Ecological impact of global climate change

Anthropogenic climate changes, especially global warming, have affected terrestrial, freshwater, and marine ecosystems in the past few centuries. If the Earth’s average global temperature continues to increase, these ecosystems will change even more radically in the future.

Background

Long before the appearance of Homo sapiens, periodic momentous climate changes had devastating effects on Earth’s ecosystems. For example, 245 million years ago, a colossal effusion of greenhouse gases (GHGs) from massive volcanoes raised average global temperatures by 5° Celsius, leading to the demise of over 90 percent of living things in the great Permian-Triassic extinction. Humans, in the few million years they have lived on Earth, have not had as cataclysmic an effect on the biosphere as have natural climatic catastrophes. However, over time and particularly since the development of advanced industrialized societies, they have been having an increasingly potent effect on the Earth’s climate, which in turn has led to the decline and even the extinction of many species.

Effects of global climate change on Plants

The response of the Earth’s land and water vegetation to anthropogenic climate change is extremely complex and varied, extending from photosynthesis in relatively simple microscopic plants to the global distributions of highly variegated plant species. Scientists researching climate-induced environmental changes and the effects of those changes have concentrated on a careful selection of flora in the distant and recent past. They have then extrapolated from those focused studies of the past to draw conclusions about present and future time periods, mainly through computer models. Paleobotanists have discovered how some large ecosystems dominated by plants responded to global climate changes in prehistoric ages, but this understanding has not been easily applicable to modern conditions. More secure understanding has resulted from studies of how vegetation responded to the climate changes during the ice ages: Migration proved a means for many species to survive glacial and interglacial climates.

While, in recent centuries, the greatest threat to plant species has been from their unsustainable harvesting by humans and the elimination of their habitats, anthropogenic global warming has also had an influence on certain plant distributions. For example, with a temperature rise of nearly 2° Celsius in the boreal zone of North America, conifer forests have moved closer to polar regions. Certain computer models relating global warming and plant survival have predicted future changes in the species composition and locations of forests, while still other forests may desiccate, burn, and disappear completely. In tropical rainforests, certain orchids are rare, because they have highly unusual ecological niches. If their environments are climatically transformed, these orchids often prove to be mediocre migrants. Some plant species, unable to tolerate warmer fresh and salt waters, will become extinct, while climate-caused habitat loss will lead to other plant extinctions. Flooding of coastal estuaries and wetlands may further the destruction of plants unable to adapt to the changed conditions.

Effects of Global Climate Change on Animals

The abundance, distribution, and ecological niches of animal species will continue to be affected by changing climatic factors. As the climate warmed at the end of the ice ages, some species expanded their ranges while other species migrated to new regions. This postglacial warming resulted in the extinction of many species of large mammals, including the wooly mammoth. Many scientists believe that climate played a role in these extinctions. Analogously, many scientists believe that in the past few centuries, when human activities have contributed to global warming, elevated global temperatures have affected certain animal species.

The declining numbers of amphibians is an important example of this phenomenon. From 1975 to 2000, certain Costa Rican forests warmed significantly, causing shifts in the habitats of birds, reptiles, and amphibians. Some frogs, unable to adapt to these changes, became extinct, while others became endangered or critically threatened. Not all scientists are convinced that climate change is to blame for amphibian declines, however. Some cite pollution and fungus as possible alternate causes. Another often-cited example of a declining species is the polar bear. From 1975 to 2005, Arctic sea ice shrank by about 20 percent, reducing the bears’ access to seals, their main prey. In the two decades from 1985 to 2005, polar bear populations fell by over 20 percent.

Because of the many variables contributing to the decline of various animal species, it has been difficult to determine with precision the role that global warming has played in these declines. Nevertheless, certain scientists have used computer models to issue warnings that accelerated global warming will inevitably lead to the extinction of many animal species. In 2004, the United Nations published a report based on the expertise of many scientists that estimated a million species of plants and animals could become extinct by 2050, unless global warming can be stopped. Environmentalists think that the ecosystems most likely to experience the greatest species loss are polar seas, arctic tundra, and coastal wetlands.

How Species Cope with Climate Change

Nature has provided species of plants and animals with a powerful mechanism of coping with environmental changes, including climate changes. Charles Darwin, who discovered this mechanism and showed how it could account for the origin and evolution of species, called it natural selection. Throughout the long history of life on Earth, plants and animals have had to adapt to changing environmental conditions, often gradually, sometimes dramatically. After the appearance of Homo sapiens and human technology, plants and animals were forced to accommodate themselves to various anthropogenic changes, chief of which were habitat destruction and global climate change.

After the period of the ice ages, many species of plants and animals had to adjust to warmer climates, and paleobotanists, paleozoologists, and paleoclimatologists have studied how various species responded. In general, because of shifting climate zones, species often migrated to live in ecological niches similar to those to which they had become accustomed. Temperate-zone species moved north, and polar species migrated more deeply into arctic regions. By studying numerous species, scientists have been able to quantify the extent of migration as zonal temperatures rose. Specifically, pollen records from northern Europe and eastern North America have revealed migration rates between 0.02 and 2 kilometers per year, with an average of about 0.4 kilometers per year, though scientists note that migration rates differed widely from species to species. These variations are evidence that some species were unable to keep up with climate change, and this probably played a role in their extinction rates.

Although migration routes for species other than trees are not so well known, the evidence that has been gathered and studied indicates that such organisms as snails, mayflies, and beetles responded to climate changes much faster than did trees. During the past few centuries of anthropogenic climate warming, examples of both range expansions and range contractions have occurred. Ornithologists have observed range extensions for some bird species, and zoologists have found rates of nearly 50 kilometers per year for certain mammals. Those species that are able to expand their midlatitude ranges may be able to cope with the future rise of global temperatures.

On the other hand, some plants and animals have experienced problems in adapting to warming temperatures, especially when new conditions have exceeded their physiological limits or destroyed their ecological niches. For example, multi-year droughts in the southern United States have caused the contraction and destruction of various salt marshes along the southeast and Gulf coasts, precipitating the loss of many species (though some species, such as certain snails, increased their numbers when their predators declined). Anthozoan polyps of coralreefs, which are very sensitive to increases in ocean temperatures, have experienced widespread declines. For example, in 1998, a 1° rise in the Indian Ocean’s temperature led to the destruction of over 80 percent of the coral reefs. Nearly all the reefs surrounding the Maldives and Seychelles disappeared.

Possible Future Scenarios

Scientists who use computer models to predict the possible ecological effects of global warming generally issue caveats about the uncertainty of their predictions, since these models necessarily involve gross oversimplifications. Nonetheless, this practice has not prevented some researchers from warning of massive extinctions produced by rising sea levels and rapidly transformed ecological zones. There are also more hopeful scientists, who, basing their models on the abilities of ancient plants and animals that adapted to disastrous climate changes, believe that global warming may bring about the flourishing of many species, particularly plants that will find high carbon dioxide levels and warm temperatures favorable to their development. Between these extremes are scientists who, like medical doctors employing the principle of primum non nocere (“first, do no harm”), urge their fellow humans to be very careful as they modify the Earth’s temperature, since living things will most likely continue to interact in complex and unexpected ways.

In constructing their scenarios for the future, scientists have used the growing body of evidence about how plants and animals have responded to climate change in the distant as well as recent past. Several scenarios predict that global warming will inevitably lead to large elevations of sea level and the massive melting of ice in the polar regions. This would lead in turn to both habitat destruction and habitat creation, during which some species adapt and increase in numbers, while others, because they fail to adapt, become extinct. If global warming continues to accelerate, some scientists predict, extinction rates will increase, leading to a loss of plants and animals second only to the gargantuan extinctions during the Cretaceous-Tertiary cataclysm of 65 million years ago. Some pessimists contend that this massive extinction cannot be halted, only slowed. Optimists, however, point out that extraordinary changes also create extraordinary opportunities for adaptive innovations.

In February 2022, the Intergovernmental Panel on Climate Change (IPCC), a scientific body sponsored by the United Nations, issued a report entitled “Climate Change 2022: Impacts, Adaptation and Vulnerability.” In a press release the IPCC warned of the dangers of inaction. Climate change related to human activity led to negative impacts to the Earth’s biodiversity. For example, temperature increases on the earth were rising beyond the tolerance of plants and animals. This was leading to large-scale mortality of living organisms such as coral and plants such as trees.

The report indicated that not only was climate change detrimental to plant and animal species in the Earth’s ecosystem, but it also directly impacted the health of human beings. Adverse effects included increasing numbers of humans subjected to water scarcity, vector-borne diseases, and hunger. Additionally, climate change could produce lasting results for ecological systems. These include non-reversible events such as the disappearance of glaciers, Arctic ice, and permafrost.

Context

Much of the analysis of the effect of global warming on biodiversity has taken place in the context of a human population whose numbers have dramatically increased in the past few centuries and may continue to increase in the future. If certain plant species (such as trees used for lumber and paper) expand their ranges, then humanity may benefit, but if habitats for edible fish are destroyed by warmer ocean temperatures, then the effects on humanity will be negative. Physicians at the Center for Health and the Global Environment at Harvard Medical School have shown how human health profoundly depends on biodiversity. For example, many important drugs derive directly or indirectly from plant species. Furthermore, if global warming increases the number of insects that carry such viral diseases as dengue, encephalitis, and yellow fever, this would seriously endanger human health. Ecosystems have served humanity well throughout its history, but many concerned scientists now believe that numerous plant and animal species in these ecosystems are threatened by human activities that these scientists feel sure have been definitely linked to global warming. However, what humans have done, humans can undo.

Key Concepts

• anthropogenic: caused by humans
• biodiversity: the entire variety of living organisms in a given location, from the local to the global
• biosphere: the ecological zones on Earth where life is found, whether on land, in the water, or in the air
• ecological niche: the relational position of a species in an ecosystem with respect to all other species, resources, and physical and chemical factors affecting life and reproduction within that ecosystem
• ecosystem: a community of different species interacting with each other and with the nonliving environment
• extinction: the total disappearance of a species from the Earth
• greenhouse gases (GHGs): lower atmospheric gases, such as water vapor and carbon dioxide, that trap heat radiated from the Earth’s surface

Bibliography

Chivian, Eric, and Aaron Bernstein, eds. Sustaining Life: How Human Health Depends on Biodiversity. New York: Oxford University Press, 2008. This lavishly illustrated, oversize book is aimed at both general readers and scholars. One of its themes is the threat posed by global warming to plants and animals that are beneficial to humans. Appendixes, references, index.

"Climate Change 2022: Impacts, Adaptation and Vulnerability."Intergovernmental Panel on Climate Change, 27 Feb. 2022, www.ipcc.ch/report/sixth-assessment-report-working-group-ii. Accessed 20 Jan. 2023.

Cowie, Jonathan. Climate Change: Biological and Human Aspects. New York: Cambridge University Press, 2007. This introductory text has sections on the past, present, and future effects of climate change on plants and animals. Illustrations, figures, tables, references, appendixes, index.

Flannery, Tim. We Are the Weather Makers: The Story of Global Warming. Rev. ed. London: Penguin, 2007. A scientist and conservationist surveys the history of climate change for the general reader. Beside dealing with its effects on plants and animals, Flannery also offers specific suggestions for politicians and citizens to reduce global warming. Illustrations, chapter notes, index.

Galey, Patrick. "Five takeaways from the UN’s 2022 climate impacts report."Climate Home News, 28 Feb. 2022, climatechangenews.com/2022/02/28/five-takeaways-from-the-uns-2022-climate-impacts-report/. Accessed 20 Jan. 2023.

Harvey, Chelsea. "Global Carbon Removal Efforts Are Off Track for Meeting Climate Goals."Scientific American. 19 Jan. 2023, www.scientificamerican.com/article/global-carbon-removal-efforts-are-off-track-for-meeting-climate-goals. Accessed 20 Jan. 2023.

"IPCC Sixth Assessment Report."The Intergovernmental Panel on Climate Change, 28 Feb. 2022, www.ipcc.ch/report/ar6/wg2/resources/press/press-release. Accessed 20 Jan. 2023.

Woodward, F. I., ed. Global Climate Change: The Ecological Consequences. San Diego, Calif.: Academic Press, 1992. Collects articles by climatologists, atmospheric scientists, and ecologists that discuss the interconnections between climatic and biological systems. Though written by academics for academics, the articles are sufficiently general to be understandable by readers with modest scientific backgrounds. Maps, charts, graphs, references, index.