming solar radiation from the Sun… • and outgoing ‘heat’ radiation into space

  16. Don’t panic! A little physics • Earth’s energy balance • Two simple laws of physics enable us to figure out the energy balance: • The Stefan-Boltzmann law... I = εσT4 • Wien’s law... λmax = 0.0029/T • S-B just tells us how much heat a hot object radiates. • Wien tells us what sort of radiation it will be. • (fortunately others have done the hard work for us!)

  17. Climate Science 101 • The H2O and CO2 in the atmosphere trap some of the IR and so the Earth heats up until it emits enough IR... • … to balance the incoming solar radiation • At present this happens at around 15oC

  18. Climate Science 101 If less energy escapes than comes in we get warmer.

  19. Climate Science 101 • Even though the H2O and CO2are only a tiny proportion of the air, they absorb the outgoing infrared (‘heat radiation’) • But how can CO2 which is only 0.04% of the atmosphere do that? (Or 390 ppm) • Simple: Nitrogen and Oxygen do not absorb infrared (IR) while H2O and CO2 do.

  20. Climate Science 101 • (There are good physics answers to that question but ...) • Here’s a simple analogy: • Water allows all visible light through • But ink blocks it ....

  21. Climate science • 300 ppm (or 0.03%) might not sound like much, but here is the effect of adding 300 ppm of ink to a glass of water:

  22. Climate Science 101 • The water is like the atmosphere – it has no effect on the light • The ink absorbs visible light just like the carbon dioxide absorbs infrared light • If we could ‘see’ in infrared the atmosphere would look quite opaque!

  23. Climate Science 101 The atmosphere traps heat and warms the Earth

  24. Climate Science 101 • This is a like a greenhouse... • So it is called the “Greenhouse Effect” • It keeps the Earth at a warm +15oC (average) instead of that freezing –18oC • Greenhouse Effect = +33oC Our place in space

  25. Climate Science 100 Steady temperature: Heat in (from you) = Heat out (IR radiation)

  26. Climate Science 100 More blankets … Harder for heat to escape … You get warmer until … heat in (from you) equals heat out (IR radiation)

  27. +33 degrees

  28. +33 + ? degrees

  29. The Biggest Experiment on Earth …ever!

  30. The BIG Experiment • Started 200 years ago • Global scale • Involves all of us • Costs a fortune • (By-passed the ethics committee) • Results are coming in fast! • Hypothesis is being confirmed • (Could be some unintended consequences) • What is it? . . . .

  31. … the release of the carbon stored by solar energy over 100 million years ... The Big Experiment is... (In the Carboniferous era from around 300 Mya to 200 Mya) Solar energy converted CO2 in the air into plant growth (forms of carbon)

  32. … the release of the carbon stored by solar energy over 100 million years … in only centuries That is, a MILLION times faster. We have to ask whether it might have an effect! The Big Experiment is...

  33. ie. 600,000,000,000 tonnes

  34. We have increased atmospheric CO2 by 40% and now we are waiting to see what the climate will do! The Big Experiment

  35. The Big Experiment 2010 • Is the Earth warming? ”But the warming has stopped”

  36. Overview • Climate science 101 – Greenhouse effect • The big experiment … • The Earth’s changing climate • Is the Earth warming? • Does it matter? • What can we do about it?

  37. Earth’s climate – looking at the past • Climate change IS natural … BUT!

  38. Earth’s climate In the last 500 million years the climate has swung between ‘Hothouse Earth’and ‘Snowball Earth’ Hothouse Earth Snowball Earth

  39. Earth’s climate • The Earth: 500 million years ago to 20 million years ago

  40. Earth’s climate Hothouse Earth Snowball Earth 20 Mya

  41. Earth’s climate • The Earth 20 million years ago • About 2oC or 3oC warmer than today • Sea about 50 metres higher

  42. Earth’s climate • The Earth today

  43. Earth’s climate Do we really want to go here?

  44. Earth’s climate • The Earth 18 thousand years ago • About 5oC colder than today • Sea about 100 metres lower

  45. Earth’s climate • Today

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