Climate change

**Climate change** refers to long-term changes in temperature, precipitation, and other atmospheric conditions on Earth.  

When people talk about climate change, they are usually talking about the problem of human-caused global warming, which is happening now. But the climate of the Earth has changed over not just thousands of years, but tens or hundreds of millions of years. It has alternated between hotter and colder periods, with some extremes like ice ages. 

## Global warming today 
*See the main article: Global warming*

Global warming primarily involves the warming of the planet due to increased concentrations of greenhouse gases in Earth's atmosphere. These gases, like carbon dioxide and methane, come from human activities such as burning fossil fuels, deforestation, and industrial processes.  
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These changes can lead to a variety of impacts, including more extreme weather events, rising sea levels, and disruptions to ecosystems and agriculture. 
## Hot Earth periods 
Sometimes, before there were people, the Earth's climate was much hotter than it is today. 

For example, about 60 million years ago there were a lot of volcanoes, which burnt a lot of underground organic matter. Squashed and fossilized dead plants and animals became coal, gas and oil. This caused a lot of carbon dioxide and methane to go up into the air, like nowadays. This made the Earth hot enough for giant tortoises and alligators to live in the Arctic. Sometimes even the whole Earth was covered in ice, and was much colder than today. 

There is no single reason why there are ice ages. Changes in the Earth's orbit around the Sun, and the Sun getting brighter or dimmer are events which do happen. Another source of change is the activities of living things (see Great Oxygenation Event and Huronian glaciation).

## History of climate change studies 
 in Laos from monsoons. Climate change can cause extreme weather events like worsening monsoons]]
Several 19th-century scientists discovered the importance of carbon dioxide (CO2) in climate change. These included Joseph Fourier in 1824, Claude Pouillet in 1827 and 1838, Eunice Foote in 1856, John Tyndall from 1863 onwards, Svante Arrhenius in 1896, and Guy Stewart Calendar (1898–1964).

Tyndall, an Irish physicist, proved there were other greenhouse gases as well. Nils Gustaf Ekholm in 1901 invented the term.

Foote's work was not appreciated, and not widely known. 

### The Sun 
The Sun gets a little bit hotter and colder every 11 years. This is called the 11-year sunspot cycle. The change is so small that scientists can barely measure how it affects the temperature of the Earth. 

If the Sun was causing the Earth to warm up, it would warm both the surface and high up in the air. But the air in the upper stratosphere is actually getting colder. Therefore the changes in the Sun are not causing the global warming which is happening now.

According to the United Nations’ Intergovernmental Panel on Climate Change (IPCC), the current scientific consensus is that long-term and short-term variations in the Sun's activity play only a very small role in Earth’s climate. Warming from increased levels of human-produced greenhouse gases is actually many times stronger than any effects due to recent variations in solar activity.

For more than 40 years, satellites have observed the Sun's energy output, which has gone up or down by less than 0.1 percent during that period. Since 1750, the warming driven by greenhouse gases coming from people burning fossil fuels is over 270 times greater than the slight extra warming coming from the Sun itself over that same time. 

Sustainable energy choices play a crucial role in mitigating the impact of human activities on the environment. 

### Solar energy 
Sunlight from the Sun, when converted, produces solar energy. It is in abundance and freely available. This type of energy is clean and easily renewable. It has low maintenance costs and can generate energy in any climate.

### Wind energy 
Another clean form of energy is wind. This energy is a plentiful source of renewable energy. However, since it is not always windy, it is only available sometimes. These kinds of cases are part of Climate change litigation.

## Related pages
*Ecology
*Environmental impact of aviation
*Intergovernmental Panel on Climate Change
*Palaeoclimatology

## References.