Wildfires am cooling Bizarro-Earth!

Australian fires had bigger impact on climate than covid-19 lockdowns: the fires had a cooling effect while reduced pollution from lockdowns exerted a slight warming influence.

"Beyond their effect on local weather, wildfires are becoming large enough, and intense enough, to have a material effect on climate," said John Fasullo, the lead author of the study. "In this work, we demonstrate their potential to influence climate variability. We are still in the process of understanding other aspects."

Fasullo and his colleagues concluded that the 2019-2020 Australian wildfire season resulted in 0.1 degrees Fahrenheit of cooling by mid-2020. The cooling, however, was tacked atop a continued net warming of the climate and had a negligible effect on slowing the pace of human-induced climate change from fossil fuel burning. [...]

The most intense wildfires produced pyrocumulonimbus clouds, or enormous plumes of smoke, ash and other aerosols, like sulfur dioxide, that towered to heights of up to 19 miles. Those fire-induced mushroom clouds ejected aerosols into the stratosphere, which surfed the jet stream eastward and gradually dispersed. The result was a volcano-like cooling of the global climate.

Smoke from wildfires has a range of effects on the Earth's climate. Black carbon actually absorbs solar radiation and heats the atmosphere, while other organic materials reflect or scatter light, yielding cooling. Smoke occasionally helps seed cloud development, blocking incoming sunlight but also retains outgoing heat. Sulphur dioxide aerosols can be converted into sulfuric acid, blocking incoming sunlight and also contributing to the destruction of ozone. Researchers noticed a "localized stratospheric ozone-hole."

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7 Responses:

  1. malcolm says:

    That reporter should be shot. To imply that a geophysicist's fingers would type the word "Fahrenheit" is gross impudence.

    At least the WP had the decency to link to the article, which as expected reports things in SI units...

    • Nick Lamb says:

      You weren't wrong:

      "anomalous global cooling of 0.06+-0.04 K" and "gradual global warming of 0.05+-0.04 K"

      I suspect that most of the target audience for this piece do not have any intuitive reference that would help them think about 0.05 K. Try this, you (the person reading this) are about 310 K now. 1 K is the difference between normal and fever (311K) or hypothermia (309K). So, yeah, 0.05K isn't a lot of change, unless of course we kept going in one direction...

      • Carlos says:

        1 relative degree Kelvin is identical to 1 relative degree Celsius, with nominal body temperature being 37C / 310K. Sorry to break it to you, but 36C isn't hypothermia, and 38C isn't a fever - they're both within the normal distribution of body temps.

        Hypothermia is core body temp below 35C.

        • Nick Lamb says:

          A "degree Kelvin" isn't a thing any more. There's no need for "degrees" of an absolute system, we don't have "degrees litre" or "degrees ampere" and we don't need "degrees Kelvin" either. You're also going to want to buy a thermometer that measures in smaller increments than a whole degree Celsius for measuring your body temperature. A broad scale is fine for your greenhouse, oven, or freezer, but not for figuring out whether to give your two year old Calpol.

          We live on a knife edge and so does the planet. I used human core temperatures because invariably someone wants to compare this to weather instead and we're used to the outside air temperature varying considerably without much of an issue. Whereas if your core temperature changes by a whole 1K you really will know about it (despite your misplaced confidence that 35°C and 38°C would both be fine), and the planet's climate is the same.

  2. ContextSans says:

    Huh, I wonder if the constant barrage of pyrocumulonimbus could net us something like The Year Without A Summer (which coincidentally brought us the novel Frankenstein).

  3. tfb says:

    This is just the same thing as a nuclear winter, or the aftermath of big impact events, where a very energetic event actually ends up causing cooling because it lofts so much crud into the atmosphere. The Chicxulub impact seems to have been equivalent to about a 5 petaton nuclear device, but probably one of its main longer-term effects was serious medium-term cooling, although there would have a lot of short-term heating: if I'm right that energy is more than 3 years worth of the TOA Solar flux, which is ... a lot, by anyone but astrophysicists' standards.

    One of the particularly nasty ways we're all fucked is that we've dumped enough CO2 into the atmosphere to cause a lot of warming, but we also puke smoke and other crud into it which tends to cause cooling while it's up there. But the crud doesn't stay up for long, while the CO2 does. So if we make things cleaner we start seeing more of the warming effect from the CO2, until the forests burn and dump more crud up there (but also dump lots of nice CO2 there too of course). The future is so bright.

  4. Sparge says:

    The article refers to sulfur dioxide as an aerosol multiple times. It's not. There are sulfur aerosols consisting of water and sulfur dioxide, but that's not the same thing.

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