Fast forward to May 24th 2006. In New York and Los Angeles the documentary film ‘An Inconvenient Truth" directed by David Guggenheim opens to rave reviews. The film, a passionate narrative about climate change and particularly about global warming, stars former US Vice-President Al Gore, a vocal supporter of environment-friendly legislation. At the Sundance Fim Festival ‘An Inconvenient Truth’ garners not one but three standing ovations. At the time of writing this article the movie has grossed upwards of US$ 23 million making it the third most successful documentary in US history after ‘Fahrenheit 9/11′ and ‘March of the Penguins’.

The documentary, yet to hit Indian shores, has been steadily gathering fans and, to a lesser extent, critics all over the world. While some have called it the right message at the right time others contend that while Gore has got his science correct he has grossly overestimated the risks. (This should not be so surprising. The producers of the movie, Laurie David and Lawrence Bender, were also the people behind the 2004 blockbuster disaster movie ‘The Day After Tomorrow’. That movie, ironically, showed the world ravaged by a latter-day ice age that freezes Manhattan down in fifteen minutes flat.)

Perhaps the effect the movie has had on viewers can best be summarized by the following lines from popular movie critic Roger Ebert’s review : "In 39 years, I have never written these words in a movie review, but here they are: You owe it to yourself to see this film. If you do not, and you have grandchildren, you should explain to them why you decided not to."

Disparate Views

So why has world view on global climate changed so dramatically in the last thirty years? Why does Nim Goldman wax eloquent about the threats of falling temperatures in 1979 while just twenty-seven years later the message of global warming finds almost universal credibility? The answer lies in a simple fact: we actually understand the dynamics of global climate better today than we ever did before. Compared to the body of world meteorological knowledge that existed just three decades today we know enough to debunk several claims and theories that were prevalent then.

This then begs a pertinent question, one that is being asked by several quarters: "What makes us think we know enough about the climate today? Is global warming, like global cooling, a passing fad?"

Global Cooling, an idea that seems utterly foolish today, was not something that seemed so outlandish in the past. In a widely quoted article in 1975 called ‘The Cooling World’, Newsweek magazine painted a grim picture of the world to come.

"There are ominous signs that the Earth’s weather patterns have begun to change dramatically and that these changes may portend a drastic decline in food production– with serious political implications for just about every nation on Earth… To scientists, these seemingly disparate incidents represent the advance signs of fundamental changes in the world’s weather. The central fact is that after three quarters of a century of extraordinarily mild conditions, the earth’s climate seems to be cooling down. Meteorologists disagree about the cause and extent of the cooling trend, as well as over its specific impact on local weather conditions. But they are almost unanimous in the view that the trend will reduce agricultural productivity for the rest of the century."

Clearly the understanding of global weather dynamics then was very different from the views prevalent today. There was undisputed data to show that global climates had indeed fallen continuously from the 1940’s till the early 1970s. Studies then showed that the temperature had on average fallen by 0.4 ^oC. At the time this fall was attributed to two main causes: Sulphate Aerosols and Orbital Forcing.

Sulphate aerosols, or a suspension of fine sulphate particles in the atmosphere, was initially believed to be the prime driver for lower temperatures globally. These particles lowered temperature both directly, by impeding sunlight from reaching the surface, and indirectly, by increasing the amount of light that clouds reflected. Recent research however have found the previous assumed impact of such aerosol cooling affects to be overestimated and, while these particles still play a key role in Global Climate Models, their impact is seen to be much more modest.

By the 1980’s research had shown us that a lot of what we knew about the Earth’s weather systems were wrong or inadequate. While there was no doubt sulphate aerosols indeed had a cooling effect greater forces were at play. As the graph above will show after the brief period of falling temperatures between the 1940s and the 1970s global temperatures have, literally, never looked back. Last year was, debatably, the warmest year in recorded history. (The debate is whether 1998 was the warmest. In any case the difference is to the order of a few hundredths of a degree.)

There are several causes, internal and external, or forced, attributed to the current trend of rising temperatures. But academic opinion is overwhelmingly in favour of the view that much of the climate change that has occurred over the last half a century is due to human intervention. Greenhouse gas emissions arising from fossil fuel usage is today considered at the core of the challenge facing global weather.

Truth Today. Ignorance Tomorrow?

‘An Inconvenient Truth’ has several captivating images of glaciers shrinking and snowlines rushing to nothingness. Al Gore is often evangelical about the need to stem the tide now or lose the chance forever. He says: "The world won’t ‘end’ overnight in 10 years.. But a point will have been passed, and there will be an irreversible slide into destruction."

But the film, perhaps a little surprisingly, has its fair share of vocal critics. A report in the Canadian Free Press quotes several of them. At least one is immediately provocative. A professor testifies: "There is no meaningful correlation between CO2 levels and Earth’s temperature over this [geologic] time frame. In fact, when CO2 levels were over ten times higher than they are now, about 450 million years ago, the planet was in the depths of the absolute coldest period in the last half billion years… On the basis of this evidence, how could anyone still believe that the recent relatively small increase in CO2 levels would be the major cause of the past century’s modest warming?"

One things is for sure. Data to show that ’something’ is happening is irrefutable. Temperatures are rising. What causes these changes, what we can do about it, if we can and should, are all debatable. Whether decades from now Greenhouse gases will seem as irrelevant as aerosols and orbital forcing remains to be seem. Perhaps the way ahead is best put by these lines from Newsweek’s infamous article on Global Cooling:

"Climatologists are pessimistic that political leaders will take any positive action to compensate for the climatic change, or even to allay its effects. They concede that some of the more spectacular solutions proposed, such as melting the Arctic ice cap by covering it with black soot or diverting arctic rivers, might create problems far greater than those they solve. But the scientists see few signs that government leaders anywhere are even prepared to take the simple measures of stockpiling food(!) or of introducing the variables of climatic uncertainty into economic projections of future food supplies. The longer the planners delay, the more difficult will they find it to cope with climatic change once the results become grim reality."

Roger Ebert says it nicely: