Global warming: What’s so significant about 1.5C?

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A major report is to set out what needs to be done to keep global temperature rises to no more than 1.5C – and what that will mean for the planet. Here’s what you need to know.

– What is significant about 1.5C of warming?

While warming of 2C above pre-industrial levels has widely been thought of as the threshold beyond which dangerous climate change will occur, vulnerable countries such as low-lying island states warn rises above 1.5C will threaten their survival.

Their concerns meant a pledge to pursue efforts to limit temperature rises to 1.5C was included – after tough negotiations – alongside the commitment to keep them “well below” 2C in the global Paris climate agreement in 2015.

– So why this report?

When the target was put into the Paris Agreement, relatively little was known about the climate risks that would be avoided in a 1.5C warmer world compared with a 2C warmer world, or about the action needed to limit temperature rises to that level.

So the UN’s Intergovernmental Panel on Climate Change (IPCC) was tasked with providing the answers.

– What does the report look at?

It sets out what would be needed to limit warming to 1.5C above pre-industrial levels, the impact of global warming of 1.5C compared to 2C and higher, and the connection between climate change and tackling poverty.

The IPCC does not do any of its own research, so the report draws on more than 6,000 research papers to reach its conclusions.

– What does it say?

The report is not being made public until Monday, but the science it is based on is already out there, and the study is likely to issue a stark warning about the scale of the challenge the world faces.

As more greenhouse gases lead to more warming, stabilising the planet’s temperature at any level will require emissions to fall to net-zero, with no more put into the atmosphere than is absorbed by measures such as planting forests.

To meet the 1.5C target that will have to happen faster than for a higher temperature, with earlier drafts of the report saying carbon emissions must hit zero by mid-century.

That will mean a massive shift from fossil fuels to clean energy, clean cars and other vehicles, and cleaner ways to heat homes and buildings in just a few decades.

There will also be a need to take excess emissions out of the atmosphere, by measures such as planting trees or, more controversially, burning plant material for energy and capturing the carbon to store underground, which is known as “BECCS”.

– Why make all that effort for 0.5C?

The science shows that a 2C rise will lead to greater sea level rises, more heatwaves and extreme rainstorms, more people facing water shortages and drought, lower yields for some crops and greater impacts on wildlife than 1.5C.

– What has been going on in South Korea for the past week?

The report’s authors and representatives of 195 governments which are members of the IPCC have been meeting to finalise the “summary for policymakers” report, which involves agreeing it line-by-line.

The aim is to make the report as clear as possible while still scientifically robust – and to ensure that everybody is behind the document. So the meeting has been politically as well as scientifically important.

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