Temperature records for the past 542 million years as determined by oxygen isotope ratios.

Earth's estimated temperature over 542 million years.

Image © Robert A. Rohde.

Climate

Earth's climate is constantly changing due to many different factors. Temperatures from various points in time can be collected through several methods, such as mapping the distribution of temperature-sensitive minerals or measuring the ratio of oxygen isotopes in ice or ocean sediments. [1]

The image to the right shows temperature records as determined by oxygen isotope ratios stretching back as far as almost 550 million years.

As you can see, the temperature shifts between warm and cool over time. These changes also occur on a much smaller scale, as you can see in this graph.

Causes of Climate Change

A number of factors may affect the climate on Earth, making the exact cause for climate change difficult to determine. Factors include:

  1. Changes in solar output.
  2. Changes in the position of Earth's landmasses.
  3. Changes in Earth's orbit.
  4. Changes in the composition of the atmosphere.
  5. Changes in ocean circulation.
  6. Changes in the reflective properties of Earth.

Many of these factors are interdependant relationship with the climate in the sense that they both affect and are affected by it.

1. Solar output varies in both long and short term cycles. Since the formation of Earth 4.6 billion years ago, solar output has increased by 30%. Solar output can change based on sunspots or other processes within the star.

2. The position of land can affect temperature for several reasons. First, solid land heats and cools faster than the oceans. This means that climate may change over millions of years as the continent's positions shift.

3. Milankovitch Cycles - changes in the Earth's orbit - can alter the amount of solar energy absorbed by the Earth. Over periods of tens of thousands of years, things such as the shape of Earth's orbital path, the tilt of its axis and the direction of tilt in relation to the sun. While their interactions are complex, these cycles are theorised to be the most likely cause of Earth's major glacial episodes (or ice ages).

4. Atmospheric composition has a large effect on climate. Particles in the atmosphere, such as dust and volcanic ash, block solar radiation, leading to a lower global temperature. This can be observed particularly after major volcanic eruptions or meteor impacts. Other gases, called 'greenhouse gases', absorb solar radiation, leading to a warmer temperature. An increase in greenhouse gases can be seen in recent years and is often attributed to human activity, though natural causes for changes in their atmospheric concentration also exist.

Atmospheric CO2 in ppm (parts per million) per year.
Year 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2009
CO2 316.91 320.04 325.68 331.08 338.68 345.87 354.16 360.62 369.40 379.76 387.35
Data source: National Oceanic & Atmospheric Administration (NOAA), Mauna Loa Observatory. [2]

5. Significant changes in ocean circulation affect the circulation of heat on Earth. Both short term and long term cycles in ocean circulation will have an effect on the Earth's climate.

6. Radiation from the sun can be reflected or absorbed. Things such as ice, snow and cloud cover reflect solar radiation back in to space, cooling the earth. Darker areas and vegetation absorb radiation and re-emit it as heat. The reflectivity of Earth is highly dependant on current climate.[3]

Further Reading: Climate Change.

This website explains and analyses various cuases of climate change, focussing particularly on analysing human contributions.

Effects of Climate Change

Climate change affects both the life on Earth and the planet itself. Currently, the planet is warming. As it warms, global snow cover will be reduced as ice melts. Sea levels will rise, potentially reducing the amount of land above sea level. The amount of available water in arid regions, such as Africa, is predicted to reduce.

The frequency of tropical storms and extreme weather is predicted to rise globally.

The results of the current trend in climate change is often depicted as negative for life on Earth, but it is not always the case. The yield of rain-fed crops will increase in certain regions, for example. [4]

Earth's temperature is still affected by all of the causes mentioned previously, and some of the causes will be affected by the increase in global temperature. Increased cloud cover and more ocean space will increase the planet's reflectivity and ocean/wind circulation will change. The atmospheric composition will shift as different reactions occur, possibly resulting in a cooling trend.

As the graph at the top of the page demonstrates, climate change often occurs in cycles. As our planet changes, the causes of climate change will shift and in time the opposite will occur.

Bibliography.