Washington - The Arctic was cooling for 1,900 years because of a natural change in Earth's orbit until greenhouse gas accumulation from the use of fossil fuels reversed the trend in recent decades, according to a study published Friday in Science magazine.

    Scientists reconstructed the temperature record of the past 2,000 years using evidence from tree rings, ice cores and lake sediment, and found a steady cooling trend in Arctic summer temperatures of about 0.5 degrees Celsius - 0.9 degrees Fahrenheit - during the first 1,900 years. The cooling was caused by a slow natural cycle in Earth orbit that continues in this century.

    "The summer cooling would likely be continuing today were it not for the increase of greenhouse gases from fossil fuel burning," said David Schneider, a scientist at the National Center for Atmospheric Research and one of the authors of the study. "The results are important in showing that the dramatic changes happening today - and particularly the rapidity of the changes - are not natural."

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George Monbiot | Not Even Wrong    â€¢

    Darrell Kaufman, a professor of geology and environmental science at Northern Arizona State University and the lead author of the study, put it this way: "The warmth in the Arctic during the second half of the 20th century, combined with the last decade, is striking against the backdrop of the previous 1,900 years. ... The second half of the 20th century was warmer in the Arctic than any other half-century of the last 2,000 years."

    Further, 1999 to 2008 was the warmest decade in the Arctic of any in that period, the report in Science said. Temperatures were about 1.4 degrees Celsius - 2.5 degrees Fahrenheit - higher than would have been expected if the natural cooling trend had continued.

    Scientists already knew that the Arctic is warming two to three times faster than the rest of the planet is.

    The new study gives a better understanding of how the climate system behaves over longer time scales, Schneider said. Previous studies with that level of detail went back only 400 years, and most of the record from thermometers in the Arctic dates back only about 50 years.

    "We have a lot more data than we had before, and better climate models for understanding that data," Schneider said.

    One of the most important findings from the study was that its findings matched the output of the National Center for Atmospheric Research's climate-system computer model, Kaufman said.

    "The climate model used in this study is among those that have been used to predict future climate. The match between our proxy temperature record and the climate-model output adds to our confidence in the model's ability to accurately simulate temperature responses to factors that influence climate change," he said. "This is especially important for the Arctic, where the influence of global warming is amplified."

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Not Even Wrong

Monday 31 August 2009

by: George Monbiot  |  Visit article original @ Monbiot.com

    We need a radical new approach to cutting greenhouse gases, and it might have arrived.

    At least - until a few months ago - government targets for cutting greenhouse gases had the virtue of being wrong. They were the wrong targets, by the wrong dates, and they bore no relationship to the stated aim of preventing more than two degrees of global warming. But they used a methodology which even their sternest critics (myself included) believed could be improved until it delivered the right results: the cuts merely needed to be raised and accelerated.

    Three papers released earlier this year changed all that. The first one, published in the Proceedings of the National Academy of Sciences in February, set the scene(1). It showed that the climate change we cause today "is largely irreversible for 1,000 years after emissions stop". Around 40% of the carbon dioxide produced by humans this century will remain in the atmosphere until at least the year 3000*. Moreover, thanks to the peculiar ways in which the oceans absorb heat from the atmosphere, global average temperatures are likely to "remain approximately constant ... until the end of the millennium despite zero further emissions".

    In other words, governments' hopes about the trajectory of temperature change are ill-founded. Most, including the UK's, are working on the assumption that we can overshoot the desired targets for temperature and atmospheric concentrations of CO2, then watch them settle back later. What this paper shows is that wherever temperatures peak, that is more or less where they will stay. There is no going back.

    The other two papers were published by Nature in April. While governments and the United Nations set targets for cuts by a certain date, these papers measured something quite different: the total volume of carbon dioxide we can produce and still stand a good chance of avoiding more than two degrees of warming. One paper, by a team led by Myles Allen, shows that preventing more than two degrees means producing a maximum of half a trillion tonnes of carbon (1830 billion tonnes of carbon dioxide) between now and 2500 - and probably much less(2). The other paper, written by a team led by Malte Meinshausen, proposes that producing 1000 billion tonnes of CO2 between 2000 and 2050 would deliver a 25% chance of exceeding two degrees of warming(3).

    Writing elsewhere, the two teams gave us an idea of what this means. At current rates of use, we will burn the ration that Allen set aside for the next 500 years in four decades(4). Meinshausen's carbon budget between now and 2050 will have been exhausted before 2030(5).

    There's another way of expressing these limits. The World Energy Council (WEC) publishes figures for global reserves of fossil fuels(6). A reserve means the minerals that have been identified, quantified and are cost-effective to exploit; in other words those that are more or less ready to be extracted. (The total amount of a mineral found in the earth's crust is called the resource). The WEC says that 848 billion tonnes of coal(7), 177,000 billion cubic metres of natural gas(8) and 162 billion tonnes of crude oil(9) are good to go. We know roughly how much carbon a tonne of coal, a cubic metre of gas and a barrel of oil contain. You can see the calculations and references at the bottom of this article: the result suggests that official reserves of coal, gas and oil amount to 818 billion tonnes of carbon.

    The molecular weight of carbon dioxide is 3.667 times that of carbon. This means that current reserves of fossil fuel, even when we ignore unconventional sources such as tar sands and oil shale, would produce 3000 billion tonnes of carbon dioxide if they were burnt. In other words, if we don't want to exceed two degrees of global warming, we can burn, according to Allen's paper, a maximum of 60% of current fossil fuel reserves by 2500(10). Meinshausen says we've already used one third of his 2050 budget since 2000(11), which suggests that we can afford to burn only 22% of current reserves between now and 2050(12). If you counted unconventional sources (the carbon content is much harder to calculate), the proportion would be even smaller.

    There are some obvious conclusions from these three papers. The trajectory of cuts is more important than the final destination. An 80% cut by 2050, for example, could produce very different outcomes. If most of the cut were made towards the beginning of the period, the total emissions entering the atmosphere would be much smaller than if most of the cut were made at the end of the period. The measure that counts is the peak atmospheric concentration. This must be as low as possible and come as soon as possible, which means making most of the reductions right now. Ensuring that we don't exceed the cumulative emissions discussed in the Nature papers means setting an absolute limit to the amount of fossil fuel we can burn, which, as my rough sums show, is likely to be much smaller than the reserves already identified. It means a global moratorium on prospecting and developing new fields.

    None of this is currently on the table. The targets and methodology being used by governments and the United Nations - which will form the basis for their negotiations at Copenhagen - are not even wrong; they are irrelevant. Unless there is a radical change of plan between now and December, world leaders will not only be discussing the alignment of deckchairs on the Titanic, but hotly disputing whose deckchairs they really are and who has the responsibility for moving them. Fascinating as this argument may be, it does nothing to alter the course of the liner.

    But someone, at least, does have a radical new plan. This afternoon the team that made the film The Age of Stupid is launching the 10:10 campaign: which aims for a 10% cut in the UK's greenhouse gas emissions during 2010. This seems to be roughly the trajectory needed to deliver a good chance of averting two degrees of warming. By encouraging people and businesses and institutions to sign up, the campaign hopes to shame the UK government into adopting this as its national target. This would give the government the moral leverage to demand immediate sharp cuts from other nations, based on current science rather than political convenience.

    I don't agree with everything the campaign proposes. It allows businesses to claim reductions in carbon intensity as if they were real cuts: in other words they can measure their reductions relative to turnover rather than in absolute terms. There's an uncomfortable precedent for this: cutting carbon intensity was George Bush's proposal for tackling climate change. As economic growth is the major cause of rising emissions, this looks like a cop-out. The cuts will not be independently audited, which might undermine their credibility with the government.

    But these are quibbles. 10:10 is the best shot we have left. It might not be enough, it might not work; but at least it's relevant. I take the pledge. Will you?

    References:

    1. Susan Solomon, Gian-Kasper Plattner, Reto Knutti, and Pierre Friedlingstein, 10th February 2009.

    Irreversible climate change due to carbon dioxide emissions. PNAS, vol. 106, no. 6, pp1704-1709.

    Doi: 10.1073/pnas.0812721106. http://www.pnas.org/content/early/2009/01/28/0812721106.full.pdf+html

    2. Myles R. Allen et al, 30th April 2009. Warming caused by cumulative carbon emissions

    towards the trillionth tonne. Nature 458. doi:10.1038/nature08019. http://www.nature.com/nature/journal/v458/n7242/full/nature08019.html

    3. Malte Meinshausen et al, 30th April 2009. Greenhouse-gas emission targets for limiting global warming to 2 °C. Nature 458, 1158-1162. doi:10.1038/nature08017. http://www.nature.com/nature/journal/v458/n7242/full/nature08017.html

    4. Myles Allen et al, 30th April 2009. The exit strategy: Emissions targets must be placed in the context of a cumulative carbon budget if we are to avoid dangerous climate change. Nature

    doi:10.1038/climate.2009.38. http://www.nature.com/climate/2009/0905/full/climate.2009.38.html

    5. Potsdam Institute for Climate Impact Research, 30th April 2009. On the way to phasing out emissions: More than 50% reductions needed by 2050 to respect 2°C climate target.

    http://www.pik-potsdam.de/news/press-releases/on-the-way-to-phasing-out-emissions-more-than-50-reductions-needed-by-2050-to-respect-2b0c-climate-target

    6. http://www.worldenergy.org/publications/survey_of_energy_resources_2007/default.asp

    7. http://www.worldenergy.org/publications/survey_of_energy_resources_2007/coal/627.asp

    8. http://www.worldenergy.org/publications/survey_of_energy_resources_2007/natural_gas/664.asp

    9. http://www.worldenergy.org/publications/survey_of_energy_resources_2007/crude_oil_and_natural_gas_liquids/638.asp

    10. On average, one tonne of coal contains 746 kg carbon - http://bioenergy.ornl.gov/papers/misc/energy_conv.html

    One cubic metre of natural gas contains 0.49 kg carbon - http://bioenergy.ornl.gov/papers/misc/energy_conv.html

    The figure for oil is less certain, because not all of its refinery products are burnt. But the rough calculation here suggests that the use of a barrel of oil releases 317kg of CO2 - http://numero57.net/?p=255. There are roughly 7 barrels to the tonne, giving an approximation of 2219kg CO2, or 605kg of carbon.

    So the carbon content of official known reserves of coal, gas and oil amounts to:

    848 x 0.746 = 633

    +

    177,000 x 0.00049 = 87

    +

    162 x 0.605 = 98

    Total conventional fossil fuel reserves therefore contain 818 billion tonnes of carbon.

    11. Potsdam Institute for Climate Impact Research, ibid.

    12. 667/3000.