In the last few years, there has been a lot of talk about a pause in global warming. Commentators argued that since 1998, there had been no significant global warming despite ever increasing amounts of carbon dioxide being emitted.
Scientists have tried to explain this in a number of ways. These include:
1) Variations in the Sun's energy output
2) Decline in atmospheric water vapour
3) Greater storage of heat by the oceans.
But so far, there is no general consensus on the precise mechanism behind the pause.
Sceptics highlight the pause as an example of the fallibility of predictions based on computer climate models. On the other hand, climate scientists point out that the hiatus occurs in just one component of the climate system - the global mean surface temperature - and that other indicators, such as melting ice and changes to plant and animal life, demonstrate that the Earth has continued to warm.
In fact, a study published in Science journal in June 2015 doubted there had been a warming hiatus in the first place.
Predictions on temperature rise in future?
In its 2013 assessment, the Intergovernmental Panel on Climate Change (IPCC) forecast a range of possible scenarios based on computer modelling. But most simulations indicate that global surface temperature change by the end of the 21st Century is likely to exceed 1.5°C, relative to 1850.
A threshold of 2°C is generally regarded as the gateway to dangerous warming.
Even if we cut greenhouse gas emissions dramatically now, scientists say the effects will continue because parts of the climate system, particularly large bodies of water and ice, can take hundreds of years to respond to changes in temperature. It also takes greenhouse gases decades to be removed from the atmosphere.
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