Out in the oceans, climate change is pushing marine
chemistry towards a critical trigger point, reports Tom
Droughts, wild and unreliable weather and tides lapping at
the doorsteps of civilisation.
It is the now-familiar reality of climate change.
Most recently, a World Bank study estimated that by 2050,
flood damage in the world's coastal cities would reach $US1
trillion ($NZ1.26 trillion) a year as sea levels rise and
global warming triggers new extremes of heat, windstorm and
Similar themes are explored in the report ''New Zealand's
changing climate and oceans: The impact of human activity and
implications for the future'', published this month by the
Office of the Prime Minister's Science Advisory Committee,
overseen by Sir Peter Gluckman.
But far from land, a shift is also under way in what Prof
Keith Hunter says is often referred to as the forgotten side
of climate change.
Prof Hunter, New Zealand's leading scientist in the field of
marine and freshwater chemistry and pro-vice chancellor
sciences at the University of Otago, has been researching the
effects on the ocean of increased levels of CO2 in the
atmosphere for some time.
For the past 12 years his research group has regularly sailed
out past the continental shelf, off the Otago coast, in the
university's research ship Polaris II, taking measurements.
Their work will be published later this year, confirming that
the world's oceans are becoming more acidic as the more
concentrated levels of CO2 in the atmosphere mix with the
It was for these insights that Prof Hunter was called to
Wellington, when Prime Minister John Key's science adviser,
Sir Peter, was asked to put together the report on climate
change and its probable impacts on New Zealand.
Together with other scientists from around the country he
spent a day sharing research, all of which was then pulled
together to fill in the blanks for the Prime Minister.
For scientists, one of the blanks in the understanding of the
world's carbon budget was, for some time, a mystery missing
third, Prof Hunter says.
Work trying to identify where it was going began about 25
years ago, based on the suspicion it was disappearing into
the ocean, mixing in as the result of wave motion where water
meets air. It proved demanding to measure.
''By the time we figured out what was going on, we suddenly
realised that this is not a good thing,'' Prof Hunter says.
It dawned on researchers just how finely the ocean is
balanced in terms of the solubility of calcium carbonate, a
critical compound for creatures at the bottom of the food
''We didn't initially realise that it wouldn't take much to
tip the balance.''
The Gluckman report puts it this way: ''Lowering the pH
[acidification] of the water below a threshold creates
conditions in which calcium carbonate, which makes up the
exoskeleton of many marine organisms, would naturally
The numbers around the changing pH are small. Measurements
made by Prof Hunter's team suggest an average pH drop of 0.02
However, the raw numbers are deceptive as pH is a logarithmic
scale, like the earthquake-measuring Richter scale.
''A change in pH of 0.3 represents a doubling or halving of
hydrogen ions. So 0.3 is 100% change.''
In the past 150 years the change in pH has been about 0.1,
what Prof Hunter calls a ''big step in the wrong direction''.
If pH continues to fall a critical point will be reached when
calcium carbonate becomes soluble. And it is expected that
will happen first in the coldest of the earth's water, as CO2
is more soluble in cold water.
Those high latitude cold waters are also where the oceans'
deep waters are formed, as surface water cools and sinks,
taking CO2 with it.
''We think that one of the earliest regions where this will
become manifest will be in the Southern Ocean around
Antarctica, and we think that those waters will become
corrosive to a group of small organisms called pteropods -
they are a few millimetres in size, and they are a kind of
snail and they are an important part of the food chain - they
will experience trouble around 2035.''
Such animals sit at the bottom of a food web that leads all
the way up to the biggest of marine mammals.
Because waters around New Zealand are warmer, it is likely to
take another century before the problem reaches here, with
the possible exception of a few hotspots where deeper waters
Nevertheless, the report says the combined effect of chemical
and temperature changes in the seas around New Zealand is
likely to have an impact on marine biodiversity and a
''significant impact'' on the fishing industry.
Prof Hunter says the most important effects could be on the
larval stage of marine animals.
''If you had, for example, a mass die-off of certain types of
larvae, then the adults those larvae would turn into, would
Gathering the information needed to arrive at such
conclusions, has taken place on the Polaris II voyages
of Prof Hunter's group.
Several times a year for the past 12 years they have sailed
out 70km from Dunedin, beyond the continental shelf, taking
continuous measurements of pH and CO2 as they go.
At eight different stations they also take samples to take
back to the lab.
''It gives us a very accurate description of CO2 in the water
column as a function of time,'' Prof Hunter says.
Those results are to be published for the first time later
this year, an event that Prof Hunter expects will spark some
What they show is that pH rises and falls during an annual
cycle, as plankton photosynthesises CO2 and then dies, but
superimposed on that, average pH is falling every year. For
the Otago offshore waters, the pH varies from 7.81 in winter
to 7.88 in summer.
They are the only such measurements done in the southern
hemisphere. Two comparable sets of measurements in the
northern hemisphere, near Hawaii and Bermuda, have both shown
the same trend.
Among the range of possible responses to the problem is
geoengineering, in which steps are taken to counter the
pH-lowering effect of CO2.
It gets a passing mention in the Gluckman report, which
suggests chemicals could be deployed in localised areas, for
example around aquaculture, to temporarily offset changing
However, the report goes on to comment that ''such
geo-engineering solutions only offer short-term solutions and
may have unintended consequences at a system level''.
Prof Hunter has not been involved in looking at such
local-level interventions, but has evaluated global-scale
geoengineering, such as iron fertilisation.
''You throw iron dust on the ocean and you absorb CO2,'' he
''There's a lot of interest in that overseas but our research
group did quite a bit of work on that and demonstrated that
it really doesn't work. And it is fraught with potential
Geoengineering might work in a more localised way, perhaps in
little coastal bays where upwelling water causes
acidification, he says.
''I think if you apply scientific principles and you are
careful about the possible side effects, I don't see why it
shouldn't be looked at.''
Acidification is not the only change going on out at sea.
Ocean temperatures are rising alongside the anthropogenic
warming in the atmosphere. Indeed the relative flattening of
atmospheric temperature increase since 1998 is thought to be,
in part, a result of the deep oceans absorbing a larger part
of the greenhouse effect.
The report for the Prime Minister suggests changes in marine
species as a result, including tropical sharks moving south.
For now, Prof Hunter says the area where attention needs to
be focused most urgently is the effect CO2 is having in the
''We have seen nearly a degree of warming already, and the
models of atmospheric physics suggest maybe two degrees more.
That's really quite severe.''
What needs to be calculated now, Prof Hunter says, is
precisely how much more CO2 can be safely emitted into the
He is critical of the approach, outlined this month by
Climate Change Minister Tim Groser following the release of
the Gluckman report, in which an emissions target was set for
2020 of 5% below 1990 levels.
''The issue is not when you put the CO2 in, it is how much
you put in from now on,'' Prof Hunter says.
''We really need to be thinking not so much about how much we
can release per year but how much of the total inventory of
the fossil fuel that is left, how much are we allowed to
''And that answer is not very large. That is where some of us
are trying to get the debate to turn.''
One estimate is that the global upper limit for CO2
emissions, to have even a 50% chance of preventing more than
2degC of warming, is 1.8 trillion tonnes, a quantity that
will be passed before 2050 at current rates.
''I would have preferred the Government to have said, 'we
will limit our fossil fuel emissions to a certain number of
billion tonnes and that's it, we will stop','' Prof Hunter
''There has to come a time when we have to stop.''
It might take 50 years to stop, but that was where the policy
debate needed to be focused.
Further impetus for such arguments is expected to come from
the Fifth Assessment Report of the United Nations
Intergovernmental Panel on Climate Change, the first part of
which is due out next month.
Leaked copies indicate the scientific consensus on the issue
has only strengthened, as has the confidence in climate
models showing continuing warming.
Prof Hunter has seen some of the work that has gone into it
and says it will annoy those still in denial.
''It will receive favourable attention from people who are
serious about the issue,'' he says.
''Because it is more definitive than it was last time and
that's just what happens, because the science is getting
better and more comprehensive.
''The scenarios it describes are quite realistic, I think.''