Author: drmarchudson

Here’s the front page story on the CO₂ Newsletter for June-July 1980. You can find out more about the newsletter here.

We knew. We knew. Brave diligent people like William Barbat tried to amplify the science, connect the dots, connect the policymakers, the publics and the evidence.

A sense of urgency was introduced to the CO₂-greenhouse problem July 30, 1979, when Wallace Broecker (Lamont-Doherty Geological Observatory) explained to the U.S. Senate Committee on Governmental Affairs, “We have good evidence that during the peak of the last interglacial period, the sea level did indeed stand 6 meters (20 feet) higher than it does now, and we don’t think the temperature of the globe was any more than 1 degree Celsius warmer than now.”

A 1 degree C warming is generally expected to be reached shortly after the turn of the century if the CO₂ buildup continues as in the past, The energy scenario of F. Niehaus (International Atomic Energy Agency) which might halt a CO₂-induced global warming just short of 1 degree C, as shown in the inset, would call for a rapid phase-out of fossil mostly by nuclear, This scenario was presented at the same Senate hearing. 

Broecker’s 6 meter rise (point ‘a’) does not appear unreasonable on a plot of temperatures vs. sea elevations ranging from ice ages to no-icecap conditions. Global average temperatures of 4 degrees to 5 degrees C cooler than now are shown for the ice ages, as used by Svante Arrhenius in his CO₂ greenhouse model of 1896. Corresponding to these periods of maximum glacial advance are vestiges of shorelines 85 to 130 meters lower than now as shown by bar +b’. (Lag in destruction of the Laurentide ice sheet precludes

other equilibrium values for conditions cooler than now.)

An approximation of the pre-glacial global temperature as shown here 5. degrees C greater than now (point ‘c’) is derived from Eocene and early Oligocene subtropical and tropical sea-surface temperatures in the literature. These sea temperatures were based on oxygen isotope measurements made on shells of pelagic foraminifera which grew at that time,

Arrhenius had also judged that the average Arctic temperatures prior to the existence of ice sheets in that hemisphere were about 8 to 9 degrees C warmer than modern temperatures, based on observations of vegetation and animal life. Allowing for 3X to 4X polar amplification, this would correspond to an average global temperature 2 degrees to 3 degrees C warmer than now, which essentially matches the consensus of estimates for global warming which may accompany a CO₂ doubling, Such a doubling is expected to be reached about 2025-2050 if growth of CO₂ production continues its historical rise.

Because the West Antarctic icecap is believed by John Mercer (Institute of Polar Studies, Ohio State) to have formed at cooler temperatures than the Greenland icecap, the potential sea elevation corresponding to the absence of the Greenland ice is shown here as the sum of the rise if both icecaps were absent, that is, 12 meters higher than present. This 12 meter height – if valid can be considered to be a minimum value, for it is likely that the East Antarctic ice cap was smaller than its present size when global temperature was 2 degrees to 3 degrees C warmer.

No estimates have been published yet for how fast the Greenland ice sheet might disappear with a CO₂ -induced warming, and much controversy still surrounds estimates of how fast the West Antarctic ice sheet may disappear due to a lack of precedents. If the CO₂ buildup continues unabated, the  expected warming over the next half century may take place in about one-tenth the time that a similar temperature rise occurred about 10,3000 degrees before present, during which time sea level was about 0.2 to 0.3 meters per decade according to the compilations of Rhodes Fairbridge.

To illustrate the seriousness of a potential equilibrium with the warmness of a CO₂ doubling, the Jefferson Memorial is depicted on the same elevation scale. For other comparisons, the absence of icecaps would correspond to sea level at the clock face of London’s Big Ben and up to the roadway of San Francisco’s Golden Gate Bridge.