Understanding Global Climate Change: Causes, Effects, and Evidence
United Nations: Changing Face of Global Climate
In 1980, scientists began to realize the increase in Earth’s surface temperature, likely caused by human activity. In 1988, the UN created the Intergovernmental Panel on Climate Change (IPCC). The IPCC predicts average temperatures to rise between 1.5°C and 5.8°C. Global warming causes climate change, abnormal functioning of ecosystems, changes in land use, and biodiversity loss.
Climate Change Indicators
- Retreating glaciers: Mountain glaciers in the northern hemisphere are retreating at an accelerating rate, affecting polar ice caps.
- Sea level rise: The sea level has risen at a rate of 1 to 2 mm/year, accelerating to 3 mm/year.
- Increase in global mean temperature: Glacial retreat and rising sea levels are symptoms of global temperature increase.
- Extreme weather events: Climate change exacerbates extreme weather events, increasing their frequency.
- Changes in living organisms: Organisms are changing their behavior and distribution, including seasonal rhythms, animal migration, and plant flowering times.
What Factors Influence Earth’s Temperature?
- Solar radiation: The distance from the Sun and solar radiation determine the amount of energy received. Venus receives twice the radiation of Earth, while Mars receives half.
- Atmospheric composition: Dry, clean air consists of 78% nitrogen, 21% oxygen, and 1% argon. CO2 accounts for only 0.036%. Air also contains water vapor and aerosols (small particles in suspension) from natural and human sources.
Natural Greenhouse Effect
The temperature of our planet would be -18°C without an atmosphere; however, it averages 15°C. This difference is the natural greenhouse effect. The atmosphere allows sunlight in but traps heat, increasing air temperature.
Greenhouse Gases
- Water vapor: The primary greenhouse gas.
- Carbon dioxide: The second most important, emitted by volcanoes and respiration.
- Methane: Released from the digestion of ruminants, landfills, and wetlands.
How the Greenhouse Effect Works
Solar radiation reaches Earth in three ways:
- 30% is reflected back into space by the atmosphere or Earth’s surface (albedo).
- 19% is absorbed by clouds and other atmospheric components.
- 51% is absorbed by the Earth’s surface, increasing its temperature.
The surface then emits infrared radiation. Greenhouse gases absorb this radiation, warming the air and hindering heat emission into space.
Changes in Sea Level
- Changes in the water cycle: During glacial periods, increased snowfall turns to ice, accumulating on continents and lowering sea levels.
- Thermal expansion of water: In warm periods, sea levels rise due to melting ice caps and the expansion of warmer ocean water.
Discovering Past Climates (Paleoclimates)
- Air bubbles trapped in ice: Ice layers contain air bubbles (fossil air) showing the atmospheric composition when the snow fell.
- Fossils: Organisms live in specific habitats. Finding a woolly mammoth fossil indicates a cold climate in that area.
Why Does Climate Change Occur?
External Causes
- Changes in solar activity: Solar activity varies, such as changes in sunspots.
- Changes in Earth’s orbit: Earth’s orbit shifts between elliptical and circular, altering radiation.
- Meteorite impacts: Meteorite impacts create dust clouds, blocking solar radiation.
Internal Causes
- Changes in albedo: The average albedo is 30% but varies by surface. Snow has a high albedo, soil has a lower albedo, and the ocean has an even lower albedo. Changes in Earth’s surface albedo affect temperature.
- Changes in atmospheric composition: Organisms, volcanic activity, burning fuel, and other human activities can alter the amount of CO2 and oxygen. Aerosols can hinder solar radiation and absorb infrared radiation.
- Changes in ocean currents: More solar radiation reaches the equator than the poles, causing temperature differences. Thermohaline circulation, driven by temperature and density differences, connects all oceans and transports heat.