93% chance global warming will exceed 4°C by 2100

Global warming will cause temperatures to rise even higher than we thought by the end of the century, a shocking new study has claimed.

Experts examined a range of modelling simulations to work out which was best able to accurately predict climate change.

Their findings suggest that there is a 93 per cent chance that global warming will exceed 4°C by 2100.

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Global warming will cause temperatures to rise even higher than we thought by the end of the century, a shocking new study has claimed. Experts examined a range of modelling simulations to work out which was best able to accurately predict climate change (stock)

Global warming will cause temperatures to rise even higher than we thought by the end of the century, a shocking new study has claimed. Experts examined a range of modelling simulations to work out which was best able to accurately predict climate change (stock)

KEY FINDINGS 

The study relied on the idea that the models that are going to be the most skillful in their projections of future warming should also be the most skillful in other contexts, including simulating the recent past.

The study eliminates the lower end of this range, finding that the most likely warming is about 0.5°C (0.9°F) greater than what the raw model results suggest.

The researchers focused on comparing model projections and observations of the spatial and seasonal patterns of how energy flows from Earth to space. 

The models that best simulate the recent past of these energy exchanges between the planet and its surroundings tend to project greater-than-average warming in the future. 

The study indicates that if emissions follow a commonly used business-as-usual scenario, there is a 93 per cent chance that global warming will exceed 4°C (7.2°F) by 2100.

Previous studies had put this likelihood at 62 per cent.

Researchers from the Carnegie Institution for Science (CIS) in Washington DC looked at a range of widely used software to make their assessment.

The programmes predict how much warming should be expected for any given increase in the concentration of carbon dioxide and other greenhouse gases in the atmosphere.

Based on existing levels of increasing concentration, raw climate model results suggest we can expect global temperatures to increase anywhere between 3.2 and 5.9°C (5.8 and 10.6°F) above preindustrial levels by 2100.

This is a difference of about a factor of two between the most and least severe projections. 

Patrick Brown and Ken Caldeira set out to determine whether the upper or lower end of this range is more likely to prove accurate.

They found that the models that are best able to recreate current conditions are the ones that simulate a reduction in cloud cooling in the future.

These are the models that predict the greatest future warming.

Dr Brown said: 'There are dozens of prominent global climate models and they all project different amounts of global warming for a given change in greenhouse gas concentrations.

'That's primarily because there is not a consensus on how to best model some key aspects of the climate system. 

'Our results suggest that it doesn't make sense to dismiss the most-severe global warming projections based on the fact that climate models are imperfect in their simulation of the current climate. 

Researchers from the Carnegie Institution for Science in Washington DC looked at a range of widely used software to make their assessment. Their findings suggest that models e may be underestimating future warming by as much as 15 per cent (stock image)

Researchers from the Carnegie Institution for Science in Washington DC looked at a range of widely used software to make their assessment. Their findings suggest that models e may be underestimating future warming by as much as 15 per cent (stock image)

KEY GOALS OF THE PARIS AGREEMENT

The Paris Agreement on Climate Change has four main goals with regards to reducing emissions:

1)  A long-term goal of keeping the increase in global average temperature to well below 2°C above pre-industrial levels

2) To aim to limit the increase to 1.5°C, since this would significantly reduce risks and the impacts of climate change

3) Goverments agreed on the need for global emissions to peak as soon as possible, recognising that this will take longer for developing countries

4) To undertake rapid reductions thereafter in accordance with the best available science

Source: European Commission 

'On the contrary, if anything, we are showing that model shortcomings can be used to dismiss the least-severe projections.' 

The uncertainty in the range of future warming is mostly due to differences in how models simulate changes in clouds with global warming. 

Some models suggest that the cooling effect caused by clouds reflecting the sun's energy back to space could increase in the future while other models suggest that this cooling effect might decrease.  

The study relied on the idea that the models that are going to be the most skillful in their projections of future warming should also be the most skillful in other contexts, including simulating the recent past.

The study eliminates the lower end of this range, finding that the most likely warming is about 0.5°C (0.9°F) greater than what the raw model results suggest.

The researchers focused on comparing model projections and observations of the spatial and seasonal patterns of how energy flows from Earth to space. 

The models that best simulate the recent past of these energy exchanges between the planet and its surroundings tend to project greater-than-average warming in the future. 

The study indicates that if emissions follow a commonly used business-as-usual scenario, there is a 93 per cent chance that global warming will exceed 4°C (7.2°F) by 2100.

Previous studies had put this likelihood at 62 per cent.

Speaking about the result Dr Mark Maslin, professor of climatology at UCL, who was not involved in the study, said: 'Our climate models are running too cold, making the Paris climate agreement 2°C target even more ambitious than we thought.   

'To achieve these targets the climate negotiations must ensure that the global emissions cuts start as planned in 2020 and continue every single year thereafter.'