JOIN USCarbon-dioxide released from burning of fossil fuels like coal has been regarded as the chief cause of global warming. it is said that it could lead to catastrophic climate changes in a few decades, like raising the global temperature by two or three degrees.
Carbon dioxide, as well as methane, nitrous oxide and water vapour are dubbed as green house gases that absorb strongly in the Infrared (IR) region, although they are transparent to visible wavelengths. So they let in sunlight, but trap it and prevent it from getting out. The IR heat radiation thus warms up all that is inside. Glass also plays a similar role so that a glass house is warm inside.
If you put layers of these greenhouse gases above the earth’s surface, sunlight would get in but when surface tries to radiate it back into space, the path of rays is impeded by this blanket of infrared absorbing gases.
The earth warms up as a result. If we keep adding more such gases, mainly carbon dioxide, by burning fossil fuels as we have been doing since the industrial revolution, we make this blanket thicker and thicker. This, in turn sets up an irreversible warming process. The mass of carbon dioxide present in the entire atmosphere is around two terra tons (two trillion tons).
This corresponds to three hundred parts per million (ppm). So if we dump seven hundred billion tons of this gas in a few decades (as we have been doing), we increase the concentration by hundred ppm, causing rise in global temperatures.
Despite all the hype about nuclear power (and renewable sources), seventy per cent of the power generated comes from burning coal. India used six hundred million tons of coal last year to generate three lakh mega watts of power. China used nearly two billion tons of coal. For every hundred million tons of coal burnt, we produce three hundred and fifty million tons of carbon-dioxide.
So the total installed power capacity in the world implies an annual generation of sixty billion tons of carbon dioxide. At this rate, by 2050, the concentration of this gas could even rise to 450 ppm, implying a two degree rise in global temperatures. A carbon footprint is measured in tons per year.
The sustainable level for every person on the planet has been estimated at one ton per person per year. Countries like the USA and China have already exceeded this on several occasions. A typical car gives five to ten tons per year of carbon dioxide. So if half the population has cars, you have already exceed the footprint by a factor of ten.
No way out
So if we considerably reduce the use of fossil fuels can global warming be averted? The answer is surprisingly a big no. Alternative power sources would also affect the climate. Our present civilisation with its modern comfortable life styles involves consumption of an enormous amount of energy which would keep growing at least a few percent annually.
Whatever you use energy for and however you produce it, it almost all ends up as waste heat. This applies to all ubiquitous use of devices like mobile phones, computers where you end up generating heat (which cannot be recycled). It costs energy even to cool.
For instance, refrigerators consume power to produce ice cream and cool drinks. Even if we switch to alternate power sources, waste heat would still warm up the ambience.
This is just the basic thermodynamic laws at work. Large scale use of nuclear (or even renewable sources) of power, for instance could cause serious thermal imbalances over large areas. It is commonly believed that nuclear fusion (as opposed to nuclear fission generating power in our present day uranium (or plutonium) reactors) could solve our future power problems.
The fuel used in so called thermonuclear fusion reactions would be deuterium (heavy hydrogen), which is abundant in our oceans (heavy water being present in one part in five thousand). Nuclear fusion generates much more power than even fission so that to produce say ten billion kilowatt hours of energy, you need only about two hundred kg of deuterium.
So fusion power would be available for a long time (you could stop throwing out billions of tons of carbon). However, there is a catch. The total solar power falling on earth is only about one-fifth of an exawatt (million trillion watts). So if our total terrestrial power production (from all sources) exceeds even five hundred terawatts, it would cause catastrophic climate changes.
Factors
Guzzling vast amounts of energy, by, say ten billion people, would cause warming irrespective of how the power is produced. Incidentally, ten billion people generate one terawatt of body heat. As we exhale more carbon dioxide, the human population is estimated to produce one giga ton of the gas annually.
Right now, we use about twenty terawatts annually. If the whole of humanity wants to consume as much power as an average individual in a developed country, 5,000 terawatts are required. At 10 per cent annual increase in power, this could be reached in a few decades.
Even if half of this is solar energy, the amount of waste heat added to the planet would cause severe global warming causing catastrophic warming. And this has nothing to do with fossil fuels or carbon.
Even large scale use of solar power, like generating thousand giga watts could cause local heating and sharp thermal gradients altering climate over several areas especially if solar ponds using concentrated focused sunlight are installed on large scales.
Even excessive use of wind power could have local and global effects on wind patterns. A terawatt is the limit for tidal, wind power, geothermal heat etc. Although a number of long term suggestions for future like geo engineering (using materials to reflect incoming sunlight into space) have been made, it appears in the long run that lifestyle changes involving less indiscriminate use of the environment is called for to avert climate disasters.