Readers letters
Neither Tim Fox’s article on geo-engineering (“Protecting the planet”, PE December) nor subsequent correspondence has addressed the other impact of rising CO2 emissions: increasing ocean acidity.
Geo-engineering solutions that reflect solar radiation but allow continued increase of CO2 run the risk of destroying the ocean ecosystem which is vital to us, but about which we know little.
Over 50% of our oxygen is produced by photosynthetic activity in the top 100m of the oceans. Two-thirds of this (one-third of our oxygen) is produced by so called “pico”-plankton (actually only sub-micron size) that comprise only 1% of earth’s biomass and that were only discovered within the last three decades. This phenomenal production to weight efficiency comes at the cost of minimal protein processes and minimal genes to code these proteins and may therefore restrict genetic adaptability to changes in ocean acidity, osmotic pressure, or concentrations of essential minerals that are transported by thermohaline convection currents.
The ocean is enormous many will argue, however it has a very slow turnover rate. Carbon isotope measurements of dissolved CO2 in the ocean show the signature of C14-depleted carbon from fossil fuels. Ocean surveys show that the CO2 emissions from the two centuries of heavy fossil fuel use have been dispersed in approximately equal ratio to the atmosphere and to the ocean. Of the fossil-source CO2 absorbed by the ocean over the last two centuries, 30% still resides within the top 200m layer, and 50% within the top 400m layer. This has resulted in an estimated 30% increase in Hydrogen ions (pH change of -0.1) in the surface layer, and if we reach 1000ppm atmospheric CO2 by 2100, the ocean surface will see a total 200% increase in Hydrogen ions (pH change of -0.5). The earth has seen high CO2 levels before, but the key parameters are the current rate of CO2 rise versus its slow mixing out into the deep ocean. This leads to a large change of acidity within a shallow surface layer where all the photosynthetic activity occurs.
We should be very sure of the impact on the ocean ecosystem before we consider unabated CO2 increase. Do we want to mess with the source of 50% of our oxygen?
References:
“Ocean acidification due to increasing atmospheric carbon dioxide” Royal Society Policy Document 12/05 June 2005
“The oceanic sink for Anthropogenic CO2” by Sabine, Feely, Gruber, Key, Lee, Bullister, Wanninkhof, Wong, Wallace, Tilbrook, Millero, Peng, Kozyr, Ono, and Rios, Science Vol.305, 16 July 2004
“The beauty in small things revealed” by Bryant, Commentary in PNAS Vol.100 No.17, 19 August 2003.
Clive Horrell