Changes

{{for|climate change now|Global warming}}

{{for|climate change now|Global warming}}

'''Climate change''' is the [[climate]] of [[Earth]] changing. The Earth's climate has been much hotter and colder than it is today.<ref name=":0">{{Cite news|last1=Rosen|first1=Julia|last2=Parshina-Kottas|first2=Yuliya|title=A climate change guide for kids |work=The New York Times|date=19 April 2021 | url=https://www.nytimes.com/interactive/2021/04/18/climate/climate-change-future-kids.html|access-date=2021-05-29|issn=0362-4331}}</ref> Climate change this century and last century is sometimes called [[global warming]], because the average temperature on the surface has risen.<ref name=":0" /> The last decade (2011{{ndash}}2020) was the warmest on record, and each of the last four decades has been warmer than any previous decade since 1850.<ref>{{Cite web|last=Nations|first=United|title=What Is Climate Change?|url=https://www.un.org/en/climatechange/what-is-climate-change|access-date=2023-04-30|website=United Nations|language=en}}</ref> The climate is now changing much faster than it has in the recent past. This is because people are putting more [[greenhouse gas]]es in Earth's atmosphere, and they block some heat from escaping from the Earth into space.  

Climate change refers to long-term changes in temperature, precipitation, and other atmospheric conditions on Earth. It primarily involves the warming of the planet due to increased concentrations of greenhouse gases, like carbon dioxide and methane, from human activities such as burning fossil fuels, deforestation, and industrial processes. These changes can lead to a variety of impacts, including more extreme weather events, rising sea levels, and disruptions to ecosystems and agriculture.  

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.<ref name="Alley" />  

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.<ref name="Alley" />  

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 [[Fossil|fossilized]] dead plants and animals became coal, gas and oil). A lot of carbon dioxide and [[methane]] went up in the air.<ref name=":1">{{Cite web|last=Lee|first=Howard|date=2020-03-19|title=Sudden Ancient Global Warming Event Traced to Magma Flood|url=https://www.quantamagazine.org/sudden-ancient-global-warming-event-traced-to-magma-flood-20200319/|access-date=2022-08-01|website=Quanta Magazine|language=en}}</ref>  

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 [[Fossil|fossilized]] dead plants and animals became coal, gas and oil). A lot of carbon dioxide and [[methane]] went up in the air.<ref name=":1">{{Cite web|last=Lee|first=Howard|date=2020-03-19|title=Sudden Ancient Global Warming Event Traced to Magma Flood|url=https://www.quantamagazine.org/sudden-ancient-global-warming-event-traced-to-magma-flood-20200319/|access-date=2022-08-01|website=Quanta Magazine|language=en}}</ref>  

At times in the past, the temperature was much cooler, with the last [[glaciation]] ending about ten thousand years ago.<ref name=":3">Imbrie J. & Imbrie, K.P. 1979. Ice ages: solving the mystery. Short Hills NJ: Enslow. ISBN 978-0-89490-015-0</ref><ref name=Alley>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</ref> [[Ice age|Ice Ages]] are times when the Earth got colder, and more ice froze at the [[North Pole|North]] and [[South Pole|South Poles]].<ref name=":2">{{Cite web|title=Problem Solving Activity: What Causes Ice Ages?|url=https://gml.noaa.gov/outreach/info_activities/pdfs/PSA_ice_ages.pdf}}</ref> Sometimes even the whole Earth has been covered in ice, and was much colder than today.<ref name=":4">{{cite journal | author=Williams G.E. & Schmidt P.W. | title=Paleomagnetism of the Paleoproterozoic Gowganda and Lorrain formations, Ontario: low palaeolatitude for Huronian glaciation | journal=EPSL | year=1997 | volume=153 | issue=3 | pages=157–169 | url=http://www.cosis.net/abstracts/EAE03/08262/EAE03-J-08262.pdf | doi = 10.1016/S0012-821X(97)00181-7 | bibcode=1997E&PSL.153..157W}}</ref><ref name=":5">{{cite journal |author=Evans D.A; Beukes N.J. & Kirschvink J.L. |title=Low-latitude glaciation in the Palaeoproterozoic era |journal=Nature |volume=386 |issue=6622 |pages=262–6 |date=1997 |doi=10.1038/386262a0 |url=http://www.nature.com/nature/journal/v386/n6622/abs/386262a0.html|bibcode = 1997Natur.386..262E |s2cid=4364730 }}</ref>  

At times in the past, the temperature was much cooler, with the last [[glaciation]] ending about ten thousand years ago.<ref name=":3">Imbrie J. & Imbrie, K.P. 1979. Ice ages: solving the mystery. Short Hills NJ: Enslow. ISBN 978-0-89490-015-0</ref><ref name=Alley>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</ref> [[Ice age|Ice Ages]] are times when the Earth got colder, and more ice froze at the [[North Pole|North]] and [[South Pole|South Poles]].<ref name=":2">{{Cite web|title=Problem Solving Activity: What Causes Ice Ages?|url=https://gml.noaa.gov/outreach/info_activities/pdfs/PSA_ice_ages.pdf}}</ref> Sometimes even the whole Earth has been covered in ice, and was much colder than today.<ref name=":4">{{cite journal | author=Williams G.E. & Schmidt P.W. | title=Paleomagnetism of the Paleoproterozoic Gowganda and Lorrain formations, Ontario: low palaeolatitude for Huronian glaciation | journal=EPSL | year=1997 | volume=153 | issue=3 | pages=157–169 | url=http://www.cosis.net/abstracts/EAE03/08262/EAE03-J-08262.pdf | doi = 10.1016/S0012-821X(97)00181-7 | bibcode=1997E&PSL.153..157W |issn=0012-821X}}</ref><ref name=":5">{{cite journal |author=Evans D.A; Beukes N.J. & Kirschvink J.L. |title=Low-latitude glaciation in the Palaeoproterozoic era |journal=Nature |volume=386 |issue=6622 |pages=262–6 |date=1997 |doi=10.1038/386262a0 |url=http://www.nature.com/nature/journal/v386/n6622/abs/386262a0.html|bibcode = 1997Natur.386..262E |s2cid=4364730 }}</ref>  

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.<ref name=":2" /> Also how much the Earth is tilted compared to the Sun might make a difference.<ref name=":6">{{Cite web|title=When and how did the ice age end? Could another one start?|url=https://www.amnh.org/explore/ology/earth/ask-a-scientist-about-our-environment/how-did-the-ice-age-end}}</ref> Another source of change is the activities of living things (see [[Great Oxygenation Event]] and [[Huronian glaciation]]).<ref name=":7">{{cite journal | author=Robert E. Kopp | display-authors=etal | title=The Paleoproterozoic snowball Earth: a climate disaster triggered by the evolution of oxygenic photosynthesis | journal=Proc. Natl. Acad. Sci. U.S.A. | year=2005 | volume=102 | issue=32 | pages=11131–6 | doi=10.1073/pnas.0504878102 | pmid=16061801 | pmc=1183582 | bibcode=2005PNAS..10211131K | doi-access=free }}</ref><ref name=":8">{{cite journal|last=Lane|first=Nick|date=2010|title=First breath: Earth's billion-year struggle for oxygen|url=https://www.newscientist.com/article/mg20527461.100-first-breath-earths-billionyear-struggle-for-oxygen.html|journal=New Scientist|issue=2746|doi=}}  A snowball period, c2.4–c2.0 billion years ago, was triggered by the Great Oxygenation Event [http://ptc-cam.blogspot.com/2010/02/first-breath-earths-billion-year.html] {{Webarchive|url=https://web.archive.org/web/20110106141826/http://ptc-cam.blogspot.com/2010/02/first-breath-earths-billion-year.html|date=2011-01-06}}</ref>

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.<ref name=":2" /> Also how much the Earth is tilted compared to the Sun might make a difference.<ref name=":6">{{Cite web|title=When and how did the ice age end? Could another one start?|url=https://www.amnh.org/explore/ology/earth/ask-a-scientist-about-our-environment/how-did-the-ice-age-end}}</ref> Another source of change is the activities of living things (see [[Great Oxygenation Event]] and [[Huronian glaciation]]).<ref name=":7">{{cite journal | author=Robert E. Kopp | display-authors=etal | title=The Paleoproterozoic snowball Earth: a climate disaster triggered by the evolution of oxygenic photosynthesis | journal=Proc. Natl. Acad. Sci. U.S.A. | year=2005 | volume=102 | issue=32 | pages=11131–6 | doi=10.1073/pnas.0504878102 | pmid=16061801 | pmc=1183582 | bibcode=2005PNAS..10211131K | doi-access=free }}</ref><ref name=":8">{{cite journal|last=Lane|first=Nick|date=2010|title=First breath: Earth's billion-year struggle for oxygen|url=https://www.newscientist.com/article/mg20527461.100-first-breath-earths-billionyear-struggle-for-oxygen.html|journal=New Scientist|issue=2746|doi=}}  A snowball period, c2.4–c2.0 billion years ago, was triggered by the Great Oxygenation Event [http://ptc-cam.blogspot.com/2010/02/first-breath-earths-billion-year.html] {{Webarchive|url=https://web.archive.org/web/20110106141826/http://ptc-cam.blogspot.com/2010/02/first-breath-earths-billion-year.html|date=2011-01-06}}</ref>

File:Common Era Temperature.svg|[[Global surface temperature]] reconstruction over the last 2000 years using proxy data from tree rings, corals, and ice cores in blue. Directly observed data is in red.

File:Common Era Temperature.svg|[[Global surface temperature]] reconstruction over the last 2000 years using proxy data from tree rings, corals, and ice cores in blue. Directly observed data is in red.

File:1951- Percent of record temperatures that are cold or warm records.svg |In recent decades, new high temperature records have substantially outpaced new low temperature records on a growing portion of Earth's surface.

File:1951- Percent of record temperatures that are cold or warm records.svg|In recent decades, new high temperature records have substantially outpaced new low temperature records on a growing portion of Earth's surface.

File:1955- Ocean heat content - NOAA.svg |There has been an increase in [[ocean heat content]] during recent decades as the oceans absorb over 90% of the [[Earth's energy budget|heat from global warming]].

File:1955- Ocean heat content - NOAA.svg|There has been an increase in [[ocean heat content]] during recent decades as the oceans absorb over 90% of the [[Earth's energy budget|heat from global warming]].

File:Projected Change in Temperatures by 2090.svg|[[Coupled Model Intercomparison Project#CMIP Phase 6|CMIP6]] multi-model projections of [[global surface temperature]] changes for the year 2090 relative to the 1850–1900 average. The current trajectory for warming by the end of the century is roughly halfway between these two extremes.

File:Projected Change in Temperatures by 2090.svg|[[Coupled Model Intercomparison Project#CMIP Phase 6|CMIP6]] multi-model projections of [[global surface temperature]] changes for the year 2090 relative to the 1850–1900 average. The current trajectory for warming by the end of the century is roughly halfway between these two extremes.