Re: Global Dimming

Hi Jim,

Global dimming is quite interesting and certainly we have more to learn. This paper: http://www.agu.org/pubs/crossref/2008/2008GL034228.shtml discusses the effect on Europe. The implication is that global dimming is suppressing the full brunt of global warming induced by humans (a negative feedback). Another interesting factor is that of the (South) Asian Brown Clouds (http://www.nature.com/nature/journal/v448/n7153/full/nature06019.html) that serve to intensify global warming. Perhaps Robert could help us out on this one. Is there a threshold concentration with particulates and aerosols that determines a positive or negative relationship?

New data and new ideas are necessary to test any hypothesis. Global dimming does not disprove the anthropogenic contribution to global warming, so we keep the hypothesis. I don't think the scientific community is dismissing the effects of particulates.

As to your last set of questions, it is difficult to respond because we don't know. There, I said it. What do you mean by "point of no return?" A Venusian runaway? Or a point at which our inputs to the system will alter climate on centennial time-scales before the dominant natural drivers overwhelm the climate signal? That the climate is changing is understood. How it will change is less well-known.

Should we be moving people out of harms way now? Well, you know from your own comments that the problem ultimately is that there are just too many people. There is no where to move them!! Too many people consuming too many resources. What to do about it? Women need to be educated and given opportunities in the work force. This will certainly confront the sensibilities of many cultures around the world, but it is the only humane way to bring down birth rates. Women who are educated and pursue careers give birth later in life, have fewer children, and are better prepared financially to take care of the children. We all know this. We also need to overcome our addiction to oil, as even GWB has acknowledged. How about another "Apollo Project" as discussed here: http://www.cbc.ca/technology/story/2008/08/01/f-apolloenergy.html

Did you ever see the movie "The Matrix?" There is a scene where Agent Smith tells Morpheus that, like a virus, humans continue to reproduce and consume resources to the point at which survival then requires a move a new host/region. We need to stop acting like a virus. We need to find balance between stable population/economy and environment. Sadly, in nature, this balance is called homeostasis, in economics it is called stagnation. We need an economist to come up with a zero growth economic model that allows health populations in balance with nature.

Jim you said:

Now for another silly question. In the 70's it was predicted that we would be heading into an ice age instead of a warmer planet. Do we now know if the observations and predictions at that time was a result of either Global Dimming or the Asian Brown Clouds?

No such thing as a silly questions when asked in an attempt to learn. In the 1970's a single scientist published a paper that predicted an ice age. The results of the paper were published in the popular press (specifically Newsweek and later Time). The study cited was "Atmospheric Carbon Dioxide and Aerosols: Effects of Large Increases on Global Climate" (Rasool 1971; Science). The paper doesn't actually predict an ice age, rather it projects that if aerosol levels were to be increased 6 to 8 times over 1970 levels and then sustained at those levels, it may trigger an ice age . In the peer reviewed scientific papers from the 1970's, very few papers (7 in total) predicted global cooling, while significantly more papers (42 in total) predicted global warming due to CO2. A good reference is
"The Myth of the 1970's Global Cooling Scientific Consensus" Peterson et. al. (2005; Bulletin of the American Meteorological Society)

Jim Babcock said:

In the 70's it was predicted that we would be heading into an ice age instead of a warmer planet. Do we now know if the observations and predictions at that time was a result of either Global Dimming or the Asian Brown Clouds? I understand that we were not aware of these phenomena back then. Global Warming had not taken hold yet, but we had been pumping out particulates.

I want a crack at this one. In addition to Robert's response, there is another reason why global cooling received some media attention in the '70s and it reads like a history of understanding glacial-interglacial cycles. Although not the first, Milankovitch predicted that glaciations were caused by orbital dynamics. We can discuss this more, but I think most people know the Milankovitch cycles. The problem was that it was difficult to test because geologists had not refined dating techniques well enough to sufficiently resolve the chronology of glaciations. In the 1950s a fellow from the University of Chicago, named Caesar Emiliani, showed that the d18O composition of foraminifera in ocean cores recorded a very detailed history of glaciations - more so than what was possible on land because glacial deposits are eroded by subsequent glacial advances. Anyway, while Emiliani correctly speculated on his isotopic curve, the chronology was insufficient because 14C dating can only go back about 50000 years. In 1973 a paper was published by Shackleton and Opdyke that showed a magnetic reversal in the marine cores that could be accurately dated to 730,000 years. Using the new chronology of the marine cores, Hayes et al (1976) published a seminal paper where they demonstrated that the marine record exhibited cycles that matched those predicted by Milankovitch. Thus orbital dynamics were interpreted as the "pacemaker" of the ice ages.

Okay, so, how does this relate to the whole global cooling swish of the '70s? Well, because glaciations were paced by orbital dynamics, another glaciation was sure to occur during the next favorable orbital configuration - though the fact that this was thousands of years away was ignored by the popular press.