Earth's Climate Background Information
Climate and Weather
Whether you have pine trees or cactus growing in your backyard is determined by your climate. Latitude, elevation, and ocean currents shape your region's temperature, precipitation, and wind patterns — or in short, your local climate.
Climate is distinct from weather; while weather can change in a matter of hours or with the seasons, climate is the long-term average weather of a region. The average of thirty years or more of weather determines the climate of a region. Your closet is probably full of clothes, shoes, coats, and hats that are appropriate for your local climate. What you choose to wear on any given day is determined by the weather.
Earth’s Global Climate Is a Balancing Act
Earth’s water, ice, air, and life will continue to interact over long-term scales to influence our climate. Humanity has now proven influential enough to fundamentally alter our local and global climate.
In the past, Earth’s climate was shaped solely by natural factors. Astronomical factors determine how much of the Sun’s energy reaches Earth, including changes that occur over thousands of years: the shape of Earth’s orbit around the Sun, Earth’s “wobble,” and the tilt of Earth’s axis. Changes to the Earth itself also influence global climate. These can be big changes, such as the configuration of the continents and the way the atmosphere and ocean circulate, as well as more subtle changes, such small alterations in the composition of Earth’s atmosphere. Together, these many details determine how much energy Earth receives and retains from the Sun.
The Sun is the source of Earth’s surface warmth; it provides over 99% of Earth’s energy. Alone, energy from the Sun is only enough for our planet to reach -2oF (-19oC), but thanks to a small percentage of heat-trapping gases Earth is warmed to an average temperature of about 57oF (14oC), warm enough to inhabit. These gases (emitted by volcanos and bacteria, and others) trap some of the heat, preventing it from escaping into space—the greenhouse effect.
Earth’s warm global climate is created by a natural greenhouse effect. Most of the Sun’s light passes through the atmosphere and warms the Earth’s surface. The warmed land and oceans emit infrared radiation. Some of the infrared radiation is absorbed by heat-trapping gases in the Earth’s atmosphere. Credit: Lunar and Planetary Institute.
Carbon dioxide, methane, nitrous oxide, and water vapor are heat-trapping gases. The atmosphere is 78% nitrogen and 21% oxygen; heat-trapping gases are a tiny fraction of the air we breathe. Carbon dioxide (CO2) makes up almost 0.04% of the atmosphere; methane is only about 0.0002%. Water vapor is highly variable, and may represent between 1-4% of the atmosphere at the surface. Even in relatively small amounts, these heat-trapping gases have a very big impact on Earth’s atmospheric temperature! Small increases in the amounts of these gases mean increased warming of our atmosphere.
In addition to the greenhouse effect, other factors help moderate Earth’s temperatures. Life — mainly bacteria — generated much of the heat-trapping gases in our atmosphere. Trees and further contributions from bacteria and other small organisms are cooling influences. They can help keep one kind of heat-trapping gas, CO2, in check. Life is possible not only because Earth has a relative abundance of water, ice, and air, but because life continues to interact with these features to shape the dynamic place we call home.
Earth's global temperatures at any one time are a result of the balance between various natural warming and cooling influences. (In the past, the balance has also tipped toward the "cool side," perhaps even covering Earth entirely in ice!) Credit: Lunar and Planetary Institute.
The study of Earth’s climate is in itself an entire field, and it is concerned with Earth’s prehistory and a myriad of complex interactions not treated here. For more information on this topic, please see resources such as:
Earth’s global surface temperatures are rising at an unusually rapid rate. The past century has seen an average global increase of over 1oF (0.74oC). A degree may not seem large to us, but today’s global temperatures are the highest of the past 500 years, perhaps even for the past millennium.
Temperature change is nothing new; the Earth has undergone many changes in global temperature in its past. Certain eras in the Age of the Dinosaurs were warmer than today, and the ice ages were colder. However, modern human society has never encountered such profound and rapid change. Large changes in temperature occurred in the last million years during the glacial cycles, but the global warming at the end of an ice age is thought to have taken 5,000 years.
Scientists attribute most of the current climate change to increases in heat-trapping gas concentrations in the atmosphere. Scientists also agree that carbon dioxide released to the atmosphere by human activities is the main culprit of climate change. It is released from burning coal, oil, natural gas in power plants, cars, factories, and to some extent, from the clear cutting of forests. Human activities also release other heat-trapping gases. Methane is released by farm animals, rice paddies, rotting garbage in landfills, mining, and extraction of natural gas. The fertilizers used to grow our food add nitrous oxide.
Human activities contribute much more CO2 to the atmosphere than volcanos. It is estimated that present-day volcanos release about 0.15 to 0.26 gigaton, globally, each year. Compare that to the amount released in 2010 due to human activities: 35 gigatons. Our use of cars, pickup trucks, and other light-duty vehicles alone release at least about 12 times as much CO2 as volcanos, at 3 gigatons per year. (“Volcanic Versus Anthropogenic Carbon Dioxide,” by T. Gerlach, Eos, Vol. 92, No. 24, 14 June 2011.)
Ice cores record the amount of carbon dioxide in Earth’s atmosphere stretching back thousands of years. A dramatic increase in the percentage of carbon dioxide in the atmosphere corresponds with the Industrial Revolution and has proceeded to climb sharply in the ensuing years. Today’s levels far exceed even the highest levels of the past 750,000 years.
The carbon dioxide (CO2) concentration in the atmosphere has been measured directly since 1957. The instruments at Mauna Loa, Hawaii reflect the seasonal uptake and release of carbon dioxide by plants as "wiggles," but show an overall sharp increase. Credit: Scripps Institution of Oceanography/ National Oceanic & Atmospheric Administration Earth System Research Laboratory, www.esrl.noaa.gov/gmd/ccgg/trends
The increases in atmospheric CO2 are clearly due to human activities, rising in parallel with the increase in fossil fuel combustion. The carbon in fossil fuels also has a unique signature: it lacks one particular type of carbon (i.e. isotope), called 14C. From 1800 to 1950, the amount of naturally occurring 14C in the atmosphere decreased as it was diluted by carbon originating from fossil fuels.
Understanding Our Changing World
Scientists work together, connecting data from all realms of science to understand our changing planet. For example, biologists note what species of flowers bloom earlier in the year and in what regions coral reefs die off as sea surface temperatures increase. Oceanographers measure how increasing carbon dioxide is acidifying our oceans as it dissolves to form carbonic acid. Satellites take data on ice cover, precipitation, temperature, and other characteristics of our planet from above.
Our planet is so complex that climate scientists use complex computer algorithms, called climate models, to weigh the influences of the myriad of factors which shape our planet’s climate. Computer models weigh the influences of heat-trapping gases from natural and human sources, changes in the Sun’s intensity, ice and cloud cover, volcanos, ways in which different life forms shape their environments — and how these different factors interact in complicated ways over time.
The scientific understanding of climate change is not as provisional as it is often portrayed. Indeed, a study in the Proceedings of the National Academy of Sciences found that 97-98 percent of actively publishing climate researchers support the basic understanding of human-induced climate change. While the contributions of natural warming are still not fully understood, climate scientists generally agree that their effects are secondary. Earth’s climate is changing mostly as a result of certain human activities.
Tomorrow’s World Will Be a Different Place
Imagine how your world might change as your local climate is reshaped by global climate change. Scientists are trying to understand how changes in temperature, precipitation, wind, and sea level will impact Earth’s diverse regions. Scientists use mathematical computer models to predict how the various warming and cooling factors will shape tomorrow’s climate.
Climate change will impact human health, agriculture, forests, water resources, coastal areas, and species and natural areas. Image courtesy of United States environmental protection agency (EPA)/Philippe Rekacewicz, UNEP/GRID-Arendal
The thawing of Earth’s freezers — the polar regions — will have far-reaching effects. The nature of the polar regions makes them more sensitive to the consequences of climate change than warmer latitudes. Reflective white ice and snow will melt into dark rivers and oceans that better absorb the Sun’s energy. Increasing temperatures will expose organic matter formerly locked away in the frozen ground of the arctic tundra. This permafrost will thaw, releasing the heat-trapping gas methane.
Changes in temperatures and reduced sea ice will impact Arctic and Antarctic ecosystems. Among other species, Emperor and Adélie penguins and polar bears face massive population losses with the predicted temperature rise.
Changes will vary across the globe. More warming is expected in the interiors of continents and in the northern latitudes of the Northern Hemisphere than at the coastal regions and tropics. Heat waves are expected to become more intense. Higher temperatures will lead to faster evaporation, and rain, when it occurs, may fall in the form of heavy downpours. More precipitation may provide additional water to some regions, but floods and droughts are also expected to become more frequent. Storms might increase in intensity; in addition, rising sea levels will impact coastal areas.
Crops may experience longer growing seasons and fewer frosts. The warmer temperatures and increased carbon dioxide in the air may help some crop varieties, but some of them will reach a point at which it is too warm to survive.
The ranges of plants and animals, biodiversity, and migratory patterns are expected to continue to change in response to climate change. Many pests, parasites, and diseases are likely to thrive in the warmer temperatures. While heat waves may contribute to heat-related illness and death, milder winters may be a benefit for health issues.
Humans Have the Power to Stabilize Global Change
Humans clearly have an impact on the global environment. Our influence can be used to stabilize or reduce climate change.
Use of fossil fuels pervades our everyday life: fossil fuels power our cars and school buses, and coal often produces the electricity that runs our air conditioners and charges our cell phone batteries. Fossil fuels are often used in the production and transportation of our goods; for instance, fossil fuels are used for the energy and materials to create plastic bottles and transport heavy drinking water across the country to the local grocery store. Thus, we can combat climate change by driving less, conserving electricity, and becoming savvy consumers of local produce and recycled goods.
In addition to carbon dioxide, the heat-trapping gases methane and nitrous oxide are by-products of everyday practices. Methane is released in large amounts by livestock. Stocking up on other proteins is one way grocery shoppers can help slow climate change. Human-produced fertilizers break down in the soil and release nitrous oxide, so composting the vegetable clippings to use as natural fertilizer can further help slow climate change.
It is amazing that something as tiny as heat-trapping gas molecules can create and change our global climate so drastically, even though they are vastly outnumbered by the nitrogen and oxygen molecules that make up the majority of our atmosphere. Though we may sometimes feel small and insignificant as individuals or communities in our complex societies, we likewise have the power to make a large impact — and make the changes necessary to manage Earth’s resources wisely!
