Earth’s temperature depends on the balance between energy entering and leaving the planet’s system. When incoming energy from the sun is absorbed by the Earth system, Earth warms. When the sun’s energy is reflected back into space, Earth avoids warming. When absorbed energy is released back into space, Earth cools. Many factors, both natural and human, can cause changes in Earth’s energy balance, including:
- Variations in the sun’s energy reaching Earth
- Changes in the reflectivity of Earth’s atmosphere and surface
- Changes in the greenhouse effect, which affects the amount of heat retained by Earth’s atmosphere
These factors have caused Earth’s climate to change many times.
Scientists have pieced together a record of Earth’s climate, dating back hundreds of thousands of years (and, in some cases, millions or hundreds of millions of years), by analyzing a number of indirect measures of climate such as ice cores, tree rings, glacier lengths, pollen remains, and ocean sediments, and by studying changes in Earth’s orbit around the sun.
This record shows that the climate system varies naturally over a wide range of time scales. In general, climate changes prior to the Industrial Revolution in the 1700s can be explained by natural causes, such as changes in solar energy, volcanic eruptions, and natural changes in greenhouse gas (GHG) concentrations.
Recent climate changes, however, cannot be explained by natural causes alone. Research indicates that natural causes do not explain most observed warming, especially warming since the mid-20thcentury. Rather, it is extremely likely that human activities have been the dominant cause of that warming.
Human activities contribute to climate change by causing changes in Earth’s atmosphere in the amounts of greenhouse gasses, aerosols (small particles), and cloudiness. The largest known contribution comes from the burning of fossil fuels, which releases carbon dioxide gas into the atmosphere.
Greenhouse gasses and aerosols affect climate by altering incoming solar radiation and outgoing infrared (thermal) radiation that are part of Earth’s energy balance. Changing the atmospheric abundance or properties of these gasses and particles can lead to a warming or cooling of the climate system.
Since the start of the industrial era (about 1750), the overall effect of human activities on climate has been a warming influence. The human impact on climate during this era greatly exceeds that due to known changes in natural processes, such as solar changes and volcanic eruptions.so we need to have control on our activities to save our future.