According to the WMO the current La Niña episode will continue to exist for at least another 2-4 months. Other sources state it may last until 2012. This La Niña could be the strongest in decades and is likely to become the costliest ever, with especially in Australia unprecedented damage to infrastructure, private property and for instance the mining industry.
So can we somehow control this notoriously irregular climate phenomenon – and can we prevent catastrophic La Niña and El Niño events? Well, in theory: yes.
We found a year-old publication in Environmental Research Letters posing that same question. In late 2009 the Pacific water temperature anomalies showed a clear El Niño pattern, with above average warm waters towards the eastern shores of the Pacific and across the Pacific equator.
Leveling El Niño through geoengineering
So El Niño is what this geoengineering study focussed on – also because El Niños are actually thought to be potentially more damaging on a global scale, as they may cause floods and mudslides in Latin America, but also month-long droughts in Southeast Asia and Australia – through man-lit Borneo forest fires also causing environmental damage with [significantly, 1998 estimates range as high as 40 percent of global antropogenic output] increased CO2 emissions and biodiversity loss.
What drives the El Niño Southern Oscillation (ENSO) is still poorly understood. Likely multiple triggering factors add up. As positive feedbacks come into play in both the case of an El Niño and a La Niña, via (weakened and strengthened respectively) trade winds, the initial causes to both phenomena can be rather small disturbances, either in ocean temperatures, or in the distribution of atmospheric pressure systems in the air above it.
The all-important ENSO feedback
ENSO is driven to its extremes by the dominance of low pressure systems over the parts of the Pacific that carry the relatively warmest water – and the dominance of high pressure systems in the air over the relatively cool parts. In the case of a La Niña, the low pressure systems are dominant in the west and in the case of an El Niño, they dominate in the east (and the central part across the equator).
Close to the equator there is no Coriolis effect so the behaviour of air is very straightforward: from high pressure to low pressure. This means during La Niña air blows from east to west, strengthening the already dominant easterly trade winds – whereas during El Niño, the air is inclined to flow from west to east, opposite to the trade winds, partly shutting them down.
This has implications for the temperature distributions as well. During La Niña the easterly winds blow more warm surface water [remember it’s the tropics, the Sun heats the water] to the west – and during El Niño westerly winds add the warm waters to the already warm eastern shores of the Pacific.
Dynamic albedo geoengineering
Using a simulation model author Douglas MacMynowski of the California Institute of Technology finds in the El Niño case this positive feedback can be disturbed, by dynamically deflecting 1 percent of solar radiation over a specific part of the tropical East Pacific, called ‘El Niño 3’.
Doing this would compensate the local temperature increase of around 2 degrees during a strong El Niño. When the water cools to normal temperatures the low pressure systems weaken and the trade winds can pick up agsain, in effect ending the El Niño.
To increase albedo over the ocean on a local scale either the colour of part of the ocean would have to change [become lighter] or the cloud cover above it [would have to increase]. Browsing through the world’s modest portfolio of geoengineering proposals – and ignoring the possibility of oil spills and algae blooms off the coast of Peru – it seems only the cloud seeders of Columbia University’s Klaus Lackner may one day prove to be up to that job.
MacMynowski seems to agree increasing clouds are the way to go, as he writes in his conclusions: “The forcing required is of a scale achievable by human intervention, and seems plausible if cloud albedo modification were being used to offset some global warming.”
Leveling La Niña through geoengineering?
Weakening a strong La Niña situation – and preventing much of the associated damage – may work through a similar route. Again the dynamic deflecting would have to take part over the relatively warm waters of the ocean, this time to the far west, perhaps sending Lackner’s ships to the coastal waters of Australia, Indonesia and the Philippines.
Before folks in Queensland reconnect to the internet, revisit Bitsofscience.org and get overly excited; first of all that dynamic fleet of ‘cloud seeders’ has yet to be built. Secondly, something may have been overlooked in the study. Cloud cover may already be very high above the waters with high positive temperature anomalies. Here the depressions form. Over the warm waters the air humidity is very high. Depressions form from the ocean surface. Huge pockets of warm air, filled with water vapour, rise several kilometres up and cool, condensing the water, forming droplets and clouds. Under such circumstances it may prove difficult to ‘only’ deflect 1 (additional) percent of solar radiation.
So, should we look into the opposite possibility, inventing geoengineering measures to decrease cloud cover over the cooler parts of the two ENSO phases? [Well, obliged to state the obvious: of course not, Earth can do without excess heat due to GHG-induced climate change.] For those who simply like to wonder how things could be done, clouds again seem ill-suited. The cooler waters during both El Niño and La Niña have permanent high pressure systems. In the tropics this means sunny skies. And you can’t decrease a zero percent cloud cover.
Albedo engineering may never be easy
Cloud geoengineering may be a bit overstated anyway. Recent studies show the infrared absorption of clouds may outweigh their albedo benefits [depending on cloud type] – which is actually very bad climate news, implying clouds act as a positive feedback to warming. [The original plan by Klaus Lackner intends to make clouds whiter, not to make more clouds. Increasing aerosols however also increases the total (3D) amount of cloud - hence the infrared absorbtion.]
The proclaimed cooling of other atmospheric albedo measures, applied on a global scale, may also have been marketed a bit too enthousiastically over recent years. A PNAS study we reported on in September estimates it would require 1 Mount Pinatubo per 18 months to compensate for the same two degrees of warming on a global scale. This means even ‘extreme geoengineering‘ can’t go without additional climate mitigation – as the world is en route to more than 2 degrees warming, quite possibly twice as much within this century.
© Rolf Schuttenhelm | www.bitsofscience.org