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UW ATMS 211 - Lecture Notes

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1Lecture 28Climate change due to volcanoes and solar cycle variationsAerosol terminologyAerosol = airborne solid or liquid particle with a typical size range of0.01-10 micronsAerosols have two effects on climate:Direct effect = absorption or scattering of radiationIndirect effect = acting as cloud condensation nuclei or modifying the tranmission of light through clouds or changing the lifetime of cloudsMechanism ofVolcanic Perturbation• particles in stratosphereincrease Earth's albedo• negative climate forcing(cooling)Duration and Evidence ofVolcanic Perturbation• duration is 2-3 years (particle lifetime in stratosphere)• Explosive volcanoes that inject SO2 into the stratosphere lower the mean global temperature but only for 2-3 yearsPinatubo - PhilippinesEl Chichon - MexicoAgung - BaliKatmai - Alaska• Why did El Chichon (1982),a large eruption, have a smallereffect on global temp. than Pinatubo?2More Sophisticated Evidence, Fig 15-6Compositing method: - calculate the average time-series for 5 major volcanic events (remove ENSO) - zero on the time axis is the moment of the eruption - zero on temperature axis is the average over the 5 years preceding the eruptionQuestion:Is this convincing evidence that volcanoes affect GAAST? Why or why not? (think "signal" and "noise")eruption beginsSunspots on Tues Feb 24, 2004www.spaceweather.comFeb 24, 2004:Sunspots:Cool, planet-sized relativelydark areas on the Sun’s diskScientists assign a numberto each new group of spots orlarge spot, as shown564565563SUNSPOT CLOSE-UP11-year solar cycle and sunspots: Fig 15 -7•Reliable sunspot data goback 150 years•11-years peak-to-peak cycle•On the sun’s surface, spots plot ona “butterfly diagram” with time(inset)WE’REHERE3Maunder Minimum1645-1745Although there were far fewer observations than today, a period oflow sunspot activity appears to have occurred from 1645-1745.It is speculated that this may have had something to do with theLittle Ice Age (LIA). (But note that the LIA began earlier: the 1500s).Sunspot record from 1750 showing "11-year" cycle and long-term fluctuationshttp://science.msfc.nasa.gov/ssl/pad/solar/images/zurich.gifNote: Amplitude of cycle changes over time Length of cycle also changes slightly (harder to see) and is often asymmetric TODAYEstimated climate forcing by solar irradiance variations 1750-2000Solar irradiance 1750-2000Can these natural forcings explain the observed surface temperature changes?How would you decide?Are the forcings correlated with the temperature changes?Are they large enough to account for the temperature changes?If the climate responded to these small changes, why would it not have responded to the much larger forcing from anthropogenic greenhouse gases?The two lines show differentestimates of solar forcing changeby different scientistsHow constant is the “solar constant” ?The “solar constant” is the total solar flux (W m -2) at the top of theatmosphere. Satellite measurements show that the annual averagevaries about 1.1 Wm-2 over the solar cycle. Source:World Radiation Centerhttp://www.pmodwrc.ch/(Compareunidirectionalforcing of about+4 Wm-2 due to adoubling of CO2).Note: no upward trendsince 1978Sun cannot accountfor recent warming.4Sun-Climate Correlation?: Fig 15-8Note: apparent correlation between:1) Length of Solar Cycle and 2) Northern Hemisphere Surface TemperatureQuestion:Is this persuasive evidence that solar variations are responsible for the temperature variations? Why or why not?Textbookfigure (orig.fromFriis-Christensenand Lassen (2000))Fig. 15-8 in the textbook: A bad use of dataFig 15-8 in the textbook is a somewhat bogus use of dataSuppose we extend the time line of the data and squash downthe solar cycle axis (because its scaling is entirely arbitary).Now the correlation looks poor for the 19th/20th century:<-This plot comes froman article thatconvincingly discreditsthe Fig 15-8 correlation:Peter Laut (2003)Solar activity andterrestrial climate: Ananalysis of somepurported correlationsJ. Atmosphericand Solar-TerrestrialPhysics 65, 801-812Climate variability timescalesDifferent timescales of climate change are driven bydifferent parts of the Earth System (and its location in space):SUMMARY SO FAR:109 years slow increase of solar luminosity108 years drift of the continents and midocean plate spreading rate106 years the carbonate-silicate cycle negative feedback103-105 years changes in Earth’s orbital parameters (ice ages)2-3 years volcanic eruptions into stratosphere11 years solar cycle variations2-10 years El Nino-Southern Oscillation (ENSO)ENSO Record**As shown by changes in sea-surface temperature (relative to the 1961-1990 average) forthe eastern tropical Pacific off PeruEl Niño yearsLa Niña yearsENSO record:


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