The global temperature is one degree higher than it was a century and a half ago at the time of the invention of the internal combustion engine, which marked the beginning of the Industrial Age. Combustion engines are powered by fossil fuels which contribute to higher concentrations of greenhouse gases that affect global warming - often referred to as "Climate change" and linked to the human effect on long-term climate patterns. It's a political hot potato.

Climate has changed many times over the course of our Earth’s history, and dramatically so, but recent patterns of higher temperature have attracted widespread concern. Melting glaciers and Glacial Lake Outburst Floods in mountainous regions have resulted in rising sea levels and the first-ever evacuation of entire island communities.

In 2005, the U.S. Department of Defense acknowledged this shift in climate as the most important influence on United States national security over the following span of 20 years. Whatever it's called, the new weather patterns that seem to be developing could spur never-before-seen uncharacteristic hot and dry weather in one area, and wet and snowy weather in another. Tracking and adapting to weather and/or long-term climate change is one of the exciting challenges of the years ahead.

Previous Shifts in Climate

Fevers and Chills, the Earth gets them too

Previous climate changes have included what is referred to as the Medieval Climate Anomaly. Occurring between 900 and 1300 AD, this period in time was characterized by a slight warming of Europe, Greenland & Asia, in addition to a dry spell on the western coast of North America. The Little Ice Age arose between 1500 and 1850 AD. During this time global temperatures were 2 degrees higher on average.

For a timeline of climate changes over the past 4 billion years, visit: http://dsc.discovery.com/convergence/globalwarming/timeline/timeline.html

All of this is fascinating, but how do scientists know what happened hundreds and thousands of years ago?

Scientific Methods in Climate Science

What bees and trees can teach us about climate

Many methods exist for determining previous shifts in global climate. Some include the study of fossilized bee pollen, called Palynology, or the study of tree rings, called Dendroclimatology. Scientists also take ice cores from the Antarctic and other glacial areas to analyze the concentration of greenhouse gases trapped in air bubbles.

Palynology provides clues to the geological distribution of plants. Because the pollen of different species of plants varies in size and texture, scientists can use changes in the type of pollen found to infer changes in plant cover. In this way, experts can determine periods of climate stability and periods when the climate shifted, since certain plants will flourish and other will wilt given specific conditions.

Dendroclimatology looks to tree rings for an understanding of historical climate changes. Where the rings are thick or wide, scientists can deduce a higher availability of water. Where they are thin or narrow, they can deduce a lower availability of water and less than ideal growing conditions. The amount of rainfall over a period of time provides one key to information on climate.

Causes of Climate Shifts

Climate bullies and their lackeys

Changes in global climate can be partly a result of what are called “climate forcings,” which include:

* Changes in Earth’s Orbit

* Changes in the Sun’s Intensity

* Volcanic Eruptions

Climate forcings can serve as a trigger for greenhouse gas concentrations and changes in ocean current, which may either lessen or intensify climate changes taking place. A body of scientists also adhere to the belief that human activity, such as the burning of fossil fuels and deforestation, can be one of a number of contributing factors in climate change.

What about the Seasons?

Spring showers bring May flowers

As most of us learned in elementary school, the Earth sits on an invisible axis and has a tilt of approximately 23 degrees. This tilt remains stationary as the Earth moves around the sun, so that when the Northern hemisphere is tilting toward the sun, it experiences summer. At the same time, the Southern hemisphere is tilting away from the sun and entering winter. Fast forward six months and these positions are reversed. As the Earth continues in its orbit around the Sun, we experience the seasons of fall and spring. (See diagram below, representing the seasons in the Northern hemisphere).

This video explains the seasons, as well as the solstices and equinoxes: http://www.youtube.com/watch?v=HlvQ1fVMqNA

To learn more about climate matters and how becoming a season spotter can contribute to the body of knowledge available to gardeners like you, visit our Why Join? Resource page.

Other Climate Resources:

EPA Climate Change Science

EPA’s Kids Site.

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Season Spotting