Sunday, November 29, 2009

Carbon equilibrium under threat: The balance between inflow and outflow of carbon dioxide has been disturbed.

Carbon dioxide is rising by 2 or 3 ppm each year.
by
Dr. Nitish Priyadarshi

Climate change is neither new nor unusual. The earth’s average surface temperature and climate have been changing through out the world’s 4.7 billion-year history. Sometimes it has changed gradually (over hundreds to millions of years) and at other times fairly quickly (over a few decades).

Over the past 900,000 years, the average temperature of the atmosphere near the earth’s surface has undergone prolonged periods of global cooling and global warming. During each cold period, thick glacial ice covered much of the earth’s surface for about 100,000 years. Most of this ice melted during a warmer interglacial period lasting 10,000 – 12,000 years that followed each of these glacial periods.

The most widely noted evidence for global warming originated during the International Geophysical Year in 1957, when an observatory was established on top of Mauna Loa volcano in Hawaii. The objective was to study air chemistry in a remote pristine environment. Surprisingly, the observatory recorded rising carbon dioxide levels every year, with concentrations growing from 315 parts per million (ppm) in 1958 to nearly 370 ppm in 1999. The increase wasn’t steady: every May, during the Northern Hemisphere spring carbon dioxide levels dropped slightly as plant growth on northern continents used up some carbon dioxide. Because a majority of the world’s land and vegetation are in the Northern Hemisphere, northern seasons dominate this signal. Subsequent studies have shown that carbon dioxide is increasing about 0.5 percent per year.

For the earth and its atmosphere to remain at a constant temperature, incoming solar energy must be balanced by an equal amount of outgoing energy.

In addition to incoming sunlight, a natural process called the greenhouse effect warms the earth’s lower troposphere and surface.

The two greenhouse gases with the largest concentrations in the atmosphere are water vapor controlled by the hydrologic cycle and carbon dioxide controlled by the carbon cycle.

Since the beginning of the industrial revolution around 1750, human activities have emitted significant amounts of greenhouse gases into the troposphere. Sharp rise is due to the use of fossil fuels, which release large amounts of the greenhouse gas carbon dioxide and methane into the troposphere.

The two largest contributors to carbon dioxide emissions are the world’s thousands of coal-burning power and industrial plants and more than 700 million gasoline-burning motor vehicles. Burning fossil fuels is contributing about 5 to 5.5 billion metric tons of carbon dioxide per year. Burning forests and other biomass, mining limestone for cement making, and other activities also contribute. Total anthropogenic production of carbon dioxide is estimated to be 6.3 billion metric tons per year. If current trends continue, carbon dioxide concentrations could reach about 500 ppm (approaching twice the pre-industrial level of 280 ppm) by the end of the twenty-first century.

Increasing carbon dioxide is warming our planet. It’s simple, as long as we pour carbon dioxide into the atmosphere faster than nature drains it out, the planet warms. And that extra carbon takes a long time to drain out of the atmosphere.

Here are a few of the many findings from such measurements that support the scientific consensus that the earth’s atmosphere is warming. The concentration of carbon dioxide in the troposphere is higher than it has been in the past 420,000 years. The 20th century was the hottest century in the past 1,000 years.

Since 1861 (when direct atmosphere temperature measurements began), the average global temperature of the troposphere near the earth’s surface has risen 0.6 ± 0.20 C, with most of this increase taking place since 1946. Nine of the ten warmest years since 1861 have occurred since 1990. The hottest year was 1998, followed by in order by 2002 and 2001. There is an apparent correlation between increases in fossil fuel use, atmospheric concentrations of carbon dioxide, and global temperature between 1970 and 2002.

Nature protects us by absorbing carbon dioxide. Plants, oceans, and rocks all drain carbon from the atmosphere, but drains are slow. Plants and soil absorb about a third each year, and ocean surface waters about a quarter. The rest stays airborne for a long time. Average time of carbon dioxide in the troposphere is 50 to 120 years. Due to large scale deforestation worldwide threat of increasing carbon dioxide in atmosphere has increased. The balance between inflow and outflow of carbon dioxide has been disturbed.

Time and again, some people claim that human activities are only a minor source of atmospheric carbon dioxide (CO2) which is swamped by natural sources. Compared to natural sources, our contribution is small indeed. Yet, the seemingly small human-made or `anthropogenic' input is enough to disturb the delicate balance. "Anthropogenic CO2 is a biogeochemical perturbation of truly geologic proportions" and has caused a steep rise of atmospheric CO2.

Ice cores show that during the past 1000 years until about the year 1800, atmospheric CO2 was fairly stable at levels between 270 and 290 ppmv (parts per million by volume). The 1994 value of 358 ppmv is higher than any CO2 level observed over the past 220,000 years. The rise of atmospheric CO2 closely parallels the emissions history from fossil fuels and land use changes. All these signs indicates that carbon dioxide rise is human made and affecting the carbon balance of our earth atmosphere.

If I take the example of Ranchi city, the capital of Jharkhand state of India, which was earlier famous for cool climate even in summer, is now passing through drastic climate change from last ten years. Summer is becoming hotter and winter is becoming less cool. All the seasons are coming earlier. Rainfall pattern has also become erratic. Credit goes to increasing carbon dioxide. Sources are the coal mines fire, thermal power stations, increased motor vehicles and above all large scale of deforestation.

Its going to take hundreds of years to remove most of the carbon dioxide that humans are pouring into the atmosphere and hundreds of thousands of years to remove it all. Stopping the rise of carbon dioxide will thus require huge cuts in emissions from cars, power plants, and factories, until inflow no longer exceeds out flow.

By 2008, the level of carbon dioxide in the atmosphere was 385 parts per million (ppm) and rising by 2 or 3 ppm each year. To stop it at 450 ppm ( which is considered dangerously high) the world would have to cut emissions by around 80 percent by 2050.

Reference:

Cunningham, W.P. and Cunningham, M.A. 2002. Principles of Environmental Science, Inquiry and Applications. Tata McGRAW-Hill Edition, New Delhi.

Miller Jr., G.T. 2004. Environmental science, tenth edition. Thomson Brooks/Cole, Australia.

National Geographic Magazine, December, 2009.

http://www.radix.net/~bobg/faqs/scq.CO2rise.html

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