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Find out how and why the Earth's climate is changing as Paris hosts a major summit to discuss global warming.
1. What is the problem?
The world is getting warmer
The average temperature of the Earth's surface has increased by about 0.85°C (1.4F) in the last 100 years. Thirteen of the 14 warmest years were recorded in the 21st Century, with 2015 on course to set another record.
How years compare with the 20th Century average
2. Why is this happening?
Greenhouse gases, mainly carbon dioxide
Scientists believe that gases released from industry and agriculture (known as emissions) are adding to the natural greenhouse effect, the way the Earth's atmosphere traps some of the energy from the Sun.
Human activities such as burning fossil fuels like coal, oil and natural gas are increasing the amount of carbon dioxide (CO2), the main greenhouse gas responsible for global warming. Carbon-absorbing forests are also being cut down.
The concentration of CO2 in the atmosphere is now higher than at any time in the last 800,000 years and reached a record high in May this year.
Monthly average CO2 concentration (parts per million)
Scripps CO2 Program, data from the Mauna Loa Observatory
3. What are the effects?
Arctic sea ice melt
Higher temperatures, extreme weather events and higher sea levels are all linked to a warming climate and could have a drastic effect on the world's regions.
Since 1900, sea levels have risen by on average about 19cm globally. The rate of sea-level rise has accelerated in recent decades, placing a number of islands and low-lying countries at risk.
The retreat of polar ice sheets is an important contributor to this rise.
Arctic sea ice is also shrinking because of higher temperatures, though it makes little contribution to raised sea levels.
An area of sea ice roughly 10 times the size of the UK has been lost when the current day is compared with average levels from the early 1980s.
Arctic sea ice min. extent: 1980, 7.8 million sq km. 2015, 4.6 million sq km
Source: National Snow and Ice Data Center
4. What does the future hold?
Higher temperatures and more extreme weather
The scale of potential impacts is uncertain.
The changes could drive shortages in freshwater, bring about major changes in food production conditions and cause a rise in the number of casualties from floods, storms, heat waves and droughts.
This is because climate change is expected to increase the frequency of extreme weather events - however linking any single event to global warming is complicated.
Projected temperature change (1986–2005 to 2081-2100)
If greenhouse gas emissions peak between 2010-2020 and then decline substantially (RCP2.6)
If greenhouse gas emissions continue to rise throughout the 21st century (RCP8.5)
Source: International Panel on Climate Change - Fifth Assessment Report (AR5)
5. What can be done?
World's top ten greenhouse gas emitters
The top 10 greenhouse gas emitters make up over 70% of total emissions
Source: Carbon Brief, figures are for 2012
6. Limiting the damage
By the end of October, 146 countries had submitted national climate plans on curbing emissions that are expected to form the cornerstone of a binding, global treaty on climate change.
According to a UN report, submissions in their current form point to a rise of 2.7°C above pre-industrial levels by 2100.
Scientists have determined that if temperature rises surpass 2°C, this will lead to substantial and dangerous climate impacts, which will hit the world's poor in particular.
Average warming (°C) projected by 2100
Source: Climate Action Tracker, data compiled by Climate Analytics, ECOFYS, New Climate Institute and Potsdam Institute for Climate Impact Research.