For climate change now, see Global warming.
**Climate change** is the climate of Earth changing. The Earth's climate has been much hotter and colder than it is today. Climate change this century and last century is sometimes called global warming, because the average temperature on the surface has risen. The last decade (2011–2020) was the warmest on record, and each of the last four decades has been warmer than any previous decade since 1850. The climate is now changing much faster than it has in the recent past. This is because people are putting more greenhouse gases in Earth's atmosphere, and they block some heat from escaping from the Earth into space. 

When people talk about climate change they are usually talking about the problem of human-caused global warming, which is happening now (see global warming for more details). But the climate of the Earth has changed over not just thousands of years, but tens or hundreds of millions of years.

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). A lot of carbon dioxide and methane went up in the air.

At times in the past, the temperature was much cooler, with the last glaciation ending about ten thousand years ago. Ice Ages are times when the Earth got colder, and more ice froze at the North and South Poles. Sometimes even the whole Earth has been covered in ice, and was much colder than today.

There is no one 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. Also how much the Earth is tilted compared to the Sun might make a difference. Another source of change is the activities of living things (see Great Oxygenation Event and Huronian glaciation).

Hot Earth
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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 like coal, gas and oil) so a lot of carbon dioxide and methane went up in the air like nowadays. This made the Earth hot enough for giant tortoises and alligators to live in the Arctic.

Cold Earth
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### Glaciations

At times in the past, the temperature was much cooler, with the last glaciation ending about ten thousand years ago.

### Ice Ages

Ice Ages are long times (much much longer than glaciations) when the Earth got colder, and more ice froze at the North and South Poles. Sometimes even the whole Earth was covered in ice, and was much colder than today. There is no one 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. Also how much the Earth is tilted compared to the Sun might make a difference. Another source of change is the activities of living things (see Great Oxygenation Event and Huronian glaciation).

History of climate change studies
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Joseph Fourier in 1824, Claude Pouillet in 1827 and 1838, Eunice Foote (1819–1888) in 1856, Irish physicist John Tyndall (1820–1893) in 1863 onwards, Svante Arrhenius in 1896, and Guy Stewart Callendar (1898–1964) discovered the importance of carbon dioxide (CO2) in climate change. Foote's work was not appreciated, and not widely known. Tyndall proved there were other greenhouse gases as well. Nils Gustaf Ekholm in 1901 invented the term.

### 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 and short-term variations in solar 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 the human burning of fossil fuels is over 270 times greater than the slight extra warming coming from the Sun itself over that same time .

Sustainable energy and environment
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Renewable energy or sustainable energy includes any energy source that cannot be exhausted. It can remain viable for a long period of time without running out or lasts forever. Examples are solar, wind, hydropower (water), geothermal, tidal and biomass.

Sustainable energy choices play a crucial role in mitigating the impact of human activities on the environment. Here's an overview of some key sustainable energy options and their environmental impacts according to research: 

### Solar energy

Sunlight from the Sun when converted produces solar energy. It is in abundance and freely available. The type of energy obtained is clean and easily renewable. It has low maintenance cost 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 source. However, it is only available sometimes.

Through history, the use of wind power has waxed and waned, from the use of windmills in centuries past to high tech wind turbines on wind farms today.

Related pages
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* Ecology
* Intergovernmental Panel on Climate Change

References.
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1. 1 2  Rosen, Julia; Parshina-Kottas, Yuliya (19 April 2021). "A climate change guide for kids". *The New York Times*. ISSN 0362-4331. Retrieved 2021-05-29.
2. ↑  Nations, United. "What Is Climate Change?". *United Nations*. Retrieved 2023-04-30.
3. 1 2 3  Alley R.B. 2000. *The two-mile time machine: ice cores, abrupt climate change, and our future*. Princeton University Press. ISBN 0-691-10296-1
4. 1 2 3  Lee, Howard (2020-03-19). "Sudden Ancient Global Warming Event Traced to Magma Flood". *Quanta Magazine*. Retrieved 2022-08-01.
5. 1 2  Imbrie J. & Imbrie, K.P. 1979. Ice ages: solving the mystery. Short Hills NJ: Enslow. ISBN 978-0-89490-015-0
6. 1 2 3 4  "Problem Solving Activity: What Causes Ice Ages?" (PDF).
7. 1 2  Williams G.E. & Schmidt P.W. (1997). "Paleomagnetism of the Paleoproterozoic Gowganda and Lorrain formations, Ontario: low palaeolatitude for Huronian glaciation" (PDF). *EPSL*. **153** (3): 157–169. Bibcode:1997E&PSL.153..157W. doi:10.1016/S0012-821X(97)00181-7.
8. 1 2  Evans D.A; Beukes N.J. & Kirschvink J.L. (1997). "Low-latitude glaciation in the Palaeoproterozoic era". *Nature*. **386** (6622): 262–6. Bibcode:1997Natur.386..262E. doi:10.1038/386262a0. S2CID 4364730.`{{cite journal}}`: CS1 maint: multiple names: authors list (link)
9. 1 2  "When and how did the ice age end? Could another one start?".
10. 1 2  Robert E. Kopp; et al. (2005). "The Paleoproterozoic snowball Earth: a climate disaster triggered by the evolution of oxygenic photosynthesis". *Proc. Natl. Acad. Sci. U.S.A*. **102** (32): 11131–6. Bibcode:2005PNAS..10211131K. doi:10.1073/pnas.0504878102. PMC 1183582. PMID 16061801.
11. 1 2  Lane, Nick (2010). "First breath: Earth's billion-year struggle for oxygen". *New Scientist* (2746). A snowball period, c2.4–c2.0 billion years ago, was triggered by the Great Oxygenation Event  Archived 2011-01-06 at the Wayback Machine
12. ↑  Tyndall J. 1863. *Heat as a mode of motion*. London & New York.
13. ↑  Easterbrook, Steve (18 August 2015). "Who first coined the term "Greenhouse Effect"?". *Serendipity*. Retrieved 11 November 2015.
14. ↑  Ekholm N (1901). "On the variations of the climate of the geological and historical past and their causes". *Quarterly Journal of the Royal Meteorological Society*. **27** (117): 1–62. Bibcode:1901QJRMS..27....1E. doi:10.1002/qj.49702711702.
15. ↑  "What is Sustainable Energy and Why Do We Need It?". *www.routledge.com*. Retrieved 2023-08-19.
16. 1 2  "Types of renewable energy". *EDF*. Retrieved 2023-08-19.
17. ↑