The long-term threat of sea-level rise


Road repair along Nippon Causeway, 2014

My recent article in Scientific American discusses how low-lying coral atolls, like the islands of Kiribati, are a lot more resilient to sea-level rise than dire stories in the media may have you think. But don’t let the nuances of reef island geology described in the article create any doubts about the reality of sea-level rise.

The oceans are rising, and the long-term picture for places like Kiribati is not pretty. This was brought home in the past few days by storm surges again damaging Tarawa atoll’s key causeway that links the most populated islet and international port to the rest of Tarawa.

Here’s a short sidebar of the science of sea-level rise which had to be cut from the article due to space considerations:

The oceans are rising, and the rate of that rise is increasing. Global average sea-level has risen 20 cm since the beginning of the last century, and may rise up to a metre or more by the end of this century.

We can blame greenhouse gas emissions and the basic physics of water.
The planet is absorbing extra heat thanks to the human enhancement of the natural greenhouse effect. The atmosphere gets all the attention, but actually receives only 1-2% of that extra heat. The majority – roughly 93% – goes into warming those deep pools of salt water covering two-thirds of the planet. When water warms up, it expands. That thermal expansion of the ocean is responsible for over half of sea-level rise since 1900.

The key issue for future sea-level is the 3% of the extra heat in the climate system going towards melting ice, especially the Greenland and West Antarctic ice sheets. The rate of melt from these great ice sheets, which hold enough water to raise sea-level by about 12 metres, will define the coasts of the future.

The most recent Intergovernmental Panel on Climate Change report concluded that sea-level would likely rise by 52 – 98 cm by the end of this century, but allowed that far greater changes were possible. It all depends on the complicated process of ice sheet melt.

We know that during periods of Earth’s history when temperatures and greenhouse gases were at levels expected for mid-century, ice sheet melt may have raised the oceans more than 5 metres above current sea-level. We don’t know exactly how long it takes for all that ice to break off or melt. Estimates run in the centuries or longer.

The long-term change is the existential concern for a place like Kiribati. From the article:

The fact that reef islands can grow in some cases and that adaptation measures can help will not save Kiribati forever, especially if the world fails to reduce greenhouse gas emissions. Climate models project that if we stay on the current emissions path, sea-level could be rising at the end of the century at more than five times today’s rate. Even in the unlikely case that islands are able to continue, on net, to accumulate material at their current rate, they may become narrower, steeper and possess less freshwater, making them prohibitively expensive to inhabit.

After a discussion of adaptation needs and ongoing initiatives in Kiribati, the article concludes with a thought I’ve had every time my local colleagues and I return to land from collecting data:

Tarawa's lagoon, visible in the distant clouds

Tarawa’s lagoon, visible to a trained eye in the distant clouds

As you travel out to sea in Kiribati, the flat islands quickly disappear below the horizon. In the old times, fishers navigated home by looking for the reflection of the shallow, greenish lagoon waters in the clouds. One day in the distant future, many of the islands of Kiribati could succumb to the sea. The people may leave, the trees may die and the land may become a submerged reef. The lagoons, still shallow in contrast to the deep open ocean, would remain green as before.

To outsiders, Kiribati would be gone. To the Kiribati people, the ghost of their former homeland would live on in the clouds.


Life as a climate change poster child: the new Scientific American article about Kiribati

???????????????????????????????I have a feature (“Fantasy Island”) in the latest issue of Scientific American and accompanying online slideshow about the reality of sea-level rise in Kiribati.

The article summarizes the complicated science of sea-level rise in coral islands and the even more complicated politics of being a poster child for the impacts of climate change on the developing world. In reflecting on years of research on the ground and on (and in) the water, I try to provide an antidote to all those well-meaning but generally inaccurate pieces of popular disaster porn written about remote island nations like Kiribati and Tuvalu.

If you are interested in what actually is happening in places like Kiribati, I encourage you to buy the issue. An excerpt:

A North American or European traveling to Kiribati may as
well be stepping through a wormhole into another universe. Combine
that naïveté with the reserved nature of the Kiribati people,
the custom of deferring to outsiders, the legacy of countless
past i-Matang asking about climate change and the lack of local scientific
capacity to verify claims, and a naturally flooding village
becomes a victim. Add in the geopolitics—the legitimate need for
a tiny country lacking agency on the world stage to raise awareness
of a threat to its existence—and the exaggeration about the
impacts of sea-level rise can look intentional, whether it is or not.
As my friend Claire Anterea of the Kiribati Climate Action Network
says, “This is not a story that you will just journalize in one
week or two weeks.”

The article is  a testament to all the wonderful people in Kiribati that I have interviewed and worked with over the years, as well as to Mark Fischetti and the editors at Scientific American, who were willing to embrace a story about the incredibly important but less glamourous nuances of climate change.


Corals suggest El Niño may become more frequent

By Jessica Carilli, Assistant Professor UMass Boston


The author at work

In a warming world, key ocean-atmosphere processes, like the El Niño / Southern Oscillation, are expected to change. An important question is whether the frequency or nature of climate oscillations like El Niño will change in the future.

During El Niño, trade winds that normally blow warm surface waters from east to west across the equatorial Pacific Ocean weaken. The extra-warm surface waters that normally pile up in the west, called the Warm Pool, slosh back towards the east, shutting off upwelling off South America and reducing fishery productivity there. Rainfall patterns also change, moving to the east over the central Pacific and causing droughts in the west. El Niño also has global knock-on effects, like higher rainfall in California and drought in Australia.

In 2010, Simon Donner and I went to the Gilbert Islands, in the Republic of Kiribati, to collect core samples from large coral heads with the intent to learn how climate and the local coral reefs had changed over the past century.

Corals build their calcium carbonate skeletons from seawater, and in the process record changes in their environment – like water temperature and salinity – within the chemistry of their skeletons. Coral skeletons also have rings like trees, so assigning dates to the resulting skeletal environmental records is straightforward.

Gilbert Islands study region map

Butaritari is near the northern edge of the Gilbert group of Kiribati

The Gilbert Islands sit near the eastern edge of the Warm Pool, and are particularly sensitive to a recently discovered variant of El Niño, called El Niño Modoki or central Pacific El Niño. These events seem to be increasing in frequency, which makes this region particularly interesting.

Along with a team of researchers in Australia, we reconstructed water temperature and salinity at Butaritari, in the northern Gilbert Islands, from 1959-2010 and compared trends to other Pacific coral records. The gradient in water temperature from east to west across the Pacific is intrinsically linked to an atmospheric circulation cell called the Walker Circulation, comprised of the trade winds at the surface, rising warm air and rainfall in the west, and sinking, cool dry air in the east.

The records from Butaritari indicate that waters there have not warmed as much as water farther east along the equator. This means the west-east water temperature gradient has weakened over the past half century, and that the Walker Circulation – which breaks down during El Niño events – is weakening.

A weaker Walker Circulation in turn means that El Niño events will be more likely to occur. We could therefore be in for a future of increased El Niño events, which has consequences for fisheries, farming, and freshwater availability – not to mention increased likelihood of natural disasters like flooding and wildfire in some parts of the world.

The original publication can be accessed here or contact Jessica for a PDF.


Warming El Ninos on a warming planet

According to the World Meteorological Organization, this year is on pace to be the warmest in recorded history. Whether or not 2014 is awarded the gold, silver or bronze in the global warming’s equivalent of the 100 m dash will probably depend on the temperature dataset. The precise placement of any one year on the medal standings is, of course, immaterial to the broader issue of the longer term trend, described beautifully by Eric RostonENSO-temps-v2-wTrends-638x431.

What is remarkable to many observers is that a record might be set without the help of a “full El Nino”, to use the WMO’s term. In the last few decades, global average surface temperature records have generally been set by a combination of the long-term warming trend and the bump from everyone’s favourite Latin American weather nickname. An increasingly common way to plot global average surface temperatures is with additional labels for El Nino, La Nina and neutral years, as was done in the WMO report and this figure from Skeptical Science. The take-home message – El Nino, La Nina, neutral, it is all warming.

The labeling is the tricky part, for two reasons. First, El Ninos normally develop and peak over the “boreal” or northern hemisphere winter, which means they span two calendar years. There’s usually a few months lag between the development of El Nino and the global temperature effect. Thus, for the global temperature analysis purposes, the “El Nino” year is the year after the onset of the event. The best example is the 1997/98 event which helped bump 1998 to a warmest year gold medal.

Second, there’s no one perfect way to classify El Nino events. For example, in the Skeptical Science plot, 2005 is classified as an El Nino year. In a plot in the WMO report, 2005 is classified as a neutral year. These conflicts arise with “weak” El Nino years because different groups use different classification systems. The U.S. agencies NOAA and NASA disagreed as to whether 2004/05 was an El Nino event.

The suggestion that El Nino events be divided into types or flavours may address some of this potential disagreement. The recent paper led by my former student Sandra Banholzer concluded that the global average surface temperature is anomalously warm – statistically-speaking – during the canonical or traditional “Eastern Pacific” El Nino events like 1997/98, but not during “Central Pacific” events or “Mixefig2 - banholzer and donnerd” events. A more nuanced classification system allows 2004/05 to get status as El Nino-ish, but not a classic El Nino.

There are a variety of ways to perform the classifications and it is safe to say that the scientists involved do not agree on the “best” method. Whatever method is used, the underlying surface warming trend is the same. As is clear from this figure from the recent paper, the warming trend is robust.

NOTE: We will have a poster on this subject at AGU on the afternoon of Wednesday, December 15th


A blast from the coral past

20141117_140418This blue coral specimen was collected during the U.S. Navy expedition to Bikini Atoll, in advance of the famous hydrogen bomb tests and forced evacuation of the Bikinians.

After years essentially collecting dust in someone’s basement, a group of corals from that expedition were donated to the California Academy of Sciences in San Francisco.

I took the photo during a recent visit to give a talk and to tour their incredible collections.


Message from communications research: Climate change is real. Repeat. Repeat again.

There is an ongoing feud about value in communicating the scientific consensus on climate change to the public. One side argues that we need to talk about the consensus in order to raise public awareness about climate change. A new review article by John Cook and Peter Jacobs (also described in the Guardian) reviews the evidence for “consensus messaging”.  The counterargument, proposed by Dan Kahan and others, is that talking about consensus will increase political polarization about climate change.

A recent paper by Kahan called “Climate Science Communication and the Measurement Problem” suggests the disagreement among communications researchers is related to the “contamination of education and politics with forms of cultural status competition”. It is a fascinating paper with a lot of important findings. But I wonder if, deep in the data, there may be evidence that the drumbeat of climate change news and outreach campaigns has actually been effective.

The core result of the paper is described by the following figure:

Kahan 2014 - Fig 7 - no legendIf people were rationally assessing scientific information, higher science comprehension would translate into higher perceived risk from climate change (left panel). Kahan’s experiments find the opposite for people on the right of the political spectrum (red, right panel). That’s been the headline: for conservatives, better knowledge of climate science might mean less concern about climate change.

In other words, when people go beyond the basics, opinions become polarized. That is not very surprising, given that someone on the right of the political spectrum with greater interest and/or ability in science who looks for information about climate change may head to right-wing media and blogs, which often house an alternate universe of “facts” about climate change.

What is more surprising are the results for people with low “science comprehension”.

Why are people with low science comprehension on both the left and the right of the political spectrum perceiving moderate to high risk from climate change? If people’s views on climate change are defined more by their cultural identity than by the facts of the case, why would people on the right of the spectrum with low science comprehension have even moderate concern about climate change?

This opinion about the risk from climate change must derive from something. It isn’t a detailed knowledge of the science, or the problem. Otherwise, the people would fall elsewhere on the graph. It also isn’t their community. Their community, if defined correctly, generally believes the risk from climate change to be low.

What’s happening? Perhaps there has been enough mention of climate change in the public domain, whether on the news, in private conversations, etc., that even those who pay scant little attention to science have been able to develop some level of concern about climate change.

It may be that, current polarization aside, the much-maligned information deficit model has actually worked, at least with very basic information, and in the way political messaging works. Years of repeating the general facts of the case – climate change is real, caused by humans, and poses a risk to the future – appears to have created a basic public consciousness about climate change.


US-China climate deal places pressure on Canada

The proposed climate agreement between the U.S. and China will put the Canadian government’s promise to harmonize with U.S. policy to the test.

Under the new agreement, the U.S. would limit greenhouse gas emissions to 26-28% below 2005 levels by the year 2025. That is a step beyond the existing U.S. target, shared by Canada, of 17% below 2005 levels by the year 2020.

The U.S. is roughly on pace to meet its 2020 target, with emissions for 2012, the most recent year available, only 8% above the target and further reductions possible due to automobile regulation, coal regulations and the shift from coal to natural gas for energy.

Canada is not; emissions were 13% above the 2020 target in 2012 and are projected to increase over the next two decades largely because of activities in the oil sands sector. According to the Environment Canada projections, Canada’s emissions are projected to reach 762 Mt of CO2e by the year 2020,  9% above the 2012 level and 25% above the 2020 target. 

The new agreement will increase the gap between U.S. and Canadian ambitions. Canadian greenhouse gas emissions are projected to be one third above the new target for the year 2025 agreed to by President Obama (assuming the Environment Canada projection for 2025 is halfway between the 2020 – 762 Mt – and 2030 – 815 Mt).

The core of the gap is the oil sands. This is not environmental rhetoric. This is math, based on the government’s own projections, submitted to the United Nations according to international reporting agreements. Roughly three-quarters of the projected growth in Canadian emissions by 2030 comes from the oil sands sector, with the remaining growth in industries like rail and heavy-duty trucks that can be related to the oil and gas activity.

Without addressing the expected growth in greenhouse gas emissions from the oil sands, Canada will not come close to even stabilizing emissions in the next couple decades, let alone keeping up with action by the U.S. and the rest of the developed world. At some point, our leaders need to address the elephant in the room.


What is, and is not, climate “data”?

The word “data” is misused a lot in conversations and publications about climate change. How many times have you heard or read the phrase “future climate data”?

Data, according to the Webster-Miriam dictionary, is factual information (as measurements or statistics) used as a basis for reasoning, discussion, or calculation. It is something that was measured. Numbers, words, sounds, emotional responses can all be data, so long as they were observed and recorded. Without a time machine, there is no “data” about the future.

Future projections from climate models are not, strictly-speaking, data. A numerical model, whether a complicated computer model of the atmosphere or a Newtonian physics equation from high school, may rely on actual data as initial inputs. The numbers produced by that model are not data. They were not directly measured. They are predictions derived from inputting the measurements into a simplified representation of the system being studied.

To clearly distinguish between actual data and numbers produced by models, climate scientists usually refer to the numbers produced by a model as “model output”, or sometimes “model results”.

The line between data and output can sometimes be blurry. For example, the ocean temperatures from a remote sensing group like NOAA Coral Reef Watch are the result of an algorithm integrating a series of point satellite observations over a region or “grid cell”, and controlling for factors like clouds. It is therefore the output of a simple model, which is why it is common to refer to those values as “satellite-derived data” rather than “satellite data”.

And if you really decompose the way much “data” is physically measured, you will find the line between data and output disappear entirely. Often the instrument, whether a simple thermometer or a complicated fluorometer, used to make measurements itself relies on some embedded empirical relationship that translates a raw independent observation into the desired variable.

Regardless, the rhetorical confusion between climate “data” and climate model “output” is not just semantics. In some settings, people’s choice of wording reflects a real confusion about what climate science can do for the world.

One of the central challenges in helping the developing world adapt to climate change is the gap between the desire for precise information about the future and the uncertain, probabilistic projections that science can deliver. During workshops, research interviews and private conversations in the Pacific Islands, I often here laments that “we need the data”. The use of the word data to describe future climate projections exemplifies that gap. People want precise, down-scaled climate predictions for their island or village, not a probabilistic range for an entire region. People want science to deliver something – precise answers – that is not possible.

Explaining and demonstrating the difference between data and output can go a long way to bridging the gap between the ability and the demands of climate science.


The climate, coral reefs, and energy policy must learn to cope with commitment


Bleached corals, Fiji, April 2014

This week, the U.S. government announced it would be listing 20 coral species found in American waters as “threatened” under the Endangered Species Act. Part of the rationale is the threat posed by climate change and ocean acidification, a potentially groundbreaking policy move. What may be missed in this announcement is that the original proposal included a longer list of 66 coral species.

The decision begs a broad question. If we are considering the research on climate change and ocean acidification in the decision, then why not list all coral species as threatened?

The Coral Specialist Group of the IUCN, of which I’ve been a part, submitted a detailed comment to the U.S. proceedings. My meager contribution to the group’s terrific dissection of coral ecology and physiology was the argument that committed climate warming may alone be sufficient evidence for all coral species to be listed as threatened. Here is the excerpt, with wording vastly improved by my colleagues:

The projected increase in sea surface temperatures due to the physical commitment from the present accumulation of greenhouse gases due to anthropogenic activity, as well as the socioeconomic commitment (i.e. it is logistically impossible to instantly eliminate anthropogenic emissions, regardless of policy decisions, because of inertia to the existing energy system), is sufficient to cause frequent and higher magnitude heat stress for the majority of the world’s coral reefs by 2050 (Donner, 2009). The primary source of uncertainty in this forecast is the ability of the coral holobiont to acclimate and/or adapt to heat stress. The fact that the future abundance of coral species depends on a rate of adjustment to heat stress that is unprecedented in geological history should be sufficient to warrant a minimum status of threatened for all coral species.

The problem of coping with commitment, the title of that cited 2009 paper, was highlighted by a terrific new paper that happened to be released almost simultaneously with the U.S. coral decision. In “Commitment Accounting of CO2 emissions”, Stephen Davis and Rob Socolow calculate the committed emissions from the operation of new energy investments, like coal plants, over the expected lifetime of those investments (see Dot Earth for a lengthy discussion). They conclude that it would  be sensible to use committed emissions, rather than the annual emissions, to inform public policy.

The socioeconomic commitment or capital “lock-in” to future emissions has implications for everything from these species listings to oil pipeline decisions. We can’t perfectly project the future of each coral species, but we can say that the oceans are committed to physical and chemical changes which may be dangerous or fatal to corals. These changes do not guarantee widespread extinction or endangerment, given potential adaptability of many species and the potential refuges in the ocean, but certainly could classify as threatening.


June was the hottest month on record for the ocean

GCDC oceanThe  oceans in June may have set an all-time heat record, according to data from the U.S. National Oceanic and Atmospheric Administration (NOAA). The global average sea surface temperature may have topped 17 °C for the first time in any month of any year since 1880.

The NOAA State of the Climate analysis reported that last month was the warmest June on the planet since records began, thanks in large part to ocean warmth. It was the 7th warmest June on land but the warmest June in the ocean, with the highest departure from normal recorded in the dataset for any month.

The temperature of 17.04°C should be seen as an estimate, given the challenge of defining “normal” for the oceans. However, we can still say with some confidence June may have been the warmest month for the ocean since these records began.

The record ocean warmth is seen particularly in the tropical Pacific, where currents, winds and temperature measurements have scientists forecasting a possible El Nino event.