How 0.5C can make a big difference to a warming world

What is this latest climate report saying?

It says time is running out. The world is warming faster than previously thought, and action is needed now to prevent average global temperatures rising 1.5C above pre-industrial levels.

But I thought governments had already committed to limiting increases to a safe limit?

The 2015 Paris climate deal committed to temperature rises of no more than 2C, but asked for a report on the feasibility of keeping them to 1.5C.

This report suggests it is feasible, but will require rapid change in how we live our lives, coupled with an enormous investment programme. A 1.5C rise will still have devastating impacts, but they will be less pronounced than in a 2C world.

What difference does 0.5C make?

Quite a bit. A 2C rise could destroy 13pc of the world’s ecosystems, this is compared with half this amount under 1.5C.

Insects and plants are twice as likely to lose half their habitat at 2C compared with 1.5C, the report warns.

In a 2C world, almost all coral reefs will be wiped out and the Arctic will be ice-free in the summer once per decade.

In a 1.5C rise scenario, up to 30pc of coral reefs can be saved and the Arctic will be ice-free in the summer once a century.

Crucially, by 2100 global sea level rise is projected to be around 0.1 metre lower under 1.5C.

This will lessen the risk for 10 million people living in vulnerable areas including small islands, low-lying coastal areas and deltas.

So what has to happen?

Everything must change. To keep temperature rises to no more than 1.5C, emissions must drop by 45pc by 2030 and to practically zero by 2050.

That means most electricity will have to be generated from renewables and nuclear; industry emissions will have to drop by between 75pc and 90pc by 2050, and an area the size of Australia will have to be given over to production of energy crops.

There will need to be a move to “less resource-intensive diets”, ie eating less meat, and more forests will have to be planted in the world.

Will it be expensive?

It will be very expensive. The report talks about annual investment in the energy system of around $2.4 trillion, somewhat higher than average investment today.

But environmentalists point out that the cost of inaction will be far more expensive as the world warms.