July 7, 2006

Corals and Climate Change

Filed under: Adaptation, Animals, Plants

A newly-released report (available here) details the results of a 2005 workshop jointly sponsored by the National Science Foundation (NSF), the National Oceanagraphic and Atmospheric Administration (NOAA), and the United States Geological Survey (USGS) on ocean acidification. Oceans are projected to become slightly more acidic because of increased absorption of atmospheric carbon dioxide. This could affect coral reefs and other marine organism that produce calcium carbonate for their skeletons. Acid dissolves carbonate.

Generally, the report concludes that 1) the world’s oceans will acidify over the 21st century, and 2) that marine calcifying organisms (including corals and coral reefs) will be greatly harmed.

Heard this before. With regard to global warming, simply substitute any object (oceans, pandas, humans) and add the words “greatly harmed.” Amazing, though, that the planet has warmed for 100 years and human life expectancies have doubled, isn’t it?

So, it’s a foregone conclusion that this report overstates its conclusions—both by overestimating current and future growth rates of carbon dioxide in the atmosphere, and by downplaying impacts of other, compensating environmental factors.

This text is extracted from the first paragraph of the NSF Report’s Introduction:

Increased fossil fuel burning associated with industrialization, cement production, and land use changes associated with agricultural activities are causing atmospheric CO2 concentrations to rise, and at increasing rates (rates of increase have risen from 0.25% y−1 in the 1960s to 0.75% y−1 in the last five years). The current atmospheric CO2 concentration is about 380 ppmv and is expected to continue to rise by about 1% y−1 over the next few decades (Houghton, 2001)

In every case, the rate numbers in this paragraph are wrong. Figure 1 shows the real atmospheric carbon dioxide growth rate (expressed as a percentage per year) as measured at Hawaii’s Mauna Loa Observatory. In the 1960s, the average rate of change was 0.30% per year, and during the last 5 years, the average rate of increase was 0.55%/yr (statistically indistinguishable from the average of the past 25 years). Thus the real change from the 1960s to the past 5 years is more than 2 times less than the Report states. This is a remarkable error, considering it comes from the National Science Foundation!


Figure 1. Annual growth rate of atmospheric CO2 (%/yr) as measured atop Hawaii’s Mauna Loa volcano.

Further, as evinced by the average rate of change observed over the past 5 years, the statement that atmospheric CO2 concentrations are “expected to continue to rise by about 1% y−1 over the next few decades” is dead wrong. If this is the type of scientific exaggeration and misinformation that is contained in just the first paragraph of the body of the report, what about the rest of the document?

Consider that coral species have been around on earth, continually evolving, for about the last 500 million years or so. During that time the atmospheric CO2 concentrations have fluctuated widely. Figure 2 shows our best understanding of CO2 levels back in time for about 500 million years (taken from the 2001 Third Assessment Report of the Intergovernmental Panel on Climate Change, IPCC).


Figure 2. Atmospheric CO2 concentration during the past 500 million years (Myr BP) (source: IPCC, 2001).

It is clear that atmospheric concentration of CO2 were higher than the present level (~380 ppm) for most of the past 500 million years. During some periods, the levels were thought to be more than 10 times current levels. And corals survived. How does the NSF Report handle this fact? With a bit of handwaving.

They write:

CO2 levels are only one parameter controlling ocean carbonate chemistry, however; alkalinity also determines the carbonate ion concentration. Ocean alkalinities could have been higher during periods with high CO2 levels, since higher CO2 levels accelerate rock weathering and CaCO3 dissolution, which raises alkalinity. Over long timescales, this feedback tends to maintain a balance between atmospheric CO2 and oceanic alkalinity. At the current rate of atmospheric CO2 increase, however, this feedback operates too slowly to raise alkalinity significantly. [emphasis added]

There is no reference given to this theory, nor any other supporting evidence offered. It is hard to believe that as the atmospheric CO2 level varied from less than current levels to 10 times current levels, that the ocean managed to keep its pH levels virtually constant throughout it all—thus allowing corals to survive to the present day, only to be threatened by current changes.

Given that CO2 concentrations have increased by about 100 ppm in the past 100 years or so, is there even any evidence that corals are being affected by increased oceanic acidification? Under controlled laboratory conditions, in experiments lasting only days to months, the answer is apparently yes. However, in the real world, the answer is no.

Reading from the report:

Identification of a “CO2 signal” is difficult because calcification rates in the field are a response to multiple variables (light, temperature, nutrients, etc.), and particularly to rising temperature. If seawater chemistry was the only variable affecting calcification, then calcification records from corals and other organisms should show a decrease in calcification over the past century. While some individual calcification records from massive corals do reveal a decrease in calcification rate over the past century, on average they do not (Lough and Barnes, 1997, 2000), and this is believed to reflect the effects of other variables on calcification. In particular, calcification rates in these and other massive corals show a strong correlation with temperature (Lough and Barnes, 1997, 2000; Bessat and Buigues, 2001; Carricart-Ganivet, 2004). [emphasis in original]

In other words, the NSF would like us to believe that the theory that increasing ocean acidification will slow coral calcification rates is correct, even though it is not readily observed because other confounding variables are involved. However, given time, these other confounding variables could be overwhelmed by the increasing acidification.

So what we have is a report by the National Science Foundation which is wrong about the historical input of carbon dioxide, wrong about the present input, wrong about the foreseeable future, and which admits that warming has not been associated with any decline the production of carbonate. But it well be so in the future, we are told. Just believe us.

It’s probably a better bet that organisms that have been around for 500 million years, on a planet that was much warmer, had much more carbon dioxide in the atmosphere, got hit by an asteroid or two, experienced ice ages, and now a slight warming, will be around long after homo sapiens hit the evolutionary road.

References:

Kleypas, J.A., R.A. Feely, V.J. Fabry, C. Langdon, C.L. Sabine, and L.L. Robbins, 2006. Impacts of Ocean Acidification on Coral Reefs and Other Marine Calcifiers: A Guide for Future Research, report of a workshop held 18–20 April 2005, St. Petersburg, FL, sponsored by NSF, NOAA, and the U.S. Geological Survey, 88 pp.




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