Bill McKibben, environmentalist, author, and founder of 350.org, took the stage in Mumbai yesterday and stated in measured but forceful words that strong, powerful action needs to be taken very, very quickly if we want to maintain the climate we are accustomed to.

He encouraged participation in the International Day of Climate Action, which will be observed on 24 October 2009 and is being organised by 350.org. The number 350 comes from a Nasa study that found a level of carbon dioxide (CO₂) of 350 parts per million (ppm) to be the upper limit that the atmosphere can safely sustain if the earth's climate is to remain substantially similar to the one we are used to and which supports life and civilisation.

The current level of CO₂ in the atmosphere is 390 ppm and rising by 2 ppm per year. The pre-Industrial Revolution level was 275 ppm.

Each summer in the Arctic, an area of ice the size of California melts away due to global warming. There is now 25 per cent less ice in the Arctic than there has been at any point in over a million years. McKibben related the projection that the sea level is expected to rise between one half and two metres by the end of the century to the fact that much of the Maldives is less than two metres above sea level. That country's government has even instituted a fund to relocate its citizens in the event their current lands are submerged by the rising sea.

The International Day of Climate Action will arrive six weeks ahead of the United Nations Climate Change Conference in Copenhagen, Denmark, later this year. The Copenhagen conference is being seen as the successor to the Kyoto climate change conference. The hope is that worldwide demonstrations that centre on the number 350 will draw the attention of the media and of world leaders as they prepare for Copenhagen.

McKibben contracted dengue fever when in Bangladesh several years ago. As he sat in a hospital bed, surrounded by Bangladeshis suffering and dying from the same condition, he was struck by how fundamentally unfair the problem of climate change is, as the people who suffer the most are those who have contributed the least to the problem. People in developing nations in the tropical and subtropical belts will be the most significantly affected even though their carbon footprints are negligible.

Cases of dengue fever in Asia have risen 200 per cent since 2000. Some experts predict that the Gangotri glacier, at the head of the Ganges, will have completely melted by 2040. Diverging from the oft-argued stance that an environmentally conscious approach to development could unduly hinder India's progress, McKibben painted a picture of an India whose development is impeded by climate change - one where the Gangotri is melting, the Bay of Bengal is rising, and clinics that now focus on fighting polio or on family planning are overrun with patients suffering from dengue fever or other newly widespread diseases that thrive in warm, wet climates.

The room was full and the audience's questions showed they were knowledgeable and experienced in the area of climate change. When one passionate questioner asked for specifics that we can implement on an individual basis, McKibben stated that, though it is ''a noble and correct sentiment to react immediately,'' it is too late to act on a household, campus, or community level. He recommended a focus on collectively exerting pressure on national governments.

Given that, McKibben urged Indians, some of whom he acknowledged create CO₂ at a rate equal to Americans on a per capita basis, to be a force for action. It is India's right to ask for financial and technological aid from developed nations, but this cannot be thought of in terms of negotiations between governments; it is, at its heart, a negotiation between human beings on the one side and physics and chemistry on the other. The laws of nature begin by stating their bottom line, and it is our job to figure out how to meet it.

The march to 350 is a long one. Even if we begin implementing CO₂-reduction measures immediately and with the greatest efficiency, it will take a lifetime to reach the 350 level. At the same time, a course that is even moderately divergent will lead to disaster.

McKibben, whose visit was facilitated by the American Center, Mumbai, and the Asia Society India Centre, seemed confident of the power of the demonstrations he was encouraging because of a similar effort he organised across the US two years ago called 'Step It Up 2007.' Several days after it was held, both Democratic candidates, Barack Obama and Hillary Clinton, changed their environmental platforms to include the goal of reducing carbon emissions 80 per cent by 2050, an aim for which the demonstrators had been strong proponents.