Image copyright Getty Images Image caption The report warns that extreme weather events like droughts will become more common unless stronger action is taken to cut emissions

A UN review of national plans to cut carbon says they are well short of the levels needed to keep the rise in global temperatures under 2C.

The report finds that by 2030 the amount of CO2 entering the atmosphere will be some 25% above that mark.

The analysis takes into account the pledges that countries have made under the Paris climate agreement.

Many scientists say that technology to remove carbon from the air will now be needed to meet the Paris targets.

The UN Emissions Gap Report, prepared by an international team of scientists, finds that by 2030, global emissions are expected to reach 54 to 56 gigatonnes of CO2.

The authors say this is far above the 42 gigatonnes needed to have a good chance of staying below 2 degrees by the end of the century, and a long way from the 39 gigatonnes needed to keep to 1.5 degrees as was promised in Paris last December.

A gigatonne is roughly the equivalent of the annual emissions produced by all forms of transport in the European Union.

While the report notes that the growth of emissions from fossil fuel use and industry is now slowing, this scale of carbon would put the world on track for a rise in temperatures by the end of this century of between 2.9 and 3.4 degrees C.

Image copyright Getty Images Image caption Securing agreement in Paris on tackling climate change was a significant diplomatic achievement

"We are moving in the right direction: the Paris Agreement will slow climate change, as will the recent Kigali Amendment to reduce HFCs," said Erik Solheim, head of UN Environment.

"They both show strong commitment, but it's still not good enough if we are to stand a chance of avoiding serious climate change."

The report suggests that there are some areas where progress can be made. The assessment of the plans of the richer G20 countries indicates that some are in line to deliver greater reductions than planned.

The UN review also suggests that the contributions from cities, businesses and other "non-state actors", as they are termed, could reduce emissions by a few crucial gigatonnes.

The UN also says that ambitious action on energy efficiency in buildings and in transport and other areas could help drive down carbon significantly. Investments in this area were up by 6% in 2015 to $221bn.

But with global temperatures in 2016 at one degree above pre-industrial levels, there is a growing acknowledgement that even the most ambitious attempts will not be enough to keep to the 1.5 degree target in play.

The UN report says that "most scenarios that limit warming to below 2 or 1.5 degrees assume the use of so-called negative emissions technologies in the second half of the century".

This will involve the active and permanent removal of carbon dioxide from the atmosphere by planting trees for example, and by the deployment of technologies like bio-energy with carbon capture and storage, or BECCS for short.

Image copyright Getty Images Image caption A drier climate is more susceptible to forest fires like this one in California

This means growing crops that absorb CO2 and then burning them for energy while capturing and storing the warming gas they produce.

"At the moment most of the discussion is about BECCS, so we need to identify suitable areas to sequester carbon and make sure it doesn't leak out. That takes time and technology," said Dr Ed Hawkins from the University of Reading, UK.

"We need to develop the understanding of what that will do for the climate. If we grow all these biofuels in places does that mean we can't grow so much food everywhere? There are these constant trade-offs that we need to consider."

With the Paris Agreement becoming operational on 4 November, and delegates from almost 200 countries meeting in Marrakech next week to consider the next steps, experts are hoping that governments will not just bask in the glory of a job well done, but will see the COP22 gathering as a chance to push forward with ambition.

"I hope that they will agree to lower their nationally determined contributions," Prof Joanna Haigh from Imperial College London, UK, told BBC News.

"It's fantastic that they got the Paris Agreement but their contributions at the moment are nowhere near the 1.5-degree target.

"I think the momentum is such that countries all understand that something extra now needs to be done. The thought process has moved on a step."

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