A new study uses unconventional but more accurate measures of the effect of climate change on the health of marine ecosystems and uncovers more reasons to be concerned

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Even though the world's oceans and seas aren't warming up as fast as landmass, there is still cause for concern for marine life. A new study published in the journal Science presents evidence that the speed and direction of climate change as well as the timing of seasonal shifts are moving just as fast in large bodies of water as in land, and these point to serious conservation problems for regions rich in marine biodiversity.

Scientists led by Scottish Marine Institute ecologist Michael Burrows calculated two metrics -- the velocity of climate change and the shifts in seasonal timing -- that they argue are more accurate gauges of biodiversity, or the health of ecosystems, than traditional temperature records. Using 50 years of global temperature and climate data, they made detailed predictions on the ability of organisms to cope with warming, including biogeographic range shifts and life-cycle changes, that involve much more than simple migration toward the Earth's poles and earlier springs coupled with later autumns. They found that some marine reserves, such as the Coral Triangle in Southeast Asia, may be in danger of losing their ambient temperatures rapidly.

"What we have done is think about warming from a different perspective: If I started off at one point experiencing a particular temperature, how fast and in what direction would I need to walk or swim or crawl to remain at exactly the same temperature?" says co-author David Schoeman. "This takes the idea of warming and turns it from a question of time to a question of space."

In the gallery below, get a glimpse of species and regions that may be threatened by climate change. Then, in the Q&A with Burrows that follows, learn more about how the study came about, why measuring the velocity of climate change is critical, and the data calculations the researchers conducted for these discoveries.

What's the backstory of this project?

The work came out of a workshop at the University of California Santa Barbara. A group of us got together to assess the evidence for ocean life responding to climate change. It struck us right away that there were no expectations available for how far organisms should shift to track temperatures or by how much earlier or later they should do things seasonally. We saw that another study had taken an approach to making predictions about speed of movement or velocity of temperatures for possible future climate scenarios on land, and we thought we could do the same for the oceans to give us expectations to go with observed changes.

What were your team's key discoveries?

When we talk about velocity of climate change, we mean the speed and direction of movement of temperature. So when temperature increases in a particular spot, anything wanting to stay at the same temperature as before needs to move to a cooler place. In an area where there is a very flat thermal landscape, or where temperatures vary little from place to place, that cooler place could be a long way away. And so velocity of climate change would be high. Where cooler places are right next door, like up a nearby mountain range or on the other side of an oceanographic boundary, life only needs to move a short distance to follow temperatures over the same time period. So, the much flatter thermal landscape in the ocean tends to increase velocities, and therefore offsets the effect of greater warming on land to bring the velocities for the two environments closer together. By a similar process, reduced seasonal changes in the ocean tend to push up estimates for seasonal shifts to values close to those for land.

Because thermal landscapes and the amount of warming or cooling are different in different parts of the world, there is a lot of variation in velocities. It so happens that there is an awful lot of species in some of the places where velocities are highest, especially in the tropical oceans. That may have damaging effects on the richness of species in those places, especially when there can be no immigrants from even hotter places to replace those that leave. And conservation measures can't usually protect species from direct effects of climate change. We should especially protect those areas, which provide longer term refuges, where velocities are low, and where refugees from climate change may arrive.

How was this study conducted?

The methods were surprisingly simple to do. What we did was combine the two important trends in temperature for each spot on the globe, one across decades and one from place to place, and that gave us the velocity. A bit like combining a rise in water level with a landscape -- if the slope was gentle we'd expect a little rise in water level to make the water's edge go far horizontally as in a flood plain, but if the slope were steep the same rise wouldn't have much effect on the spread of the water. Working out seasonal shifts was pretty much the same, but for this we used the change in temperature from month to month instead of from place to place.

Once we got hold of the publicly available datasets from the U.K.'s University of East Anglia Climate Research Unit and from the Hadley Centre, all we had to do to calculate velocity was to determine the temperature trend over 50 years and the average temperature for every 1-degree grid cell. The next step was to compare each grid cell to its immediate neighbors to find the direction and steepness of the temperature slope, like hills and plains on a landscape. Dividing the 50-year trend by the temperature slope gave us the velocity in the direction of the slope.

For seasonal shifts we had to calculate the 50-year trends in temperatures for each month, and get the rate of seasonal change in temperature by taking the difference between temperatures between preceding and following months. Dividing the 50-year trends by rate of seasonal change gave us the seasonal shifts. We picked April and October to show what spring and fall shifts would be.

What are the implications for scientists as well as for people in general?

The main thing for me was the realization that life may need to move fast to track even small temperature changes in some parts of the world. And in other places, larger temperature changes might need only small displacements for animals and plants to stay in their preferred temperatures. So an average rate of shift may not be that useful.

In essence, regions where we show the fastest velocities may be most prone to the loss of species and potentially gaining new ones, while where velocities are slower there may be some movement of the boundaries of species, fishes ranging further north for example, but probably keeping the same mix for a much longer time.

It will be interesting to see who in the scientific world picks up on this approach. For the wider world I would hope that we have highlighted how we might expect life to respond to climate changes, and how much that might change from place to place. Those changes might be startlingly rapid in some areas, with species arriving from hundreds of miles away over just a few years. Although we didn't highlight this in the paper, my view is that area of slower velocities immediately outside the tropics are worthy of special measures. Coral reefs may need new areas to colonize if they are not to go extinct. We need to be ready for those migrants when they arrive.

Image: Megan Saunders.

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