John, Glacial mass balance is certainly related to temperature but also to precipitation. While increased precipitation is typically related to increased temperature, the relationship is confounded by changes in atmospheric circulation. There may also be delays between these effects. Braithwaite (2009, Annals of Glaciology 50:191) argues that glacial mass balance had a relatively constant small negative balance from 1976-1995 while temperature (HadCRUT3g) was rising quite rapidly. He finds that from 1996-2005 there was a strong decrease in mass balance when global temperatures leveled off.
The warmest temperature in a long time was in 1998, a year with a major El Nino which adds heat to the atmosphere. I find that all 7 well-dated large volcanic eruptions since 1600 are followed within 6 to 8 years by particularly severe El Ninos based on the summary by Bradley and Jones (1992). This correlation with such a large delay seems preposterous at first and there are likely many causes of El Ninos, but I am considering the possibility that it is a result of changes in ocean currents known to have begun following Pinatubo. The ocean integrates atmospheric effects over considerable amounts of time. Sulfur in the troposphere has very different effects than sulfur in the stratosphere. In the stratosphere, SO2 plus water and OH forms an aerosol that is spread worldwide at a very specific height controlled by temperature and the availability of OH at that height. At that height, winds are primarily horizontal (the stratosphere is stratified) spreading the aerosol worldwide and thus causing world-wide cooling. It takes ~3 years for the aerosol to dissipate. In the troposphere SO2 tends to last until it is oxidized by OH or H2O2. Normally this is hours to weeks. But ultraviolet light to form these oxidants normally is significantly reduced in the troposphere compared to the stratosphere and thus the concentrations of OH and H2O2 are much reduced. Furthermore air currents are more chaotic in all directions. What is really interesting is that the sulfate deposited in Greenland during the 20th century increases in proportion to known anthropogenic sulfur emissions. This means the SO2 remained in the atmosphere long enough and high enough to go from smoke stack to Greenland. Since emissions are more or less continuous, the concentration of SO2 in the troposphere might also be quasi continuous. SO2 is a greenhouse gas but it also decreases oxidizing capacity causing other gases such as CH4 and CO to accumulate. Hence the warming. Thus we need to continue to reduce SO2 emissions. Ships, as you mention, are a major source, since they tend to utilize cheaper high-sulfur fuel. I don't think any body yet regulates ships on the high sea, but some ports are now instituting controls. Peter --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en -~----------~----~----~----~------~----~------~--~---
