Climate Time Lag of the Mt. Pinatubo Eruption

On June 15, 1991 Mt. Pinatubo in the Philippines erupted over the course of 9 hours.  That single eruption had a measurable impact on the Earth’s temperature for three years after the eruption.  This is a very good case for studying how quickly the Earth’s temperature responds to changes in the climate system.  The time that it takes for the Earth to respond matters a great deal in the climate debate.  A quick response would indicate that even if CO2 does cause warming of the Earth’s climate, the effects are felt quickly and and not delayed far into the future.  This would indicate that the full effects of 390 ppm of CO2 are in full effect and that the warming is already fully realized for the current emissions of CO2.

The Inconvenient Skeptic

Mt. Pinatubo Erupting

The eruption is useful for measuring the time lag because it is an event that happened at a single instance and then stopped.  In engineering terms there was a step (or a single pulse) function change to the Earth’s atmospheric system on that date in June.  The peak altitude of the eruption was 34 km (21 miles).  The height of the eruption is what allowed the SO2 to reach the stratosphere.  Once there it was able to slowly spread out and cover the entire Earth at the stratospheric level.  This is why the eruption of Mt. Pinatubo had such an impact on the Earth’s climate.  If the gas stayed in the much more humid troposphere it would have mixed with water and dissipated from the atmosphere much more quickly.  Since it was in the dry stratosphere it stayed there for much longer.

This is evident in that the eruption only released 17 million tons of SO2.  While that seems significant, it is comparable to the amount of SO2 released annually by the United States in 1991.  The only difference is altitude.  Much of the gas from the eruption reached the upper atmosphere and so it was able to spread globally there.  That is why injecting SO2 into the stratosphere is one of the ideas floated by warmists to combat global warming.

Once in the stratosphere the SO2 did slowly mix with water vapor to form H2SO4 (sulfuric acid), but in the stratosphere there is no precipitation to allow for it to be quickly removed.  So it stayed there in a mix of SO2 and H2SO4.  Satellite studies show that until the end of July 1991 the effects stayed mostly in the equatorial region of the world, but after that the cloud spread further and further around the world.  By early 1992 the concentration of SO2 and H2SO4 had increased around the world in the stratosphere to a small degree.  By June of 1992 after a full year the cloud of sulfur gases had completely blanketed the Earth.  This is also evident as the winter of 1992 saw the largest ozone hole ever recorded in Antarctica.

As the tropics had the gas cloud first it was the first to show a significant temperature effect.  From June to Oct of 1991 the temperature anomaly of the tropics decreased by 0.7 °C.  The concentration in the tropics decreased as the gas spread to other portions of the atmosphere.  This helped the temperature in the tropics recover to normal anomalies.  The rest of the world experienced the main cooling as the concentration of the gases helped reduce the amount of energy from the sun that reached the ground.

The Inconvenient Skeptic

In the 4 months after the eruption the average temperature in the tropics dropped 0.7C. This strongly shows how quickly the Earth's temperatures respond to a change in the climate.

As the gas cloud reached its maximum size and concentration a year after the eruption, the strongest effect of the cooling was felt.  July-September of 1992 showed a world that was about 0.5 °C cooler than the year before.  The rate of temperature change for the 13 month period from the eruption was -0.03 °C/month.  A rate of cooling that strong over a 5 year period would drop the Earth’s temperature by almost 2 °C.  That effect was felt as quickly as the gas cloud spread from the point of the eruption.  The time lag was negligible for this event.

The Earth also warmed up at the same rate that the gas cloud dissipated.  In late 1993 the concentration of the cloud in the atmosphere was greatly weakening and that also shows in the global temperatures.

The Inconvenient Skeptic

The rate of temperature change matches the time periods associated with the spread of the gas cloud and its dissipation. In both the cooling period and the warming period there is negligible time lag. In other words there is almost no delay between cause and effect.

This is a great case study of how quickly the Earth responds to a change in the climate.  Radiative Heat Transfer is a fast response mechanism and there is no basis for the idea that it would take decades for warming to take place for any given change to the greenhouse gases in the atmosphere.  It did not take a decade for the Earth to cool from this eruption.  It took 4 months for the cloud to spread around the tropics and drop the average temperature anomaly by 0.7 °C.

There is no evidence for the idea that it takes the Earth a long time to respond to changes in radiative energy.  There is overwhelming evidence that the Earth changes within a matter of months to those changes.  While this case does show that the Earth’s climate can be disrupted, it also shows that the response is almost instantaneous.  The theory that it takes longer than a few months for warming to take place as a result of a change in the Earth’s atmosphere has no basis.

Posted in Climate and Radiative Heat Transfer by inconvenientskeptic on March 1st, 2011 at 2:33 pm.


This post has 7 comments

  1. Richard111 Mar 3rd 2011

    Currently high pressure over the UK. BBC met forecasts no longer predict minimum temperatures, only maximums. At bedtime last night the outside temperature was +1C with no cloud and no wind. Advised my wife to do her frost precaution stuff on the new plants.
    Sure enough this morning the outside temperature is -2C and there is a hard frost.
    My question then is did the water vapour freezing out of the air provide a positive feedback to the temperature drop?
    This indicates a pretty rapid response to a change in GHGs in the atmosphere. Just a few hours.
    There is a largish estuary nearby, Milford Haven, which has just had three consecutive days of sunshine.

  2. Richard111 Mar 3rd 2011

    The frost this morning got me thinking. I don’t know when it formed but is was certainly present at 6:00am local time and lasted until full sunlight fell on any frosted surface. The melt time eppeared to be less than a minute. I looked at some of the frost through a magnifying glass and saw it was made of tiny thin crystals poking up every which way, a bit like early morning beard fuzz.
    I attemped to measure the length of the crytals with a small steel rule, not very good, but recon most of the crystals were just under 2 millimetres in length.
    Personal observation confirmed these crystals existed for about 3 hours before sunlight melted them.
    My question: Why didn’t “backradiation” from the GHGs in the air melt these tiny crystals before the sun arrived? Or even cause them to sublimate away?

  3. Gene Zeien Mar 3rd 2011

    Richard111 Mar 3rd 2011
    My question then is did the water vapour freezing out of the air provide a positive feedback to the temperature drop?

    Quite the contrary, when relative humidity reaches 100%, the temperature drop slows dramatically. As the vapor condenses or freezes out of the air, the humidity drops and the temperature can drop further. If the wind is blowing, the whole dynamic changes 😉

  4. inconvenientskeptic Mar 3rd 2011

    My question then is did the water vapour freezing out of the air provide a positive feedback to the temperature drop?

    As Gene says if there is ongoing cooling and the humidity reaches 100% the rate of cooling decreases. If one assumes that the rate of energy loss stays the same (generally safe assumption) then instead of just changing temperature, the heat of fusion or vaporization of water vapor also needs to be considered. That causes the rate of cooling to decrease. That is why there is a lower daily temperature range in areas with high humidity compared to ones without. Well, also less heat loss because the effective temperature of the sky is warmer with high humidity.

  5. inconvenientskeptic Mar 3rd 2011

    Why didn’t “backradiation” from the GHGs in the air melt these tiny crystals before the sun arrived? Or even cause them to sublimate away?

    Backradiation is part of a two part equilibrium. The object with a higher temperature gives energy to the body with the lower temperature.

    In the night time frost condition the Earth is giving energy to the cooler atmosphere. The means the Earth is losing energy faster that it is gaining and hence the temperature drops and frost forms.

    The sun simply transfers energy to the surface and frost is gone. Notice that the high albedo of frost doesn’t help either.

  6. Richard111 Mar 6th 2011

    Thanks John, and Gene, I think I have it now. Looking up my notes I see:
    “The isothermal melting of ice requires some 334 kilojoules per kilogram at 273.16K”

    And that frost, ice crystals with large surface area, will be radiating at some 300W/m^2 up into the atmosphere. Any downwelling “forcing” from clear skies will be lost.

  7. Malaga View Mar 6th 2011

    Interesting post…

    The down leg kicks in quickly…
    but the climb back takes about twice as long.

    The 1991 Pinatubo eruptions released an estimated 6 to 16 cubic km of ash… so it was a relatively small VEI 5 or 6…

    The Tambora eruption in 1815 was at the low end of the VEI 7 classification with an estimated ejected volume of 160 cubic kilometres… and that caused the year without a summer in 1816.

    The last VEI 8 was Taupo about 26,500 years ago… but I don’t want to think about what resulted from that eruption.

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