The world’s carbon emissions will have to be cut to zero in around half a century to avoid dangerous climate change, the UN has warned.
The UN Environment Programme (UNEP) said that carbon emissions from human activities such as burning fossil fuels should hit net zero by between 2055 and 2070 to prevent temperatures rising more than 2C above pre-industrial levels.
Other greenhouse gases, such as methane, nitrous oxide and hydrofluorocarbons (HFCs), need to follow suit so that overall greenhouse gas emissions reach net zero between 2080 and 2100, a report from UNEP said.
Emissions need to peak within the next 10 years, with all greenhouse gas emissions halving by mid-century.
Countries have agreed to limit temperature rises to no more than 2C – beyond which dangerous impacts of climate change are expected – but UNEP said if the world carries on as it is greenhouse gas emissions would be “way beyond safe limits”.
Even if countries meet their existing pledges to cut emissions, the world will bust the budget for the amount of greenhouse gases that can be emitted and still keep temperature rises to 2C by 10 billion tonnes by 2020 and 17 billion tonnes by 2030, it warned.
To have a likely chance of staying below 2C, greenhouse gas emissions should drop by about 15% or more by 2030, compared to 2010 levels, and be at least 50% lower by 2050 on the way to net zero emissions.
It could be possible for there still to be some emissions at the end of the century, if they are compensated for by measures that take in carbon, such as planting trees, to achieve “carbon neutrality”, the report said.
But delaying taking stringent action now until after 2020 would lead to higher costs and greater risks to society, it warned.
The Emissions Gap report is published ahead of UN climate talks in Lima, Peru, which are working towards a new global deal to tackle climate change that it is hoped will be agreed in Paris next year.
UNEP executive director Achim Steiner said: “An increase in global temperature is proportional to the build-up of long-lasting greenhouse gases in the atmosphere, especially carbon dioxide.
“Taking more action now reduces the need for more extreme action later to stay within safe emissions limits.”
WWF chief executive David Nussbaum said the report was another stark reminder of the “worrying chasm” between what scientists said needed to be done to avoid dangerous climate change and what governments had promised to do so far.
“If we don’t close this ’emissions gap’ within this decade, our task will not only become harder and more expensive, but threatens the very survival of some of the world’s most vulnerable communities and habitats.
“Prevarication and delay are our enemies. As the report rightly notes, postponing rigorous action until 2020 will lock in much higher costs and risks later on. This is an unacceptable legacy to bequeath to our descendants.
“We must end the era of dirty fossil fuels and move to an era of clean renewable energy as fast as possible.
“We cannot ignore one of the report’s key findings, namely, that energy efficiency offers a triple win: emissions reductions, energy security and green jobs.”