Thursday, May 17, 2007

Global Dimming, Global Warming & Peak Oil

Okay. Hands up all of those who have even heard of Global Dimming. You'd be forgiven if you hadn't. After all, it hasn't exactly been the bread and butter of the morning newspaper or the evening TV newscast. The majority of those, in fact, in the Peak Oil movement and a good share of those in the Global Warming movement haven't yet heard of it either. If you are not yet aware of it I suspect it will distress you to hear that it may be more important and more serious and more complicated than either Peak Oil or Global Warming, and is intricately bound to both.

The Global Dimming phenomenon is not new to those like Stanhill and Cohen or Farquhar and Roderick(2,3) who have been studying it for over a decade. It is only in the past three or four years, however, that it has been understood and accepted by a significant portion of the climate science community. Despite that it still seems to have not made it into the 2007 IPCC report that has raised such a clamour in recent weeks, a shortcoming that will hopefully be corrected in the next report.

What is Global Dimming? Briefly, Global Dimming is the reduction of sunlight striking the planet's surface from a combination of factors such as particulate matter suspended in the atmosphere from pollution such as soot, ash, sulfur
emissions, volcanic eruptions, CFCs, chemtrails, contrails, and from increased cloud formation and cloud density, also at least partially a result of atmospheric pollution. Atmospheric pollution increases the density of clouds by causing greater water droplet formation around microscopic specks of pollution.(1, 2, 4) That all means that a greater amount of the sunlight striking the earth is being reflected back into space, reducing the amount striking the earth's surface.

Okay. So what? That can't be all bad. Can it?

That depends, of course, on your perspective. Scientists now understand that this has had two effects on global warming, one predictable and one quite surprising. Understandably the decrease in sunlight striking the earth's surface has had a significant neutralizing effect on the potential global temperature increase caused by anthropogenic Global Warming. It may, in fact, be responsible for slowing that temperature increase to a fifth or a tenth what it would have been without Global Dimming. This has raised doubts and concerns about efforts throughout the world to reduce visible atmospheric pollutants. "We're going to be in a situation, unless we act, where the cooling pollutant is dropping off while the warming pollutant is going up. That means we'll get reduced cooling and increased heating at the same time and that's a problem for us," says Dr Peter Cox, one of the world's leading climate modellers.(2) Climate experts are beginning to believe that we could be facing as much as a 10C rise in global temperature by 2100.

The surprising finding was to do with plant photosynthesis. It had long been believed that a reduction in sunlight would decrease the amount of plant photosynthesis. It is now understood that quite the opposite is true. The amount of photosynthesis actually increases. It is thought this is a function of the sunlight being more diffuse due to the same conditions causing the global dimming. The more diffuse light reaches more of the plants below the forest canopy increasing their photosynthesis while having only a small negative impact on the photosynthesis in those plants normally exposed to the sunlight. This greater level of photosynthesis increases the amount of CO2 being absorbed by plants, thus reducing the amount of CO2 in the atmosphere, one of the primary Greenhouse Gases responsible for Global Warming.

At first glance, therefore, Global Dimming appears to a blessing in disguise. It reduces two of the prime contributors to Global Warming; increased surface temperature and increased CO2. The prime contributor to anthropogenic Global Warming, however, is our burning of fossil fuels, a source of both Global Warming (in CO2 and other GHG emissions) and Global Dimming (in atmospheric particulate matter like soot, ash and smoke). But we are fast approaching peak oil, peak natural gas and even peak coal. Once we pass peak our burning of all these fossil fuels will gradually decrease on the downslope on the other side of the peak. Once that reduction begins, the short term problem is that the particulate matter in the atmosphere that causes Global Dimming will quickly begin to settle out of the atmosphere while the Greenhouse Gases like CO2 and Methane will continue to increase. These gases will also take much longer to settle out of the atmosphere than do suspended particulates.

There will also be an unusual side effect which will be important from a perspective of global carrying capacity. As the concentration of suspended particulates reduces and the effects on global cooling diminish, the enhanced levels of photosynthesis will reduce as well. This will reduce the amount of CO2 uptake by plants, meaning it will take longer for earth to cleanse the atmosphere of anthropogenic Greenhouse Gases. It also, unfortunately, means that the level of plant photosynthesis will be declining at the same time as our ability to produce and afford petrochemical agricultural additives like artificial fertilizers and pesticides will be on the decline. With the wholesale destruction of natural soil fertility throughout the planet over these past fifty years through the use of those petrochemicals, we will be faced with a double hit in our ability to produce enough food to support our still exponentially growing population.

There is a very good documentary produced by BBC which I strong suggest you should watch to understand the interconnections between Peak Oil, Global Warming, and Global Dimming. It is available on Google Video at;

Global Dimming is also believed to be responsible for other important events and impacts. It is now believed that Global Dimming is responsible for blocking the seasonal shift of the Monsoon Belt from the tropics into the northern hemisphere sub-tropics. This is believed to have been responsible for the droughts in the 1970s and '80s that caused the deaths of hundreds of thousands in Ethiopia. The fear is that if it halts the monsoons in Asia it could affect billions, half the world population. The potential impact would dwarf the loss of life in the African droughts.(2)

More on this important topic later.


1) Global dimming
2) Global Dimming
3) Goodbye sunshine


galewhitaker said...

I have read about global dimming in the past. In 1816 the earth experienced “the year with no summer”. Ash from volcanic activity the previous year cooled the atmosphere to the point that there was snow in June and crops failed. It was a mini disaster for the people alive at that time. It may sound ridiculous to suggest that humans might be able to control the earth’s temperature but is it possible that we could use airplanes to carry manmade “ash” up to high altitude and inject it into the atmosphere as a way of defeating global warming? I realize that it would take millions (maybe billions of tons) to have any affect but our very survival may be at stake. The payload of a 747 is 140 tons so it would take a large fleet and years of effort. Maybe science could come up with artificial ash that would be more affective than the real stuff so it wouldn’t take as much to do the job. Maybe the artificial ash could be designed to benefit the soil when it falls to the earth like the dust that blows from the Sahara desert and fertilizes the Amazon each year. If all the countries in the world shared in the effort it would spread the cost and create a lot of new jobs. We might need a new discipline in our universities, “Climate Control Engineering”.

Georg said...

Bonjour everybody,

Well, I did write an article about "global dimming". However, yours is by far more complete. Congratulations.


john newson said...

It seems to me that diffused lighting causing enhanced sub-canopy photosynthesis is not going to affect fully-exposed crops by varying, as the light input for these crops should remain constant at ground level. Or do I have this wrong?

Dick Dalton said...

Excellent summary. I had seen the BBC film and a search then led me to your blog. I am putting your link up so my college students can read the story. In the BBC film, I thought the famine in Ethiopia killed 50 million instead of just hundreds of thousands; a small point to us, but significant to them. Thanks for your excellent Post. Dick Dalton