1.3 Global Warming
Almost everyone has heard of the term “global warming”, and knows that it means a warming of the planet. However, most of us do not know exactly what this means or how it is measured.
Global warming is the significant increase in the Earth’s temperature over a short period of time due to the result of human activities.
Changes in climate typically take tens of thousands of years. Although 1° or 2° Celsius may not seem like a lot, small temperature changes can have significant effects. After all, the difference between ice at 0° and water at 1° is only 1°, and ice in many parts of the world that has been frozen for thousands of years is now beginning to melt. Small differences in global temperature can even be the difference between our world today and an ice age. When you hear the term “ice age,” you probably think of the whole world being covered in snow and ice, but the ice during ice ages in Earth’s history has only ever covered a small part of the Earth’s surface. During the last ice age, when northern North America and northern Europe were covered by glaciers up to 2 miles thick, so much of Earth’s water was frozen that the world’s sea level fell by more than 100 meters. But, the average global temperature was only 5°C cooler than it is today [3, 4].
The Intergovernmental Panel on Climate Change (IPCC) is a group of over 2,500 scientists from countries across the world. They met in 2007 to advance climate research. Figure 1-8 shows their findings on changes in global temperature and sea level. One of the conclusions of this meeting was that the last 15 years have been the warmest since 1850.
- Glaciers and snow have decreased in the northern and southern hemispheres. Average arctic temperatures have increased by twice the global average during the last 100 years.
- Rain has increased in the Americas, northern Europe and parts of Asia. South Africa and the Mediterranean have been experiencing drying trends.
- Hot days have become more frequent, and cold days have become less frequent and severe.
Natural changes in climate such as heating due to volcanic activity, radiation from the sun, and changes in the chemistry of the atmosphere usually take thousands of years to change only 1°C, but human activity is causing that much change in a much shorter amount of time [3, 4, 5].