Climate change is any significant change in the Earth’s climate over a long period. Global temperatures have fluctuated (gone up and down) throughout the Earth’s history.
The Quaternary period is the most recent geological time period, spanning from 2.58 million years ago to today.
The Earth’s climate was warmer and more stable in the period before the Quaternary. Since then, things have changed quite significantly.
Global temperatures have shifted between cold glacial periods and warmer interglacial periods. As you can see from the graph below glacial periods have lasted around 10 times longer than interglacial periods.
Ice core data for the past 400,000 years, with the present at right. Note the length of glacial cycles averages ~100,000 years. The blue curve is temperature, the green curve is CO2, and the red curve is windblown glacial dust (loess). Image a derivative of By Vostok-ice-core-petit.png: NOAA derivative work: Autopilot (Vostok-ice-core-petit.png) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons
Since the last glacial period, 15000 years ago, the climate has been warming. Global warming is the term used to describe the rapid increase in global temperatures over the last century.
Evidence for Climate Change
A range of evidence has been used by scientists to work out changes in the Earth’s climate.
Ice and Sediment Cores
An ice core is a sample taken from a glacier or ice sheet. It involves drilling down into the ice and removing a cylinder of ice. As ice is formed in layers it is possible to analyse gasses from each year. From this scientists can work out the temperature at the time. Ice cores can be taken from Antarctica that provides information for the last 400 000 years. Samples of sediment taken from the ocean floor can also provide an indication of temperature over time. It has been possible to gather data from the last 5 million years by using this technique.
Thermometers have been used to accurately measure temperature since the 1850s. This provides reliable, short-term data on climate change.
For each year a tree grows it forms a new ring. The width of the ring gives an indication of the climatic conditions for the year. The thicker the ring the warmer and wetter the climate for that year. Tree rings are useful for giving an indication of climatic conditions over time.
Analysing pollen preserved in peat bogs or the bottom of lakes gives an indication of the species that were living in the past. This gives an indication of temperatures based on what we know about the conditions different plants thrive in.