Our Common Future Under Climate Change

International Scientific Conference 7-10 JULY 2015 Paris, France

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Mark Ziembicki

Mark Ziembicki

The Global Imprint of Warming on Life

201507-10

By Camille Parmesan Professor, Marine Institute, Plymouth University, England

Camille Parmesan is presenting "The Global Imprint of Warming on Life" on July 7 at the conference Our Common Future Under Climate Change. 

To understand future impacts on nature in a time of rapid climate change, it helps to understand what we can already observe today: We have seen large changes in wild plant and animal species in response to relatively small levels of warming.  

These changes in nature are a clear and simple indicator that climate has indeed been altered, and they also give us a sense of what is in store for coming decades.

To date, there have been 5 major global meta-analyses pulling together data from some 4,000 wild plants and animals(1).  Results are very similar across these studies, with 82-92% of observed changes in wild life consistent with local or regional climate change. 

Overall, about half of all species have changed where they live, and some 2/3 of species have changed when they live - altering the timing of life events to match a moving temperature window.


“Moving as a way to adapt”


In an absolute sense, land has warmed more than the oceans, the Arctic has warmed most, and the tropics have generally had little warming. But at any given time, temperature is more constant as we travel over the oceans compared to traveling that same distance over land.   These lines of temperature that cross the earth are called temperature "isotherms", and the movement of these isotherms through space as climate warms is called the "velocity of climate change" (VoCC). Looking at VoCC now see a very different picture, as the VoCC is faster in the oceans than on land, slow in some parts of the Arctic, and very fast across much of the tropics, giving us different expectations of impacts (2).

For example, as climate warms, a sea urchin in the ocean has to move further than, say, a reindeer on land to maintain a constant temperature environment. Such movement of species' ranges is one way in which wild plants and animals are adapting to climate change.  

It's no surprise, then, that movements of plants and animals  in the oceans match the marine VoCC and are faster than land, despite the oceans warming less than the land. Marine species have shifted 75 km/decade pole-ward on average, while estimates from land range from 6 to 17 km/decade pole-ward.

Taking averages of how large numbers of species have been responding to recent climate change hides the fact that some species are moving very fast over very short time frames. In addition, at the extremes, poleward range shifts have been just as fast on land as in the ocean. For example, Atlantic cod has moved 200 km poleward per decade, but the purple emperor butterfly colonized northward at the rate of 200km in just 5 years.


Taking our observations to predict the future


A number of very rapid range shifts can be predicted by VoCC.  E.g. for the seas surrounding Europe, we can predict rapid movements out of and through the North Sea, which matches the observed shifts of Atlantic cod.  

For European land masses, we predict the Baltic Sea to be a barrier for terrestrial species, but that once that barrier is breached, further movements pole-wards should be rapid.  Again, this is what has already happened with the purple emperor: it's northward colonization lagged behind warming.  The purple emperor took 10 years after warming began to shift from Denmark into Sweden, and 20 years after warming to shift from Estonia into Finland.  But once it had successfully formed new populations in Fenno-Scandia, it rapidly expanded northward at the rate of 200km in just 5 years.(3)

But what about the species which can not migrate?  The most cold-adapted species on our planet - those that live at the poles (especially those for whom sea ice is their only habitat) and on mountain tops have "nowhere to go”.(4)

For mountaintop species that are already living at the top of mountains, we have been observing extinctions of the lowest elevation populations, contracting their ranges upward as they become increasingly restricted to the highest peaks. In France, the Apollo butterfly has gone extinct on all mountains with peaks < 1,000 m high. 

The timing of spring events
 

The other major type of change we're seeing is earlier timing of spring events. 

Amphibians are showing the largest advance in breeding dates. Birds & butterflies are advancing their emergence and breeding more than are plants.(5)  And in the oceans, predators are advancing in time more than their prey.(6)  This suggests that species that traditionally have interacted with each other may be getting out of sync.  For example, butterflies may emerge too early and not find flowers to provide them nectar.

While these patterns dominate, in every study there are some species showing no response: e.g. no change in its distribution or no change in timing.  Looking just at timing, we also observe a few species that have delayed spring events even in places where it has warmed.  

To begin to understand what may be driving these 'unexpected' responses (or apparent lack of response), we studied a particularly rich set of data on the dates of first flowering of hundreds of plants in spring in northern England over the past 5 decades.  Instead of just looking at how the timing of flowering related to spring temperatures (as has typically been done in previous studies), we analysed how flower timing related to temperatures across the entire previous year.

We found that most species (some 3/4) indeed are sensitive only to spring temperatures, and respond to warming spring by flowering earlier, with a  mode (peak) at 1 day/decade advancement.(7)

But for the rest - nearly 20% of the total -  we found something much more interesting.  This group of species appeared to be insensitive to spring warming - with a peak at "0", or no change in flowering time.  Some were even going counter to expectations, actually delaying their flowering.  It turned out that these were the species that were very sensitive to winter temperatures, and actually required winter chilling to 'reset' their clocks.  This process is well-understood and is called "vernalization".   The recent trend towards warmer winters were not giving these species their "cue” that winter had indeed come and gone, driving them to delay flowering.   

But these same species were also sensitive to spring temperature in the more usual way, and if they were given a cold winter, they would flower earlier in warmer springs.   So it was the sum of these two opposing drivers, (warming winter driving delay and warming spring driving advance), that led to many of them showing no change in flowering date over nearly 50 years of warming.(7)

A typical retired person tending their English garden might have noticed that the field maple has been flowering earlier and earlier, and correctly concluded this was a sign of anthropogenic climate change.  They would have not seen any change in flowering date for the very common plant, old man's beard.  But old man's beard is actually just as sensitive to warming springs as is the field maple.  One might wrongly conclude that old man's beard does not care about climate change, when, in fact, it's being strongly driven by recent warming trends, simply in very complex ways.  

In summary, many of the species categorized as "non-responders" or "counter" to expectation were, in fact, very sensitive to spring warming, but they also needed winter chilling, and weren't always getting it.  In this study, simple analyses estimated 72% of species were responding to recent warming trends, when, in fact, 90% of plants were responding to climate change, just in more complex ways than we expected.(7)       

The moral is:  such complex, sophisticated responses mean that we are likely under-estimating the proportion of species sensitive to anthropogenic climate change.  

References
(1)Parmesan & Yohe Nature 2003; Root et al. Nature 2003; Root et al. PNAS 2005; Rosenzweig et al Nature 2008; Poloczanska et al. Nature Climate Change 2013
(2)Burrows et al. Science 2011
(3)Parmesan et al. Nature, 1999;   Henriksen & Kreutzer 1982;  Ryrholm unpub.;  Kaila & Kullberg pers. comm 
(4)Parmesan Annual Reviews Ecology Evolution and Systematics 2006
(5)Parmesan Global Change Biology 2007
(6)Poloczanska et al Nature Climate Change 2013 
(7)Cook, Wolkovich & Parmesan PNAS 2012

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