The Genetics of Global Warming
As climates continue to change, so does the DNA of the species around us.
Two weeks ago, the Intergovernmental Panel on Climate Change (IPCC) released its latest report taking stock of the physical basis of climate change. It examines the data on increasing greenhouse gases, rising temperatures, shrinking polar ice sheets, and climbing sea levels—and attempts to predict just how screwed we are under different future scenarios.
But what most people really care about are the biological consequences that accompany the physical changes to our global climate. What new threats will our crops face? Which forests will shrink, how many species will go extinct, and what can we do to stop ecosystems from deteriorating? If forecasting the response of the atmosphere, oceans, and ice sheets to increased greenhouse gases seems complex, predicting what biology will do in a warmer world is a nightmare. And yet if we're going to retool our civilization to face the results of climate change, it's critical that we develop the ability to anticipate how the world's ecosystems might change.
Biology is highly non-linear, which means that the biological response to climate change is bound to have surprises in store.
The living world is already feeling the heat. Even within the last few decades, plants and animals have changed their behavior in response to earlier springs and later falls, and have shifted their ranges to higher latitudes and higher altitudes. Researchers have been tracking the movements of plants and animals, and they have repeatedly found that the recent shifts in species ranges largely follow changes in temperature. Large numbers of land and ocean species are expanding or retreating into new habitats, and, as a consequence, worlds are colliding. Scientists are struggling to work out what the results will be.
To predict what will happen when an ecosystem changes typically involves knowledge from a variety of scientific fields, ranging from paleobotany to network theory. Increasingly, scientists who study the world's changing ecosystems are turning the field of genetics, gauging the present and future impact of global warming by studying DNA. Why DNA? By warming the world, we're in essence conducting a global-scale experiment in evolution, causing massive genetic changes as species adapt, invade a new niche, or head toward extinction. Scientists are attempting to analyze what's happening on a genetic level in order to predict a species' future trajectory. This approach is the basis of a growing scientific field called landscape genetics, a field that promises a better understanding of what changes are in store for the biosphere.
An example of how this works is found in a study of alpine chipmunks in Yosemite National Park, published last year by a team of scientists at the University of California-Berkeley. Over the course of the past 100 years, alpine chipmunks in Yosemite have moved to higher altitudes as the average temperature of the park has increased by three degrees Celsius. As the chipmunks have moved upwards, their numbers have declined and their geographical range has shrunk. Are these chipmunks adapting to the new environment, or are they at risk for extinction?
To answer this question, the researchers compared the DNA of historical specimens collected in 1915-16, with that of today's alpine chipmunks. What they found was "genetic erosion," evidence that the alpine chipmunk population was fragmenting into isolated, genetically limited groups. As a population, the Yosemite alpine chipmunks are losing diversity at the level of their DNA. That diversity is the genetic resource they'll need to adapt to a changed environment. They're becoming more vulnerable to extinction by random extreme events like disease or an unusually dry year. The chipmunks' poor prospects are evident in their genes.
On the other hand, DNA evidence suggests that the European wasp spider is evolving into a new form. Until the 1930s, European wasp spiders were primarily found in Mediterranean regions, and no further north than Austria and southern Germany. Over the last 80 years, these spiders have moved northwards, expanding into Poland, Scandinavia, and the Baltic region. Some of their movement was likely made possible by a warmer climate, but the spiders are not just following the warming trend. They've managed to colonize regions that are much colder than their original habitat.
Scientists at Germany's Max Plank Institute found genetic evidence that these invasive spiders are hybridizing with cold-tolerant spiders, resulting in an invasive species that has gained the ability to survive freezing temperatures that would kill its more southern relatives. This is happening, the researchers argue, because populations of spiders that were once isolated can now interbreed with each other, creating new genetic forms that are highly capable of adapting to new environments. As habitats shift with global warming, previously separated populations will interact with increasing frequency, generating the genetic potential to spread and adapt in unexpected ways.
Biology is highly non-linear, which means that the biological response to climate change is bound to have surprises in store. Non-linear systems have tipping points, or, more technically, “critical transitions;” as one group of scientists put it, we "need to improve biological forecasting by detecting early warning signs of critical transitions." Scientists hope that genetics will help us anticipate those transitions and either avoid them or manage the consequences of the new environment we're creating.