Science & Impacts

Scientists now know for certain that the Earth has been warming for the past century. They know that human activities, mainly the burning of coal and oil, have dramatically increased concentrations of heat-trapping gases in the atmosphere. And they understand the science of how these gases are causing the observed warming. As a result, they predict that the world will continue to warm in the centuries ahead, with significant impacts on sea levels and weather patterns, and consequences for human health, ecosystems, and the economy. Avoiding the most severe impacts, scientists say, will require substantial reductions in emissions of the greenhouse gases that are contributing to climate change.

Behind the Science:

  • Greenhouse Gases Warm the Earth - The greenhouse effect is a naturally occurring process in the Earth’s atmosphere whereby certain gases (known as greenhouse gases or GHGs) absorb heat that would otherwise escape to space. This process keeps the world habitable; in the absence of a greenhouse effect, the average temperature at the Earth's surface would be approximately 16.5o C colder.  Learn more.
  • Human Activity is Increasing Concentrations of Greenhouse Gases - Current concentrations of the primary GHGs (such as carbon dioxide and methane - gases generated by natural processes such as plant and animal respiration) cannot be accounted for without considering human activities, particularly the combustion of fossil fuels. Global warming may also increase the release of GHGs from natural sources.

  • The World is Getting Warmer - Average global temperatures have risen by more than 0.6o C over the last century, with greater warming in some regions, such as the Arctic.   
    • Globally, surface air temperatures increased by approximately 0.84oC during the 20th century.  Some regions of the world have experienced much greater warming; Alaska and the Antarctic peninsula, for example, have warmed by approximately 2.4oC over the same time period.

    • The latest projection for 21st century average global temperature increases is 1.5-6.24oC, depending on future manmade GHG emissions.
Impacts of Global Warming:

  • We are Starting to See the Impacts - It is not just rising average global temperatures that concern scientists but also their effects on weather extremes, declining global ice cover and sea-level rises, and how those changes affect people, plants and animals. The observed warming over the 20th century was accompanied by a 10% increase in precipitation in the Northern Hemisphere and an accelerating rise in global sea-levels.

  • Rising Sea-Levels - Increases in temperature and changes in precipitation will have significant impacts on water resources, either reducing or increasing water availability along with increasing the risk of floods or droughts.      
    • By the end of the century, if nothing is done to rein in emissions of greenhouse gases, global sea-levels could be 1-1.8 metres higher than today and rising.

    • Rising sea-levels will have severe impacts in low-lying coastal communities throughout the world. In Bangladesh, for example, even a 3-foot rise would inundate 17% of the country.

  • Melting Polar Ice - The Arctic ice cap declined to a record minimum size in 2007 and studies show that this accelerated shrinkage of Arctic sea ice is caused by a response to a strong warming trend.
    • Antarctica is also losing massive amounts of ice to the melting and slipping of glacier ice into the ocean, a natural process that has been accelerated by global warming. The result is a net loss of polar land ice that is adding billions of tonnes of water each year to the world’s oceans.
  • Increased Severity of Weather Patterns - Scientists predict that climate change will have a significant effect on global weather patterns, causing both more floods and more droughts. Extended heat waves, more powerful storms, and other extreme weather events have become more common in recent years and will continue on this trend.  


  • More Droughts and Flooding - Future changes in weather patterns will affect different regions in different ways. In the short term, for instance, farms and forests may be more productive in some regions and less productive in others. Among the reasons–precipitation will increase in high-latitude regions of the world, while southern Africa, Australia and Central America may experience consistent declines in rainfall.  
    • As a result of these changes, agriculture in developing countries will be especially at risk.  Wheat, for example, may virtually disappear as a crop in Africa, while experiencing substantial declines in Southern Asia and South America.
  • Human Health May be Affected - Extreme temperatures (i.e., heat waves), exacerbation of air pollution, severe weather, and increased spread of infectious diseases pose serious health risks to humans globally, especially the elderly and children.  
    • A recent United Nations report blamed climate change, along with worsening air and water quality and poor disposal of solid waste, for an increase in malaria, cholera and lower respiratory tract infections in African societies.  

  • Effects on Ecosystems - Climate change holds the potential of inflicting severe damage on the ecosystems that support all life, from hazards to coral reefs due to warmer and more acidic ocean waters to threats to polar bears because of declines in sea ice. Ecosystems around the world already are reacting to a warming world.
    • One study found that 130 species, including both plants and animals, have responded to earlier spring warming over the last 30 years. These organisms have changed their timing of flowering, migration and other spring activities. The changes occurred regardless of regional difference and were linked directly to enhanced greenhouse warming.

    • Climate change is driving some species to extinction. In the past 20 years, dozens of species of mountain frogs in Central America have disappeared because of a disease that formerly did not occur where they live. In 2006, a paper in the journal 'Nature' revealed that the disease-causing fungus has spread to higher elevations as a result of climate change.
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