More sulphur trails from the stratosphere

 
Plot of Calipso readout The Calipso lidar measures backscatter from aerosol particles at different heights in the atmosphere

Tiny aerosol particles in the atmosphere are perhaps the second most important way - after greenhouse gas emissions - in which human activities are changing the Earth's climate.

But changing it how?

The last major Intergovernmental Panel on Climate Change (IPCC) report in 2007 concluded that aerosols "remain the dominant uncertainty in radiative forcing" - partially because of the direct effects the particles have, such as reflecting and scattering the Sun's energy, and partly because they can affect cloud formation.

Since that report was compiled, researchers have gone deeper into the known unknowns of aerosols - one of the main aims being to build a picture of how they behave naturally, in order that any man-made perturbation can be more accurately assessed.

The satellite era has made things easier, with instruments on board orbiting platforms such as Calipso deploying lidars and other instruments capable of sensing how much material is present at what kinds of altitudes.

But still, obtaining a global picture is not easy - and to make things worse, observations have begun in earnest during the very period in which human activities are changing the atmosphere's aerosol load.

But scientific groups are on the case.

A couple of weeks ago, we had some insights into how increased coal-burning - notably from China - could be pumping the stuff into the atmosphere so quickly as to ameliorate the temperature rise from greenhouse gas emissions.

Calipso satellite Calipso has brought more accurate and more global measurements of aerosols

Last week, a different research group unveiled new findings on the impact of volcanic eruptions, which pump vast amounts of particles into the air, some rising as far as the stratosphere.

The conclusion was that volcanoes may have a greater cooling effect than previously recognised.

And this week, in Science, comes a fresh analysis of aerosols in the stratosphere itself, and their impact on global temperatures.

The top line message is that the increase in concentrations over the "noughties" has partially masked temperature rise - similar to the conclusion of the research released two weeks ago, but using a radically different line of inquiry.

And climate models, the researchers say, mostly understate the impact of aerosols in the stratosphere, so may be projecting that temperatures will rise faster than they actually are.

Volcanoes have massive impacts on the stratospheric load of these tiny sulphate particles. But they're fairly short-term, producing stark spikes that decay away after a few years.

But the background aerosol concentration is also changing, the researchers find - for reasons that are not immediately obvious.

When I called one of the researchers, Ells Dutton from the National Oceanic and Atmospheric Administration (Noaa), he described the top line message as "relatively mild".

"When you account for this additional aerosol that's not been accounted for previously, that weakens the overall net forcing that existed over the 2000s.

"So the positive forcing was partially negated by this negative forcing, so you'd expect warming to have been less."

Pinatubo plume Plumes from tropical volcanoes spread, and enter the stratosphere

But there are also things it doesn't tell us.

The sources could be entirely natural; "but if you then ask whether some of the Chinese stuff is getting into the stratosphere, it could be - we can't sort that out."

Another question is this; if all or most of the sources are natural, what are those sources, besides vulcanism?

So, lots more to research - and one potential implication outside the realm of understanding climate change.

The cheapest of all geo-engineering techniques yet conceived involves putting multiple tonnes of this stuff into the stratosphere, where it would reflect sunlight back into space, cooling the Earth's surface.

Controversial, of course; but a number of eminent people such as UK renewable energy pioneer Stephen Salter suggest that research should begin in earnest, because they don't believe our society is going to curb greenhouse gas emissions at anything like the rate needed to slow global warming.

Mt Pinatubo's caldera Data on stratospheric aerosols have largely come from studying volcanoes such as Pinatubo

Clearly, if this is ever to be attempted, understanding how the particles will behave in the upper atmosphere would be of paramount importance.

David Keith from the University of Calgary, one of the leading lights in the field, told me this: "I don't see any strong implications for solar geo-engineering, [but] it may help to dispel naive assumptions that solar geo-engineering would be an all or nothing affair.

"In fact, if it ever did make sense to try it, it would make sense to try incremental additions of sulphur coupled with an intense observation campaign that looked for problems."

It's interesting to note by comparison how another geo-engineering option - iron fertilisation of the oceans - has been investigated in practice.

The mass of evidence generated over more than a decade of experimentation has told researchers a lot about the various things that are likely to determine how well it works - and the biggest trial of all, the German Lohafex project, suggested it might not work at all.

By comparison, our knowledge about sulphate aerosol injection is tiny.

The title of the Science paper - The Persistently Variable "Background" Stratospheric Aerosol Layer and Global Climate Change - is well-chosen in that it indicates both that significant research has been done, and that the findings it's produced are somewhat frustrating - and honestly given as such.

 
Richard Black Article written by Richard Black Richard Black Former environment correspondent

Farewell and thanks for reading

This is my last entry for this page - I'm leaving the BBC to work, initially, on ocean conservation issues.

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  • rate this
    -1

    Comment number 35.

    Why are scientists not considering water vapor as the major greenhouse gas that is transforming climate?

    Water vapor increase in atmosphere is the logical result of retreat of ice sheets or the melting of the polar caps. It is also the outcome of global deforestation, a human activity, that has not been given due consideration as to its impact on climate. Water is the cause of climate change.

  • rate this
    0

    Comment number 34.

    @19
    @32
    goo.gl/Oj62Y (URL: Die Welt article)

    Quote from CERN's Heuer: "You have to be clear that concerning cosmic rays it is only one parameter of many."

    Considering how many variables humans are actually influencing directly (temp., humidity, aerosols, carbon-soaking processes and biodiversity etc.) I seriously doubt cosmic rays to be a force majeure. It's just another variable.

  • rate this
    0

    Comment number 33.

    @Asopus #31:

    I've been gathering evidence for the existence of the Tooth Fairy for the last 15 years. So far, nobody from the 'sceptic' side has offered any valid counter-evidence. Pathetic!

  • rate this
    -1

    Comment number 32.

    @19 Ah. So easy to say everything is down to mankind.

    Didn't the earth come into being, evolve with lakes of sulphurous lava and mud long before man existed?

    The article mentioned (in Die Welt) was about professional research by scientists at Cern.

    It may turn out that it indicates a lot more of the "effects" that your refer to may have more natural, solar or even interplanetary causes.

  • rate this
    0

    Comment number 31.

    The first book I read on AGW dated from nearly 15 years ago and stated that aerosols were the greatest area of uncertainty. So I wonder who from the "sceptic" side has been researching that area in that time - nobody. Now genuine scientists are are doing what scientists do - narrowing uncertainty - the response of the deniers here are just expressions of personal incredulity. Pathetic.

  • rate this
    0

    Comment number 30.

    Those states affected by the new EPA rule must also reduce emissions of nitrogen oxides (NO x ), which are precursors to ground-level ozone, or smog, & contribute to fine particulate pollution. The goal (along with other state actions), will reduce SO2 by 73% and NO x by 54% from 2005 levels by 2014.

  • rate this
    0

    Comment number 29.

    Pollution in the eastern half of US will be slashed under a rule EPA. New rule is designed to prevent drift of harmful, airborne pollution from one state to another state. Regulation affects 28 states, mainly in the East and Midwest. Starting in 2012, power plants in 23 states from Texas to New York must curb emissions of sulfur dioxide, a component of fine particulate pollution.

  • rate this
    +2

    Comment number 28.

    22. Peter317
    3 HOURS AGO
    @John Russell #3:

    That'll teach me. I gave it a +1 as I thought it was a great satire.

  • rate this
    -1

    Comment number 27.

    @24 Peter317

    Carbondioxide is like fire under the kettle; it adds (solar) warmth to the atmosphere.
    Maybe 100 GJ this year, but another 100 GJ next year and another 1000 this decade.
    Even if emissions stopped right now, existing CO2 wil keep on raising the temperatures on Earth for the coming decades.
    Temperature change starts small, yes..

  • rate this
    -1

    Comment number 26.

    @24 Peter317

    Carbondioxide is like fire under the kettle; it adds (solar) warmth to the atmosphere.
    Maybe 100 GJ this year, but another 100 GJ next year and another 1000 this decade.
    Even if emissions stopped right now, existing CO2 wil keep on raising the temperatures on Earth for the coming decades.
    Temperature change starts small, yes..

  • rate this
    -1

    Comment number 25.

    It is astonishingly boneheaded of the denialists to call this research in aid of their fantasies. It's as if they were claiming that hypothermia wasn't a problem, as long as you had a raging fever. Both can kill you, though your thermometer might be (briefly) fooled.

  • rate this
    +2

    Comment number 24.

    @John Russell #19:

    "Our emissions are unbalancing the carbon cycle"

    say what??

    "and this means the planet must warm in response"

    Few deny that. The BIG question is by how much. Empirical evidence suggests very little.

  • rate this
    -3

    Comment number 23.

    Despite a lot of verbal flak from those individuals who discount expert opinion on climate change, the consideration of massive Chinese coal burning and aerosols indicates that warming is very likely a lot worse than measurements indicate and that the future of climate change is more perilous and immanent. Stephen Salter is likely right about having to consider options beyond CO2 reduction.

  • rate this
    +4

    Comment number 22.

    @John Russell #3:

    So let's get this straight - you feel no shame in milking me and other taxpayers for your FIT payments, which really do nothing except feed your pocket, but heaven forbid that anyone do anything which might actually mitigate a severe global problem, that is IF it is a severe global problem - which if it's not then you have less than no justification for taking money from us.

  • rate this
    -1

    Comment number 21.

    Re #1: "Danger to the planet"

    That's a very alarmist thing for a climate skeptic to say.

    Shouldn't you be arguing that stratospheric sulphur emissions would be fine? Shouldn't you be arguing that dangers from sulphur emissions are based on models and therefore are not proven?

    Youd scream murder if anyone suggested 30 billion tons of uncontrolled CO2 emissions were a "danger to the planet"

  • rate this
    -1

    Comment number 20.

    @14 Labmunkey

    Actually it is!
    Sulpher-content in coal vary between 0.5 and 6.5 %

    P.S. The cooling effects are only temporary. As some of you may know; these are highly polar molecules who readily dissolve in atmospheric water and the oceans.

  • rate this
    +2

    Comment number 19.

    @costmeabob

    So humans dig up and burn 7bn tonnes of coal and 30bn barrels of oil each year thus pushing up CO2 concentrations in the atmosphere from 280 to 390 ppm in just 120 years -- and you're suggesting that humans are not contributing to climate change?

    Our emissions are unbalancing the carbon cycle and this means the planet must warm in response. Anything else is not physics.

  • rate this
    -1

    Comment number 18.

    If you go to the IPCC website, Richard refers to Figure TS5 in the technical summary to Working Group 1 of IPCC 2007 you will see a a series fo error bars produced on radiative forcing and a column labeled LOSU (Level of Scientifc Understanding)

    No 'con', it's there printed in colour, work peer reviewed, freely available for you to look at. The equations to create are in IPCC 2001.

  • rate this
    -1

    Comment number 17.

    Think of all the taxes they will raise for the mass burning of Sulpher.
    I'm not going to pay for that..
    You know what? I'm going to buy a solar-panel instead.

  • rate this
    +2

    Comment number 16.

    don't forget the effects found in the CERN CLOUD project.
    the results are to be "kept quiet" from climate change modelling because they might undermine the "man-made argument". May be natural cosmic processes contributing to the effects discussed here. translate for yourself. [Unsuitable/Broken URL removed by Moderator]

 

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