Introduction to Climate Change

Evidence for Climate Change and its Impacts

The Inter-Governmental Panel on Climate Change (IPCC), the world’s leading international scientific body for the assessment of climate change, releases periodic reports on the causes and effects of climate change. In the Fifth Assessment Report released in 2014, the IPCC reported:

  • Human influence on the climate system is clear, and recent anthropogenic emissions of greenhouse gases are the highest in history;

  • Each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850;

  • Recent climate changes have had widespread impacts on human and natural systems;

  • Warming of the climate system due to human-induced greenhouse gases is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia – the oceans and atmosphere have warmed, the amounts of snow and ice have diminished, and sea level has risen;

  • Changes in climate have caused impacts on natural and human systems on all continents and across the oceans;

  • Since the beginning of the industrial era, oceanic uptake of carbon dioxide has resulted in acidification of the ocean – the ocean has absorbed about 30% of the emitted anthropogenic CO2;

  • Greenland and Antarctic ice sheets have been losing mass, glaciers have continued to shrink almost worldwide, while Northern Hemisphere spring snow cover has continued to decrease in extent;

  • In many regions, changing precipitation or melting snow and ice are altering hydrological systems, affecting water resources in terms of quantity and quality;

  • Many terrestrial, freshwater and marine species have shifted their geographic ranges, seasonal activities, migration patterns, abundances and species interactions in response to ongoing climate change;

  • Negative impacts of climate change on crop yields and marine organisms have been observed;

  • Changes in many extreme weather and climate events have been observed – including a decrease in cold temperature extremes, increase in warm temperature extremes, an increase in extreme high sea levels and an increase in the number of heavy precipitation events in a number of regions;

  • Climate change will amplify existing risks and create new risks for natural and human systems


Causes of Climate Change

  • The ‘natural’ greenhouse effect makes life as we know it possible on Earth, without which the average global temperature would be about - 18°C rather than its current +14°C. Earth’s surface temperature is determined by the radiative balance, the net difference between the energy gained from incoming energy from the sun and the amount lost into space as infrared radiation. The Earth’s atmosphere acts like a transparent blanket (or greenhouse), letting in light but trapping some of the heat it generates. Without an atmosphere, all of this energy would be lost to space. This natural effect relies on ‘greenhouse’ gases in our atmosphere allowing sunlight to pass through, and trapping some of the resulting heat energy that radiates back up from the Earth’s surface.

  • Since the start of the Industrial Revolution in about 1750, human activities such as the burning of fossil fuels including coal and oil which emit carbon dioxide and other greenhouse gases, have dramatically increased the concentration of greenhouse gases in our atmosphere. As a result, the rate of heat-loss from the Earth has slowed, creating a warming effect. More than 85% of the additional heat in our atmosphere is absorbed by the oceans. Concentrations of carbon dioxide in the Earth’s atmosphere in 2013 was approximately 395 parts per million, and is now at a level higher than at any time over the past 800,000 – and possibly 20 million – years.

  • As levels of carbon dioxide and other greenhouse gases rise, the delicate chemical balance in the atmosphere is affected, resulting in global warming that affects key elements of the climate. The enhanced greenhouse effect caused by increases in human-induced emissions of greenhouse gases is expected to change many of the basic weather patterns that make up our climate, including wind and rainfall patterns and the incidence and intensity of storms.