Monday, October 22, 2012


Science and technology

[Bold is mine - D.G.]


Difference Engine: Cloudy with a chance of...

Oct 22nd 2012, 7:34 by N.V. | LOS ANGELES
Definitely unsettled
IT WAS no accident that Manchester, that gumptious and radical heart of Victorian Britain, became the first industrial city and the cotton capital of the world. It is situated 50km or so from the coast, with its back to the hills, and on the brunt end of southwesterly winds which, laden with moisture from the warm Gulf Stream, dump their drizzle across the Manchester basin as they are forced up and over the Pennine chain. Nowhere else in nineteenth-century Europe was there such mild, moist air so perfect for spinning cotton.
With an abundance of it, Mancunians have good reason for being connoisseurs of climate. A quick glance at the clouds flitting across the sky each morning is usually enough to decide whether to leave the brolly behind or grab a mackintosh and galoshes. Growing up in the city’s hillier northern fringes, your correspondent learned from an early age to recognise the various species of cloud—from the low-lying layered sheets of stratus, up through the billowy cumulus forms, to the high-flying tufted wisps of the cirrus family.

Clouds are something he does not get to see so much beneath the blue skies of southern California—where, during the summer months, the only cumulus tend to be signs of wildfire in the mountains. True, along the coast in late spring, the morning “marine layer” is especially thick, giving rise to the local weather-lady’s cheery remarks about “May Gray” or “June Gloom” and the possibility, just perhaps, of rain.

Though frequently dismissed as a Californian euphemism for fog, the marine layer is not actually mist or cloud. Strictly speaking, it is simply a medium in which clouds can form—a layer of air trapped between the surface of the cold ocean and an inversion layer above formed by hot air spilling out of the high desert. When the relative humidity of the trapped air reaches 100%, condensation commences and a sheet of stratus begins to form below the inversion layer. Fog, by definition, is stratus in contact with the ground or the sea.

In southern California, the marine layer is at its thickest just before dawn. As the onshore breeze picks up, the layer migrates inland—only to evaporate as the sun rises in the sky. Being 220 metres (720 feet) up the hillside, your correspondent is usually above it all, though there are times when the marine layer is thick enough at night to envelop even his eyrie. Then, as far as he is concerned, it is plain and simple fog, requiring a car’s ankle-height fog lamps to illuminate the road.

Foggy days invariably occur when the Pacific High—a large mass of high-pressure air which tends to hover over southern California and its adjacent ocean—is at its strongest. At such times, the high-pressure air sinks faster than usual, gaining additional heat as it is compressed still further. It is this extra warm air descending from above that strengthens the inversion layer, and allows thicker and more persistent clouds to form.

The inversion layer along the Californian coast is also affected by conditions far out to sea, such as El Niño-Southern Oscillation—a mechanism operating in the Pacific that helps regulate the flow of heat from the tropics to the poles. Because the Pacific is such an enormous reservoir of heat, it is the main engine driving the global wind pattern. Any change in the Pacific's temperature alters weather around the world.

Known in the media as simply El Niño (“the boy child” in Spanish)—because it was first noticed off the coast of Ecuador and northern Peru around Christmas time—the phenomenon occurs when there is a rise in temperature of the surface of the tropical eastern Pacific, coupled with an increase in the surface air pressure in the western Pacific. The average rise in temperature is only 0.5ºC or so above normal, and lasts for just nine months to a year or two at most.

In California, El Niño brings a warmer, wetter winter. The opposite effect, La Niña, occurs when conditions in the tropical Pacific reverse, with cooler surface temperatures in the east and lower air pressures in the west. This results in dryer winters on the West Coast. Oscillations between the two siblings are irregular, occurring every two to seven years. Whichever prevails determines whether places around the world will suffer flood, drought, famine, hurricanes or any of the other plagues of mankind.

Early in 2011, computer models were predicting a Niño, albeit a weak one. In the end, the Pacific decided to give La Niña another turn at influencing global weather. No-one is sure what is in store for this winter. Most models say that, after two Niñas, sea temperatures imply a Niño is on the cards. A few suggest a third Niña is still a possibility. Others say it could be neither (La Nada). For the record, the United States National Weather Service has officially declared last year’s Niña to have dissipated.

Whatever, the cycle seems to be getting out of whack. For several decades, Niños have been coming more frequently, Niñas less so. Fingers point to global warming. But scientists caution that more research needs to be done before any direct correlation can be established. Satellite data go back only so far.

Circumstantial evidence, though, suggests that something new is underway. A variation of El Niño has been detected in the central Pacific, well away from the ocean's eastern edge where it is normally born. This phenomenon, known as El Niño Modoki (Japanese for “looks like, but slightly different from”), causes unusual effects—including a lowering of tide heights, a strengthening of waves, and a tendency to make storms move south.

Beaches from Washington state to southern California took a pounding during the winter of 2009-10, with the shoreline being eroded hundreds of feet in some places by storms heading in a southward direction. Local climatologists blame El Niño Modoki for the damage, and predict more of the same in the years ahead. Again, it is too early to say whether this new phenomenon in the mid-Pacific is the result of global warming. What is not in doubt is that sea levels are rising. Add the effects of El Niño Modoki, and it is clear that coastal erosion along the western seaboard of North America could get a whole lot worse.

Certainly, a shift to a warming Niño this winter, following two successive years of cooling Niñas, could trigger a record high in the surface temperature of the eastern Pacific. Justified or not, that may be taken in some quarters as evidence of the anthropogenic origin of global warming. In reality, climate science is no closer to answering that conundrum than it is to finding how precisely clouds respond to global warming.
An assorted bunch of optimists believe clouds will save the world from the catastrophic impact of greenhouse gases. They put their faith in the notion that, as the atmosphere warms up, there will be fewer of the thin cirrus clouds in the upper atmosphere—the ones that normally let sunlight through, but trap the infra-red being radiated back from the surface. With fewer cirrus around, they imagine the atmosphere will behave like a thermostat, venting excess heat into space.

A pity all the evidence says otherwise. The conventional wisdom held by working climatologists is that clouds are unlikely to change enough to offset the effects of global warming. The best that can be hoped for is that they remain neutral. The worst is that they amplify the warming trend, as rising temperatures deplete the thicker layers of clouds in the lower atmosphere. These are the crucial clouds that reflect much of the incident sunlight back into space and keep the Earth cool. 

On both issues—the increasing frequency of Niño events and the role that clouds are expected to play in global warming—there are nowhere near enough historical data from weather satellites to refute, finally and categorically, all the crackpot notions about climate change (or lack thereof). [Hmmm - so exactly what is "all the evidence" referred to in the previous paragraph!]Another problem is the difficulty of simulating both effects on computers. To date, the machines and software have not been up to the job of modelling the fine detail needed to make meaningful projections. That, thankfully, is about to change.

In the end, though, everything hinges on learning, unambiguously, how sensitive the climate is to greenhouse gases. Sceptics believe it is not particularly so. But the fact is that, without the data, no-one knows for certain. Meanwhile, the whole climate issue has become so politically charged that the policy debate has become paralysed and bogged down in entrenched positions. The danger, of course, is that if the climate's sensitivity to greenhouse gases turns out to be as high as some researchers fear, and nothing has been done about it, then the children and grandchildren of the present generation are stewed. 

On a lighter note, the marine layer beneath your correspondent’s hillside home thickened today, and cumulus clouds formed out to sea. For a wistful moment, it looked as though a shower might be on its way.