Teaching about the relationship between climate and life is supported by five key concepts:
a. Individual organisms survive within specific ranges of temperature, precipitation, humidity, and sunlight. Organisms exposed to climate conditions outside their normal range must adapt or migrate, or they will perish.
b. The presence of small amounts of heat-trapping greenhouse gases in the atmosphere warms Earth's surface, resulting in a planet that sustains liquid water and life.
c. Changes in climate conditions can affect the health and function of ecosystems and the survival of entire species. The distribution patterns of fossils show evidence of gradual as well as abrupt extinctions related to climate change in the past.
d. A range of natural records shows that the last 10,000 years have been an unusually stable period in Earth's climate history. Modern human societies developed during this time. The agricultural, economic, and transportation systems we rely upon are vulnerable if the climate changes significantly.
e. Life—including microbes, plants, animals and humans—is a major driver of the global carbon cycle and can influence global climate by modifying the chemical makeup of the atmosphere. The geologic record shows that life has significantly altered the atmosphere during Earth's history.
Life affects the climate system and in turn, the climate dictates where and how species can survive.
Life affects the composition of the atmosphere and therefore the climate because different life forms take in and release gases like carbon dioxide, methane and oxygen at different rates. Climatic conditions help to shape various ecosystems and habitats around the globe. A particular climate can be a boon to one species and a devastation to another. As the climate changes, species and ecosystems respond by adapting, migrating, or reducing their population. Gradual shifts in the climate are easier to adapt to than abrupt swings, and this is certainly true for humans as well as other species. Studies of Earth's climatic history indicate that climates have changed in the past and resulted in dramatic shifts in ecosystems. The most recent geological period the Holocene (about last 10,000 years), however, has been unusually stable.
The manner in which the earth sustains life is of vital importance on many levels.
- The conditions on Earth such as temperature, moisture, oxygen concentration, and sunlight, are what sustain life.
- Throughout geologic history, life on Earth has affected the climate system and vice versa.
- Extinctions of species, both in the geologic past and in the present day, can be linked to changes in climate.
- Unraveling past climatic changes is key to understanding present and future shifts in the climate.
- Changes in climate will result in shifting ecosystems. It is not possible to predict the details of specific effects of climate change on each of the world's ecosystems.
- Although the concentrations of greenhouse gases have changed throughout Earth's history, there is no natural analog to today's rapid increases in human-created greenhouse gas emissions.
Like much of climate science, these concepts span multiple scientific disciplines. Teaching these ideas is a way to illustrate how scientific thinking benefits from sharing expertise among different types of scientists.
This topic can be introduced by brainstorming for conditions that are needed for life to thrive. Students can explore how life exists in many parts of the earth system, such as in the depths of the oceans or in acidic hot springs. Life is robust and versatile. Nonetheless, all organisms need certain conditions to live.
The planet currently exists at a temperature that is neither boiling nor permanently frozen. This is due to the natural greenhouse effect that causes the atmosphere to retain outgoing heat. A possible misconception is to confuse the natural greenhouse effect with the enhancement of this effect caused by emissions of greenhouse gases from fossil fuel burning (McCaffrey & Buhr, 2008). This is an ideal opportunity to discuss the difference between natural processes and human effects. For example, if a certain amount of a greenhouse gas allows life on Earth to flourish, then is more of it better?
When teaching about the interplay between climate and life, the differences between natural and human caused changes should be emphasized. Questions may arise such as: Are all natural changes good? Are all human-caused effects bad? Is our current climate the "right" climate? It's important to emphasize that the recent increases in greenhouse gas concentrations in the atmosphere are unprecedented in the geologic past. Comparing natural and human-caused changes can foster stewardship of the planet among students.
Teaching about the limited ability of organisms to adapt to climate change should not lead to gloom-and-doom scenarios. Instead try to foster an understanding that humans have a responsibility to stabilize the natural climatic conditions in order to preserve the environments in which humans and the surrounding ecosystems thrive.
Bringing these ideas into your classroom
Many of these ideas are part of the life science curriculum but they integrate concepts from physical sciences, geography, and other disciplines. Possible topics to teach an understanding of this principle are:
- Seasonal migrations of species.
- The effects of the spring "green up" in the northern hemisphere and the resulting seesaw pattern in atmospheric CO2 concentrations as as illustrated by the Carbon Dioxide Exercise.
- Decade-scale events such as insect outbreaks, forest succession, or drought.
- The role of life to shape climate, particularly in the creation of Earth's oxygen-rich atmosphere.
- The 100,000 year cycle of ice ages, the role of CO2 in enhancing the temperature swings, and the response of biologic systems to these dramatic shifts in climate.
- Periodic mass extinction events that punctuate the geologic record and were likely related to climatic changes.
Another approach that may be engaging for older students is the delicate relationship between life and the climate. Many students will be surprised to learn of past mass extinction events and other sharp swings in the balance of the biosphere. This is a key place to discuss the role of humans in changing our environment and climate.
Teaching materials from the CLEAN collection
- Temperature and precipitation as limiting factors in ecosystems - Students correlate graphs of vegetation vigor, temperature, and precipitation data for four diverse ecosystems to determine which climatic factor is limiting growth.
- The Ocean's Green Machines is a video about phytoplankton - the base of the marine food web, the source of half of the oxygen on Earth, and an important remover of CO2 from the atmosphere.
- Classroom experiments such as Uptake of Carbon Dioxide from Water by Plants can visibly show effects that are normally not observable. These demonstrations show the role of plants in mitigating the acidification caused when CO2 is dissolved in water.
- Students can explore climate-driven ecosystem effects such as with an animation that shows Pine Bark Beetle Outbreaks and Climate. There are many resources about pine beetles in the CLEAN collection, including several videos.
- Why Fly South? How Climate Change Alters the Phenology of Plants and Animals will walk students through the process of plotting 30 years of data that shows the date of the first lilac bloom and the number of days of ice cover of nearby Gull Lake.
- The Once and Future Corals is a narrated slide show that illustrates how coral reefs are in danger from pollution, ocean temperature change, ocean acidification, and climate change. In addition, scientists discuss how taking cores from corals yields information on past changes in ocean temperature.
- Carbon Dioxide Exercise offers a clever group activity to plot data points of atmospheric carbon dioxide. The seasonal removal of CO2 becomes very evident in the data.
- Climate and Civilization: The Maya Example - Students dive into geophysical and geochemical data to determine climate in Central America during the recent past and to explore the link between climate and population growth/demise among the Maya.
- PETM: Unearthing Ancient Climate Change is a video that looks at the Paleocene-Eocene Thermal Maximum, which is the closest analog we have to the rapid rise in greenhouse gases that we are experiencing today.
- Investigating Coral Bleaching Using Real Data - A sequence of 5 activities using real-world data to explain the importance of coral reefs and the relationship of coral reef health to the surrounding environment. There are several resources about coral bleaching in the CLEAN collection.
Carbon Cycle - NASA information - brief overview on the components of the carbon cycle.
Cititzen Science Project - Project Bud Burst - A citizen science project about the growth of plants throughout the season.
xkcd Timeline of Earth's Average Temperature illustrates the stable climate throughout the Holocene.
PETM: Global Warming, Naturally, an article from Weather Underground that summarizes the Paleocene-Eocene Thermal Maximum, which happened 56 million years ago and offers insights into our current climate conditions. This is an area of ongoing research, particularly because of its relevance to modern climate change.
McCaffrey & Buhr, 2008: Clarifying Climate Confusion - journal article in Physical Geography about common misconceptions in climate science.