Commentary: Greenhouse gases at root of new geologic epoch

Greenhouse gases at root of new geologic epoch

Our planet is probably beginning a transition to a new geological age caused mainly by greenhouse gases we continue dumping into the atmosphere.

Nobel Prize-winning atmospheric chemist Paul Crutzen popularized the term "Anthropocene" for this new epoch. This term has not yet been adopted formally by geologists, but a proposal to do so is being studied by the Geological Society of London. The Geological Society of America titled its 2011 annual meeting "Archean to Anthropocene: The past is the key to the future," and many scientists are using the term. The primary marker for the new era will be a monumental spike in greenhouse gas concentrations occurring over a mere three centuries beginning around 1800, as recorded, for example, in ice cores drilled into Greenland and Antarctica, in the widths and densities of tree rings, and in the radioactive carbon content of biological matter.

Greenhouse gas concentrations far above normal will last about 30 millennia after we shut off carbon emissions. Temperatures, ice cover, plant growth and other factors will differ from today. Such changes will be difficult to deal with because we have built our present lifestyle on the presumption of present climate conditions. Homo sapiens will survive, but we could pollute ourselves back into the middle ages or worse.

The science supporting these conclusions is straightforward for all except those determined to resist anything that doesn't fit their pre-conceived opinions.

It's simple: The sun sends radiation to Earth, and Earth re-emits that radiation at a lower temperature. The sun's radiation is mostly high-energy visible and ultra-violet, but Earth's re-emitted radiation is mostly lower-energy infrared that is preferentially absorbed in Earth's atmosphere by a few "greenhouse gases," especially carbon dioxide (CO2). This "greenhouse effect" increases Earth's temperature by 60 Fahrenheit degrees. This is good, because it's helped warm our planet for at least a billion years.

The problem is, humans have recently increased atmospheric carbon dioxide and this warms the planet unnaturally. Since the last ice age ended 12,000 years ago, CO2 concentrations have remained around 280 parts per million (ppm), meaning that out of a million atmospheric molecules such as oxygen and nitrogen, 280 are carbon dioxide molecules. That figure was slowly declining during the past 2,000 years until about 1800, when a sudden spike drove the concentration up to more than 400 ppm today (see "carbon dioxide spike" on Google images). This spike is quite striking and unnatural. Anybody in his right mind would conclude it's caused by industrialization.

So, just as you would expect, the temperature has been increasing, especially since 1970 when CO2 concentrations reached really unusual levels. The four hottest years on record, in order, have been 2014, 2010, 2005 and 1998. The hottest decade on record was 2001-2010. Mountain glaciers are melting worldwide. The Arctic ocean, Greenland and West Antarctic are melting. Sea levels are rising. According to James Hansen, NASA's chief climatologist, now retired and devoting much of his time to fighting global warming, we could see a 10-foot sea-level rise by 2100.

Computer models predict disaster, but the best way to see what the carbon dioxide spike means is to look instead at actual geological history. The era of the ice ages, known as the Pleistocene epoch, persisted from about 2.5 million years ago to today, comprising cold "glacial" periods of about 100,000-year duration each, and warmer "interglacial" periods of about 10,000 years such as the one we are in today. During the entire 2.5 million years, carbon dioxide concentrations varied between about 180 ppm during glacial periods to 280 ppm during interglacials. Since 1800, concentrations have suddenly risen to more than 400 ppm, 43 percent higher than any level that could be considered "normal" for the past 2.5 million years.

For a historical analog, we must go back to the era before the Pleistocene, called the "Pliocene" epoch, lasting from about 5 million to 2.5 million years ago, when carbon dioxide concentrations were about 400 ppm. Compared with today, this era was characterized by much warmer north and south poles, slightly warmer equatorial regions, global average temperatures 6 Fahrenheit degree warmer, with smaller Antarctic and Greenland ice sheets and sea levels 80 feet higher. Anything resembling this would indeed be a new geological age.

Do not be fooled by the siren song of the fossil fuel industry, which grows rich by destroying the possibility of a healthy future for your children and grandchildren. We're in deep trouble, we've known this for decades, and it's long past time to get serious about it.

Commentary on 05/12/2015

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