By Donella Meadows
–July 16, 1992–
For 20 years I’ve recorded the date of every first frost, first robin, first apple blossom, first sweet corn on my farm. My records show clearly that springs have been coming sooner and frosts later. I’ve come to count on a growing season almost a month longer than when I first moved here.
What happens on one small farm is no proof of a climate change for an entire planet. But I can’t help being impressed by my own experience. I believe in global warming.
If I believed ONLY my experience, however, I would be having doubts right now. Last July, after the warmest spring ever, the weather pattern suddenly snapped back to the 1970s. The first frost came the third week of September as it used to. This spring was as slow and cold as any in my records.
Scientists say that’s because the eruption of Mount Pinatubo in the Philippines last June threw enough ash into the atmosphere to make a cooling sunshade for several years. When the Pinatubo dust settles, the warming is expected to be back worse than ever.
If I had my way, I’d hold the climate right where it was pre-Pinatubo. But of course I don’t get to set the earth’s thermostat. We all do that together, by increasing or abating our output of greenhouse gases. It’s a tricky venture, because volcanoes and El Ninos jerk the temperature up and down and make it hard to get a firm reading. Furthermore, there are long delays between cause and effect. If we stabilized greenhouse gases today, the climate would go on changing for decades. The earth adjusts only slowly to disturbances in its heat balance.
Another problem with the idea that we can set the climate is that we deeply, profoundly don’t understand what we’re doing. The workings of the planet are complex. We’re assaulting it in many ways at the same time. Scientists are working hard to keep up, but they are still learning.
For example, they now think that the chemicals called CFCs may not contribute as much to global warming as was once believed. CFCs do erode the earth’s ozone layer — there is no disagreement about that. They are also strong greenhouse gases. Molecule for molecule CFCs trap the earth’s heat thousands of times more effectively than the more common greenhouse gas carbon dioxide. But their destruction of ozone apparently cancels out their warming effect, because the ozone they destroy is ALSO a greenhouse gas. CFCs undo just about as much heat-trapping capability as they create.
There’s another new theory about one kind of pollution cancelling out another, sort of. It seems that particulates released by human activity — smoke, ash, dust, sulfur dioxide — add up to a “human volcano” as powerful as Pinatubo. Particulates reflect the sun’s energy back into space and cool things down. They may explain why warming is more pronounced in the cleaner southern hemisphere than in the smokestack-studded north, and why warming is more apparent at night than during the day.
Though our airborne junk may be cooling us a bit, that’s not a cause for rejoicing. Greenhouse gases last much longer in the atmosphere than particulates and will eventually overwhelm them. Meanwhile the particulates, which occur mainly around cities, have their own spotty effect on the weather. Winds and ocean currents are propelled by small temperature differences. Scattered clouds of pollution could produce strange shifts. Thomas Karl of the National Climatic Data Center in Asheville, North Carolina, sums up the particulate effect by saying, “It’s pretty hard to say whether this is a godsend or a curse.”
These new findings suggest that global warming may come more slowly than scientists had thought. But the scientific community has also recently discounted two theories that there may be no warming at all — both quoted loudly by greenhouse skeptics. One was a suggestion by scientists at Scripps Institution of Oceanography that the sun might be cooling. The other was an idea of MIT meteorologist Richard Lindzen that high clouds in the tropics would limit warming. The 300-plus scientists from around the world who form the Intergovernmental Panel on Climate Change now take neither of these propositions seriously.
There’s another new idea that’s downright scary. It is the realization that the earth’s climate system is chaotic. It doesn’t change smoothly or politely. Rather, it seems to jump suddenly from one behavior pattern to another. Just such an abrupt (and unexplained) shift took place in the atmospheric circulation over the North Pacific in 1976, causing wild weather for a decade. That shift affected everything from storms in California to freezes in Florida. It was nothing compared to a worldwide, greenhouse-induced chaotic jump. If we keep putting out the greenhouse gases, they may produce more than a simple, gentle warming for New England farms.
Despite the constant revisions, greenhouse science does rest upon a solid foundation. Greenhouse gases are rising in the atmosphere. They do trap outgoing heat. Their main source is human fossil-fuel burning. No scientist questions those facts. How much warming will occur, how fast, with exactly what consequences — those are the areas where the surprises keep coming. The biggest surprise would be if humans could continue to put billions of tons of pollutants into the atmosphere with no effect at all.
Last spring the Royal Society of London and the U.S. National Academy of Sciences (not exactly hotbeds of radical scientific opinion) released a remarkable document in preparation for the Rio conference. It says, in part: “If current predictions of population growth prove accurate and patterns of human activity on the planet remain unchanged, science and technology may not be able to prevent either irreversible degradation of the environment or continued poverty for much of the world…. One issue alone, the increase in atmospheric carbon dioxide, has the potential for altering global climate with significant consequences for all countries…. The future of our planet is in the balance…. The next 30 years may be crucial.”
Copyright Sustainability Institute 1992
