This is a re-post from Yale Climate Connections

“Drought, water, war, and climate change” is the title of this month’s Yale Climate Connections video exploring expert assessments of the interconnections between and among those issues.

With historic 1988 BBC television footage featuring Princeton University scientist Syukuru (“Suki”) Manabe and recent news clips and interviews with MIT scientist Kerry Emanuel, Ohio State University scientist Lonnie Thompson, CNN reporter Christiane Amanpour, and New York Times columnist and book author Tom Friedman, the six-minute video plumbs the depths of growing climate change concerns among national security experts.

Friedman, in footage from the 2014 Showtime “Years of Living Dangerously” nine-episode documentary, points to a NOAA analysis that climate change has caused the Mediterranean region, in Friedman’s words, “to dry up . . . . leading to longer and more severe droughts.” Friedman in that piece pointed out that severe droughts struck Syria – “which is right at the epicenter” of the worst impacts — in the four years leading up to the Syrian revolution.



Why were the ancient oceans favorable to marine life when atmospheric carbon dioxide was higher than today?

Posted on 12 November 2015 by Rob Painting

When we look back through the geological record, we see that for much of the last 500 million years there was an abundance of life in the oceans and that atmospheric carbon dioxide was much higher than today for the vast majority of that time. Though it may seem counterintuitive, especially considering that ocean pH was lower than present-day, the ancient oceans were generally more hospitable to marine calcification (building shells or skeletons of calcium carbonate) than they are now [Arvidson et al (2013)].

Numerous examples exist to support this, such as the enormous coccolith deposits that make up the White Cliffs of Dover in England. These tiny coccolith shells are made of calcium carbonate (chalk) and date from the Cretaceous Period (Cretaceous is Latin for chalk) about 145 to 65 million years ago - when atmospheric CO2 concentration was several times that of today. So conducive to marine calcification was the Cretaceous ocean that it also saw the emergence of giant shellfish called rudists as a major reef-builder.


Figure 1 - Rudist fossils dating from the Cretaceous Period. Marine calcification during this time of higher-than-present atmospheric CO2 concentrations was very clearly not a problem for this marine organism. Image from Schumann & Steuber (1997).

Given the relationship between the concentration of carbon dioxide in the atmosphere and the pH of the ocean, why are scientists concerned about falling ocean pH when it was lower for much of the last 500 million years?  The simple answer is that these were not times of ocean acidification per se, and the key difference is in understanding the time scales and chemical processes involved. Ocean acidification only occurs when atmospheric carbon dioxide increases in a geologically-rapid manner because pH and carbonate ion abundance decline in tandem, and it’s the decrease in carbonate ions that makes seawater corrosive to calcium carbonate forms [Kump et al (2009)] . While the increase in dissolved CO2 and hydrogen ion concentration (falling pH) would have proven stressful for some ancient marine life, such as coral [Cohen & Holcomb (2009), Cyronak et al (2015)], the corrosive state of surface waters likely delivered the decisive blow. 

A perfect illustration of the marked difference between high and low carbonate saturation states is shown in Figure 2. Both marine fossils (discoaster) are from ancient periods of high atmospheric CO2 (i.e. low pH), however the fossil on the left pre-dates the Paleocene-Eocene Thermal Maximum (PETM) some 55-56 million years ago. Carbonate ions were abundant prior to the PETM, however a geologically-rapid pulse of CO2 entered the atmosphere during the PETM, and thus lowered the abundance of carbonate ions. The fossil on the right dates from the PETM and shows clear signs of dissolution, indicating that the oceans back then were corrosive to marine calcifiers, as we'd expect, because ocean acidification was underway (Penman et al (2014).