Monday, November 8th, 2010
When CO2 from fossil fuels accumulates in the atmosphere, some of it dissolves into the oceans where it reacts with water to form a weak acid (H2CO3) —carbonic acid— that lowers seawater pH and makes it increasingly difficult for corals and other calcitic organisms to form their calcium carbonate (CaCO3) skeletons.
A new study in the Proceedings of the National Academy of Sciences by Rebecca Albright and colleagues suggests that the negative effects of ocean acidification don’t stop with adult organisms. The colonization and establishment of juvenile corals appear to be severely impacted. They studied a common coral found in the Caribbean—Acropora palmata (elkhorn coral, which is not the same as the staghorn coral species pictured above).
A snapshot of their results:
This is potentially very bad news because if you shut down the capacity for new corals to establish, you reduce the ability of coral reef systems to persist in the face of disturbances like hurricanes, wave action, nutrient pollution, bleaching, and disease.
Rebecca Albright, Benjamin Mason, Margaret Miller, and Chris Langdon (2010). Ocean acidification compromises recruitment success of the threatened Caribbean coral Acropora palmata Proceedings of the National Academy of Sciences
Thursday, October 14th, 2010
At the 2009 meeting of the American Geophysical Union, renowned climate scientist Richard Alley (Penn State) gave a keynote address, The Biggest Control Knob: Carbon dioxide in Earth’s Climate History, in which he used a variety of paleoclimatological proxy data to show how CO2 changes over much of Earth history have exerted a strong influence on global temperatures.
In this week’s issue of Science, Andrew Lacis and colleagues published an article, Atmospheric CO2: Principal control knob governing Earth’s temperature (abstract only; subscription required), following up on this theme. Unlike Alley’s talk, which mainly focused on the role of CO2, this team starts by going after water vapor and confronting a widely held perception that it is the dominant greenhouse gas:
It often is stated that water vapor is the chief greenhouse gas (GHG) in the atmosphere. For example, it has been asserted that “about 98% of the natural greenhouse effect is due to water vapour and stratiform clouds with CO2 contributing less than 2%”. If true, this would imply that changes in atmospheric CO2 are not important influences on the natural greenhouse capacity of Earth, and that the continuing increase in CO2 due to human activity is therefore not relevant to climate change. This misunderstanding is resolved through simple examination of the terrestrial greenhouse.
Water vapor is a main reason why the world has a pleasant and life-sustaining average temperature of 16 degrees C. Based on the distance of Earth from the Sun, physics tells us that Earth should be about 0 degrees C—a giant snowball hurling through space. The reason why we are warmer than this is because of the natural envelope of greenhouse gases, including water and CO2 that absorb longwave heat radiating from the surface. This warms the surface of the planet just like a thick blanket keeps your body heat near your skin on a cold night.
In round numbers, water vapor accounts for about 50% of Earth’s greenhouse effect, with clouds contributing 25%, CO2 20%, and the minor GHGs and aerosols accounting for the remaining 5%.
So water vapor and clouds make up about 75% of the greenhouse effect, which sounds like the definition of “the dominant greenhouse gas” to most of us. How does one show that CO2 really is more important than water vapor as a primary greenhouse gas driving temperature change when it looks like water is so important?
Monday, October 4th, 2010
Scientists wrapped up their first global census of sea life today, documenting an underwater world that turns out to be livelier and more connected than they thought it would be when they began the project 10 years ago.
The raw numbers behind the $650 million Census of Marine Life are impressive enough: Almost 30 million observations by 2,700 scientists from more than 80 nations spent 9,000 days at sea, producing 2,600 academic papers and documenting 120,000 species for a freely available online database.
Australian marine ecologist Ian Poiner, who chairs the project’s steering committee, said the results will serve as a “global baseline” for assessing the state of the ocean’s species over the decades to come. “That’s not only something that wasn’t available in 2000,” he told me from London, where the census’ final results were shared with the world today. “Many said it was too big a challenge and could not be done.”