Global Warming: Look At Lessons From The Past
By Art Hobson
In 2005, following the release of Al Gore’s climate change documentary “An Inconvenient Truth,” the single most-common criticism of the fi lm focused on the animation showing ocean water fl owing into the World Trade Center memorial site. Global warming skeptics called these scenes unbelievable, irresponsible, absurd. Yet last Oct. 29, the surging seas of superstorm Sandy sent millions of gallons of ocean water into the basement levels of the trade center site, damaging equipment and electrical systems. The flooding, years ahead of the schedule predicted in typical global warming scenarios, was caused when seas rose 13 feet above normal and rushed down city streets.
Human-caused climate change contributed significantly to Sandy’s devastation of the eastern coastline. Because global temperatures have increased by 1.5 Fahrenheit degrees since 1900, there’s now 4 percent more water vapor in Earth’s atmosphere. This increases the severity of extreme weather events such as Sandy. Additionally, the ocean water east of New Jersey was 9 degrees above average as Sandy approached the coast, partially because of global warming. It’s just such high ocean temperatures that provide the energy for hurricanes. Similarly, Hurricane Katrina, which devastated New Orleans in 2005, was driven by recordhigh ocean temperatures east of Florida and along the Gulf Coast. Global warming caused at least some of that temperature increment.
Science magazine is arguably the world’s most respected scientifi c journal. In recent years, each weekly issue has contained several high-quality articles about climate change. An Aug. 2 article, based on calculations done independently at 25 computer modeling centers, projects that continuation of today’s greenhouse gas emissions will create warming during this century that is comparable to the largest planetary transformations of the past 65 million years but is orders of magnitude more rapid. Temperatures in 2050 will be 3.5 degrees warmer than today, and 7 degrees warmer in 2100.
Several recent articles have looked at lessons we can learn from past conditions. One historical analogue to our current global warming is the Paleocene-Eocene Thermal Maximum that raised global temperatures by 7 to 14 degrees 55 million years ago, and ushered in a new geological age — the Eocene. It was caused by large natural releases of carbon dioxide and methane that were comparable to the amounts that will be released by human activities by 2100 if we continue along our present path. During the Eocene, temperatures were too warm to support polar ice caps, causing sea levels to be 150 feet higher than they are today.
An article on June 21 concerns a more recent period when the configuration of the continents was similar to today’s confi guration, and when carbon dioxide levels were similar to today’s. According to the article, “The geologic record makes it clear global temperatures are intimately linked to changes in atmospheric greenhouse gas concentrations.” Data from the Russian Arctic region show how climate varied during the Pliocene era 3.6 to 2.2 million years ago when carbon dioxide levels were about 400 parts per million (meaning that, for every million air molecules, there were on average 400 carbon dioxide molecules) — the same as today’s levels. Polar summertime temperatures during this period were 18 degrees higher than today, making it too warm for the polar ice caps to exist, and sea levels were 70 feet higher than today. As Earth adjusts or “equilibrates” to our present high carbon dioxide concentrations, will Pliocene conditions return?
Beginning about 2 million years ago, carbon dioxide levels dropped and the planet cooled into the Pleistocene period, characterized by alternating ice ages and warmer “interglacials.” During the Pleistocene, carbon dioxide levels varied between 180 parts per million during the long cold intervals, and 280 parts per million during the warm intervals. Civilization arose 10,000 years ago as the last ice age ended and Earth entered its present interglacial period, with carbon dioxide levels at 280 parts per million. Now, just since about 1800, we have driven the level of this key climate control up to 400 parts per million, comparable to Pliocene levels. Unless we come to our senses and reduce emissions enormously, carbon dioxide will reach levels not known since the Eocene era 55 million years ago.
Humans are now the primary force causing planetary geological change. Our activities are driving Earth toward a new geological era that is likely to persist for thousands of years. Yet business continues as usual, and some U.S. senators complain that global warming is a hoax. I am astonished at our epic immorality, and I shudder for my grandchildren.
Art Hobson is a professor emeritus of physics at the University of Arkansas.