Global dimming masks the effect of global warming

This sounds more like pseudo-science fallout from The Day After Tomorrow than a serious scientific study. The UN's Intergovernmental Panel on Climate Change (IPCC), whose studies have been the starting point for most serious serious discussion of the issue, did consider the impact of aerosols. Even so, and even though they make assumptions about the underlying global economics that barely any economist believes, their worst-case projection finds a sealevel rise of only 0.8 meters. (For Americans, that's 2 foot 8.) That would be significant, but nowhere near catastrophic for New York and London.

Source: IPCC Third Assessment Report -- Climate Change 2001: The Scientific Basis:Summary for Policy Makers (pdf here). You may be especially interested in page 14, Table 5.

no, there was no pseudo science - the investigations into evaporation had been going on for decades as a rather boring, only slightly fluctuating experiment - until recent years when the water evaporation had slowed down by 25% - now that is a dramatic change. Pan evaporation was the term as they were huge pans of water just left out and measured minutely each day to see how much water was needed to refill them.

The dimming of the sun because of vapour trails from aircraft etc was the cause. They explained the work of the sun in the process of evaporation and showed how astronauts had noticed global dimming as well.

They explained how the lack of rains in Africa was directly due to the pollution from Europe for instance.

Their arguement was that this is running alongside global warming but masking the global warming effects (many global warming scientists have been surprised that things aren't worse and this seems to be the reason). The trouble is, the measures to reduce pollution will mean more global warming in this scenario in a short space of time.

Back when physicists were sure that light was only a wave, they were faced with the problem of defining just how sunlight or celestial radiation could pass through empty space. They invented the concept of the invisible, undetectable aether as the medium through which the light waves passed. Voila! Problem solved. Later when the Michaelson Morely experiment and other findings utterly demolished the possibility of such an aether they scrambled to find other theories.

This "discovery" of "global dimming" looks suspiciously like the aether of the 19th ceentury - a fiction necessary to preserve a false or incomplete theory.

A 21% reduction in solar intensity corresponds to the difference between the solar energy received at the equator and what is incident at latitude 38 deg. north or south. I note that Edinborough and Oslo are indeed much colder than Cairo, and suggest to you that under no conceivable scenario could the accumulated greenhouse gases produce an effect to mask such a change over the globe.

You're right, it is. Mine was not a "let's knock America" post, we're all guilty to a greater or lesser degree, but the USA is quoted as being highest.


Me neither



With due respect, not all TV programmes are made like that. This one, which impressed me and I'm quite choosy, was well researched and well argued, and not alarmist nor overly dramatised. It is a very dramatic subject however.

London has a moveable flood barrier to protect the centre of the city from flooding on high tides combined with adverse weather conditions. It is 20 years old. It was used once in its first year. Last year it was needed about 25 times.

I love that little gem.

It's got to the stage where even some otherwise reasonable people believe it.

It wasn't true when Rush Limbaugh wrote it and it still aint true now.

The scientist working in Israel who published his "global dimming" findings was indeed thought by the scientific community to have been wrong. The research was discounted and forgotten for twenty years because no-one could see how it could possibly be true.
It was not until more recently when an independent researcher duplicated the results using different methodology that this theory moved from the realm of the impossible.

McTag,

I'm willing to credit the impression of objectivity and completeness the program left you with.

I do have a problem though with the suggestion that there has been a 21% reduction in the intensity of solar radiation reaching the earth's surface -- indeed even one-tenth that, 2.1 % is well beyond plausibility. Green plants grow only in the presence of such radiation (if they are kept in the dark, even if kept warm, plants don't grow.) We have excellent world-wide data on crop yields on every continent and nearly every country. If there were even a very small such trend operating over these two dacades, it would have been detected in the agricultural output of nations throughout the world. No such phenomenon has been observed, and the isolated results of a single point observation twenty years ago in the Negev desert just don't count for much. Possibly his observation was confined to only a narrow band in the spectrum. If so then the energy impact would be negilgable, and the point still highly suspect.

My vote is for selective reporting by a TV producer out to create a good show.

I deal every day with such absurdities, usually involving isolated data taken out of context and without regard to the necessary collateral effects or other factors which inherently limit such excursions in nature.

Point taken, and it's a good one. The programme drew its scientific basis from weather researchers in Germany, Australia and Israel, and included an interesting section about an American who used the clear, vapourless skies when aircraft were grounded after 9/11 to get data in the USA.

I think you would be as fascinated as I was in the results and conclusions. Is there no way to access BBC Horizon programmes in your country?

Judging by a search on scholar.Google.com for stanhill and "global dimming", this does not appear to be the case. It appears that Stanhill, the scientist working in Israel, wrote a review article in 2001. (Stanhill G, Cohen S. 2001. Global dimming: a review of the evidence for a widespread and significant reduction in global radiation with discussion of its probable causes and possible agricultural consequences. Agricultural and Forest Meteorology 107, 255-278) For those readers unfamiliar with the customs of scientific publication, review articles compile the findings published in earlier primary sources, and sometimes comment on them. They almost never contain any original research.

When you search Google Scholar without constraining the search to Stanhill, the number of hits increases from 13 to 19. Changing "global dimming" into "global warming" increases it to over 30000. All this suggests that from the scientific community's point of view, "global dimming", of the magnitude described by BBC, is a marginalized concept which peer review has not treated kindly. The idea was barely revived by one review article containing no original research. But science reporting doesn't sell on the basis of findings being well-substantiated, but on the basis of them being spectacular. So BBC went by the one review article with spectacular results, and ignored several hundred articles on original research that did consider the impact of aerosols, but unfortunately yielded much less spectacular findings.

An interesting aside from all of this is the proliferation of analysis on every conceivable subject and the not-very-scientific selection and proliferation of it by the various elements of the media. One must still work hard to find real truth amidst all the appealing and well-presented, often convincing distractions. Yet another illustration of nature's fourth conservation law -- (mass, energy, momentum and...The Conservation of Difficulty.)

Thomas illustrates another new "scientific" indicator - the number of Google hits on various word groups and the interpretation of the result to model (in this case) the choices and behavior of scientific researchers. Fascinating.

I have seen brief studies suggesting a higher incidence of high cirrus cloud cover, partly a result of aircraft flight at high altitudes. The contrails should not be the problem - that's just condensed water vapor. Instead it is the 180,000 or so pounds of fuel every transatlantic flight deposits in the upper atmosphers. I don't know the net effect on heat balance though. My guess would be that the vertical circulation in the atmosphere is sufficient to deal with it.

Thank you, gentlemen , for these analyses. As I said before, plainly I am not an expert in the field but I wished to bring this subject up for discussion.

Surely, programme makers seek controversial subjects and are sometimes not too concerned with objectivity nor presenting both sides of an argument where this might interfere with audience impact.

I was particularly interested in this because I am involved in the water industry, and we are currently experiencing more marked and violent, and frequent, rainfall events than previously was the case. Historic rainfall data seems to be of little guidance when predicting future patterns. Popular belief attributes this to global warming. If the dimming effect is actually mitigating the worst effects of warming, this is a subject which concerns us all. An interesting sideline on the greater problem of global warming.

Absolutely, and don't get me wrong: aerosols do have the qualitative effect you described, and the IPCC's publications reflect that. It is 'only' the magnitude of the effect that the BBC report has grossly exaggerated. I put 'only' in scare quotes because the same could be said of The Day after Tomorrow. In this movie, a 20 meter sea level rise buries New York in a few minutes whereas IPCC projections show 0.3-0.8 meters over 100 years. Just a difference in quantity, not quality, you see.

McTag,

Thank you for an interesting topic that made me think and reshape a few ideas. I would feel more like an 'expert' if I was able to get to the heart of the matter at the first step. I was not.

Rainfall is up in the Midlands I guess. We are just emerging from a mild drought in the Mid Atlantic states. Northern California is having a good rainfall year, but there the rainfall follows a fairly predictable but large variation with a cycle period of about 14 years. In the water business aspect of all this, demand is up significantly, exacerbating the consequences of even mild natural variations. It is a big investment issue here and some British water companies, Severn Trent and Thames Water (I think) have bought up a few local utilities and some water resource consulting companies as well. (The Brits are generally smarter investors than the Japanese, but the Yankee traders often outsmart them both.) On the flip side of excess water, I believe that increased environmental regulation has added greatly to the complexity of stormwater management. Nature is usually a good deal more complex that the various models so proudly put forward by the analysts and regulators, and a lot of energy goes into fixing their fixes.

Parting shot on global warming noted. I am more skeptical than Thomas who readily concedes it exists and will continue. I do like his summary of it though -- 'It isn't worth fixing'.

Hi again. A major climate change report is due out tomorrow:

Excerpt from newspaper article

The report says this point will be two degrees centigrade above the average world temperature prevailing in 1750 before the industrial revolution, when human activities - mainly the production of waste gases such as carbon dioxide (CO2), which retain the sun's heat in the atmosphere - first started to affect the climate. But it points out that global average temperature has already risen by 0.8 degrees since then, with more rises already in the pipeline - so the world has little more than a single degree of temperature latitude before the crucial point is reached.
More ominously still, it assesses the concentration of carbon dioxide in the atmosphere after which the two-degree rise will become inevitable, and says it will be 400 parts per million by volume (ppm) of CO2.
The current level is 379ppm, and rising by more than 2ppm annually - so it is likely that the vital 400ppm threshold will be crossed in just 10 years' time, or even less (although the two-degree temperature rise might take longer to come into effect).
"There is an ecological timebomb ticking away," said Stephen Byers, the former transport secretary, who co-chaired the task force that produced the report with the US Republican senator Olympia Snowe. It was assembled by the Institute for Public Policy Research in the UK, the Centre for American Progress in the US, and The Australia Institute.The group's chief scientific adviser is Dr Rakendra Pachauri, chairman of the UN's Intergovernmental Panel on Climate Change.
The report urges all the G8 countries to agree to generate a quarter of their electricity from renewable sources by 2025, and to double their research spending on low-carbon energy technologies by 2010. It also calls on the G8 to form a climate group with leading developing nations such as India and China, which have big and growing CO2 emissions.
"What this underscores is that it's what we invest in now and in the next 20 years that will deliver a stable climate, not what we do in the middle of the century or later," said Tom Burke, a former government adviser on green issues who now advises business.
The report starkly spells out the likely consequences of exceeding the threshold. "Beyond the 2 degrees C level, the risks to human societies and ecosystems grow significantly," it says.
"It is likely, for example, that average-temperature increases larger than this will entail substantial agricultural losses, greatly increased numbers of people at risk of water shortages, and widespread adverse health impacts. [They] could also imperil a very high proportion of the world's coral reefs and cause irreversible damage to important terrestrial ecosystems, including the Amazon rainforest."
It goes on: "Above the 2 degrees level, the risks of abrupt, accelerated, or runaway climate change also increase. The possibilities include reaching climatic tipping points leading, for example, to the loss of the West Antarctic and Greenland ice sheets (which, between them, could raise sea level more than 10 metres over the space of a few centuries), the shutdown of the thermohaline ocean circulation (and, with it, the Gulf Stream), and the transformation of the planet's forests and soils from a net sink of carbon to a net source of carbon."

Source: http://news.independent.co.uk/world/environment/story.jsp?story=603975

Judging by the arbitrary threshold-setting, business managers were involved in that task force all right. (Sorry George, couldn't resist. ) All that's missing is the 12-step plan. I expect to read the report this evening. But the Independent piece has left me with little hope of learning something new.

I will also be pleasantly surprised if any good information comes from the report. Confidence of the researchers comes across as bad science and arrogance to me. They seen to hope we will assume it is two degrees c warmer than 1750 in the first paragraph, later admitting the rise is 0.8 degrees c. They write as if the only possible cause of warming is the carbon dioxide level, and assume any change has to be for the worse. I think they have funding and egos to protect with half truths and false inferences. Neil

It wouldn't be the first time such factors and worse have influenced such peddlers of future trends. Thomas has cited the false forecasts of "The Population Bomb" and "The Limits to growth", both hailed as holy writ by the cognoscenti, before they were revealed as rather sophomoric extrapolations of current trends, without any provision for the known limiting factors in the respective dynamics.