Ocean Acidification science: insightful and essential

Turfs overgrowing coralThe concentration of carbon dioxide in the atmosphere is rapidly increasing as we burn fossil fuels. Nobody doubts this. One of the emerging global consequences of this activity is Ocean Acidification (OA); approximately 30% of the CO2 that we emit into the atmosphere is dissolved into the oceans, forming carbonic acid and reducing the pH of the seawater. This is basic chemistry and can already be measured in many marine waters of the world.

The biological and ecological consequences of OA are, however, more complex to understand. Therefore, over the past two decades there has been a dramatic increase in the number of scientific studies investigating the effects of OA. Last week, a review of over 465 of these studies, written by Christopher Cornwall and Catriona Hurd, was published in the ICES Journal of Marine Science. They assessed a number of different scientific methods for rigour and concluded that overall OA science is well designed and executed, and provides useful insights into a complex problem.

There has been some good coverage of Cornwall and Hurd’s paper (e.g. in the journal Nature). Unfortunately, some media outlets misrepresent the findings of the paper. This is of great concern, as the inaccurate and sloppy journalism threatens an essential branch of marine science. I asked Cornwall to write something for this post:

Recently the Daily Mail reported that climate scientists are doom-mongering because their work is flawed. This report is misleading and only serves to introduce misinformation into the public arena.

The Daily Mail quotes an article in Nature by Cressey (2015) that highlights research by Cornwall and Hurd (2015).  Science is always evolving, and its aim is to improve both methods and theory in any given field, to be better equipped to answer the most complex of questions.   Cornwall and Hurd was merely a call for improvement in only one aspect of research amongst a multitude of methods.  The report in the Daily Mail misrepresents our findings.  There is overwhelming evidence that the effects of ocean acidification will impact our oceans through reductions in the growth and calcification rates of calcified organisms (e.g. shellfish, corals, etc., that make calcium carbonate ‘skeletons’), and an alteration of the behaviour of other marine invertebrates and fish.  This fact is unequivocal.  Rather than being “flawed”, the majority of ocean acidification studies have been carried out carefully, using a multitude of methods, and most provide extremely useful and insightful data on this complex problem.

Certainly, the consequences of OA are complex and modified by interactions with other stressors (e.g. nutrient pollution, global warming) and biotic interactions such as herbivory, competition and habitat complexity. This does not mean that the OA science to date is flawed, it simply means that we have more research to do to understand the future impacts. We need to understand all of the effects of OA, from the physiology of single organisms, through population dynamics and up to ecosystem-level interactions. This pattern of discovery is across all of science. For example, Einstein’s theory of relativity is complex. Physicists are making great discoveries but still have research to do. Ocean Acidification is no different.

When global warming and shifting-baselines syndrome collide

We are having a strange summer in South Australia. First it was mild, then it was late, now it’s hot. So, the weather is a hot topic (pardon the pun) in every conversation. Invariably, conversation then leads onto climate and global warming. And that’s where things get interesting because, as I’ve discussed before, humans and all other organisms experience weather, not climate. In one such conversation with a friend I brought up an excellent article published recently in The Conversation. The article outlines a scary truth; by the end of February 2015 the global temperature has been above the long-term average for 30 years (see the second figure from NOAA, below). My friend said to me, in a very tongue-in-cheek way, “well, I’m 30-ish, which means that they ARE average temperatures to me!”

And that is part of the problem with climate change. It is now easy to demonstrate that temperatures are warming. In Australia, we’re starting to get used to hot summers and bush fires. Even amongst normal inter-annual variation, it’s certainly not difficult to see where the temperature trend is going from the temperature records:

This pattern is repeated globally:

But why can’t we seem to accept the data to all agree that the earth is warming and that we’re the cause?

The problem is three-fold. First, there is the shifting-baselines syndrome. Basically, the idea behind this syndrome is that what you experience in your lifetime is “normal” to you. As with my friend, if you’re only 30 years old (or younger!) then these current temperatures are “normal”. But that doesn’t mean that they ARE normal; the data clearly show that we’re warming outside pre-industrial climatic patterns.

Second, and related to the first, is that we only experience weather. If it rains, we get wet. If it’s winter, we put on a jacket. If it’s summer, we go swimming. We don’t experience “averages.” Some colleagues and I recently published a paper explaining the different effects of climate and weather, noting that without understanding these differences we will not be able to predict what will happen to our marine ecosystems. Yet, policy-makers generally conflate climate with weather, and so we continue to hold to bad policy.

The third, and possibly worst reason, is that in an attempt to “sell the story” the global media still pretends to provide a balanced report. What this means for them is that one person who speaks out against the science underpinning our understanding of climate change gets equal voice to the thousands of scientists who recognise the rigor of this science. That is not only unbalanced, but simply confuses the public into thinking that there is some debate. There is not. To paraphrase the start of the Conversation article, let’s call it, the climate has changed and we’re the cause.

Can nature compensate for human impacts?

Algal turfs dominating under acidified conditions at cold-water (temperate) CO2 seeps, which we use at "natural experiments". You can just see the fronds of a solitary kelp plant in the right of the photo, otherwise they are rare at the site (when they should be 8 - 10 plants per metre!).

Algal turfs dominating under acidified conditions at cold-water (temperate) CO2 vents, which we use at “natural experiments” to try and understand the effects of carbon emissions on our oceans. You can just see the fronds of a solitary kelp plant in the right of the photo, otherwise they are rare at the site (when they should be 8 – 10 plants per metre!). This is a system that has been pushed past its ability to resist or compensate for human activities.

One thing that humans are really good at is having an impact on the environment through their activities. The problem is that we generally don’t realise that we’re having an impact until something changes in a drastic way. We talk about things called phase-shifts, where the environment changes from one “phase” to another. Good (and unfortunately common) examples are the loss of kelp forests for bare reef, seagrass meadows for bare sand, or coral reefs for algal habitats. In all of these cases, the environment has been degraded to the point where it no longer functions as it should, meaning that biodiversity and productivity are massively reduced.

There are two questions to ask here, (1) why don’t we see these phase-shifts coming, and (2) does nature have any resistance to them? A new paper by one of my PhD students, Giulia Ghedini, shows that nature may actually try to resist human-caused stressors (such as increased nutrient pollution, ocean acidification, warming) by increasing the strength of compensation. In this case, Giulia found that the compounding effects of multiple disturbances increasingly promoted the expansion of weedy algal turfs (which replace kelp forests), but that this response was countered by a proportional increase in grazing of those same turfs by gastropods. This is a natural compensatory mechanism, but it has limits.

What does this mean for our understanding of phase-shifts? First, it means that nature is stronger at resisting than we realised. BUT, because it is extremely difficult to either see or quantify this resistance we generally don’t realise it is happening…. until it stops. Then, once we push the systems past their ability to compensate for the increased pressure we place on them we see a sudden shift. It’s like watching a duck on a river – it may look extremely calm on the surface, seemingly stationary, but underneath it is paddling extremely hard. At some point the current strengthens too much and it can’t paddle harder and so, seemingly suddenly, the duck begins to float down the river.

Unfortunately, when put together, this means that more systems may be more stressed than we realise, and the only way to stop detrimental phase-shifts is to take the conservative approach and start to reduce our impacts on these systems. For example, we know that nutrient pollution, carbon emissions, overfishing and many other activities have damaged marine ecosystems, why not begin to reduce our impacts before we add more systems to the list of those we didn’t realise were at breaking point?