Week 2 - Reflections on Past Climate Change 3-2-2014

 

      This discussion is for an assignment in Week 2 of the Climate Change course from Exeter University.  Section 2.8 asks for our reflections the week's topic, "Past Climate Change."
      This week's material  dealt with both ancient and more recent climate changes.   The significance of understanding these changes is that they are pathways to understanding what changes are occurring in our climate now, what trends we have set in motion, and to what kind of future climate these projected trends could lead.
      Ancient Climate Change:  One of the most interesting things about the history of Earth over the long haul is how the climate has "self-regulated" for most of that time to be habitable for life.  Consider: 

1. The age of Earth is about 4.5 billion years.
2. Earth has been covered in water for about 4.2 billion years.
3. Life on earth began as far back as 3.8 billion years ago.
4. The sun was 25 to 30% cooler then, which would work out to 44 degrees F. colder, and Earth would have been frozen.
5. However, it was actually warmer then, due to a higher amount of greenhouse gases--in particular, CO2 and water vapor.
6. So today, with the sun much warmer, we should be far hotter, but we are not.
7. The reason is that CO2 has been greatly reduced compared to 4.5 billion years ago, due to chemical and biological processes which transferred CO2 through the ocean and into sedimentary rocks.  The higher the temperature, faster this process occurred--so we have stayed within a range that supports life.

    However, there have been two "Snowball Earth" episodes, once 2.2 billion years ago, and again 700 million years ago.  In these episodes Earth froze over completely.  It is not known exactly what touched it off.  It is thought that ice completely covered Earth even at the equator, though there may have been more of a "slushball" effect in places.  In any case, when the 700-million-year-ago event occurred, life had only evolved to the level of very small organisms, all living in the oceans.  (After the thaw, the "Cambrian Explosion" of forms of life took place.)  The fact that life survived at all was one of the arguments against the theory that the snowball ever occurred.  That objection was not dispelled until rather recently, when it was discovered that in the Antarctic, there was enough light under 5 meters of ice--provided it was clear ice--to support photosynthesizing and eukaryotic life.
     A Russian researcher developed the Snowball Earth theory in the 1960's, having worked out mathematically that if the earth froze such that it reflected about half the sun's energy (equivalent to glaciers reaching to about Texas), there would be a runaway cooling effect.  He was unable to explain how the effect would not have remained permanent, so the theory was stalled for a while.  Finally by 1998 it was theorized and accepted that CO2 from volcanoes would have gradually accumulated in the atmosphere enough to start the thawing process.  Normally the CO2 would not have accumulated so much--see point 7 above--but the ice everywhere prevented the CO2 from being transferred into the earth's crust.  Of course, it took...  10 million years!
      The story above is quite simplified.  However, three things amaze me:
          1)  that such extremes can occur when a particular "tipping point" is reached, 
          2)  that the original mathematical prediction of runaway cooling was correct, and 
          3) that CO2 is such a powerful and long-term determinant of Earth's climate.
 
(Relatively) Recent Past Climate Change:  This deals with periods from several million to just the last few hundreds of years.  Some of the influencing factors are predictable, like changes in the Earth's axis, wobble, and orbit.  It takes about 100,000 years, for example, for the Earth's orbit to change from nearly circular to more elliptical and back again.  Other factors are unpredictable, such as cooling effects due to ash clouds from volcanic eruptions.   For example, the Medieval Warm Period (around 11th century) occurred during a period of increased solar activity.  However, it happened only in the Northern hemisphere, and was not part of a global effect.  The warm period was followed by the "Little Ice Age" for a few hundred years, and there is evidence of more volcanic activity at that time.   These climate changes were tiny compared to the ancient ones, but still they had major effects on European history.  Records like tree rings, ice cores and pollen samples help us recreate "recent" past climate changes.  

The present and future:  The dramatic temperature increase over the last 100 to 150 years cannot be explained by changes in solar activity or vulcanism.  The major predictive determinant is the rise in carbon dioxide.  
      One of the most striking things I learned from this week's recommended reading is that today's warming is happening at a very fast rate compared to climate changes of the past.  It is useful to compare today's rate of change to the rate of warming at the end of the last ice age.  Part of NASA's website, called "Earth Observatory," notes that over the last century, global warming is happening five to ten times faster.  The prediction of next century's warming is that it will happen at a rate twenty times faster than when the last ice age ended.

      One final note from my own further web-exploring:  http://www.truthdig.com/report/item/carbon_output_will_climb_29_by_2035_20140208

     BP’s Energy Outlook 2035 says CO2 emissions are likely to increase by 29% in the next two decades because of growing energy demand from the developing world.