Note to readers: This is the third and final part of this commentary on climate change.
The Earth's climate has changed throughout its history; could all the "evidence" of global warming simply be the result of natural variability, and the observed increase in carbon dioxide in our atmosphere simply be irrelevant? The bottom line here is that natural variability is a possible but unlikely explanation. There are at least three reasons:
1. Time scale. Natural changes in climate typically take thousands to millions of years to occur, but the current evidence suggests significant changes over centuries, even decades. The gradual descent towards our current Ice House climate, for example, took tens of millions of years. The alternation between Ice Age climates, in which ice sheets grow and advance over land and those in which they retreat, takes thousands of years, though unstable climate events have occurred over hundreds of years. If the glacial retreat enjoyed by prehistoric humans beginning some 20,000 years ago is due to be followed by another glacial advance (i.e. if we are still in an Ice Age), it will be thousands of years before we suffer from glacially cold climates.
2. Coincidence? - I think not! An increase in the severity of hurricanes could be the result of natural fluctuations, as could heat waves, or droughts, or a decrease in the numbers of some species, or any one of the possible indirect effects of a supposed warming, as could the observed increase in global average temperature itself. But the fact that all of these effects are taking place is consistent with one single cause -- global warming -- and unlikely to be the result of a variety of unrelated factors that all 'just happen' to be fluctuating in the same way now.
Natural variations are most certainly also occurring. The 1960s and 1970s were indeed cooler, snowier times (when I arrived in Binghamton in the late 1970s, it appeared as if we had re-entered the Ice Age!). But that fluctuation is superimposed on a trend of warming dating back to at least the mid-1800s. And regardless of those mid-20th century temperature variations, by the 1990s the trend had sharply increased, and still dominates the temperature picture completely.
3. The warming is predictable. Climate science can directly tie the observed global warming to the increase in carbon dioxide (and other greenhouse gas) emissions from human activity. Scientists have been using supercomputers to model the Earth's climate system for decades -- a daunting task because the models must account for the heat input from the Sun, the resulting circulation of the atmosphere (winds and high- and low-pressure weather systems), and the associated circulation of the oceans, the latter including currents driven by both winds and heating effects, plus the feedback effects of warm ocean waters on the overlying atmospheric circulation. Until 1996, however, supercomputer models attempting to project the effects of carbon dioxide emissions on the global average temperature failed, predicting an increase twice as large as what is observed.
Climate scientists, perhaps more than anyone else, have always been aware of how complex the Earth system is. But it was particularly mind-expanding to discover that air pollution (e.g. from burning coal) has become so widespread that tiny flakes of sulfur compounds, floating in the atmosphere world-wide, have been able to reflect enough sunlight back into space to counteract global warming with some global cooling (a lesson we would do well to remember: any global-scale experiments we humans might consider performing on nature are not likely to remain controlled experiments!).
Since 1996, then, supercomputer models of the climate system have been able to reproduce the observed increase in global temperature, by inputting into the models the observed increase in greenhouse gases and the observed increase in sulfur pollution.
These three reasons are not rock-solid proof of global warming. For instance, the supercomputer models may still be incomplete; and their spatial resolution may not be sufficient to represent all of the regional physical processes and underlying atmospheric 'micro'-physics needed for accurate predictions. And, though most natural shifts in climate have been long-term, there have also been some short-term changes in climate unrelated to global warming. One example of this is the "Little Ice Age," which afflicted North America and Europe from the 14th into the 19th centuries, possibly beginning and ending over a span of decades. (Connections of this cold spell to unusual behavior of the Sun at the time suggest that its rapid start and finish are associated with solar forcing, and thus - if solar radiance has not been trending up over the past few decades -- its relevance to current global warming is doubtful.
This issue is clouded, however, by ongoing debate about the satellite data measuring variations in solar radiance, in part because of the way the data is analyzed and in part because some leading solar scientists have joined with political think-tanks to disseminate anti-global warming literature falsely claiming to be from established scientific journals. Few climatologists or other Earth scientists have been involved in such activities, to my knowledge.)
As frustrating as it might be that Earth science cannot demonstrate the reality of global warming with 100% certainty, it is worth noting that no science -- by design -- is 100 percent certain. Scientific theories and laws are meant to be treated merely as the best explanations for the time being, until subsequent observations, experiments, and understanding prove them wrong and suggest better explanations. But clearly there is a lot of evidence that would have to be refuted, dismissed, or otherwise explained away for scientists to discard global warming as its single, common explanation.
The trouble with Kyoto
Recognizing the probability and potential severity of global warming and its consequences, representatives from 159 nations met 10 years ago this month in Kyoto, Japan, to decide on a way to deal with the threat. Their focus was on the 38 industrialized countries -- understandable since, at the time, the latter's fully developed economies were responsible for two-thirds of the yearly greenhouse gas emissions, and had cumulatively produced 90 percent of all the emissions over the past century.
Their plan of action, the Kyoto Protocol, called for drastic reductions in those countries' emissions, to levels below that of 1990. At the same time the other 121 developing countries were told to adopt no such limits to their economic growth. This protocol, though eventually ratified in 2005 by enough of the participating countries to make it international law for all signatories, was never consented to by the U.S. Congress; the United States, despite being the number one source of greenhouse gas emissions in the world, has never agreed to the terms of the Kyoto Protocol.
Opposition by some pro-business political groups, concerned about the Protocol's impact on our economy, has probably been a factor in our country's failure to join the Kyoto call to action; but the essential unfairness of the Protocol in its demands on industrialized versus developing countries has also diminished support from groups and politicians who would otherwise have pushed strongly for its ratification. One of the key goals of the current conference in Bali is to correct that unfairness. That will be difficult to achieve if the 'Third World' continues to view countries like us as having reaped the benefits of years of unrestrained, carbon dioxide-emitting economic growth but denying them similar opportunities to industrialize.
If a Bali accord achieves balance, there is a greater chance that the United States will participate in humanity's joint effort to counter the future effects of global warming. Participation would increase our national security and delay the onset of peak oil. But it would also require major changes to our personal habits and economic policies. The cost of not joining the effort? Well, are you willing to risk the consequences?
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Topic: Action in the face of global warming uncertainty (Read 438 times)
