Tomorrow the Paris agreement – reached at COP21 in December last year – comes into effect, but those pledges made by countries fall far short of what is necessary to avoid dangerous levels of climate change, a UN report says.

A major report released by the UN Environment Programme states that global ambition to limit climate change must "urgently and dramatically increase" to cut emissions predicted for 2030 by an additional 25%. Even this action will only limit climate change to a 2˚C increase, rather than the 1.5˚C goal outlined in the Paris agreement.

This is necessary, the report says, in order to reduce the likelihood of increasingly intense storms, longer droughts and rising sea levels.

What we stand to lose

If we just stick to the Paris agreement, the world is still going to warm by up to 3.4 ˚C this century, the report says.

"We are moving in the right direction," says Erik Solheim, head of UN Environment. But the Paris agreement would not be enough to avoid "serious climate change", he says.

"If we don't start taking additional action now, beginning with the upcoming climate meeting in Marrakesh, we will grieve over the avoidable human tragedy. The growing numbers of climate refugees hit by hunger, poverty, illness and conflict will be a constant reminder of our failure to deliver. The science shows that we need to move much faster."

polar bear
Climate change is reducing Arctic ice cover and making it harder for polar bears to hunt Reuters

The scale of the challenge

1 Gigaton of carbon = the emissions generated annually by transport in the European Union

12 Gt = the minimum reduction needed to limit warming to 2˚C, in addition to the Paris pledges. This is equivalent to the total carbon emissions of OECD countries in 2015

15 Gt = the minimum needed to limit warming to 1.5˚C. Equivalent to three times the US's emissions in 2015

Source: UN Environment's Emissions Gap report

What to do about it

The UN Environment report suggests several measures to help further reduce emissions. It calls on companies, cities and citizen groups to cut several Gigatons off the gap in agriculture and transport.

Investment in energy efficiency could also knock significant quantities of emissions off the shortfall, and points to encouraging figures showing that investment in this area rose by 6% last year.

Another half a Gigaton of emissions is likely to be saved by energy efficiency projects established in developing countries in the past decade, the report says.

Operation IceBridge Antarctic sea ice
Ice floats near the coast of West Antarctica Mario Tama/Getty Images