Saturday, 29 November 2014

The real threat of global warming

by Zeeshan Hasan

Many people have a false perception of an ongoing 'debate' regarding the dangers of global warming and climate change. In particular, elected politicians intent on avoiding unpopular carbon taxes and higher fuel prices continue to assert that the relevant scientific issues are doubtful. Unfortunately, until now the non-scientist public has been deceived by a large number of books and newspaper articles by misinformed 'skeptics' of climate science who themselves have no understanding of the science involved. Fortunately, a glimpse into the real world of climate science is available through Global Warming: Understanding The Forecast by David Archer, an ocean chemistry professor at the University of Chicago. Archer's book is an introductory climate science text which aims to make the basics of climate science comprehensible to any one with a high school background in science.

The basic science of how carbon dioxide emissions raise global temperatures is outlined by Archer. On the one hand, the earth is constantly being heated by sunlight. On the other hand, the Earth is also cooled by loss of heat into space as infrared radiation. These two continuous mechanisms of heat gain and heat loss by the Earth result in a thermal equilibrium at the average global temperatures which we experience.

Heat gain from the sun is relatively constant, varying only slowly over time; however, heat loss into space has been reduced significantly by humans over the last century. Atmospheric 'greenhouse gases' such as carbon dioxide have the property of absorbing the infrared radiation which carries heat from the earth into space, and thus reduce the cooling of the earth. This effect of carbon dioxide is called the Greenhouse effect; it was discovered over a century ago and is undisputed. Since the Industrial Revolution, humans have been continuously burning fossil fuels such as coal, oil and gas, and thus adding huge amounts of carbon dioxide to the atmosphere. This has resulted in an increase of the carbon dioxide concentration in the atmosphere from 320 parts per million in 1960 to about 400 parts per million today, or about 20%. This additional carbon dioxide functions like a blanket or greenhouse around the planet, slowing down loss of heat into space. If the same amount of solar heat comes into the Earth, while simultaneously heat loss from the Earth to space is reduced by additional carbon dioxide, then the Earth has to get warmer. At a higher temperature the Earth's heat loss by radiation into space increases, because hotter objects lose more heat through infrared radiation than cooler ones; and the planet once more reaches a stable temperature.

A good analogy to the above is a pot of food simmering on an oven above a low flame; putting the lid on the pot does not change heat gain from the oven, but reduces heat loss through evaporation from the open pot and thus makes the food cook at a higher temperature. Our carbon dioxide emissions are effectively putting a lid on the earth, making heat from the sun 'cook' the planet at a higher temperature.

The question is whether a hotter stable temperature of the globe would be one capable of sustaining human life as we know it. Climate scientists have evidence from ancient ocean sediments that increasing the level of greenhouses gases in the atmosphere can cause temperatures to rise. Such an event took place 55 million years ago, when thousands of billions of tons of greenhouses gases were released into the atmosphere (probably because of a peak in volcanic activity). This event is known as the Permian Eocene Thermal Maximum (PETM). During the PETM, global average temperature rose by about 5 degrees C and 90% of life on the planet perished. Such an increase in global average temperature today would have terrible consequences, rendering much of tropical and sub-tropical Asia, Africa, central America and southern Europe too hot and dry for agriculture. The consequences would be famine on a scale never seen before, and billions of deaths.

Dangerous global heating events like the PETM may seem distant and irrelevant. But as a comparison, burning all world's known reserves of coal would release about 5000 billion tons of carbon dioxide, comparable to the surge in greenhouse gases which caused the PETM. Our current course is to exploit not only existing coal reserves but also oil and gas. So it is entirely within our power to destroy our planet.

Continuing our current policies of exploiting all fossil fuels available will literally ensure the end of the Earth as we know it. The only way to stop it is to keep fossil fuels in the ground and switch to solar, wind or nuclear power, none of which emit carbon dioxide. This will require worldwide imposition of carbon taxes to raise fuel prices and make investment in alternative energy feasible. The leaders of all countries need to make some hard decisions, which they have failed to do in 20 years of climate negotiations. They will only do so now if the public demands it of them. The public needs to make their voices heard.

 (Printed in Bangladesh on Nov. 30, 2014 by the Dhaka Tribune.)