Climate change: causes and consequences

What is climate change?

Climate change is the significant and lasting change in the statistical distribution of weather patterns over a period ranging from decades to millions of years. It may be a change in average weather conditions, or in the distribution of weather around the average conditions (i.e., more or fewer extreme weather events). (See Wikipedia: climate change.)

Global warming refers to an unequivocal and continuing rise in the average temperature of the climate system of the Earth (see Wikipedia: global warming).

  See also the European Commission’s Climate change factsheet (pdf, 6 pages). The fact-sheet exists in 21 languages. See for other language versions: go to General climate change publications and click on the balloon-shaped icon at the end of the row to see all language versions of the document.

For a few decades, the climate has been warming on a global scale

Climate is a measure of the average pattern of variation in temperature, humidity, atmospheric pressure, wind, precipitation, atmospheric particle count and other meteorological variables in a given region over long periods of time. Climate is naturally variable, as shown by the lack of regularity of the seasons from one year to another (see Wikipedia: climate).

This variability is normal. It’s due to the variation of ocean streams, volcanic activity, solar radiation and other components of the climatic system that we don’t fully understand yet. Our climate also has its extremes (such as floods, drought, hail, tornadoes, hurricanes, etc.), which can have devastating impacts.

In the last decades, a lot of indicators and studies have been showing that the climate has been warming at a global scale.

The Summary for Policymakers of the 5th report of the IPCC (Intergovern­mental Panel on Climate Change) published in October 2013 states: “Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and oceans have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased.”

You can appreciate the changes of temperature through NASA images:

What causes global warming?

Temperatures on Earth are liveable because of a natural process called the greenhouse effect. When the sun’s radiation reaches our atmosphere, some is reflected back into space, and some passes through and is absorbed by the Earth. This causes the surface of the Earth to warm up. Heat from the Earth is radiated outward and absorbed by gases present in the Earth’s atmosphere, the so-called “greenhouse gases”. This process prevents heat from disappearing, providing an average temperature of around +15°C instead of -19°C.

There are several greenhouse gases responsible for an additional warming of the atmosphere, which are produced by humans in a variety of ways. Most come from the combustion of fossil fuels in cars, factories and electricity production. The gas responsible for most of the warming is carbon dioxide, also called CO2. Other contributors include methane released from landfills and agriculture (especially from the digestive systems of grazing animals), nitrous oxide from fertilizers, gases used for refrigeration and industrial processes, and the loss of forests that otherwise would have stored CO2.

Picture: Human induced greenhouse effect, source: US National Park Service

IPCC Summary for Policy Makers of 2013 states: “Human influence on the climate system is clear. This is evident from the increasing greenhouse gas concentrations in the atmosphere, positive radiative forcing, observed warming, and understanding of the climate system.(…)It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.(…)Continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system. Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions. (In this Summary for Policy-makers, the term “extremely likely” refers to a probability of 95–100%)


Climate change is changing our economy, health and communities in diverse ways. Scientists warn that if we do not substantially curb climate change now, the results will likely be disastrous. If the Earth gets hotter, some of these changes will happen:

  • Water expands when it’s heated and oceans absorb more heat than land, so sea levels will rise.
  • Sea levels will also rise due to the melting of the glaciers and sea ice.
  • Cities on coasts would flood.
  • Places that usually get lots of rain and snowfall might get hotter and drier.
  • Lakes and rivers could dry up.
  • There would be more droughts making it hard to grow crops.
  • Less water would be available for drinking, shower, agriculture and food production.
  • Many plants and animals might become extinct.
  • Hurricanes, tornadoes and other storms caused by changes of heat and water evaporation may get more common.