THREATS FROM OCEAN ACIDIFICATION
source : Roger Harrabin - BBC News Environment Analyst BBC News Website (Science and Nature)
Threats from ocean acidification
Acid test Explanation
By Roger Harrabin
Environment analyst, BBC News
Many shellfish struggle to survive as seawater becomes more acidic
Carbon dioxide emissions from human activities are acidifying the oceans and threaten a mass extinction of sea life, a top ocean scientist warns.
Dr Carol Turley from Plymouth Marine Laboratory says it is impossible to know how marine life will cope, but she fears many species will not survive.
Since the Industrial Revolution, CO2 emissions have already turned the sea about 30% more acidic, say researchers.
It is more acidic now than it has been for at least 500,000 years, they add.
The problem is set to worsen as emissions of the greenhouse gas increase through the 21st Century.
"I am very worried for ocean ecosystems which are currently productive and diverse," Carol Turely told BBC News.
"I believe we may be heading for a mass extinction, as the rate of change in the oceans hasn't been seen since the dinosaurs.
"It may have a major impact on food security. It really is imperative that we cut emissions of CO2."
Dr Turley is chairing a session on ocean acidification at the Copenhagen Climate Change Congress.
The problem is most acute for creatures which make calcified shells. OCEAN ACIDIFICATION
Up to 50% of the CO2 released by burning fossil fuels over the past 200 years has been absorbed by world's oceans
This has lowered the pH value of seawater - the measure of acidity and alkalinity - by 0.1
The vast majority of liquids lie between pH 0 (very acidic) and pH 14 (very alkaline); 7 is neutral
Seawater is mildly alkaline with a "natural" pH of about 8.2
The IPCC forecasts that ocean pH will fall by "between 0.14 and 0.35 units over the 21st Century, adding to the present decrease of 0.1 units since pre-industrial times"
Natural lab shows sea's acid path
Laboratory tests suggest starfish may be wiped out before the end of the century if current emissions trends continue.
Scientists fear mussels may not be able to cope, either. Oysters may be less vulnerable, and farmed oysters may fare better than wild oysters.
"One thing is certain," says Dr Turley. "Things will change. We just don't know yet exactly how they will change.
"It is not a very wise experiment to be making."
Professor Andy Watson, an ocean biologist from the University of East Anglia, believes climate change and overfishing may ruin the seas before acidification does.
He condemns increases in CO2 from human activities, but points out that ocean acidity also fluctuates naturally.
He also wonders if some creatures might adapt to the changes over time.
"(In) many of the experiments that are being done at the moment, sudden changes are made; the CO2 is quickly raised, for example, or the acidity is quickly raised.
"Of course, that's not really what will happen in the real world," he told BBC News.
"There will be instead a gradual ramping up of CO2 and acidity. And we don't know whether organisms will be able to adapt or how quickly they'll be able to adapt."