Global ChangeIntersection of Nature and Culture

In this week’s issue of Nature: Will species be able to keep up with climate change and how does this impact how we think about parks?

Thursday, December 24th, 2009

One of the outcomes of climate warming is that species will have to move to remain within climatic zones that match their physiological tolerances.  Some common examples include the northward migration of boreal forest species into areas that are currently tundra and the upward migration of mountain species.

As Scott Loarie and colleagues note¹ in this week’s Nature (subscription required), we often think of mountain ecosystems as being particularly threatened because alpine species have nowhere to go.

To analyze this challenge, they looked at the spatial gradients of temperature across land masses of the world.  These data indicate how temperature changes over a known distance (temperature gradient = degrees C per kilometer).

Then, they used climate model model projections to determine how fast the temperature of a region will change (warming rate = degrees C per year).

By dividing the warming rate by the temperature gradient, they determined what they called the temperature velocity (kilometers per year)—which is basically represents how fast you (or another species) needs to move along the earth’s surface to maintain a constant temperature (check this division for yourself to see how the units cancel).

What did they find?

Here is the rank order of temperature velocities for biome types (from lowest to highest, with average velocity—km/yr— in parentheses)

• tropical and subtropical coniferous forests (0.08)
• temperate coniferous forests (0.11)
• montane grasslands and shrublands (0.11)
• Mediterranean forests, woodlands, and scrub (0.26)
• tundra (0.29)
• tropical and subtropical moist broadleaf forests (0.33)
• temperate broadleaf and mixed forests (0.35)
• tropical and subtropical dry broadleaf forests (0.42)
• boreal forest (0.43)
• temperate grasslands, savannas, and shrublands (0.59)
• tropical and subtropical grasslands, savannas, and shrublands (0.67)
• deserts and xeric shrublands (0.71)
• mangroves (0.95)
• flooded grasslands and savannas (1.26)

These data suggest that species in the latter categories will have to move much faster than those in former categories to keep up with climate change.

This make sense if you think about it because mountains have steep climate gradients where there is a lot of temperature change over little distance.  We can therefore say that these kinds of habitats have a bit of a buffer against climate warming—indeed, in most of these regions, species only have to be able to move 0.11 km/yr—about the length of a football field.  This runs counter to what most people have thought about mountain ecosystems being especially fragile to climate change.

However, when you look at globally conserved areas, the picture is less rosy.  The authors claim that only 8% of conservation areas have residence times greater than 100 years, meaning that existing climate will be gone in that time.  Put another way, in 92% of conservation areas, climate will be uncharacteristic of the region in less than a century.

This makes conservation extremely challenging—it means that the traditional notions of park boundaries no longer work because species will likely need to move by the end of the century.

There are a few important caveats that the authors point out.  One big one is that the fate of species depends on their breadth of physiological tolerance.  Species with the capacity to tolerate a wide range of climates will not need to move as rapidly (if at all) compared to those with narrow physiological tolerances.

This is an interesting way to show how fast the climate space will move over time, allowing biologists to work more on physiological tolerances to see what species or ecosystem types might be most vulnerable to warming and to develop adaptation plans for them.

¹Loarie, S. et al. (2009) The velocity of climate change. Nature 462: 1052-1057.

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