Smokers probably have something to teach us about why it's so hard to believe in global warming.

Sure, smoking is unhealthy, but a lot of smokers never get cancer, and everyone claims to know an 85-year-old who smokes a pack a day and is still as strong as a horse. Maybe it's the human capacity for wishful thinking, but few smokers really believe they will be dealt a losing hand.

Are we taking a similar gamble with global warming and climate change? The warnings are certainly loud enough (like a smoker's cough), and the idea that human activities threaten the health of our planet makes sense. But the leap from acknowledging this global possibility to it becoming a personal reality remains inconceivable to most people. When fears do creep in, we are most likely to humor them away with thoughts of milder winters and mikan growing in Moscow.

But concerns about global warming and climate change do not go away; nor do contradictory scientists, angry environmentalists, lingering uncertainties and disbelief.

If climate change is a reality, what does it look like? What do we know? And, more importantly, what don't we know? Are we talking shirtsleeves in February, or killer typhoons and Japan's coastline moving a kilometer or two inland? Is there a bright side if the Earth really is warming? All of this matters, not simply because you might want to shelve plans to buy a retirement beach house. It also matters because the Kyoto Protocol to the U.N. Framework Convention on Climate Change is expected to go into effect next year -- and many respected scientists are saying the global average temperature could have risen almost 6 degrees by 2100.

Last month in Marrakech, Morocco, national parties to the Kyoto Protocol finally hammered out an agreement on operating rules. This means that the treaty, first drafted four years ago in Japan, can now be ratified by participating nations, who will be required to reduce their carbon dioxide emissions to 5 percent below 1990 levels by 2012. But depending on who you talk to, this is either wonderful news, inconsequential . . . or something in between.

Last March, Robert Watson, chair of the U. N. Intergovernmental Panel on Climate Change, called the protocol "an incredibly important first step." However Watson, who is also the chief scientist at the World Bank, also said it "will do very little to limit temperature increases in the atmosphere." But with humans pumping 6 billion tons of carbon into the atmosphere annually, and carbon dioxide levels now more than 10 percent up on 1990's, Watson said he believes the treaty will help stop runaway emissions, which we must begin stabilizing immediately.

Massachusetts Institute of Technology's Richard Lindzen, a professor of meteorology, agrees that the protocol won't solve the problem of climate change. In fact he doesn't believe there is a problem -- which is why he doesn't support the treaty.

Indeed, Lindzen was reported in Newsweek on July 23 to have advised President George W. Bush earlier this year that the Kyoto Protocol would "do nothing at great expense." Back in May, when this darling of climate contrarians testified before the U.S. Senate Environment and Public Works Committee, he said that if the protocol is viewed as a sort of insurance policy, "it is a policy where the premium appears to exceed the potential damages." He added: "A large part of the response to climate change, natural or anthropogenic, will be adaptation, and that adaptation is best served by wealth." If this sounds like wishful thinking from someone who prefers building sea walls to cutting carbon emissions, perhaps it's worth mentioning that Lindzen is also a smoker.

Points of agreement

So who to believe? Well, most scientists do agree on several basic points.

As even Lindzen told the U.S. senators, "informed scientists agree that global mean temperature has probably increased over the past century; that carbon dioxide in the atmosphere has increased over the same period; that the added carbon dioxide is more likely to have caused global mean temperature to increase rather than decrease; and that man, like the butterfly, has some impact on climate."

Additionally, Scientific American magazine reported last month that Lindzen "agrees with the IPCC and most other climate scientists that the world has warmed about 0.5 degrees over the past 100 years or so." Although he accepts that human activities have raised atmospheric carbon dioxide levels by about 30 percent, unlike the vast majority of other climatologists, he does not accept that there is a clear link between the warming and the higher emissions.

Over the last century, atmospheric carbon dioxide levels have risen from about 280 parts per million to today's level of 360 ppm. This rapid increase, in combination with the 6 billion tons we produce annually, is often cited in support of reducing emissions. Lindzen, though, is concerned that alarmism is guiding the climate debate. He maintains that the keys are careful science and keeping things in perspective.

To understand climate change, it is essential to understand the role carbon plays in our planetary ecosystem. There are many variables influencing climate, and water vapor is by far the most important "greenhouse gas" contributing to atmospheric warming. However, it is the variable humans influence most, both directly and indirectly, and it is the primary greenhouse gas resulting from industrial activity, transportation and energy generation.

As carbon dioxide levels are also influenced by agriculture and forestry, environmentalists and climatologists are very interested in what carbon dioxide does, how it moves and where it goes. In this respect, the importance of the oceans covering about two-thirds of the globe can hardly be overstated. As Richard Alley said in his book "The Two-mile Time Machine" published last year: "Earth's atmosphere now contains about 800 gigatons -- i.e., 800 billion tons -- of carbon, almost all of which occurs as carbon dioxide . . . [whereas] the oceans contain a huge amount of carbon dioxide that has dissolved and reacted with the water -- about 50 times as much as in the atmosphere."

The author, a professor of geosciences at Pennsylvania State University, notes that, "Because the stores of carbon that can experience significant natural changes over millennia are dominated by oceans, the carbon dioxide changes over ice-age cycles almost certainly depended largely on the oceans."

Clearly, as human carbon emissions weren't an issue when things warmed up after the last Ice Age, a key question is how much do carbon dioxide levels fluctuate naturally over time. The answer is closely tied to climate-change cycles involving ice ages, and interglacial periods, that have occurred consistently over the past 500,000 years.

Blowing hot and cold

According to Shin Sugiyama, a glaciologist at the Institute of Low Temperature Science, Hokkaido University, over the past 400,000 years, there have been four glacial periods. The most recent ended about 10,000 years ago. Previous interglacials occurred 140,000, 240,000 and 340,000 years ago. In the current, 10,000-year-old interglacial period, average global temperature has risen 5 degrees -- similar to rises in other interglacial periods.

Meanwhile, Arctic and Antarctic ice-core samples show that atmospheric carbon dioxide and methane levels rise in interglacial periods too. Though the reasons for this are not well understood, the samples show that atmospheric carbon dioxide fluctuates between interglacial temperature peaks (280 ppm) and glacial troughs (180 ppm) -- making global cooling possible too, judging from temperature graphs for the last 500,000 years.

Nothing, though, is as simple as it looks on a graph. According to Alley: "For most of the last 100,000 years, a crazy jumping has been the rule, not the exception. Slow cooling has been followed by abrupt cooling, centuries of cold, and then abrupt warming, with the abrupt warmings generally about 1,500 years apart, although with much variability."

He adds: "One can almost imagine a 3-year-old who has just discovered a light switch, flicking it back and forth, losing interest for a while, and then returning to play with it again."

Not surprisingly, some scientists question whether today's warming trend is not simply the result of natural fluctuations in climate. Such skepticism is made all the easier because conclusions about atmospheric gases and temperatures are based on information imbedded in ice and earth, tweaked by numerous influences over thousands of years. Potential errors and misinterpretations are myriad.

But that's just the tip of the global-warming iceberg. Thanks to growing public concern, knowledge of carbon dioxide and climate interaction is advancing rapidly since, as Sugiyama puts it, "Fashionable research attracts funding." In short, it's a cash magnet. Even so, piecing together the carbon dioxide puzzle is only a small part of the task scientists face. Many other variables influencing climate must also be considered on the road to the ultimate goal of creating computer models able to replicate complex climate changes of the past -- which can then be projected into the future.

In fact, to say "numerous other variables" is to massively understate the complexity of it all -- and the potential for scientific disputes. Not only is the role of carbon dioxide disputed, but so too is that of water vapor -- the single most important greenhouse gas.

IPCC's Watson notes that water vapor makes up 90 percent of atmospheric gases. While humans are not directly generating it, he says we are emitting "carbon dioxide and other greenhouse gases that lead to a warming of the Earth's surface, that leads to more evaporation." But in some models, rather than amplifying the greenhouse effect, extra evaporation would counteract it. So, with no consensus on carbon dioxide or water vapor, it is easy to imagine how divergent the scientists can get on forests, wetlands, methane and nitrogen oxide.

That's not to mention other variables in the algebra of any climate-change model, many of which are covered in "The Great Ice Age" by R.C.L. Wilson, a professor of earth sciences at the Open University in England. These include thunderstorms, weather systems, changes in atmospheric circulation, volcanic eruptions, major droughts and floods, changes in ocean circulation, changes in plant distribution, ice-sheet dynamics, plate tectonics, glacials and interglacials.

Computers may be able to beat us at chess, but are they up to calculating the interactions of these forces? The mind boggles as Wilson explains that computer models also require the inputting of "solar insolation, the extent of ice sheets, deep and surface oceanic temperatures, land albedo, cloud cover, carbon dioxide and water vapor content in the atmosphere." Some other known variables he does not mention are methane, nitrogen oxide and chloroflourocarbons. In short, the science is monumentally complex.

Despite all the variables and accompanying uncertainties, the October issue of Scientific American reported that researchers now believe, "with a fairly high degree of confidence," that the 1990s was the warmest decade of the millennium -- and that carbon dioxide levels are the highest for 20 million years.

Nevertheless, with so much climate knowledge still up in the air, the questions remain whether the Kyoto Protocol will make any difference -- and are its benefits worth its costs? Both questions are impossible to answer. We simply do not understand the science or the economics well enough. But since global environmental problems tend to be long-term and relatively abstract, and economics is quantifiable in quarterly reports, climate decisions are primarily guided by the latter, easier policymaking.

Changing the landscape

Writing in the October issue of Scientific American, George Musser phrased the problem succinctly: "Nobody knows for sure how much curtailing greenhouse gas production will cost. It could yield a net benefit [for example, by improving energy-efficiency], or it could stop the economy cold." Watson of the IPCC agrees the protocol "won't solve the problem," but he believes it will inspire industries to develop new technologies and push governments to craft a new policy framework to deal with climate change.

On a wider front, some critics regard the Kyoto Protocol as environmental policymaking at its worst; law based on politics not science. Conversely, even many of its supporters characterize the treaty as too little, too late, by too few. For better of worse, though, now that the protocol can be ratified, it will enter into force as soon as nations comprising 55 percent of the emissions to be cut adopt it. If the European Union, Russia and Japan all ratify next year, the agreement could take effect soon afterward. If this happens, as it is expected to, the scientific and political landscape of the climate debate could change dramatically.

No one was surprised when the U.S. reiterated its refusal to adopt the protocol. One surprise, though, was Prime Minister Junichiro Koizumi's pledge that Japan will ratify it by next September. Many observers are pleased to see Japan leaving Big Brother behind and going its own way for a change. Others are simply happy to see Japan taking the lead on a treaty bearing the name of its ancient capital.

Whether the protocol will offer substantive benefits, time will tell. Watson is enthusiastic about its "flexibility mechanisms," such as carbon trading, that will allow countries to buy and sell carbon-emission rights, making carbon dioxide reduction more efficient. He also sees agro-forestry in developing countries as a way to reduce atmospheric carbon, while improving rural incomes and productivity and reducing erosion.

Many environmentalists expect the treaty will hasten removal of subsidies on fossil fuels (such as tax breaks for oil companies), thereby reducing carbon dioxide emissions, acid rain and particulates. It should also reduce subsidies on fertilizers that add greenhouse gases to the atmosphere and contribute to lake, river and marine pollution. As these subsidies are cut, the adoption of environmentally friendly technologies will become more appealing.

In all likelihood, however, the Kyoto Protocol will prove its greatest worth in the abstract -- not by dramatically reducing carbon dioxide emissions, which it can't in its present form; and not by arresting warming, which it won't. Instead, it will play the role of a milestone, increasing awareness of how far we have come, and how far we have to go, on environmental issues overall.

At its best, it will encouraging scientists, politicians and chief executive officers to think outside the box of their status quo. After all, 1987's Montreal Protocol on Substances that Deplete the Ozone Layer began as a small step in the right direction. Then, as science confirmed the nature and extent of ozone-layer depletion, the agreement was strengthened. Today, ozone holes remain a threat, but they are not expanding, and ozone-safe chemicals have become the norm.

Following the Kyoto Protocol, in a decade we might all be riding hydrogen-fueled buses through car-free city centers, or pedaling on urban bike paths through greenbelts. The climate may be hotter than ever, waves may be lapping the subway doors, but at least we won't be sucking in diesel particulates and trapped in the traffic jams of pre-Kyoto Protocol Japan.