Most people know that global warming is the result of excessive emissions of greenhouse gases such as carbon dioxide and that it has dire consequences for the planet.

But our understanding of global warming and climate change is the result of accumulated discoveries in disparate fields of research.

"The Discovery of Global Warming" by Spencer R. Weart gives a detailed account of the history of climate studies and discoveries, and how they led to consensus (pretty much) on the problem.

Citing the theory of the "commons," (shared meadows in old England), Weart makes the case that policy changes are imperative.

The research goes back to the early 19th century when climatologists first studied the way the atmosphere traps heat. They wanted to explain the earth's ice ages to prevent another ice age.

Many important names were involved in these studies, including climatologist John Tyndall, who first identified CO2 as a heat absorbing "greenhouse gas" in 1859, and Svante Arrhenius, who was the first to link the amount of CO2 in the atmosphere with the earth's temperature change.

However, it rarely occurred to scientists at that time that warmer temperatures could be harmful, not even when a warming trend of the climate was identified in the 1930s.

Besides, few scientists considered that this trend was man-made, as it was widely believed at the time that nature's powerful balance would scarcely be affected by human activities and that oceans absorbed excess CO2.

No wonder "in the 1930s, citizens had been happy to see smoke rising from factories, for dirty skies meant jobs," writes Weart.

The real shift in understanding began in the mid-1950s.

A series of scientific researches and studies showed that contrary to common belief, oceans did not absorb excess CO2 emissions. This fact also proved the postulate that human activities such as burning fossil fuels would cause the CO2 level to rise in the atmosphere.

As more CO2 would block more heat radiation within the atmosphere, it would cause temperatures to rise, thus leading to global warming.

Much research and many studies, such as those on fossils and ancient pollens, proved the global warming theory.

And the invention of computer modeling simplified the process by enabling scientists to predict future climate based on CO2 levels by analyzing past data.

"Increased haze and jet contrail clouds, ancient catastrophic droughts, fluctuating layers in ice and in seabed clays, computer calculations of planetary orbits and of energy budgets and of ice sheet collapse: each told a story of climate systems prone to terrible lurches," Weart summarizes.

Despite all these seemingly irrefutable facts, it is still a challenge to persuade the public, especially certain interest groups, to make necessary sacrifices to help slow down the climate change.

As Weart observes, "The atmosphere is a classic case ... of the 'commons': in the old shared English meadows, any given individual was bound to gain by adding more of his own cows, although everyone lost from overgrazing. In such cases ... public interest can be protected only by public rules."

Fortunately, more and more countries have realized the severity of global warming and are taking action, though far from enough.

In 1987, nations adopted the Montreal Protocol to restrict ozone-depleting emissions.

The UN Intergovernmental Panel on Climate Change (IPCC) was also formed to assess the scientific, technical and socio-economic information relevant to the understanding of the risk of human-induced climate change.

And there is the famous Kyoto Protocol (adopted in 1997, in force in 2005, expiring in 2012), which was framed to reduce greenhouse emissions the world over. A new protocol is needed to replace it and it is expected to be drafted in Copenhagen this December.

Last month the British government published "The Road to Copenhagen," a manifesto for a global climate deal, according to the British Consulate-General Shanghai.

As UK Climate and Energy Secretary Ed Miliband emphasized when publishing the document, "This is a make or break time for our climate and our future ... The world's got no option but to work together to get a global climate deal that's ambitious, effective and fair.'"

(Shanghai Daily July 6, 2009)