Climate change is a global phenomenon, affecting all countries and areas on Earth. Scientists agree that it is caused by human activities, such as the burning of fossil fuels, and has the potential to cause devastating effects worldwide.
The Sun is a main source of energy on Earth and plays a major role in the climate system by emitting longwave (or infrared) radiation that heats the planet and causes clouds to form. Small changes in the way this radiation is absorbed or reflected will affect climate.
Atmospheric gases such as carbon dioxide are known to absorb and re-radiate some of the energy that enters the atmosphere, changing the balance between incoming solar radiation and outgoing radiative heat. This is called the greenhouse effect.
Natural variation in the amount of carbon dioxide in the atmosphere has occurred throughout history, but there has been an acceleration of this process in recent decades. These fluctuations in the levels of carbon dioxide have been linked to changes in the climate, especially to warming of the earth’s surface and melting of ice sheets.
Greenhouse gases are also emitted by human activity, including deforestation, agribusiness and modernisation of transport. These emissions alter the energy balance between incoming and outgoing solar radiation, which will lead to warming of the planet.
Observational evidence shows that the Earth’s climate is changing rapidly, and that most of the warming is due to human influences. This has been documented in a variety of ways, ranging from data collected by the Intergovernmental Panel on Climate Change (IPCC) to observations from scientists working around the globe.
The IPCC’s Fifth Assessment Report cites thousands of studies describing a range of observed and projected changes to climate, including rising temperatures, melting of glaciers, diminishing snow cover, shrinking sea ice, ocean acidification, increasing intensity and frequency of rainfall, hurricanes, heat waves, wildfires, droughts, and more. It estimates that further warming of 2.6 to 4.8 degrees C (4.7 to 8.6 degrees F) would be expected over the 21st century, unless greenhouse gas emissions were significantly reduced.
Many people around the world are already suffering from the consequences of climate change. For example, flooding has increased in some regions of the world, while extreme heat and drought have impacted food production and health.
Temperatures are now higher than they have been in at least 400 years, according to the IPCC. These increases have a dramatic impact on food availability, crop yields, and the ability of farmers to grow crops, and are contributing to rising food prices worldwide.
Water shortages are also increasing. The United Nations estimates that the world will lose up to 50% of its freshwater resources by 2100, primarily due to climate change and population growth. This will have an adverse effect on agriculture, fisheries and hydropower.
Weather conditions are becoming more unpredictable, which means that farmers must adjust their growing schedules and food supplies. This can result in higher levels of food insecurity, putting people at risk of hunger and malnutrition.