Humpty Dumpty and the Global Climate System: A Weighty Analogy

Fragilecologies Archives
19 December 2005

Humpty Dumpty sat on a wall
Humpty Dumpty had a great fall
And all the King’s Horses and all the King’s Men
Could not put Humpty together again!
— Children’s nursery rhyme, Anon.

It is now obvious to most observers that the global climate has warmed up by almost a degree Centigrade since 1900. Glaciers around the globe are melting. Sea level is rising. Warm-temperature ecosystems are moving upslope of mountainsides to higher elevations as the lower atmosphere becomes increasingly warm. And now we are told that the percentage of Arctic sea ice reduction may have reached a “tipping point,” or a point at which there is more heat being absorbed by the dark-colored ocean waters than is reflected back by the lighter-colored sea ice.

Researchers expect the climate to continue on a warming trend throughout the 21st century. The Intergovernmental Panel on Climate Change, composed of a couple thousand scientists from around the globe, suggests that global temperatures can continue to increase by 2.5 to 5.8 degrees C by the end of this century. Some of this increase is the result of burning fossil fuels into the atmosphere and the release of other greenhouse gases (GHGs) as a result of land-use activities, the use of certain chemical fertilizers in agriculture, cement production, and the cutting down of tropical rainforests in Brazil and elsewhere. These are the human contributions to GHGs. There are also natural changes that occur as a result of warming, whether or not that warming is caused by people or by natural occurrences: the melting of Arctic sea ice, and the thawing of permafrost in the northern latitudes.

Once GHGs are in the air, they have a long residence time in the atmosphere — on the order of a century of more. So, we have already committed the atmosphere to additional warming, even if there were to be a drastic reduction today in the use of fossil fuels (coal, oil, and natural gas) and in tropical deforestation (forests absorb carbon dioxide; scientists say that they are a “sink” for carbon dioxide).

The point I want to raise is this: if by some major scientific breakthrough, we were able to reduce GHGs back to the 1900 level (or, for that matter, any other level of the 1900s), and global temperatures were reduced back to earlier levels, would regional and local climates return to be the same as they were at those lower levels? In other words, by controlling GHG emissions (either human-induced or naturally occurring), would we be able to return to the climate of 1900 — or, for that matter, to any other climate regime of the past that we might like? I have identified an analogy that suggests that the answer to that question is “no.”

The analogy I have in mind is a personal one. Many Americans today are very concerned about their body weight. Medical reports remind the public about their habits of overeating and about how overweight Americans are in general. I decided to see if I had the willpower to lose weight by returning to my weight when I was 26 years old (four decades ago). I managed to lose 17 pounds in a year. The loss of weight apparently came from different places on my body, such as my face and waist. People have since told me how my face looks thinner, making me look somewhat older. They suggested to me that I put those 17 pounds back. That got me to wondering: if I were now to add them back to my body, would they return to the same places where they were lost?

My gut feeling is that the 17 pounds would not necessarily go back to the places from where they originally came. By analogy, can one assume then that the regional climates, exhibited during a time of lower GHG concentration, will be restored as they had previously existed? The analogy to me suggests that the answer would be “no.” It forces me to question whether societies have put themselves on a proverbial “slippery slope” of climate change with unknown consequences and over which they have no control. In other words, I assume that there is no going back to a favored climate regime as the result of a policy to alter greenhouse gas concentrations in the atmosphere. Idyllic climates of the past may be a thing of the past.

Whether we like it or not, we are playing Russian roulette with global and regional climates. We have catalyzed changes in the climate system to such an extent that attempts to reverse those adverse changes and return to favored past climates will likely fail.