Global warming: Is the Sun heating the Earth? Lecture 8: The Sun-Earth Connection

Transcription

1 Global warming: Is the Sun heating the Earth? Lecture 8: The Sun-Earth Connection

2 Solar influence on Earth The variable activity of the Sun affects Earth in many ways: short term long term Space weather : Disturbances in the Magnetosphere, Ionosphere, Upper atmosphere Satellite systems, Communication and Energy supply Global climate change Modulation of galactic cosmic rays hitting Earth

3 Space weather Cause: variability of Sun & solar wind (CMEs, flares, high speed wind streams) Solar components: solar energetic electro-magnetic (UV, X- rays, γ-rays) & particle radiation (ev to MeV) Affected natural systems: Earth s magnetosphere, ionosphere, thermosphere, stratosphere Technical systems in space & partly on Earth affected Potential health hazard: astronauts, airplane passengers & crew, inhabitants at high latitudes (ozone hole)

4 Causes of space weather Variations of solar electromagnetic radiation, specially UV- and X-radiation Solar wind Suprathermal particles (energies of ev) Energetic particles (kev to MeV) From Sun Cosmic rays (MeV to GeV) Meteorites, interplanetary dust, galactic Gamma-Ray-Bursts, etc. Other sources

5 The Sun and space weather: CMEs Composite of Sun and its extended corona (LASCO C2 + C3 EIT 304 Å) Bright, overexposed dots are planets (Mercury, Venus, Jupiter, Saturn), fainter background objects are stars R. Schwenn

6 Halo CMEs Halo CMEs: CMEs directed towards (or away from) Earth. The main cause of Space Weather Most difficult to detect! Most difficult to predict propagation speed.

7 Effect of a CME directed to Earth The largest solar particle events appear to result from shock associated coronal mass ejections (CMEs)

8 Space Weather: the Aurora

9 Influence of solar activity on technical systems L. Lanzerotti

10 Ionospheric heating by UV radiation Most important for Earth s upper atmosphere is Lyα: its strength changes by factor of 2 over a solar cycle Larger temperature means larger scale height: ionosphere expands drag on spacecraft increases

11 Increased Drag on Satellites Expanding atmosphere causes increased drag on low orbit satellites. They loose altitude & non-symmetrical satellites can start tumbling Skylab re-entered several years earlier than planned Hubble Space Telescope drops km per year (Re-boosted by the Shuttle More than 12 satellites lost due to Space Weather Effects HST

12 Astronaut safety The Earth s magnetosphere helps to protect the astronauts on, e.g. the ISS Astronauts flying to moon etc. are at risk SEPs are a major handicap for manned Mars mission

13 Bright Sun causes dark night Blackout in Canada and NE USA due to solar damage to transformers (2003, at last activity maximum)

14 Bright Sun causes dark night Satellite based telecommunications growing most rapidly Navigation now also largely satellite based: GPS, Galileo Satellite payloads increasingly sensitive Humans in Space: more and longer manned missions Importance of Space Weather warnings will increase

15 Bright Sun causes dark night Satellite based telecommunications growing most rapidly Navigation now also largely satellite based: GPS, Galileo Satellite payloads increasingly sensitive Humans in Space: more and longer manned missions Importance of Space Weather warnings will increase

16 Does the Sun influence climate? Answer depends on the considered time scale Time scales of billions of years: yes! The Sun s evolution makes it increasingly brighter Time scales of years: Indirectly. Ice ages are probably caused by changes in the Earth s orbital parameters Time scales of decades to millenia: Probably. There are increasing indications of a solar contribution to global climate change days to a year: Unclear

17 Evolution of solar luminosity Today Sackmann et al. 1997

18 Evolution of solar luminosity Runaway greenhouse effect through evaporation of oceans Today Sackmann et al The future of the Earth?

19 Climate evolution: the broader context The Earth today is cooler by 4-6 K than it was 10 million years ago

20 Ice ages and warm periods

21 Milankovitch theory Ice ages are due to variations of Earth s orbit The dominant parameter

22 Cause of ice ages Standard theory: Milankovitch theory of orbital parameter changes of Earth, combined with non-symmetric distribution of continents. Largest is effect of the change of the eccentricity of the Earth s orbit. It shows a good correlation with Earth s temperature

23 Has the Earth warmed? Is this warming significant and important?

24 Die Has Sonne the Earth als Klimatreiber? warmed? Klima: Beeinflusst die Sonne das Klima und trägt sie Is this warming significant and important? zum gegenwärtigen Klimawandel bei?

25 Has the Earth warmed? Is this warming significant and important?

26 Has the Earth warmed? Muir & Riggs Glaciers, Alaska Is this warming significant and important?

27 Is the Recent Temperature Rise Extraordinary? Various temperature reconstructions suggest that the Earth is hotter now than in the last 2000 years Mann et al.; Moberg et al.

28 Is Global Warming Manmade? CO 2 main man-made greenhouse gas Source: NASA

29 IPCC Predictions until 2100 Scenarios for emission of Greenhouse Gases Predicted temperature over next 100 years Expect o warming by 2050

30 Extreme weather events Some Consequences of Global Climate Change Rising sea level

31 Is everything understood?

32 Could the Sun be to blame? The Sun delivers 1.36 kw / m 2. We get 1 kw / m 2 (at equator, at noon, if no clouds) In min the Sun provides to Earth the yearly energy needs of Humanity Without sunlight, no life (Our atmosphere would cool to below -200 o C within weeks)

33 Maunder Minimum & Little Ice Age H. Avercamp The Maunder Minimum corresponded to the Little Ice Age: Is there a connection? The coldest decade in England since the 1690s; 1813/1814 last Christmas Fair on the Thames Dalton

34 Paths by which Sun can affect climate Variations of total irradiance: change in total energy input to Earth s atmosphere [irradiance] = W/m 2 = flux at 1AU (above Earth s atmosphere) Variations of UV irradiance: influence on atmospheric chemistry (e.g. stratospheric ozone production and depletion) Modulation of cosmic rays: has been proposed to affect cloud cover. Energy carried by particles at 1 AU W/m 2 (mainly protons and electrons) vs W/m 2 from radiation

35 Measured total irradiance 0.1% C. Fröhlich, PMOD

36 Measured total irradiance 0.1% C. Fröhlich, PMOD

37 During activity maximum, when the number of sunspots is largest, the Sun is also brightest. How can this be consistent with what we have seen on the last slide? Irradiance Sunspots

38 Faculae and Plage Area increase of faculae from activity min to max is factor of greater than of sunspots

39 Passage of a Facular Group

40 Evidence of influence of solar cycle irradiance variations on climate Solid line: Earth global surface temperature after removal of linear trend Dashed line: solar total irradiance Global temperature varies by 0.2 o between solar activity minimum and maximum Camp and Tung (2007), Tung and Camp (2008)

41 3- Component Model F(λ) F(λ) α (t) s F(λ) quiet Sun flux (Fontenla et al. 1993) sunspot flux; separate umbra/penumbra (cool Kurucz models) filling factor of sunspots (MDI continuum) facular flux (modified model-f; Fontenla et al. 1993; Unruh et al. 2000) α (t) filling factor of faculae f (MDI magnetograms)

42 B as source of irradiance changes Wenzler, Solanki, Krivova 2005

43 Are there longer term variations of solar irradiance? Irradiance during current minimum is lower than in earlier times No direct records of irradiance variations on longer time scales. Need to use models. Need to distinguish different periods Since ~ 1800: good direct sunspot number measurements Since 1611: telescopic sunspot number measurements On longer time scales: first a proxy of the solar magnetic field must be reconstructed.

44 Reconstruction of open flux back to Be Open solar flux Interplanetary field Solanki et al Nature Model also predicts very similar trend for solar total magnetic flux solar irradiance should also show secular trend

45 Reconstruction of open flux back to Be Open solar flux The model and its results were described in detail in Lecture 5 on the solar dynamo Interplanetary field Solanki et al Nature Model also predicts very similar trend for solar total magnetic flux solar irradiance should also show secular trend

46 Solar irradiance since 1610 based on magnetic field reconstruction There is a clear long-term (secular) trend in total solar irradiance from the Maunder minimum till today Estimates of rise in total solar irradiance since Maunder minimum W/m 2 Krivova et al. 2007, 2010

47 Solar irradiance since 1610 based on magnetic field reconstruction There is a clear long-term (secular) trend in total solar irradiance from the Maunder minimum till today Estimates of rise in total solar irradiance since Maunder minimum W/m 2 A secular variation of total solar irradiance > 1.5 W/m 2 cannot be ruled out, but is not likely to be based on variations of solar surface magnetic flux Krivova et al. 2007, 2010

48 Solar Irradiance and Climate