Mankind has never seen the extremely warm climates that global warming is expected to produce in the next century. Humans may have the ability to adapt to almost any climate through technology, but many plants and animals have adapted to one particular environment and may face serious consequences in the face of climate change. What will happen to plant and animal communities that lose a key part of their ecosystem, or are living in areas isolated from new suitable habitats when the climate changes? Predictions to these questions vary, but most researchers forecast extensive changes in the natural world that will likely create completely new ecosystems.
The Consensus
Before getting too in depth with predictions, one must first understand that a majority of scientists now agree that within the next 60 or so years the average global temperature will rise approximately three degrees Celsius and about twice that much at the polar ice caps. Along with this, the amount of C02 present in the atmosphere will double due to anthropogenic sources. A consensus of researchers agree at least upon these predictions and many will argue these as minimal predictions.
With the predicted certainty of the above facts, many researchers are attempting to diagram how these climatic changes will affect regional ecosystems as particular species respond to the rapidly changing environment. In doing so, it appears that many researchers have gotten caught up trying to understand how ecosystems operate at present in order to predict how they will evolve with the climate. Currently, the greatest confidence in predictions exists on a global scale, with regional changes being much less certain.
The System to be Analyzed
The short-wave radiation of the sun is the principle source of energy for the global atmospheric system. The Earth emits radiation in long-wavelengths in equal proportions to what it receives from the sun in a perfect system. Human impacts on the atmosphere which cause energy to be trapped in the atmosphere are causing what is now commonly referred to as global warming. How this seemingly simple accumulation of excess energy will affect biological systems on Earth involves many, many more parameters than energy input-output though.
Assessment
To predict how a particular ecosystem will react to climate change, the future climate for that area must be assessed. The most common method of doing this is with General Circulation Models, or GCMs. These computer models are three-dimensional and simulate climate and climate change by the means of numerical weather prediction techniques.
Researchers need to take caution when using these models to predict climate. Literally thousands of parameters exist to the rapidly changing environment. In doing so, it appears that many researchers have gotten caught up trying to understand how ecosystems operate at present in order to predict how they will evolve with the climate. Currently, the greatest confidence in predictions exists on a global scale, with regional changes being much less certain.
To predict how a particular ecosystem will react to climate change, the future climate for that area must be assessed. The most common method of doing this is with General Circulation Models, or GCMs. These computer models are three-dimensional and simulate climate and climate change by the means of numerical weather prediction techniques.
Researchers need to take caution when using these models to predict climate. Literally thousands of parameters exist that may affect climate and climate change. The GCM models only react to the set of circumstances imposed upon them by the researcher and may not be including and processing all of the relevant data.
One example of this is the fact that some plants react positively to enhanced C02 content in the air by increasing growth rates. Plant growth may affect temperature as with the east coast of the United States, where it has been noted that the warming of spring has been halted for a week or two when all of the foliage appears during that time period as compared to the rate of warmth before first leaf.
Considering these facts, the increased C02 in the atmosphere may promote plant growth and therefore stabilize the warming. This type of parameter is difficult to model with exact certainty in any type of computer model.
Another problem with GCMs is the impact of clouds. Many researchers concede that clouds are a crucial factor in global warming, yet their net effect on the system is not fully understood. This unknown effect is also hard to predict with computer models.
Once a fairly reasonable GCM is attained, the ecosystem to be analyzed for its response to climate change presents an even more complex array of parameters to be measured.
Being at the bottom of the food chain, plants are the most important component of ecosystems to be studied. The distribution of plants is dependent on the temperature, moisture solar radiation, soil type, other plants, pollinators, seed vectors, competitors and symbionts. In order for a plant to be able to adapt to climate change (likely by means of migrating to more suitable habitat) all of the above components essential to that plant’s survival must be present in the proper proportion after the climate change.
One method of determining what plants will exist in the new climate scenario being used is for researchers to look at fossil records of ancient climates to determine what type of plants lived in the different climate scenarios of the past. This method does not ensure, however, that certain plants will be able to make the rapid shift to the climate change expected to occur, but it does show some ecosystem possibilities under the expected climate changes.
One example of how the different parameters can affect a single species is available through the example of the Ponderosa pine. The Ponderosa pine could lose approximately one-third of its current habitat with a doubling of current C02 levels as illustrated by one computer model. Doubling C02 content is only one of the many factors dictating habitat for this species. When other factors are added in, it is clear that this species would have a difficult time adjusting to climate change.
The most inhibiting factor of all exists in the sheer speed at which plants like the Ponderosa will have to adapt to the changing climate. The changes are expected to influence populations within 50-100 years, which is less than one generation for many plants. Typically, it requires ten generations of study to understand the dynamics of a species’ population.
An example of this situation in effect is illustrated when observing soil bacteria that have a close relationship with certain tree species. The bacteria that have a generation time of a few minutes may adapt well to a rapidly changing climate, but the trees growing in the same soil may not and the relationship they share would then quickly disintegrate, possibly forming new species-species interactions or simply eliminating both species in a particular region. The exact outcome is yet to be determined.
One species’ relationship to another species is important in other ways as well. Some researchers believe that the natural ecosystems that exist today are composed of opportunistic species that have somewhat luckily found their niche in the struggle for survival, while others believe that the species interactions that take place in ecosystems today have taken millions of years to evolve and that species are extremely limited by their interactions with-others. If species are extremely dependent upon others for survival, then the consequences of global warming will undoubtedly be extremely severe. A small change that negatively affects one species will have drastic influence upon that species’ entire ecosystem. It may be that only species that are very opportunistic under unfavorable conditions end up thriving in the new world climate.
Important Factors of Succession and Migration
Some researchers stress the importance of determining keystone species within an ecosystem, or species that have key roles in the behavior of an ecosystem. The logic behind this is that if the keystone species are able to survive climate change, then the ecosystem has a better chance of succeeding as well.
A plant or animal is considered a keystone species if: it is the only species at that particular level in the food chain, its preferred food is the dominant herbivore in the ecosystem, it is present in a system with a dominant herbivore and so on. An example of this is the sea otter. Sea otters feed on sea urchins, which in turn feed on kelp. If the sea otter is removed from the ecosystem, the urchins grow out of control, destroying the kelp forests and thus destroying the entire ecosystem. In a system this simple, any one of the three (otter, urchin or kelp) species could be considered keystone. More and more often, studies are showing that there are more keystone species in ecosystems than previously thought.
The theory that keystone species will be important in the face of global warming may not hold much truth, however, if other species in an a ecosystem are not able to migrate to new climate as efficiently as the keystone species, thus taking away the importance of the keystone. There are many natural and man-made barriers that exist that could prevent certain species from migrating to new climate and cause this effect.
One of these, of course, is the speed necessary for migration. One estimate states that to match the rate of changing temperatures, plants would have to migrate northward at a rate of one meter per hour to remain in suitable habitat. This is likely impossible for plants without the assistance of favorable wind direction to spread seeds. Vegetation with heavy seeds loses even this possibility.
One factor that may assist such migrations somewhat is the fact that most mountain ranges and valleys, in the United States mainly, are orientated in north to south fashions. This may allow species to make the necessary migrations northward, except those, of course, already at the northern edge of the
Mammals are typically capable of adapting to climate variation and of making necessary migrations to new habitat. Because of their mobility, mammals are limited by the availability food and suitable habitat in the face of climate change.
This advantage over plants still does not seem to give many mammals the means necessary to survive global warming.
A computer model by researchers McDonald and Brown was constructed to map the survival potential for 14 different mammal species in western North America that are currently living on mountain ranges. The model was constructed to show elevational relief, so it contained limited potential habitats for the species in an altered climate because each species was programmed to live in a certain range of conditions.
When the average temperature of the model was raised by three degrees Celsius and the lower edge of timberline was elevated 500 meters to simulate the expected climate towards the middle of the 21st century, the effects were substantial.
Of the 14 different species, three became extinct in all areas that they presently occupy. Only two were predicted to survive on all current ranges and the remaining nine species survived on some mountain ranges and became extinct on others.
There are many reasons that some species are expected to survive while others are not. The most common is that animals living at high elevations essentially live on islands that are separated from other suitable habitat by unbridgable gaps. Although these are only a handful of the total species living on a mountain range, the loss of one species typically signals the decline of another.
There are some basic critical factors to be considered when assessing a species susceptibility to extinction through the changing climate. The most susceptible populations are: those living at the edge of the specie’s range, geographically localized species, highly specialized species (ones that feed on only one other species), poor dispersers, those living in alpine or arctic communities and those living along the coast.
Increased Disturbance and cohabitation
The most important factor affecting species that comes along with global climate change is the expected increase in strong disturbance events such as floods. These events are expected to increase in frequency and intensity with global warming, and to be the earliest observed effect of climate change. Such events may favor certain species over others.
An example of this is flooding that wipes out all of the grasses in a particular area for a short period of time. In the meantime, woody plants have no competition for resources and therefore thrive. After the flooding, the woody plants have become so abundant that they block out sunlight and thus inhibit the growth of grasses, permanently changing the entire ecosystem.
This type of shift in ecosystem composition is thought to be a natural part of ecosystem evolution. Pollen data shows that the species co-habitating together today are not necessarily the ones that lived together in the past. The data shows that plant ecosystems are in a constant state of flux. This may be a positive factor in an ecosystem’s ability to survive global warming, because many of the species co-habitating today will not likely make the necessary migrations at the same rate and therefore be forced to co-habitate with the species that do.
What the Future Holds
Undoubtedly, the current arrangement of ecosystems, at least on land, will be extensively rearranged with the impending climate change. The exact redistribution of biota after the change is far too complicated to determine with the current amount of knowledge on ecosystem operations. Certain predictions such as large increases in boreal forests which respond positively to increased C02 in the atmosphere have been made. Predictions such as this are difficult to qualify without considering every other factor important to the survival of boreal forests and should probably be avoided.
One common suggestion has been made to assist the regenerative process of ecosystems through global warming and that is to preserve all old growth areas. Ecosystems that have been in existence for longer periods of time are typically more stable and resistant to competition and predators. These ecosystems may be the key to maintaining a thriving globe through the chaos of rapid climate change.
It is also evident that managed ecosystems around the country may require the assistance of mankind to remain productive. Likely, nature preserves are in the wrong locations at present to be effective through a changing climate. Species transportation, genetic engineering, predator maintenance and feeding assistance may all be means which humans assist ecosystems through the climate change. Some researchers are calling for methods of management that begin to plan for and adjust to the climate to ensure ecosystem success. The extent to which mankind should assist the natural world in this progression, however, is a topic which raises a variety of ethical and moral questions.
Until more is known about ecosystem dynamics and the extent of climate change, the best measure humans may take is to become more educated on these topics through intense research, so eventually an intelligent management plan can be constructed.
Bibliography
Gates, David, M., Climate Change and its Biological Consequences, U of Michigan, 1993.
Gordon and MacDonald and Sertorio, Global Climate and Ecosystem Change, Plenum Press, NY, 1990.
Mooney, Harold, A., Fuentes, Kronberg, Earth System Responses to Global Change; Contrasts Between North and South America, Academic Press Inc., 1993.
William, R., and Pielke, R., Human Impacts on the Weather and Climate, Cambridge University Press, 1995.