Global warming

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Global average temperature, shown by measurements from various sources, has increased since the Industrial Revolution.
Places that got warmer (red) and cooler (blue) over the past 50 years

Global warming is the current rise in temperature of the air and oceans. It is happening mainly because humans burn coal, oil, and natural gas; and cut down forests.[1] Average temperatures today are about 1 °C (1.8 °F) higher than before people started burning a lot of coal around 1750.[2] In some parts of the world it is less and some more. Most climate scientists say that by the year 2100 temperatures will be 2 °C (3.6 °F) to 4 °C (7.2 °F) higher than they were before 1750.[3]

The present global warming is mostly because of people burning things, like gasoline for cars and natural gas to keep houses warm. But the heat from the burning itself only makes the world a tiny bit warmer: it is the carbon dioxide from the burning which is the biggest part of the problem. Among greenhouse gases, the increase of carbon dioxide in the atmosphere is the main cause of global warming. Svante Arrhenius predicted this more than a hundred years ago. Arrhenius confirmed the work of Joseph Fourier 200 years ago.

When people burn fossil fuels like coal, oil and natural gas this adds carbon dioxide into the air.[4] This is because fossil fuels contain lots of carbon and burning means joining most of the atoms in the fuel with oxygen. When people cut down many trees (deforestation), this means less carbon dioxide is taken out of the atmosphere by those plants. Animals which have four places in their stomachs, like cows and sheep, also cause global warming, because their burps contain a greenhouse gas called methane.[5]

As the Earth's surface temperature becomes hotter the sea level rises. This is partly because water over 4 °C (39 °F) expands when it gets warmer.[6] It is also partly because warm temperatures make glaciers and ice caps melt. The sea level rise causes coastal areas to flood.[7] Weather patterns, including where and how much rain or snow there is, are changing. Deserts will probably increase in size. Colder areas will warm up faster than warm areas. Strong storms may become more likely and farming may not make as much food. These effects will not be the same everywhere. The changes from one area to another are not well understood at present.

In the Paris Agreement almost all governments agreed to keep temperature rise below 2 °C (3.6 °F), but current plans are not enough to limit global warming that much.[8] People in government and the Intergovernmental Panel on Climate Change (IPCC) are talking about global warming. But governments, companies, and other people do not agree on what to do about it. Some things that could reduce warming are to burn less fossil fuels, grow more trees, eat less meat, and put some carbon dioxide back in the ground. People could adapt to some temperature change. A few people think nothing should change.

Temperature changes

A graph of temperatures over the past two thousand years. The so-called Medieval Warm Period and Little Ice Age were regional phenomena, and were not experienced worldwide.

Climate change has happened constantly over the history of the Earth, including the coming and going of ice ages. But modern climate change is different because people are putting carbon dioxide into the atmosphere more quickly than before.[9][10]

Since the 1800s, people have recorded the daily temperature. By about 1850, there were enough places measuring temperature so that scientists could know the global average temperature. Compared with before people started burning a lot of coal for industry, the temperature has risen by about 1 °C (1.8 °F).[2] In 1979, satellites started measuring the temperature of the Earth.[11]

Before 1850, there were not enough temperature measurements for us to know how warm or cold it was. Climatologists use proxy measurements to try to figure out past temperatures before there were thermometers. This means measuring things that change when it gets colder or warmer. One way is to cut into a tree and measure how far apart the growth rings are. Trees that live a long time can give us an idea of how temperature and rain changed while they were alive.

For most of the past 2000 years the average temperature of the world didn't change much. There were some times where the temperatures were a little warmer or cooler in some places. One of the most famous warm times was the Medieval Warm Period and one of the most famous cool times was the Little Ice Age (not really an ice age). Other proxy measurements like the temperature measured in deep holes[needs to be explained][source?] mostly agree with the tree rings. Tree rings and bore holes can only help scientists work out the temperature back to about 2000 years ago. Ice cores are also used to find out the temperature back to about half a million years ago.

Greenhouse gases

Fossil fuel related CO2 emissions compared to five IPCC scenarios. The dips are related to global recessions.

There are several greenhouse gases that cause the Earth to warm. The most important one is carbon dioxide (CO2). CO2 comes from power plants, where coal and natural gas are burned to make electricity. Cars also emit CO2 when they burn petrol. About 23 billion tons of carbon dioxide and other greenhouse gases are released into the Earth's atmosphere each year. The amount of CO2 in the air is about 50% more than it was around 1750.[12] About three-quarters of the CO2 that people have put in the air during the past 20 years are due to burning fossil fuel like coal or oil. The rest mostly comes from changes in how land is used, like cutting down trees.[13]

The second most important greenhouse gas is methane. About 40% comes from nature, like wetlands; and the rest is because of humans, like cows, landfill and leaks when oil and gas are produced.[14][15]


Dust in the air may come from natural sources such as volcanos,[16][17] erosion and meteoric dust. Some of this dust falls out within a few hours. Some is aerosol, so small that it could stay in the air for years. The aerosol particles in the atmosphere make the earth colder. The effect of dust therefore cancels out some of the effects of greenhouse gases.[18] Even though humans also put aerosols in the air when they burn coal or oil this only cancels out the greenhouse effect of the fuel burning for less than 20 years: however the carbon dioxide stays in the atmosphere much longer and keeps on warming the earth.[19]

When people burn stuff the aerosols, for example smoke, are bad because when people breath them they make people ill. But some people say that in a climate change emergency the Earth could be kept cool by reflecting some sunlight back into space, for example by putting aerosols very high in the air or making clouds whiter. They say this would give more time to do a proper fix.[20] This is so easy and cheap that even a middle-size country could do it.[21] But there are a lot of problems: for example it might be good for that country but bad for some other countries.[22]

Slowing climate change

Some people burn less fossil fuel. Countries try to emit less greenhouse gases. The Kyoto Protocol was signed in 1997. It was meant to reduce the amount of greenhouse gases in the atmosphere to below their levels in 1990. However, carbon dioxide levels have continued to rise.

Energy conservation is used to burn less fossil fuel. People can also use energy sources that don't burn fossil fuel, like solar panels or electricity from nuclear power or wind power. Or they can prevent the carbon dioxide from getting out into the atmosphere, which is called carbon capture and storage (CCS).

Dealing with impacts of climate change

People can change how they live because of the effect of climate change. For example, they can go to places where the weather is better, or build walls around cities to keep flood water out. This cost money, and rich people and rich countries will be able to change more easily than the poor.

History of climate change science

Joseph Fourier; first to explain climate change
Svante Arrhenius; believed climate change would take many years

As early as the 1820s some scientists were discussing climate change. Joseph Fourier believed that light from the Sun can enter the atmosphere, but cannot leave nearly as easily. He tried to prove that air can absorb the infrared radiation and will be given back to the Earth’s surface. Later in 1859, John Tyndall discovered that water vapor and CO2 trap heat waves given by the sun. In 1896, Svante Arrhenius tried to prove that it would take thousands of years for the industrial production of CO2 to raise the Earth’s temperature 5-6°C.

In the mid 20th century, scientists worked out that there was a 10% increase in carbon dioxide in the atmosphere over the 19th century, which made it a bit warmer. It was at this time that people believed the emissions of CO2 would increase exponentially in the future and the oceans would absorb any surplus of greenhouse gases. In 1956, Gilbert N. Plass decided that greenhouse gas emissions would have an effect on the Earth’s temperature. He argued that not thinking about GHG emissions would be a mistake. Soon after, scientists studying all different kinds of science began to work together to figure out the mystery of GHG emissions and their effects. As technology advanced, it was in the 1980s that there was proof of a rise in CO2 levels. An ice core, captured through drilling, provided clear evidence that carbon dioxide levels have risen.[23]

Effects of global warming on sea levels

Sea level is rising because water over 4 °C (39 °F) expands when it gets warmer.[6] Probably more important is the melting of ice sheets. The Antarctica and Greenland ice sheets are melting. Sea level will rise between half and one metre by 2100, and between 2 and 7 metres by 2300.[24]

Low-lying areas such as Bangladesh, Florida, the Netherlands and other areas face massive flooding.[25][26]

Cities affected by current sea level rise

Many cities are sea ports and under threat of flooding if the present sea level rises.

These and the other cities have either started trying to deal with rising sea level and related storm surge, or are discussing this, according to reliable sources.

All other coastal cities are also in danger.

Further reading

Related pages


  1. "What Is Global Warming?". National Geographic. 2019-01-22.
  2. 2.0 2.1 IPCC (2018). "IPCC SR15 Summary for Policymakers 2018" (PDF). p. 6.
  3. "Long-term Climate Change: Projections, Commitments and Irreversibility" (PDF). IPCC.
  4. Thompson (Climate Central), Andrea (May 19, 2016). "Atmospheric CO2 May Have Topped 400 PPM Permanently". InsideClimate News. Retrieved August 12, 2016.
  5. Staff, Guardian (2019-06-29). "'Are a cow's farts the worst for the planet?' Children's climate questions answered". the Guardian. Retrieved 2022-08-05.
  6. 6.0 6.1 Mosher, Dave. "A bizarre property of water is flooding coastal cities like New Orleans". Business Insider. Retrieved 2020-12-07.
  7. Justin Gillis (3 September 2016). "Flooding of coast, caused by global warming, has already begun; scientists' warnings that the rise of the sea would eventually imperil the United States' coastline are no longer theoretical". New York Times. Retrieved 18 October 2016.
  8. "Analysis: Do COP26 promises keep global warming below 2C?". Carbon Brief. 2021-11-10.{{cite news}}: CS1 maint: url-status (link)
  9. "Is the current climate change unusual compared to earlier changes in Earth's history?". European Environment Agency. Retrieved 2019-12-09.
  10. Lee, Howard (2020-03-19). "Sudden Ancient Global Warming Event Traced to Magma Flood". Quanta Magazine. Retrieved 2022-08-01.
  11. Hausfather, Zeke (2017-06-30). "Major correction to satellite data shows 140% faster warming since 1998". Carbon Brief.{{cite news}}: CS1 maint: url-status (link)
  12. World Meteorological Organization (2021). WMO Statement on the State of the Global Climate in 2020. WMO-No. 1264. Geneva. ISBN 978-92-63-11264-4.
  13. "Climate change 2001: the scientific basis". Archived from the original on 2004-01-03. Retrieved 2010-11-03.
  14. "Methane Tracker 2020". International Energy Agency. Retrieved 2021-12-27.
  15. "Methane much more sensitive to global heating than previously thought – study". the Guardian. 2022-07-05. Retrieved 2022-08-06.
  16. "Sun-dimming Volcanoes Partly Explain Global Warming Hiatus". Scientific American. Retrieved 23 January 2017.
  17. Volcanoes that act as air-conditioning for a warming world; Many small eruptions over the past decade or so have helped restrain climate change May 2014 issue Scientific American
  18. "Aerosols: Tiny Particles, Big Impact". 2010-11-02. Retrieved 2019-05-02.
  19. Harrison, Anna. "'No sudden jump in warming' from emissions cuts". Retrieved 2019-10-11.
  20. "Solar Radiation Management | Wilson Center". Retrieved 2022-08-06.
  21. Smith, Wake; Wagner, Gernot (2018-11-22). "Stratospheric aerosol injection tactics and costs in the first 15 years of deployment". Environmental Research Letters. 13 (12): 124001. doi:10.1088/1748-9326/aae98d. ISSN 1748-9326.
  22. "Solar Radiation Management (SRM): Who should control the weather?". One Earth. Retrieved 2022-08-06.
  23. "The Carbon Dioxide Greenhouse Effect". Retrieved 2017-11-01.
  24. "RealClimate: Sea level in the IPCC 6th assessment report (AR6)". 2021-08-13. Retrieved 2022-02-25.
  25. McKie, Robin (7 March 2009). "Scientists to issue stark warning over dramatic new sea level figures". Retrieved 23 January 2017 – via The Guardian.
  26. President Trump, Military Split on Climate Change at YouTube
  27. Floods in London. [1] Archived 2015-09-24 at the Wayback Machine Royal Geographical Society
  28. "Sea Level Rise - NYS Dept. of Environmental Conservation". New York State Department of Environmental Conservation. Archived from the original on 27 January 2017. Retrieved 23 January 2017.
  29. interactive map from Climate Central
  30. "Mapping Sea Level Rise to Help Recovery after Hurricane Sandy". U.S. Global Change Research Program. Retrieved 23 January 2017.
  31. 31.0 31.1 World Bank, World Development Report 2010, 91.
  32. Noguchi, Yuki (2014-06-24). "As Sea Levels Rise, Norfolk Is Sinking And Planning". NPR. Retrieved 2014-11-25.
  33. "National Security and the Accelerating Risks of Climate Change". CNA Military Advisory Board. May 2014. Retrieved 10 November 2015.
  34. Archived 2015-04-02 at the Wayback Machine Investigation of Air Pollution Standing Conference
  35. Montgomery, David (2013-10-24). "Crisfield, Md., beats back a rising Chesapeake Bay". Washington Post. Retrieved 2013-10-27.
  36. Two cities, two very different responses to rising sea levels July 2, 2015 PBS NewsHour
  37. Jeff Goodell (June 20, 2013). "Goodbye, Miami". Rolling Stone. Retrieved June 21, 2013. The Organization for Economic Co-operation and Development lists Miami as the number-one most vulnerable city worldwide in terms of property damage, with more than $416 billion in assets at risk to storm-related flooding and sea-level rise.
  38. Climate Change Economics February 2015 National Geographic
  39. "Coastal floods in Russia". Retrieved 23 January 2017.
  40. "Most at risk: Study reveals Sydney's climate change 'hotspots'". Australian Broadcasting Corporation. 29 April 2008. Retrieved 23 January 2017.
  41. Cities, Connecting Delta. "Cities : Jakarta : Climate change adaptation :: Connecting Delta Cities". Archived from the original on 14 April 2017. Retrieved 23 January 2017.
  42. Khan, Sami (2012-01-25). "Effects of Climate Change on Thatta and Badin". Retrieved 2013-10-27.

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