Many observations indicate that global warming has taken place during the 20th century. This has resulted in an increase of the average surface temperature, a decrease in the snow cover and ice extent, and a rise in the sea level. The amount of precipitation, the amount of cloud cover, and the presence of extreme temperatures, especially in places where it's unusual to have extreme temperatures, are affected by global warming.
There are natural reasons that will affect global warming, as carbon dioxide is naturally in the air due to the fact that all living organisms that breathe in oxygen, exhale carbon dioxide, which is then taken in by trees and other plant life, which in return, give out oxygen for humans, animals, and other organisms that utilize oxygen. However, human activities over the last 50 years have significantly increased the levels of carbon dioxide (CO2) and other household gases in our atmosphere. This has led to the global warming that is occurring on Earth today. CO2 and other greenhouse gases tend to warm the Earth's surface, while anthropogenic aerosols tend to cool the Earth's surface.
Other current facts about global warming include
- The average surface temperature has increased by about 0.6 C (1.0 F) over the last 100 years. - Snow cover and ice extent have decreased. - The sea level has risen by 4-8" (10-20 cm) over the past 100 years. - About 75% of the annual increase in atmospheric carbon dioxide is due to the burning of fossil fuels, while the other 25% is attributed to anthropogenic changes in land use, like deforestation, overgrazing, and over cultivation, that reduces the net uptake of carbon dioxide. - In the 20th century, precipitation has likely increased in some land areas and decreased in others. - There has been some increase in cloud cover. - It's very likely that there has been less extreme low temperatures and slightly more extreme high temperatures. - There have been more warm episodes of the El Nino since the mid-1970s. - There's been an increase of droughts in some regions (especially in parts of Asia and Africa) over the last few decades, which is different from the pattern of small global increases in severe drought or severe wetness over the 20th century.
However, it seems that global warming has NOT changed some important aspects of climate:
- Some areas of the globe, like parts of the Southern Hemisphere oceans and parts of Antarctica, have not warmed in recent decades.
- There are no significant trends in the Antarctic sea-ice extent since 1978, the first year that reliable satellite measurements were used.
- There are no significant trends of global changes in tropical and extra-tropical storm intensity and frequency evident over the 20th century. Instead, there are variations within decades and across different decades, but not enough evidence to conclude that there were any significant changes across the 20th century itself.
- There are no systematic changes in the frequency of tornadoes, thunder days, and hail events in the limited areas that were analyzed.
It is clear that there is much evidence present in today's world that global warming is a real phenomenon, not something that is made up to scare people. Knowing these facts should help you learn what global warming exactly is and what you can do to help reduce or reverse global warming.