Low-lying countries will disappear. Regions such as the Mediterranean will have to survive on a fifth less water, as droughts become more common. All of the planet’s coral reefs will die.

These are just some of the events predicted if global warming reaches more than 2C above pre-industrial levels.

For these and many other reasons, the leaders of 195 countries two years ago in Paris agreed to a target of keeping global warming well below 2C, and an ideal goal of keeping it below 1.5C.

Each country represented in Paris pledged to make their own contribution to reducing the CO2 emissions that trap heat in the atmosphere and drive up global warming.

However, even with these pledges, the United Nations says global warming still looks likely to exceed 2C.

To stand a chance of keeping global warming below 2C, countries need to fix what the UN calls the “emissions gap”.

What is the emissions gap?

The pledges to cut greenhouse gas emissions made by world leaders in Paris in 2015 are known as Nationally Determined Contributions (NDCs).

In its latest Emissions Gap Report, the UN says that these pledges will only bring about a third of the reduction in emissions required by 2030 to meet climate targets.

The report was published ahead of the UN climate conference in Bonn, Germany. The global gathering, known as COP23, aims to speed up climate action to meet the goals of the Paris Agreement.

As things stand though, even full implementation of NDCs makes a temperature increase of at least 3C by 2100 very likely. The report finds that current Paris pledges make 2030 emissions likely to reach 11 to 13.5 gigatonnes of carbon dioxide equivalent (CO2-e) above the level needed to stay on course to the 2C target.

To put this in context, one gigatonne is roughly equivalent to one year of transport emissions in the European Union (including aviation), and annual global emissions are currently around 52 gigatonnes of CO2-e.

Image: UN

The emissions gap in the case of the 1.5C target is 16 to 19 gigatonnes of CO2-e, higher than previous estimates as new studies have become available.

The UN’s report warns that if the emissions gap is not closed by 2030, it is extremely unlikely that the goal of holding global warming to well below 2C can still be reached.

Part of the Paris Agreement stipulates that NDCs must be revised every five years. The UN’s report says that governments will need to deliver much stronger pledges to stand a chance of meeting the 2C target. The first opportunity for governments to formally submit revised pledges is in 2018.

How can it be closed?

Despite the sizeable emissions gap, there has been substantial progress in tackling climate change, offering some hope that it might still be possible to meet the 2C target.

Since 2014, the world has been experiencing a phenomenon unprecedented since the dawn of the industrial revolution: economic growth has decoupled from CO2 emissions.

Despite the global economy growing in each of the past three years, CO2 emissions from energy and industry (which account for 70% of global greenhouse gases) have remained flat.

The UN’s report credits the adoption of renewable energy by large fast-growing economies like China and India as one of the main reasons for this decoupling.

“Although we still have a long way to go to reduce emissions at the scale needed to address climate change, there are clear signs that we are moving in the right direction,” says World Economic Forum Head of Climate Initiatives Emily Farnworth.

“Transformational changes are likely to come from increased collaboration between public and private sectors and across value chains to realize the win-win nature of shifting to low-carbon solutions.”

The UN’s report identifies six sectors – agriculture, buildings, energy, forestry, industry and transport – where greater collaboration and investment in technology could help put the world back on track towards meeting the 2C target.

It says technology investments in these sectors could save up to 36 gigatonnes of CO2-e per year by 2030.

Much of the potential across the sectors comes from investment in solar and wind energy, efficient appliances, efficient passenger cars, planting more trees and ending deforestation.

Focusing only on recommended actions in these areas could cut up to 22 gigatonnes of CO2-e by 2030.

These savings alone would put the world well on track to hitting the 2C target, and unlock the possibility of reaching the aspirational 1.5C target.