|During the past 150 years, the global average surface temperatures have increased by about 0.76°C. In addition to warming up of the Earth's surface, there have been increased incidences of heat waves; accelerated melting of continental glaciers and polar ice caps; rise in sea level of up to 20 cm; heavy
rainfall in some regions, resulting in frequent floods; reduced rains in other regions of the world, resulting in severe drought. Some plants and animals have even changed their location or the timing of seasonal activities. For instance, in the Alps, some plant species have been migrating upwards by 1 to 4 m every decade in search of cooler climes. Sadly enough, some plant species that were previously found only on mountain tops have already disappeared and have possibly become extinct. Similarly, in Europe, the mating and egg-laying of some bird species is occurring earlier every year when compared to the previous year.|
The temperature change is not just measured using regular thermometers. There are several Natural
Thermometers also that are sensitive to changes in our climate, and that have helped scientists learn
more about global warming. Examples of such natural thermometers are the tree rings and coral rings.
TREE RINGS: The tree rings indicate how much a tree has grown each year, with each ring representing one year. In warmer, wetter years, the tree will grow more so the ring for that particular year will be wider than the ring formed during a colder year. By studying the width of the tree rings, scientists can learn about the changes in weather over the tree's lifetime.
CORAL RINGS: Corals build up rings made of calcium carbonate as they grow. If the sea temperature is
warm the coral rings will grow faster than if the temperature is cold. So, warmer years will produce wider growth rings and colder years will create thinner rings. By studying these rings we can get an idea of what the sea, and therefore the surface temperatures, were like each year.
ICE CORES: Ice is formed during glaciations through the process of continuous deposition
and compaction of snow layers. Since permanent 'pack ice' rarely melts even in
summer, it is a reliable indicator of climatic conditions in the earth's history, with the age
of deposition increasing with depth. A circular sample of such permanent ice drilled to study
the ice layers is called an 'ice core'. Greater density in ice layers indicates cooler
temperatures, and lower density, or the presence of the heavier Oxygen 18 isotope,
indicates warmer climates. In the past 50 years, scientists have noticed that the growth
rings in corals as well as the width of the tree rings have been getting wider, which indicates
that the global temperatures have been increasing.