When talk turns to climate change, the prevailing view is of land. With the exception of the melting Arctic ice cap, it’s all about animals on land, plants on land, ice on land. The one aspect of the oceans that’s made a popular impact is sea-level rise—and that’s really about water covering up land.
We’re on the road to the fifth assessment report from the Intergovernmental Panel on Climate Change—work on the fourth won the Nobel Prize—and wondering how 71 percent of the planet has missed a starring role in every preceding iteration. The fourth report’s section on impacts and adaptations, for example, had 20 chapters, including eight on geographic regions (e.g. Africa, Polar Regions, Small Islands), but none on oceans.
Australian marine ecologist Elvira S. Poloczanka of the Commonwealth Scientific and Industrial Research Organisation remembers looking at the IPCC documents, including the particular working group’s section on impacts, and being perplexed. “I just thought, ‘Well, where’s the marine observations?’ There’s 25,000 terrestrial and 85 marine.’ So I spoke to some of my colleagues and we sort of got together and thought, ‘Why haven’t we got any marine observations in this study?’”
Thus in 2009 was born an international working group based at the National Center for Ecological Analysis and Synthesis, which produced the first-ever global synthesis of climate change’s effects on the world’s oceans. Poloczanka is the lead author of a paper describing that synthesis published earlier this month in the journal Nature Climate Change. The paper is expected to inform the IPCC’s fifth assessment, which will include a chapter on the marine environment, although what ends up in the final report will first pass through the IPCC’s own rigorous peer-review process.
Meanwhile, not all land species head north—some move uphill into cooler zones, at least until they top out. At sea, the inverse might be going deeper, but only some species do well with the greater pressure and darkness and less abundant food of greater depths.
But what the group unveiled in their synthesis—which reviewed 208 studies researching 857 species, each study covering at a minimum two decades—is worth at least a chapter. A quick takeaway of what’s already happened: While the ocean surface is warming three times slower than air over the continents, marine life is responding much faster than species on land, moving their ranges poleward on average by 72 kilometers (45 miles) a decade compared to the six-kilometer stroll we’re seeing for land species. “That’s a lot faster,” Poloczanka said. “We really didn’t expect to find rates that were so rapid in the ocean.”
There are other stressors on the ocean—pollution, overfishing, ocean acidification—but the academics found enough "diagnostic fingerprints" to convince them that climate change was the primary driver of the changes. (Ocean acidification is caused by the oceans taking in more carbon, which lowers seawater’s pH, it’s sort of a twin to climate change since it too is exacerbated by higher levels of carbon dioxide in the atmosphere.)
With a planet’s full complement of plants and animals to review, there’s lots of ways to slice and dice these findings. Some species migrate slower or faster toward the poles, where it’s cooler and better matches the past temperature ranges they’re comfortable at, assuming that their food supply precedes or at least advances with them. In general, the marine species are moving between 50 and 200 kilometers a decade, with some having shifted 400 kilometers. And 24 percent of the marine species they studied didn't move at all.
Meanwhile, not all land species head north (or south in the Southern Hemisphere)—some move uphill into cooler zones, at least until they top out. At sea, the inverse might be going deeper, but only some species do well with the greater pressure and darkness and less abundant food of greater depths.
And some species just go extinct. Biologist Benjamin Halpern, director of the University of California Santa Barbara Center for Marine Assessment and Planning and one of the paper’s 19 co-authors, reflected that in enclosed seas like the Mediterranean, species migrate to the middle until they get “trapped and squeezed out.” He noted that the NCEAS group’s next paper would deal more with extinction, which was outside the remit of this paper.
The meta-analysis also found the coming of spring and summer events, equivalent on land to seeing budding trees and newborn lambs and knowing spring has sprung, advanced by four days, roughly double the amount seen on land. In part, the scientists believe, this figure may reflect that a majority of the underlying studies were conducted at higher latitudes, generally in the Northern Hemisphere, which tend to warm up faster over the ocean than over land anyway. And while many of the spring events are tied more to the length of the day than the temperature, changes in when plankton bloom is incredibly important since plankton are the base of the oceanic food chain. In fact, the biggest spring advancement, 11 days, was reported for zooplankton and zooplankton’s fellow travelers, larvae of bony fish (i.e. most fish except species like sharks, rays, and lampreys). It’s worth noting that zooplankton also saw some of the largest range extensions observed, as much as a thousand kilometers in a decade.
The authors went to some pain to combat various biases that creep into academic work, both Poloczanka and Halpern explained. The bias toward the Northern Hemisphere, for example, and to a smaller extent, the Tasman Sea area off Australia. “That’s where the research funding comes from,” Halpern explained, noting that rich-world institutions tend to study rich-world areas. Poloczanka said the researchers made an extensive literature search both for less-studied regions, like the Indian Ocean, and among non-English language research.
“Yeah, unfortunately, this is a bias that happens on land as well,” she said. “We hope our study can raise awareness that we do have knowledge gaps in the ocean and that maybe we should be focusing some of our efforts on these systems.” That geographic bias also influenced the team’s insistence that studies cover at least 20 years, which helps overcome the influence of routine oscillations—think El Niño—in natural systems.
Halpern expects the findings, even if not perfectly spread out around the world, to ring true globally. “But it would be really weird if everything else was not being affected,” he argued. “Our most parsimonious understanding is that climate change is affecting species everywhere.”
The academics were also on guard against so-called “publication bias,” in which work that shows negative or null results can be hard to get published in the peer-reviewed literature. Ignoring ‘nothings’ might overstate what is happening as a result, a parlous outcome given the politically based opposition to even acknowledging climate change in some quarters. “This group, more than any I’ve worked with, spent time agonizing over publication bias,” Halpern said.
Mitigating such potential bias in this case, Poloczanka suggested, is that marine science is both difficult and expensive. Fieldwork often looks at a number of species, and so pedestrian zero and negative responses get reported alongside sexier stuff. In that same vein, “because it is so costly, we tend to address a whole suite of questions [at the same time], and climate change might be just one part of the study. So even if it’s coming up with a null response for climate change, it’s still addressing enough other questions to merit publication.”
And despite the pioneering aspects of their own synthesis, the authors were surprised that many top-flight academic journals they approached were reluctant to publish their paper (and despite having accepted relatively granular looks at terrestrial effects many times over). “There was kind of a feeling that this had already been done,” Poloczanka recalled. “But we said, ‘Yes, but not for marine systems.’ There was this feeling that we needed to get marine systems onto people’s radar.” As of today, their paper is the most read on the Nature Climate Change site.
Given the terrestrial bias that has kept oceanic warming off many people’s radar, or perhaps sonar, shifts in the locations of species we care about will impact people. The fishing industry is one obvious candidate for impact. Local artisanal fisheries really can’t mitigate 400-kilometer shifts, and so must adapt quickly or die. Commercial fisheries are better placed to travel to the fish, but if fish stocks swim over jurisdictional boundaries expect trouble if the purse seiners follow.
Warming oceans are also creating little ecological surprises, some positive from a human point of view and some negative. In Poloczaska’s backyard, the East Australian Current—it brought Nemo to Sydney—is strengthening and going farther south. With it comes a grazing sea urchin that’s mowing down kelp forests. Those urchins’ only predators are large lobsters, which, she notes, implies that humanity’s adaptation would be to reintroduce these lobsters to the kelpy areas, either for the dinner plate or as a protected kelp protector.
As the paper concludes:
A focus on understanding the mechanisms underpinning the nature and magnitude of responses of marine organisms to climate change can help forecast impacts and the associated costs to society and facilitate adaptive management strategies effective in mitigating these impacts.
“We shouldn’t be complacent about climate change in the ocean,” Poloczanka said, “despite the fact that oceans are warming three times slower, marine life is responding to climate change—and there’s going to be repercussions for our societies and industries.”