Humanity could be destroyed by 'catastrophic' climate change within the next century.

That's the shocking claim from US researchers who say there is a 1 in 20 change we'll be wiped out in the next 100 years as a result of 'low-probability high-impact' events.

They say an increase greater than 3°C could lead to 'catastrophic' effects.

However an increase of more than 5°C will 'unknown' consequences which could lead to the end of life as we know it.

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Climate change events which are statistically unlikely but could cause the extinction of humanity could strike by the end of the century, a new study warns. Researchers projected warming scenarios that vary based on what societal actions are taken to reduce emissions

RISK ASSESSMENT Their risk assessment stems from the objective stated in the 2015 Paris Agreement regarding climate change that society keep average global temperatures 'well below' a 2°C (3.6°F) increase from what they were before the Industrial Revolution. Even if that objective is met, a global temperature increase of 1.5°C (2.7°F) is still categorised as 'dangerous,' meaning it could create substantial damage to human and natural systems. A temperature increase greater than 3°C (5.4°F) could lead to what the researchers term 'catastrophic' effects. An increase greater than 5°C (9°F) could lead to 'unknown' consequences which they describe as beyond catastrophic including potentially existential threats. The spectre of existential threats is raised to reflect the grave risks to human health and species extinction from warming beyond 5° C, which has not been experienced for at least the past 20 million years. Advertisement

Veerabhadran Ramanathan, a professor of climate and atmospheric sciences at the University of California said: 'When we say five per cent-probability high-impact events, people may dismiss it as small but it is equivalent to a one-in-20 chance the plane you are about to board will crash.'

Researchers at the Scripps Institution of Oceanography at the University of California San Diego have used this analogy to try and illustrate the situation currently facing the planet.

They performed calculations to work out what would happen if temperatures rose by varying degrees between now and 2100.

'We would never get on that plane with a one-in-20 chance of it coming down but we are willing to send our children and grandchildren on that plane,' said Ramanathan.

Their risk assessment stems from the objective stated in the 2015 Paris Agreement regarding climate change.

It was agreed that society keep average global temperatures 'well below' a 2°C (3.6°F) increase from what they were before the Industrial Revolution.

Models of future climate scenarios led to the creation of two new risk categories, 'catastrophic' and 'unknown', which deal with low probability high impact scenarios. More than a 5°C rise in heat could result in life-ending consequences for humanity

Even if that objective is met, a global temperature increase of 1.5°C (2.7°F) is still categorised as 'dangerous,' meaning it could create substantial damage to human and natural systems.

A temperature increase greater than 3°C (5.4°F) could lead to what the researchers term 'catastrophic' effects.

An increase greater than 5°C (9°F) could lead to 'unknown' consequences which they describe as beyond catastrophic including potentially existential threats.

DANGERS OF CLIMATE CHANGE The researchers defined the risk categories based on guidelines established by the Intergovernmental Panel on Climate Change (IPCC) and previous independent studies. 'Dangerous' global warming includes consequences such as increased risk of extreme weather and climate events ranging from more intense heat waves, hurricanes, and floods, to prolonged droughts. Planetary warming between 3°C and 5°C could trigger what scientists term 'tipping points' such as the collapse of the West Antarctic Ice Sheet and subsequent global sea-level rise, and the dieback of the Amazon rainforest. In human systems, catastrophic climate change is marked by deadly heat waves becoming commonplace, exposing over seven billion people to heat related mortalities and famine becoming widespread. Furthermore, the changes will be too rapid for most to adapt to, particularly the less affluent, said Dr Ramanathan. Risk assessments of global temperature rise greater than 5°C have not been undertaken by the IPCC. Drs Ramanathan and Xu named this category 'unknown??' with the question marks acknowledging the 'subjective nature of our deduction.' The existential threats could include species extinctions and major threats to human water and food supplies in addition to the health risks posed by exposing over seven billion people worldwide to deadly heat. Advertisement

The spectre of existential threats is raised to reflect the grave risks to human health and species extinction from warming beyond 5° C, which has not been experienced for at least the past 20 million years.

Dr Ramanathan and his colleague and former Scripps graduate student Yangyang Xu, now an assistant professor at Texas A&M University, describe three strategies for preventing the gravest threats from taking place.

Aggressive measures to curtail the use of fossil fuels and emissions of so-called short-lived climate pollutants such as soot, methane and HFCs would need to be accompanied by active efforts to extract CO2 from the air and sequester it before it can be emitted.

Climate change, or global warming, is the result of humans having released carbon dioxide and other greenhouse gases, causing an accumulation of heat in the Earth's climate system. How fast the Earth is warming is a key question for decision makers, scientists and the public

It would take all three efforts to meet the Paris Agreement goal to which countries agreed at a landmark United Nations climate conference in Nov 2015.

Short-lived climate pollutants are so called because even though they warm the planet more efficiently than carbon dioxide, they only remain in the atmosphere for a period of weeks to roughly a decade whereas carbon dioxide molecules remain in the atmosphere for a century or more.

The authors also note that most of the technologies needed to drastically curb emissions of short-lived climate pollutants already exist and are in use in much of the developed world.

They range from cleaner diesel engines to methane-capture infrastructure.



The full findings of the study were pubished in the journal PNAS.