The Velocity of Climate Change

By Philip Duffy, Scott Loarie and Healy Hamilton

One of the most important and scientifically challenging questions about climate change is how it will affect species individually and collectively (i.e. how it will affect biodiversity). The importance of this question is difficult to overstate. We depend upon natural ecosystems to purify our air, soils, and water, to control pests, to limit erosion, to break down waste that we dump into the environment, and even to stabilize the climate. Many new medicines and agricultural advances are derived from obscure plants and animals.

So what happens to species as climate changes? We can observe what climate (for example what range of temperature) individual species live in. We can also predict how those climatic zones might move as climate change proceeds. Thus we can predict where we think the suitable climate for individual species will be at any date in the future. Retrospective “predictions” show that these methods work very well in one sense: species are almost never found in regions where models predict they should not be. On the other hand, the methods work very poorly in another sense: it is common for species not to move into regions where the climate is suitable. This can happen for a number of reasons: there may be physical barriers (such as a freeway) that prevent species from moving. Or there may be nothing to eat in the new territory, or too many predators.

A new paper by Scott Loarie et al. explores a third possibility: zones of suitable climate may move too quickly for species to keep up with. In general, when the climate warms, species need to move poleward (towards the north in the northern hemisphere and towards the south in the southern hemisphere) to maintain a constant temperature environment. In flat landscapes, the speed a critter needs to move across the surface to stay in a zone of constant temperature can be relatively high. On the other hand, species that live on the slopes of mountains can move upslope to stay at the right temperature; often the speed they need to travel is much less than those for flat-land species, because in steep terrain temperatures can drop quickly a short distance up hill. Thus, “the velocity of climate change,” the speed at which zones of suitable climate move across the landscape, is generally faster — and more difficult to keep up with& mdash; in flat terrain.

This view runs contrary to the traditional viewpoint that climate change threatens mountain ecosystems more than those in flat terrain. There is validity to this traditional viewpoint: mountain ecosystems may be fragile to begin with, due to their harsh environment, and species near the tops of mountains may have “nowhere to go” as their environment warms. Nonetheless, one critical aspect of adaptation to changing climate — the speed of tracking their preferred climate — will in general be more challenging in flatter landscapes.

The research conducted by Loarie and colleagues provides support for certain types of conservation strategies. Historically the main focus of conservation has been the establishment of protected areas where negative human impacts are restricted.  But with climates on the move, many plant and animal species will be tracking their preferred habitats right out of the very areas designed to protect them.  Establishing corridors among existing protected areas to give plants and animals landscapes through which they can move is increasingly recognized as a crucial step in conserving biodiversity. This new work by Loarie et al strongly supports the strategy of corridors, especially in mountainous habitats.

Our understanding of how climate change will affect species and natural ecosystems is primitive, and the methods we use to predict these impacts have obvious limitations. Yet conservation groups and natural resource managers need and want to act now in order to preserve species into the future. If they don’t, we may learn this science by watching extinctions unfold.