ATMOSMARE - JOTTA PALLO PYSYISI VIILEÄNÄ.

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Kansainvälinen merenkulkujärjestö IMO päätti lokakuussa 2008 rajoittaa laivapolttoaineiden rikkipitoisuuden 0,5 prosenttiin vuoteen 2020 mennessä ja 0,1 prosenttiin erityisalueilla, kuten Itämerellä. Tällä hetkellä laivapolttoaineissa on rikkiä keskimäärin 2,7%. Päätöksen taustalla olivat tutkimukset rikkipäästöjen terveyshaitoista.

Päätös saattoi olla kokonaisuudessaan varsin harkitsematon. Laivojen rikkipäästöjen arvioidaan viilentävän ilmastoa heijastamalla suoraan auringon energiaa ja vaikuttamalla pilvipeitteeseen. Arvioiden mukaan rikkipitoisuuden väheneminen polttoaineissa vähentää globaalin laivaliikenteen viilentävää vaikutusta 0,58 W/m2:sta 0,27 W/m2:een. Laivaliikenteen ilmastoa viilentävästä vaikutuksesta häviäisi siis noin 0,3 W/m2. Tällä hetkellä maapallolle tulee arviolta 0,85 W/m2 +- 0,15 W/m2 enemmän lämpöenergiaa kuin täältä poistuu. Mikäli laivaliikenteen rikkipäästöt pienenevät huomattavasti, kasvaa maapallon lämpöepätasapaini ja lämpeneminen kiihtyy. Rikkipitoisuuden rajoittaminen voi siis koitua kohtalokkaaksi.

Selvyyden vuoksi on syytä korostaa, että rannikkoliikenteessä ja Itämerellä rikkipitoisuuden rajoittaminen voi olla kokonaisvaikutuksiltaan perusteltua. Tosin näilläkin alueille saattaisi olla kokonaisuuden kannalta järkevämpää kohdentaa toimenpiteet laivaliikenteen hiilidioksidipäästöjen rajoittamiseen.

Large freight ships currently burn heavy fuel oil (bunker oil), which contains, as a global average, about 2.7 per cent of sulphur. In October 2008 the International Maritime Organization decided, that the maximum allowable sulphur content in the fuel used by ships should be reduced to 0.5 per cent by 2020, and to 0.1 per cent in the more stringent local Emission Control Areas (ECAs).

According to one study (Corbett et al, 2007) the global number of deaths caused by sulphur and particulate pollution from shipping might amount to 60 000 per year, and could rise to 80,000 by 2012 unless no action is taken, and if the shipping industry continues to grow as predicted.

For public health reasons it probably makes sense to cut the ships sulphur, soot and other particulate matter emissions whenever a major part of the particulate matter would be likely to fall down over densely populated lands.

Ships contribute to global warming by producing approximately 1.1 billion tons of carbon dioxide (275 million tons of carbon) per year, which is roughly three per cent of all human-made carbon dioxide emissions. The ships also heat the planet by producing black carbon (soot) and nitrogen oxides that can be converted to ozone, which is a strong greenhouse gas.

On the other hand, the ships' exhaust gases also produce a number of cooling impacts on the climate. Nitrogen oxides generate ozone, but they also destroy methane, another important greenhouse gas. Above all, the sulphur particles emitted into the air by freight and passenger ships cool the planet both directly (by reflecting solar radiation back to space) and by acting as cloud condensation nuclei. Ships can thus both assist cloud formation and increase the number of cloud droplets inside a cloud, which makes the cloud whiter and more reflective (Lauer et al, 2007; Salter et al, 2008; Twomey, 1977).

The indirect aerosol effect of ships on climate has been found to be far larger than what was previously assumed. It is now estimated, that ships might contribute up to 39 per cent to the total indirect effect of anthropogenic aerosols (Eyring et al), even though their sulphur emissions only amount to 15 or 20 per cent of the total. This is because ships often spread their emissions over marine regions where there is otherwise very little air pollution or bioaerosols, and thus only a very limited number of cloud condensation nuclei.

What comes to ships and climate, the cooling impact of the sulphur is, at the moment, the clearly dominant factor. However, because carbon dioxide can stay in the atmosphere for centuries or more, it has a cumulative impact, unlike the sulphur aerosols which do not stay in the atmosphere for a very long time.

For example Jan Fuglestvedt and his co-workers have estimated (Fuglestvedt et al, 2007) that when we count all the negative and positive radiative forcings (like the cumulative impact of carbon dioxide and the various impacts of nitrogen oxides, sulphur oxides and black carbon) together, the ships would start to heat up the climate after 500 years or so, unless no action was taken to curb their carbon dioxide emissions.

It is likely, that the era of fossil fuels will come to an end already during this century, so the ships will not be able to keep on burning oil for five hundred more years. Above all, we are now faced with frighteningly rapid climatic destabilization. A five-hundred-year perspective is not relevant in the present situation. It now seems that we must think in terms of ten, twenty or fifty years, if we want to prevent a global climate catastrophe.

A little bit more than fifty years ago, on 3rd August, 1958, the US nuclear submarine Nautilus became the first submarine to reach the North Pole. According to the submarine's sonar, Nautilus had been under surprisingly sturdy polar ice throughout the journey. The thickness of the ice had varied between two and a half and twenty-five metres. Here and there the keels of higher pressure ridges had penetrated to the depth of forty or fifty metres (Anderson, 1959).

In 2006 the official prediction was that summertime sea ice would not disappear from the Arctic Sea before the year 2070 or 2080, even if the climate were to continue to warm up in line with the predictions of the Intergovernmental Panel on Climate Change (IPCC). But in the summer of 2007 the National Ice and Snow Data Center (NISDC) of the USA announced that the whole Arctic Sea could become ice-free already in 2020 during the height of the melting season (NISDC, 2006-2009).

The reason for altered tone was obvious: the extent of sea ice in the Arctic Ocean had diminished very rapidly in just a few years. In 2007 the extent of the area covered by marine ice was only half of what it had been in the 1950's, and the remaining ice masses were much thinner than before (NISDC, ibid).

The loss of marine ice may well have profound consequences for the climate, because snow and ice typically have a reflectivity (albedo) of 70 to 90 per cent. In extreme cases fresh-fallen, pure-white snow can reflect 98 per cent of solar radiation straight back to space. Even melting snow and ice still have an albedo of 50-60 per cent. Open water only reflects 4-10 per cent of the sunlight back, depending on the angle of the coming solar radiation. In other words, watery surfaces absorb 90-96 per cent of the solar energy falling on them. Dark soils and dark coniferous forests also have a very low albedo, typically less than 10 per cent (Serreze and Barry, 2005).

For example during the early Eocene period, 55 million years ago, the Earth was 13 degrees Celsius warmer than now. The average temperature at the North Pole, however, was 43 degrees higher than at present, plus 20 Celsius instead of minus 23, because there was no ice and snow to reflect sunlight back to space. In other words, the loss of snow and ice cover is likely multiply the effects of global warming in the Arctic.

This, in turn, might have truly disastrous consequences because the Arctic has literally thousands of millions of hectares of land and water areas with huge reservoirs of organic carbon and methane. Many of these greenhouse gas reservoirs have been frozen without interruption for a very long time, sometimes for more than a million years in a row.

New studies have estimated that there is at least 1,500 billion tons of organic carbon stored in the terrestrial permafrost areas (CSIRO, 2008). Most of this has been frozen into the so-called yedoma permafrost regions, into wet permafrost. In yedoma areas most of the permafrost and its carbon become covered with water when the ground begins to melt. Therefore, most of the carbon in the permafrost is released as methane, and not as carbon dioxide.

The difference is important, because as long as methane stays in the atmosphere, it is approximately one hundred times more effective as a greenhouse gas than carbon dioxide. Methane's relative global warming potential becomes smaller if we posit calculations on a longer perspective, because it breaks down in the atmosphere relatively quickly, which means that large eruptions of methane are the more dangerous the faster they occur.

There is more methane under the permafrost, in sediments known as methane clathrates or methane hydrates. In the clathrate deposits methane gas has been trapped inside small molecular-level cages of ordinary ice. The first methane clathrates were discovered by Russian scientists already in the 1960's, but we still have only a vague idea of the size of these reserves. According to one regularly quoted estimate there could be at least 400 billion tons of methane in the clathrate stores beneath the terrestrial permafrost.

The submarine methane clathrate deposits on the continental slopes are even larger. According to the best current estimate they might contain about 10,000 billion tons of methane, part of this inside the ice and the rest in gas pockets under the ice (Suess et al, 1999). These formations may be the greatest threat to our future survival, because they are only stable under a high pressure and when the temperature of the surrounding water is close to the freezing point of water. The clathrates in the Arctic Sea can exist much closer to the surface than in the other oceans, because the water is very cold.

Furthermore, most of the seabed of the Arctic Sea is covered by permafrost. Roughly one half of the bottom of the Arctic Sea consists of submerged continental shelves, and they are covered with permafrost. In other words there is many times more yedoma under the water than above the water. There are not even educated guesses on how much organic carbon these submarine permafrost areas may contain.

Russian scientists reported in 2005 that the whole West Siberian permafrost region had suddenly started to melt. According to Sergei Kirpotin and his co-workers, the whole one million square kilometre permafrost area had suddenly become full of small, round lakes. Some of the lakes no longer froze during the winter because the methane bubbling up from the permafrost kept them ice-free (Pearce, 2007, Walter et al 2006). In Spring 2009 Katey Walter, a researcher of the University of Alaska, said that the combined area of the melt water lakes in the West Siberian permafrost area had increased five-fold in three years, from 2006 to 2009 (Pearce, 2009).

During the summer 2008 Canadian and Russian scientists reported, that on many sites large amounts of methane had started to bubble to the surface of the Arctic Sea from the sea bottom, from the submarine permafrost. Moreover, people living at Greenland's western coast told British and Canadian researchers about “large explosions” in the sea, and about dead whales that had subsequently floated to the surface. It has not been possible to confirm these reports, but for example a partial breakdown of a small methane clathrate bed would produce eruptions with a resemblance to water bomb explosions.

If the situation gets worse, eruptions from such “natural” sources in the Arctic might soon dwarf the man-made greenhouse gas emissions. It is very important to halt this vicious circle, before it is too late and the warming really begins to feed itself.

We might only have ten or twenty years left to stabilize the situation. This might be the worst imaginable moment to eliminate the ships' sulphur emissions, because such a move would, with a 100-per cent certainty, accelerate the warming of the strategic marine regions.

Above all, it may be that we have seriously underestimated the cooling impact of sulphur aerosols. This far the standard estimate has been, that sulphur and other aerosols may have cancelled roughly one quarter of the global warming (Pearce, 2007). The above-mentioned calculations are based on this figure.

Paul Crutzen, the only climate scientist to have won a Nobel price in science, presented new and more than a little bit frightening calculations about the same subject in a workshop that was held in Dahlem, Germany, in June 2003. According to Crutzen's new assessment the aerosols and clouds generated by them have actually cancelled at least one half and possibly three quarters of the warming (Pearce, 2007).

In 2005 three prominent climate modellers, Meinrat Andreae, Chris Jones and Peter Cox, refined Crutzen's calculations (Andreae et al, 2005). According to their assessment the amount of expected global warming by the year 2100 would increase from the official prediction of 1.5 - 4.5 degrees to 6-10 degrees, if the cooling impact of man-made aerosol emissions was also removed, at the same time.

If Crutzen, Andreae, Jones and Cox are right, or even close to the truth, it would be extremely dangerous and possibly suicidal to cut the ocean-going ships' sulphur emissions before we have reduced and stabilized the atmosphere's greenhouse gas concentrations back to a safer level.

According to the measurements made by a NASA satellite, the Earth's current heat imbalance (also known as global warming) is now almost exactly 1 watt per square metre. In other words, the Earth now receives from the Sun a little bit more energy than what it radiates back to space. The difference is 1 watt per square metre, or 500,000 gigawatts for the whole planet. This is the current sum total of all the negative (cooling the planet) and positive (heating the planet) radiative forcings.

If Crutzen's higher estimate is correct, and the aerosols currently cancel three quarters of the global warming impact of the greenhouse gases, black carbon, jet plane condensation trails, artificial cirrus clouds and the reduced reflectivity of the northern areas, and if the ships' sulphur emissions amount to 39 per cent of our total anthropogenic “particle parasol”, the sudden removal of this sunshade might almost instantly increase the rate of global warming from 1 watt per square metre to more than 2 watts per square metre.

Moreover, the additional heating impact would not be evenly distributed over the globe, but instead concentrated over some of the heavily trafficked marine areas. This might lead to accelerated heating of surface waters, which, in turn, might further speed up the melting of the Arctic sea ice and the destabilization of the carbon and methane stores in offshore methane hydrate beds and in the submarine permafrost.

the sulphur emissions from the ships do not have any significance for human health or for the health of marine ecosystems when they enter into the atmosphere over the ocean, far away from the nearest shore

replacing bunker oil with more refined oil that contains less sulphur would actually increase the ships' carbon dioxide emissions, when also the carbon emissions from the oil refining processes are taken into account (DK Group, 2008)

the switch to distillates would increase the shipping industry's fuel bills by USD 200 billion per year (DK Group, 2008), which would greatly reduce the ability of the shipping companies to adopt other fuel-saving technologies and/or integrated propulsion systems that would have a lot of potential to reduce the ships' carbon dioxide emissions

it would be better to encourage the shipping companies to invest for instance on ducktails, air greasing, sail kites, Flettner rotors and thin-film solar panels instead of adopting measures that would increase both the ships' fuel bills and their carbon dioxide emissions, and largely eliminate the shipping industry's cooling impact on the climate.

Because the issue (of reducing sulphur emissions) is highly political, most climate researchers have been reluctant to say that some of the planned moves might actually be very dangerous. However, the only climate scientist who has won a Nobel price in science, and a number of his prominent colleagues have repeatedly spoken about the risks related to reducing the amount of sulphur in the air. The stakes are now so high, that this must be considered a sufficient warning. We must not reduce the sulphur emissions of ocean-going ships, at least not before we have got a better and more reliable picture about the situation.

Ideally, ships should have multiple tank systems so that they could burn cleaner fuel when they are close to the harbour/shore, and switch to bunker oil when they get farther, or when the wind blows toward the ocean.

Capaldo, Kevin, Corbett, James J., Kasibhatla, Prasad, Fishbeck, Paul and Pandis, Spyros N.: Effects of ship emissions on sulphur cycling and radiative climate forcing over the ocean, Nature 400, 743-746, 19 August 1999

Eyring, Veronika, Corbett, James J., Lee, David S. and Winebrake, James J.: Brief Summary of the impact of ship emissions on atmospheric composition, climate and human health, Document submitted to the Health and Environment sub-group of the International Maritime Organization on 6 November, 2007

Fuglestvedt, Jan, Berntsen, Terje, Myhr, Gunnar, Rypdahl, Kristin and Bieltvedt Skeie, Ragnhild: Climate forcing from the transport sectors, Climate forcing for the transport sectors - Proceedings of the National Academy of Sciences, approved October 5, 2007, www.pnas.org

Lauer, A., Eyring, V., Hendricks, J., Jöckel, P. and Lohmann, U.: Global model simulations of the impact of ocean-going ships on aerosols, clouds and the radiation budget, Atmospheric Chemistry and Physics, 7, 5061-5079, 2007.

Salter, Stephen, Sortino, Graham and Latham, John: Sea-going hardware for the cloud albedo method of reversing global warming, Philosophical Transactions of the Royal Society, 366: 3989-4006, 29 August, 2008.

Maritime traffic concentrates on a small number of densely packed shipping routes between the main harbours. Ships favour the shortest routes, because they want to deliver their cargoes to their destinations as quickly as possible.

If shipping routes and ships were dispersed more evenly over the oceans, the sulphur dioxide produced by the ships would most probably produce many times more marine stratocumulus clouds. Outside the Arctic and Antarctic regions, such clouds have a strong cooling impact on our planet. If the ships were equipped with taller chimneys or with other devices lifting the exhaust gases to higher altitudes, the sulphur particles would be spread still more widely and even more cloud cover would probably be generated.

If the freight ships of the future had both a diesel engine and a wind propulsion system like a Flettner rotor or a sail kite, and if they aimed at minimizing their oil consumption, they would almost automatically become widely dispersed and scattered over the oceans. When a ship is partially wind-powered, the most direct route will no longer be the route that consumes the least fuel, because the wind conditions and the direction of the prevailing winds also influence the calculations.

For a ship equipped both with an engine and with sails or a sail kite it would often make sense to use a much longer route. This means that even if the ship would consume 30 or even 50 per cent less oil and produce 30 or 50 per cent less sulphur, it could still produce (much) more cloud cover.

The British scientist Sean Twomey showed, at the late 1970's, that the reflectivity of a cloud is influenced by the average size of cloud droplets. Most clouds consist of relatively small amounts of water which have condensed on even tinier particles floating in the air, on the so called cloud condensation nuclei. If the water in the cloud is divided between a very large number of very small cloud droplets, the cloud is whiter and reflects sunlight better than if the average size of the cloud droplets is larger and there is a lesser number of them.

It has been estimated that in the clouds over the oceans the average size of the cloud droplets is 25 microns, while the average over land is only 7 microns. This means that the clouds over the continents are, on average, more reflective than the clouds over the oceans. John Latham, a researcher at the National Center for Atmospheric Research in Boulder, Colorado, proposed already in 1990 that the Twomey effect could perhaps be utilized in efforts to prevent a disastrous global warming. Latham said that it might be possible to make certain types of clouds more reflective simply by adding more cloud condensation nuclei, so that a larger number of cloud droplets would be formed.

In 2006 Latham and the Scottish engineer Stephen Salter, the inventor of the world's first wave power station, developed the idea further. They proposed that the albedo of the marine stratocumulus clouds could be increased by 1,500 special, unmanned ships that would use large Flettner rotors - originally invented by the German engineer Anton Flettner -- to spray seawater into the air in the form of tiny, 0.8-1.0 micron-wide droplets. The salty seawater droplets would act as cloud condensation nuclei, making the marine clouds whiter and more reflective.

The idea might have real potential and should be investigated further. However, we do not really know why the cloud droplets over the seas are, on average, larger than the cloud droplets above the continents. It may be that this is because the cloud condensation nuclei over the land are more numerous, or it may be because there are more giant cloud condensation nuclei (salt particles) in the air above the oceans. Large salt particles are superbly efficient cloud condensation nuclei. So it is possible that they just capture moisture so efficiently, that they leave less of it for the smaller nuclei. If this is the case, even adding a huge number of small nuclei into the clouds would not change things in a significant way. On the other hand, we do know that the tiny sulphur particles in ships' flue gases do give birth to marine clouds and often make the already existing clouds more reflective.

It would probably be a good idea to organize a series of small trials to find out, how well the approach works in practise. However, Salter's and Latham's 1,500 unmanned Cloud Maiden ships would probably cost between 2,500 and 4,500 million euros.

It might be cheaper to install spray-generating units on existing freight, passenger, research and pleasure ships. According to a very tentative calculation by the Atmosmare Foundation, a single spraying unit might only cost between 50,000 and 150,000 euros. The only problem with this approach is that freight and passenger ships tend to flock on densely populated shipping routes. There is often no lack of condensation nuclei along such marine highways, because the ships already produce a lot of sulphur dioxide. In other words the impact of each spray-producing unit operating along the main shipping routes would be relatively small. If some of the marine traffic would be dispersed, in order to combat global warming, the situation would of course change in a most dramatic way.