Climate, Energy, and Earth Process
OVER SEVERAL BILLION YEARS, living organisms have evolved from single cells to highly complex creatures as they draw matter from the Earth and energy from the sun. Life has steadily transformed both itself and the earth as a whole toward miraculously greater diversity and complexity. While many cycles and processes contribute to this “earth process,” two are relevant to our topic.
Geological process involves changes over long periods of time in the earth’s crust. Through geological process, the Earth’s atmosphere, oceans, and living creatures have evolved together to create and sustain conditions in which life can flourish. Substances essential to life—water, carbon, nitrogen, and others—circulate between the biosphere (where life exists), and the Earth’s mineral crust in such a way that life adapts to and participates in stabilizing the physical and chemical characteristics of the biosphere.
Ecological process involves the relationship of plants and animals with one another and the Earth. Plants get matter from the Earth and energy directly from the sun. Animals get both matter and energy by eating plants or other animals. We humans, through technology and social organization, have increased the matter and energy we use far beyond our basic animal needs. Until the 19th century, most of the energy used by humans came from the ecological process, from fire, plants, other animals, water, and wind. Then one human culture (our own), began using for fuel fossil matter that had been created over millions of years—first coal, and then oil and natural gas. Burning large quantities of fossil fuels has changed the chemistry of the atmosphere by putting carbon, stored for eons underground, back into the atmosphere in a very short time. This change in the chemistry of the atmosphere is accelerating the rise in our planet’s temperature to rise.
What is the greenhouse effect? This term, "greenhouse effect," comes from the way a greenhouse can maintain a tropical climate even when the weather is cold outside. Much the same thing happens inside a car that is parked in the sun with the windows rolled up.
Scientists explain the "greenhouse effect" in this way:
The energy of sunlight, which has short wavelengths, eaily passes through glass. After it warms the objects inside the greenhouse, the energy is converted into longer-wavelength heat radiation, which cannot pass as easily back through the glass, so the greenhouse traps heat.
How high a greenhouse temperature rises depends on many factors. For example, if there is more dense matter ("thermal mass") in side to absorb heat, the temperature rises and falls more slowly; and as the difference between indie and outside temperature increases, the heat is lost to the outside more quickly. As a result of these and many other factors in combination, the actual temperature changes toward an equilibrium temperature, at which the heat coming in is in balance with the heat going out, or until the factors change. If things get too hot inside for the plants growing there, the greenhouse may have to be shaded or ventilated to shift the equilibrium temperature downward.
After greenhouses came into use, scientists discovered that the earth's atmosphere works a lot like greenhouse glazing—admitting shorter-wavelength light while trapping longer-wavelength heat radiation. There are several gases in the atmosphere, particularly carbon dioxide (CO2) and methane, that make the earth's equilibrium surface temperature about 60 degrees Fahrenheit higher than it would otherwise be, which makes life possible. Without the presence of these "greenhouse gases" all fresh water and most of the oceans would be frozen.
How does the greenhouse effect relate to climate?
Because of the earth's rotation, the tilt of its axis, the size and location of continents, and numerous other factors, the weather created by heat stored in the atmosphere, oceans, and land surface is different everywhere and constantly changing. However, the average temperaures, winds, rainfall, and growing season in any one place have been remarkably stable over many thousands of years. The stability of the greenhouse gas concentrations in the atmosphere is largely responsible for this.
Climate change occurs naturally over very long periods of time, due to periodic changes in the intensity of the sun, the position of the earth in relation to the s un, and the shape and location of continents. When climates change very gradually, plant and animal species are able to evolve to adapt to new conditions. The relative stability of climate has made possible the evolution of more complex forms of life and the development of agriculture and civilization.
What is global warming and how does it relate to the greenhouse effect and climate change?
Climate scientists have learned that both greenhouse gas concentrations and the earth's average temperature have been rising steadily for the past half century. Human activities are adding greenhouse gases to the atmosphere. This creates an "enhanced greenhouse effect," and thus the earth's equilibrium temperature is being shifted upward.
We who inhabit this global greenhouse are beginning to experience significant changes in the weather and climate. Because of all the factors that affect climate, many regions are getting warmer, while some are getting colder. But climate patterns are changing everywhere, weather is becoming more variable, and extreme weather events are increasing. Scientists are concerned that continued global warming may cause abrupt changes in ocean currents or sea level that would have major effects on agriculture and large human populations.
What scientists know
1. Global warming/global climate change is being caused by human activities.
Carbon dioxide (CO2) has increased about a third (from 280 parts per million to 368 ppm) since 1750. About 80 percent of the increase is from the burning of fossil fuel and 20 percent from deforestation (trees which would capture CO2). Excess carbon dioxide (that which is not absorbed by natural means) remains in the atmosphere for over 100 years.
Methane has increased about one and a half times (from 700 parts per billion to 1750 ppb). Methane comes from burning fossil fuel, from decomposing plant matter in swamps, bogs, and rice paddies; from digestive processes of animals like cattle and termites; and from landfills. Excess methane stays in the atmosphere for only about 15 years, but traps much more heat than CO2.
Synthetic industrial gases (such as CFC’s) have accumulated in the past 50 years. They are beginning to have a significant effect because they trap even more heat than methane, and they last much longer than CO2.
2. The Earth’s average surface temperature increased about 1º F in the 20th century, which appears to be the largest and steadiest change of any time in recorded history. This seemingly small change creates large changes in regional climate and weather patterns. Much of the increase has been in the last 20 years. The 10 warmest years on record have all been since 1990. Temperatures have warmed more at higher latitudes, more at night, meaning that there are fewer frost days, and more over land than the ocean.
3. Average rainfall increased by 5 to 10 percent between 1900 and 2000. Rainfall patterns are also changing, with increases in the frequency and severity of both droughts and storms.
4. Average sea level has risen 1 to 2 mm a year since 1900 (6 to 10 total inches) — mainly because the volume of water increases as it warms.
5. Snow and ice cover have decreased. Snow cover has decreased about 10 percent since 1960. The period that ice covers lakes and seas has decreased by about two weeks in the past century. Arctic sea ice has thinned by 40 percent and decreased in extent by 10-15 percent since the 1950s. Many glaciers are retreating, some quite rapidly.
6. Flowering, growing, and breeding seasons have lengthened. In the northern hemisphere, growing seasons have increased from 1 to 4 days per decade in the last 40 years, and habitat ranges for plants, birds, fish, and especially insects are shifting toward the warming poles and higher elevations.
7. Loss of life and property due to weather-related events have increased. The increase has been dramatic during the past ten years, although growing populations and economies are also contributing factors.
What scientists understand and project
1. The global climate system is exceedingly complex, and has many interacting features.
- Self-regulating features (negative feedbacks) limit change; an example is the tendency of plants in warm conditions to grow faster, absorbing more carbon dioxide and reducing the greenhouse effect (with a reverse effect in cold conditions).
- Destabilizing features (positive feedbacks) amplify change; an example is that warming conditions increase the amount of water vapor in the air, which traps more heat, which creates warmer conditions.
- Unpredictable features are feedbacks that may be positive or negative; an example is the increase in clouds in warmer conditions which, depending on how they form, may reflect more sunlight or may trap more heat.
- Natural fluctuations are features that vary from place to place and year to year, like temperature, rainfall, and sea level. These make overall change difficult to determine, which is why scientists report their findings as a range.
2. Only a few features of the climate regime in the past can be measured directly. Air bubbles trapped in ice cores in Antarctica and Greenland indicate the level of greenhouse gases in the atmosphere over 160,000 years. But historical temperatures, sea levels, ocean currents, and ice and snow covers, must be estimated from biological and chemical evidence. Still, some features are now clearly understood:
- Global temperatures and greenhouse gas levels have risen and fallen together over time. In the past, temperature began to change due to geological process, and the destabilizing features of biological process accentuated the change by increasing or decreasing natural greenhouse effect. Now human activities are adding carbon directly and creating the enhanced greenhouse effect.
- Oceans absorb and release heat much more slowly than air or land, so there is a delay of 50 to 100 years between a change in greenhouse gas levels and the change in global temperature. Also, because carbon dioxide remains in the atmosphere for up to 100 years, it will be a long time after greenhouse gas emissions are reduced before the global temperature adjusts and the climate begins to stabilize.
3. In the past climate usually changed gradually, but occasionally rapid changes have occurred, such as a shift in the ocean currents that increased ice cover in northern Europe in less than a decade. While rising greenhouse gas levels can be expected to increase global temperature and sea level gradually, at some point a major shift in the whole system may lead to “surprises” of either more rapid warming, or a reversal into rapid cooling.
4. The long term effects of global warming are totally unpredictable. Even for the shorter term, scientists cannot make specific predictions because of the size and complexity of the system, and above all the unpredictability of future human activity. But highly sophisticated computer models enable them to make projections, based on different scenarios, from which they conclude, with a high level of certainty, that by the end of the 21st century:
- With no surprises global temperature will rise a minimum of 2½ degrees Fahrenheit, and 10½ degrees Fahrenheit in the worst case.
- Sea level will rise of 10 to 30 inches.
- Precipitation will increase at least 1 percent for every 1º F rise in temperature, with more extreme weather events
- The likelihood of a major “climate surprise” due to unforeseen events or a combination of events will increase.
The effects of these changes on climate and weather, ecosystems, people, and economic costs, will be due not to the averages but to extremes of heat waves, droughts, storms and flooding; of fewer freezes that determine the ranges of insects and diseases they carry; of changes too rapid for trees and other plants on which animals depend to evolve or migrate; of societal crises requiring more energy and water when less is available and the costs are higher.
For these reasons, in 1990 climate scientists strongly urged governments to adopt policies that would reduce greenhouse emissions as quickly as possible. Since 1990, new knowledge suggests that climate changes will be greater than was expected then, especially because greenhouse gas emissions continue to rise. Climate scientists estimate that emissions will have to be reduced 60% or more from 1990 levels before the atmosphere will begin to stabilize. It will be long after that before global temperature stops rising unless there is a shift in ocean currents or some other dramatic change.
Those who say we can wait until we have better science don’t seem to understand the limitations of science, the irreversibility and unpredictability of the changes, and potential severity of the consequences for life as we know it.