Introduction

It may disturb you to know that global warming was understood and accurately predicted long before these problems became evident. In his bestseller The Weather Makers, Australian scientist Tim Flannery explores the history of climate change science, and reveals that in the 1890s, Swedish chemist and Nobel Prize winner Svante Arrhenius calculated the warming that the best evidence now suggests will be a reality. Arrhenius did not have the wealth of data available to today's scientists. He and his colleagues reached their conclusions through pure science, the basic principles of physics and chemistry which enabled them-and enable us-to understand, with 100% certainty, that greenhouse gases such as carbon dioxide (CO2) trap heat.

Greenhouse Gases

These gases are so named because they operate in a similar way to glass greenhouses, which farmers have used for centuries, trapping heat to grow tomatoes and other plants that could not otherwise be grown in the colder regions of the world. Like glass greenhouses, they allow sunlight to pass through unhindered, but trap heat radiation on its way out. The molecular structure of CO2 is such that it is "tuned" to the wavelengths of infrared (heat) radiation emitted by the Earth's surface back into space. The molecules resonate, their vibrations absorbing the energy of the infrared radiation. It is vibrating molecules that give us the sensation of heat, and it is by this mechanism that heat energy is trapped by the atmosphere and re-radiated to the surface. The molecular structure of methane (CH4) is even more finely tuned to infra-red wavelengths, making it the next most important greenhouse gas, despite its relatively low concentration. Other greenhouse gases include ozone and CFCs. The greenhouse gases together act as the world's thermostat. The higher their concentration, the more heat is trapped. If it is getting too warm we need to turn down the thermostat by lowering the concentration of these gases.

Climate Sensitivity

At the moment, the Earth is warming because the solar energy entering the atmosphere exceeds the infrared energy that is radiated back into space. If the concentration of greenhouse gases can be stabilized, a certain equilibrium temperature will eventually be reached where the radiated infrared energy will balance the incoming solar radiation. Just as your home air conditioner takes time to readjust the temperature of your home after you adjust the thermostat, the Earth takes a considerable period to rise to a new equilibrium temperature after its thermostat has been turned up by increasing emissions of greenhouse gases. The change in the equilibrium temperature due to a given change in the concentration of greenhouse gases is known as the "climate sensitivity," and you may find it useful to search for this term when doing your own research.

Proven in the Laboratory

Most principles of physics are beyond question because both cause and effect are well understood. A relationship between cause and effect is proved by repeatable experiments. This is the essence of the scientific method, and the source of knowledge on which we have built our technological civilization. We do not question Newton's laws of motion because we can demonstrate them in the laboratory. We no longer question that light and infrared radiation are electromagnetic waves because we can measure their wavelengths and other properties in the laboratory. Likewise, there should be no dissent that CO2 absorbs infrared radiation, because that to has been demonstrated in the laboratory. In fact, it was first measured 150 years ago by John Tyndall using a spectrophotometer. In line with the scientific method, his results have been confirmed and more precisely quantified by Herzberg in 1953, Burch in 1962 and 1970, and others since then.

Verified in the Atmosphere

Given that the radiative properties of CO2 have been proven in the laboratory, you would expect them to be same in the atmosphere, given that they are dependent on CO2's unchanging molecular structure. You would think that the onus would be on the climate skeptics to demonstrate that CO2 behaves differently in the atmosphere than it does in the laboratory. Of course they have not done so. In fact, since 1970 satellites have measured infrared spectra emitted by the Earth and confirmed not only that CO2 traps heat, but that it has trapped more heat as concentrations of CO2 have risen.

The above graph clearly shows that at the major wavelength for absorption by CO2, and also at wavelength for absorption by methane, that less infrared was escaping in to space in 1996 compared to 1970. After 150 years of scientific investigation, the impact of CO2 on the climate is well understood. Anyone who tells you different is selling snake oil.

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