Volcanoes Cooled Earth Less Than Thought

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By Becky Oskin

 

Global cooling caused by some historic volcanic eruptions wasn’t as extreme as climate scientists recently thought, according to newly revised ice core records from Antarctica.

Volcanic eruptions blast sulfur-dioxide gas into the stratosphere, where it turns into tiny particles called sulfate aerosols that reflect the sun’s energy and cool the Earth. Snow falling in Antarctica records the levels of sulfate in the air at the time, and it eventually becomes ice drilled by researchers in long, tubular cores.

Researchers have measured sulfate concentrations in 26 ice cores from 19 different locations in Antarctica that cover the last 2,000 years of Earth’s history — the best record yet, the researchers said. The team synchronized the sulfate records with ice cores from Greenland, to determine if the eruptions had a truly global effect.

Along with finding previously unknown volcanic eruptions in the ice cores from before A.D. 500, the researchers discovered that some historic eruptions weren’t as hard on the planet as earlier climate models suggested.

Sorting out these signals helps improve climate models, said Michael Sigl, a climate scientist at the Desert Research Institute in Reno, Nevada, and lead author of the study, published July 6 in the journal Nature Climate Change.

The team identified 116 volcanic eruptions in the ice cores from the nearly 20 sites covering the past 2,000 years, including historic events such as Tambora in 1815, Kuwae in 1458 and Samalas (or Mount Rinjani) in 1257. Not all of these 116 eruptions are recorded in Greenland’s ice cores, but for their next project, the researchers are planning to assess sulfate levels in the Greenland cores.

“I think there will be more tropical eruptions there than we can detect at the moment,” Sigl said.

 

6 COMMENTS

  1. Volcanism always produces a double effect.
    It produces fine ash dust and sulphates which produce short-term local or global cooling, (depending on the extent of the spread and volume of ejecta).

    They also erupt large volumes of CO2 which produce greenhouse warming over a longer period.

  2. True but as NDGT pointed out in Cosmos, volcanism contributes to only a small fraction of the total CO2 poured into our atmosphere every year (just in case some climate denier is thinking about using your statement as “proof” that global warming is natural and not man-made).

  3. (just in case some climate denier is thinking about using your statement as “proof” that global warming is natural and not man-made).

    Sorry if I appear pedantic calling you out on a single point but global warming (lets call it climate change) does occur through entirely natural processes. In fact, based on the actual evidence, it would be highly unusual if climate wasn’t changing through entirely natural processes, given that the data suggests that climate is pretty much in a constant state of change.

    Based on the actual data, some of these natural changes have occurred very rapidly in geologically recent (almost historic!) times. The Younger Dryas (the most recent significant glaciation event) is a great example of this, where temperature swings of >5 degrees Celsius over time periods of 50-100 years have been recorded based on ice core data, which are also backed up by similar results (5.5 to 9 degrees temperature shift in <200 years) from lake sediment core data. The IPCC recognise major recent events with warming of up to 8 to 16 degrees Celsius occurring over timeframes of a few decades in extreme cases. These ‘global warming events’ were all entirely due to ‘natural’ causes, with outcomes (in terms of temperature change/climatic effect/sea level effects) that are up there with many ‘worst case’ predictions for the effects of current anthropogenic global warming.

    I’m not pointing this out to deny AGW – I’m a firm believer that as a species we should limit our impact on the biosphere as much as possible for the benefit of the rest of the planet. But in driving the debate forward we should at least aim to be realistic in addressing the actual data. This means accepting the data for ‘natural’ as well as ‘man made’ causes of climate change. Otherwise we begin to sound just as dogmatic and keen to ‘cherry pick’ data to fit our agenda as the ‘climate deniers’.

    • Steve_M Jul 10, 2014 at 4:09 pm

      But in driving the debate forward we should at least aim to be realistic in addressing the actual data. This means accepting the data for ‘natural’ as well as ‘man made’ causes of climate change.

      I have made the point many times in arguments with deniers, that physics is physics, and CO2 has the same effect in the atmosphere, regardless of if it comes out of a volcano, out of a natural peat fire, or out of a factory chimney.
      AGW is of course about the additional warming from billions of tons of man-made CO2 in addition to the baseline of the natural cycles.

      When there are rapid natural changes, this is usually because the natural cycles have lined up to all push temperatures in the same direction, or where there has been a major cataclysmic event such as the KT meteor strike. http://en.wikipedia.org/wiki/Cretaceous%E2%80%93Paleogene_boundary

  4. Thus, as one would expect, sulfate aerosols are trapped in the snow that falls on the poles and the land nearby them. Now, I wonder if the winds are important in this process of deposition. Since the system is composed by fixed points (the volcano erupting and the poles), what if the direction of the winds in the specific region of the eruption leads the particles away from the poles? In this case, the effect of the eruption could be underestimated, right? It may seem a silly question, and maybe it is… I don’t know if the aerosols produced by an eruption are homogeneously distributed through all the atmosphere or not.

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