Climate change is common in the geologic history of the Earth; climatologists have documented many periods of climate change, some of which have occurred very rapidly. In today's world, scientists are concerned about climate change because if it happens too quickly, several dangerous situations could arise:

• If the Earth warms rapidly, partial melting of polar ice could cause sea levels to rise, partially submerging many major cities and leaving others more susceptible to flooding during storms. Since most of the world's population lives only a couple of meters above sea level, this could create a hazardous situation for billions of people.
  
• Increasing temperatures will likely alter the relatively stable patterns of circulation in our atmosphere. This will change weather patterns dramatically in many areas. Since agriculture is dependent on certain weather patterns, such changes could significantly reduce food production in the face of a large and rapidly growing global population. Some regions will likely experience increases in the number and duration of drought events, threatening both agriculture and drinking water supplies.

• With an increase in the average global temperature, it appears that both the number and intensity of storms is increasing in some regions of the world. However, even if this did not occur, the shifting of weather patterns will likely result in more natural hazards simply because many locations will experience unusual weather. For example, a location that is usually dry may begin to receive a lot of rain, resulting in flash flooding.
  
• Species extinctions are expected to increase markedly as global temperatures increase. Species extinctions are currently at one of the highest rates in geologic history, mostly due to habitat loss caused by a variety of human activities. Combined with global warming, the extinction rate could be catastrophic. Since humans depend on countless species for our food, water, and medicines, the results could have dire implications for a rapidly growing global population.

Hundreds of scientific studies have shown that global warming is mostly caused by increases in greenhouse gases from human activities. These activities include the burning of forests and other vegetation, the burning of fossil fuels (such as oil) for transportation, and the burning of fossil fuels (such as coal) for energy production.

Currently, many different types of observations indicate that average temperatures at many locations around the world are increasing:

• As of 2009, carbon dioxide levels are higher than they have ever been for over half of a million years.
• Most glaciers around the world are rapidly retreating, from Africa to Alaska.
• Sea ice cover has decreased substantially in the Arctic Ocean.
• Migratory bird nesting and breeding patterns have shifted dramatically.
• Lakes are freezing later in the winter and thawing earlier in the spring around the world.
• More record high temperatures have been recorded in the last decade than any other time in history.
• Weather stations have recorded significant increases in average annual temperatures at several locations around the world.
• Hurricane intensity appears to be increasing in the Atlantic Ocean, possibly the result of the availability of additional heat energy.
• Permafrost in the northern tundra regions is melting.
• The length of heat waves in Europe has doubled in the last century.

Where is climate change occurring?
Most warming is currently occurring in the Arctic, where temperatures have increased by as much as 11 degrees F over a period of several decades. However, all regions of the planet are at risk from the hazards produced by climate change. The amount of risk at any location will depend on the nature of the changes in weather patterns and the characteristics of the local environment. It should be noted that "global warming" is not likely to be global, at least at first. That is, the average temperature of the Earth may increase, but some locations may initially experience cooling. With regard to natural hazards, climate change (warming or cooling) is the issue of greatest importance, and it is usually most important at regional and local scales.

When is climate change a hazard?
Evidence from several geologic investigations shows that climate change can be gradual, occurring slowly over a period of thousands of years, or rapid, shifting dramatically in time periods as short as ten years. In the next century, all seasons are likely to experience some increase in both the number and severity of natural hazards as global temperatures rise.

How do we cope with climate change?
Human activities are greatly accelerating natural climate change. In this case, preventive medicine is the best kind of medicine; curbing the activities that are likely contributing the most to climate change, such as fossil fuel burning, may eventually decrease the rate and extent of climate change. Implementing renewable energy sources, such as solar and wind, and high-efficiency automobiles (such as the Honda Civic and Toyota Prius) are important steps towards reducing fossil fuel emissions. Building cities that emphasize walking, biking, and mass transportation can reduce fuel consumption and improve physical health. These steps also work toward improving the quality of the air that we breathe and decreasing our dependency on fossil fuels, which are non-renewable resources with dwindling supplies. In other words, addressing the cause of climate change also works to solve several of the other environmental and economic problems our societies face today. Unlike most other natural hazards, climate change is a relatively slow hazard in our lives. This allows for some preparation, but it can also create complacency.