Dr. John Bally: No doubt climate change is human-caused
Ryan Summerlin May 5, 2012
Martin Hertzberg, whose views were highlighted in a full-page in the April 22 SDN, does not understand the basics of the “global warming theory.” The “global warming” or “climate change” theory is based not only on strong observed evidence, but also on excellent understanding of the underlying mechanisms.
This is the subject that physicists and atmospheric scientists call “radiative transfer” – the study of how radiation (light, infrared, and all forms known as “electromagnetic energy”) moves from place to place. Global average temperatures have been increasing at an unprecedented rate in the last century. This is well documented by meteorological records around our planet Earth. The question is, why?Atmospheric carbon-dioxide (CO2) concentrations have increased from a little under 300 parts per million to over 385 parts per million within the last 100 years – a 28 percent increase. Human burning of fossil fuels has been identified as the only plausible source causing this increase in CO2. Hertzberg states that a gas – CO2 – with a current abundance of only ~ 0.04 percent of the more common constituents of our atmosphere (nitrogen, oxygen, argon, and water vapor) could be “responsible for all this weather phenomenon is nonsense”. Not only is it NOT nonsense … it is responsible.CO2 is the single atmospheric constituent that has a very strong absorption band close to the wavelengths of the infrared light re-emitted by the planet. Infrared is heat. Earth absorbs visual wavelength light from the sun at wavelengths where our eyes are most sensitive (this is probably no coincidence, but rather, a product of biological evolution). The Earth then converts the sun’s light energy into infrared energy (heat). This heat (with some addition from the planet’s internal heat) is then radiated back out through Earth’s atmosphere into space. Here is why Hertzberg is wrong: CO2 absorbs at wavelengths between 14 and 16 micrometers – the same wavelengths that Earth radiates most of its heat into space. CO2 significantly blocks this natural “cooling” of the Earth. Humans have put increasingly more CO2 into Earth’s atmosphere since the 17th century through burning of fossil fuels. This has caused increased heat absorption and radiation back to the ground. This trapping of heat is the so-called “green house effect.”Hertzberg further argues that water vapor is also a “greenhouse” gas. True, so are methane, ozone and other minor constituents of our atmosphere. Many of these gases make our planet habitable by keeping Earth sufficiently warm for life to exist. (Without these constituents, Earth would be a frozen ball of ice.) But CO2 has a trait not shared by the other gases … it is THE gas that has the STRONGEST absorption at the very wavelengths where the Earth balances its temperature. This is the key point that he misses.We have an accurate record of Earth’s temperature with its atmospheric composition, including CO2, extending back more than 400,000 years from ice cores pulled from deep Antarctic ice layers. There is a direct correlation between CO2 abundance and average temperature – temperature rises soon after (within a few centuries) after CO2 levels increase. This provides clear evidence that when CO2 abundance increases, so does global temperature. Today’s CO2 levels are higher than they have ever been in the 400,000 year Antarctic record, in fact, most of the increase has occurred in the last 300 years. During this period, no natural causes (including all the known volcanic eruptions) can account for this. Only human burning of fossil fuels. Increasing CO2 increases global warming. The correlation between temperature and CO2 levels clearly demonstrates this. Infrared absorption is why. And, importantly, the records rule out everything except human burning of fossil fuels as the cause. The seemingly insignificant levels of CO2 we (humans) have and continue to inject into our atmosphere will raise global temperatures to catastrophic levels. Dr. John Bally of Breckenridge is a professor of astrophysics at the University of Colorado at Boulder.