Image copyright SOPA Images Image caption Some observers believe that the return of Mr Guterres to these talks is a sign that significant progress is not being made

The UN secretary-general has warned negotiators at a major meeting that failing to increase efforts on climate change would be "not only immoral but suicidal" for the planet.

Antonio Guterres has flown back to Poland to try and push COP24 to a successful conclusion.

At the UN talks, a group of countries have said they will enhance their climate plans before 2020.

The EU and others say they are responding to the urgency of science.

Some observers believe that the return of Mr Guterres to these talks is a sign that significant progress is not being made.

In his remarks to the conference, he underlined that fact, imploring the delegates to speed up the pace of negotiations and to be open to compromise.

He said that key political issues here in Poland remain unresolved.

"To waste this opportunity would compromise our last best chance to stop runaway climate change," Mr Guterres said. "It would not only be immoral, it would be suicidal."

What's worrying many delegates and observers here is the complexity of the task of delivering a strong rulebook on the Paris pact.

There is a fear among some delegates that ministers who are here to make the final political decisions on the outstanding issues may oversimplify the situation.

There are still outstanding questions over how to have a single set of rules for every country that is flexible enough to not overwhelm poorer nations with huge amounts of red tape.

Increasing ambition

As well as an effective rulebook, the negotiators here are also pushing for countries to increase the level of their ambition, their plans to cut carbon emissions.

To that end the EU in an alliance with Canada, the UK, Norway, many small island states as well as the least developed countries group, is to push for greater efforts in their enhanced national plans to be submitted by 2020.

The "high ambition coalition" says that this has to be done to ensure an adequate response to the risks and impacts of climate change that were highlighted in the IPCC special report on 1.5C issued in October.

"For the EU it is unacceptable not to have any decision taken that acknowledges positively the special report on 1.5C," said EU climate commissioner Miguel Arias Canete.

"We represent both developed and developing countries from all the continents and the EU is committed to an ambitious outcome in Katowice but the texts in front of us are not bold enough,"

While the atmosphere at the talks is generally positive, a lingering row over climate science also rumbles on.

Over the weekend the US and Saudi Arabia, back by Russia and Kuwait, refused to welcome the IPCC report on how a temperature rise of 1.5C would impact the world.

Saudi officials, perhaps stung by the widespread criticism of their stance, have spoken out to defend their position.

"We have accepted a welcome for all other IPCC reports in the past because they are done right, within the rule and procedures of the IPCC," a member of the Saudi delegation told journalists.

"We never had reservations on other reports, so we know that there are some things that are not as good as the other reports we have used. It does not, in our view, stand up to the same level as the others."

Other senior figures at these talks have defended the IPCC and said that by the end of the discussions here, the key role of the research needs to be recognised.

"Let me make this perfectly clear," said Fijian prime minister Frank Bainimarama, who presided over last year's conference of the parties.

"Fiji welcomes the IPCC Special Report on 1.5 degrees. We must all accept the science, which is irrefutable. We accept science in virtually every single other form of human endeavour. So simple logic dictates that we must do it."

Follow Matt on Twitter @mattmcgrathbbc.

UN climate conference 03 Dec- 14 Dec 2018

The summit comes three years after the 2015 Paris accord on climate change, at which all countries agreed a plan to limit carbon emissions. Now is the moment governments must start deciding what to do to make sure that plan is put into effect.