Nir Shaviv

Nir Shaviv

Nir Shaviv, 2009
Born (1972-07-06) July 6, 1972
Ithaca, New York
Nationality Israeli American
Fields Astrophysics
Institutions Hebrew University of Jerusalem
Influences Jan Veizer
Henrik Svensmark

Nir Joseph Shaviv (Hebrew: ניר יוסף שביב‎, born July 6, 1972) is an Israeli‐American physics professor, carrying out research in the fields of astrophysics and climate science. He is a professor at the Racah Institute of Physics of the Hebrew University of Jerusalem,[1] of which he is now its chairman.

He is best known for his solar and cosmic-ray hypothesis of climate change. In 2002, Shaviv hypothesised that passages through the Milky Way's spiral arms appear to have been the cause behind the major ice-ages over the past billion years. In his later work, co-authored by Jan Veizer, a low upper limit was placed on the climatic effect of CO2.[2]

His best known contribution to the field of astrophysics was to demonstrate that the Eddington luminosity is not a strict limit,[3] namely, that astrophysical objects can be brighter than the Eddington luminosity without blowing themselves apart. This is achieved through the development of a porous atmosphere that allows the radiation to escape while exerting little force on the gas. The theory was correctly used to explain the mass-loss in Eta Carinae's giant eruption, and the evolution of classical nova eruptions.[4]

Education and career

Shaviv studied, during 1987–90, physics at the Israel Institute of Technology in Haifa and finished his BA as best in class. During his military service (1990–93) he continued his studies 1992 and co-authored his first papers in astrophysics. In 1994 he received a Master of Science in physics and a doctorate during 1994–96. During 1996–99 he was a Lee DuBridge Prize Fellow at Caltech's TAPIR (Theoretical Astrophysics) group. During 1999–2001 he was in a postdoctorate position at the Canadian Institute for Theoretical Astrophysics. In 2001–6 he was a senior lecturer at Racah Institute of physics at the Hebrew University of Jerusalem. In 2006-2012 he was an associated professor, and full professor since 2012. Between 2008 and 2011 he was the head of the faculty union of the Hebrew University, and he served as the chairman of coordinating council of faculty unions between 2010 and 2014. In 2014 he became a member of the Institute for Advanced Study in Princeton.

Scientific research

Eddington luminosity limit

In 1999 Shaviv has shown that inhomogeneities in stellar atmospheres reduce the effective opacity and thus increase the Eddington luminosity.[5] Shaviv later showed that atmospheres are inherently unstable as the Eddington luminosity is approached,[6] that these atmospheres will develop continuum driven winds that explain the appearance of eta-Carinae and classical nova eruptions.[4]

In 2010 Shaviv made the prediction that Type IIn supernova should have super-Eddington outbursts before the main supernova explosions since the super-Eddington states can naturally explain the circum-stellar material present around the supernova at the time of explosion (Giving the narrow lines observed in the spectrum, i.e., the “n” in the Type IIn).[7] Such precursors were later detected with the Palomar Transient Factory, making them the first systematically detected supernova precursors.[8]

Cosmic rays and climate

Shaviv has been one of the proponents of a cosmic ray climate link. In 2003 he has shown that the cosmic ray flux over the past billion years can be reconstructed from the exposure ages of Iron meteorites, that these flux variations are expected from spiral arm passages, and they correlate with the appearance of ice age epochs on Earth.[9] In a later work with Ján Veizer, it was demonstrated that the temperature reconstruction over the Phanerozoic correlates with the cosmic ray flux, but it does not correlate with the CO2 reconstruction, thus placing an upper limit on the effects of CO2.[2] This prompted several reactions by the climate community and rebuttals by Shaviv and his colleagues.[10]

He has also shown[11] that the Cosmic Ray climate link explains part the faint sun paradox, since the slowly decreasing solar wind will give rise to a cooling effect that compensates the solar irradiance increase. Moreover, long term star formation activity in the Milky Way correlate with long term climate variations.

In a more recent work with Andreas Prokoph and Ján Veizer,[12] it was argued that the reconstructed temperature has a clear 32 million year oscillation that is consistent with the solar system’s motion perpendicular to the galactic plane. The oscillation also appears to have a secondary modulation consistent with the radial epicyclic motion of the solar system.

Solar variation and climate sensitivity

Because the existence of a significant cosmic ray climate link implies that solar variability will also have a large effect on the climate, Shaviv advocated the idea that natural climate variations play a significant role in 20th century climate change. Moreover, if solar activity increase over the 20th century contributed to warming in addition to the anthropogenic forcing, then the overall climate sensitivity should be lower than advocated by standard scenarios which do not include solar forcing.[13]

In 2008, Shaviv used the oceans as a giant calorimeter to quantify the solar radiative forcing. He found that the peak to peak variations are close to 1 W/m2, significantly more than can be expected from the changes in the solar irradiance.[14] In 2011 he published a paper with Shlomi Ziskin arguing that the solar variability explains about half the 20th century warming, with the other half attributable to anthropogenic forcing.[15]

Shaviv’s solar hypothesis has been disputed by Mike Lockwood and Claus Froehlich in an analysis of the sun’s output over the last 25 years. They argue that the sun’s activity has been decreasing since 1985 while global temperatures have continued to rise.[16] Shaviv argues that Lockwood and Froehlich's analysis is flawed for a number of reasons.[17] Firstly, while sunspot activity declined after 1985, cosmic ray flux reached a minimum in 1992 and contributed to warming during the 1990s. Secondly, Shaviv argues that short term variations in radiative forcing are damped by the oceans, leading to a lag between changes in solar output and the effect on global temperatures. While the 2001 maximum was weaker than the 1990 maximum, increasing solar activity during previous decades was still having a warming effect, not unlike the lag between noon and the hottest hour of the day. The recent lack of warming is consistent with the decreased solar activity.

Thoughts on global warming

Shaviv was interviewed for The Great Global Warming Swindle documentary. In the film he states:

“ A few years ago if you would ask me I would tell you it's CO2. Why? Because just like everyone else in the public I listened to what the media had to say.[18] ”

In 2012, he contributed, along with Werner Weber, Henrik Svensmark and Nicola Scafetta, to the book Die kalte Sonne. Warum die Klimakatastrophe nicht stattfindet (The Cold Sun) of Fritz Vahrenholt and Sebastian Lüning, a book expressing skepticism of anthropogenic global warming, which attracted considerable interest in Germany.[19] Numerous scientists criticised the book and considered its underlying assumptions to be either outdated or highly speculative.[20][21][22][23]

Prizes and awards

Selected papers

Lectures (Selection)

See also

References

  1. ↑ Prof Nir Joseph Shaviv (personal world wide web site), Recah Institute of Physics, Hebrew University of Jerusalem, retrieved 2007-04-18
  2. 1 2 ————————; Veizer, Jan (2007-04-19), Celestial driver of Phanerozoic climate (PDF) (PDF), Geological Society of America, S. 4–10 Check date values in: |year= / |date= mismatch (help).
  3. ↑ ———————— (September 2000). "Research Summary and Goals" (PDF). CA: U Toronto. Archived from the original (PDF) on 2011-06-09. Retrieved 2008-04-23.
  4. 1 2 Shaviv, Nir J. (2001). "The theory of steady-state super-Eddington winds and its application to novae". Monthly Notices of the Royal Astronomical Society 326 (1): 126–146. doi:10.1046/j.1365-8711.2001.04574.x. ISSN 0035-8711.
  5. ↑ Shaviv, Nir J. (1998). "The Eddington Luminosity Limit for Multiphased Media". The Astrophysical Journal 494 (2): L193–L197. doi:10.1086/311182. ISSN 0004-637X.
  6. ↑ Shaviv, Nir J. (2001). "The Nature of the Radiative Hydrodynamic Instabilities in Radiatively Supported Thomson Atmospheres". The Astrophysical Journal 549 (2): 1093–1110. doi:10.1086/319428. ISSN 0004-637X.
  7. ↑ Supernova Precursor
  8. ↑ Ofek, E. O.; Sullivan, M.; Cenko, S. B.; Kasliwal, M. M.; Gal-Yam, A.; Kulkarni, S. R.; Arcavi, I.; Bildsten, L.; Bloom, J. S.; Horesh, A.; Howell, D. A.; Filippenko, A. V.; Laher, R.; Murray, D.; Nakar, E.; Nugent, P. E.; Silverman, J. M.; Shaviv, N. J.; Surace, J.; Yaron, O. (2013). "An outburst from a massive star 40 days before a supernova explosion". Nature 494 (7435): 65–67. doi:10.1038/nature11877. ISSN 0028-0836.
  9. ↑ Shaviv, Nir J. (2003). "The spiral structure of the Milky Way, cosmic rays, and ice age epochs on Earth". New Astronomy 8 (1): 39–77. doi:10.1016/S1384-1076(02)00193-8. ISSN 1384-1076.
  10. ↑ Climate Debate
  11. ↑ Shaviv, Nir J. (2003). "Toward a solution to the early faint Sun paradox: A lower cosmic ray flux from a stronger solar wind". Journal of Geophysical Research 108 (A12). doi:10.1029/2003JA009997. ISSN 0148-0227.
  12. ↑ Shaviv, Nir J.; Prokoph, Andreas; Veizer, Ján (2014). "Is the Solar System's Galactic Motion Imprinted in the Phanerozoic Climate?". Scientific Reports 4: 6150. doi:10.1038/srep06150. ISSN 2045-2322.
  13. ↑ Nothing New Under the Sun
  14. ↑ Shaviv, Nir J. (2008). "Using the oceans as a calorimeter to quantify the solar radiative forcing". Journal of Geophysical Research 113 (A11). doi:10.1029/2007JA012989. ISSN 0148-0227.
  15. ↑ Ziskin, Shlomi; Shaviv, Nir J. (2012). "Quantifying the role of solar radiative forcing over the 20th century". Advances in Space Research 50 (6): 762–776. doi:10.1016/j.asr.2011.10.009. ISSN 0273-1177.
  16. ↑ "Solar activity cleared of global warming blame", The Age, Australia, 2007-07-11.
  17. ↑ Nir Shaviv: Why is Lockwood and Fröhlich meaningless? (blog), Google, 22 July 2007.
  18. ↑ Martin Durkin (director) (March 8, 2007), The Great Global Warming Swindle (Documentary), United Kingdom: WAGtv for Channel 4, event occurs at 2min23–2min31
  19. ↑ Fritz Vahrenholt, Sebastian Lüning: Die kalte Sonne. Warum die Klimakatastrophe nicht stattfindet. Hoffmann und Campe, Hamburg 2012, ISBN 3-455-50250-4.
  20. ↑ Toralf Staud (August 10, 2012). "Klimawandel-Debatte: Forscher fühlen sich von Klimaskeptiker Vahrenholt instrumentalisiert". zeit.de. Retrieved April 2016.
  21. ↑ Michael Odenwald (July 30, 2012). "Umstrittenes Buch „Die kalte Sonne“: Halbwahrheiten über die CO2-Lüge". Focus Online. Retrieved April 2016.
  22. ↑ Toralf Staud (June 11, 2013). "Erderwärmung: Skeptiker im Faktencheck". zeit.de. Retrieved April 2016.
  23. ↑ Sven Titz (15 August 2015). "Rezension Die kalte Sonne, Fritz Vahrenholt, Sebastian Lüning". spektrum.de. Retrieved April 15, 2016.

External links

This article is issued from Wikipedia - version of the Friday, April 15, 2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.