As frustration grows with the protracted political process of penning a world climate pact for 2020, rich nations face ever-louder calls to take action in the coming five years to stop planet warming spiralling out of control.

Increasingly, poor and developing countries and small island states at high risk of climate change damage, are insisting at UN climate negotiations that rich nations slash greenhouse gas emissions even before the envisaged agreement enters into force.

With the clock ticking and Earth-warming emissions continuing to rise, they also demand more financial help to make the shift to greener energy and adapt to unavoidable warming effects.

The UN has set a target of limiting warming two degrees Celsius (3.6 Fahrenheit) over pre-Industrial Revolution surface temperatures -- a level at which climate effects like rising seas, more droughts and floods and species loss are thought to still be manageable.

The average global temperature has already risen 0.8 C, and some predict the 2 C level may be reached by mid-century -- climbing as high as 4.8 C by 2100 if emissions continue at their current rate.

"Are we going to sit and wait until 2020 to act when the world is already being hit by climate change?" climate activist Harjeet Singh of ActionAid International asked this week in Bonn, where country negotiators are engaged in the latest round of talks on the wording of the pact nations have agreed to finalise in Paris in December.

"Look at the unprecedented heat wave in India that killed more than 2,000 people. Look at the devastation in Vanuatu (in the South Pacific)," hit by a cyclone in March, he said.

Scientists cannot say with certainty that extreme weather events today are caused by climate change, but most agree that things will be dramatically worse under a 4.8 C scenario.

A UN conference in the French capital from November 30-December 11 will seek to crown a six-year wrangle of the 196-member UN Framework Convention on Climate Change (UNFCCC) with an historic pact on curbing greenhouse gases, to enter into force in 2020.

Pre-2020 action is very much part of the negotiating agenda, but has taken a back seat to the sensitive issue of cutting emissions from burning fossil fuels powering our houses, offices, factories, farms and transport.

The process has been marred by years of wrangling as nations disagree on how to divvy up responsibility for emissions curbs and climate finance.

Developing economies insist that rich countries, rattled by the economic crisis, show how they will keep a promise of mustering $100 billion (92 billion euros) a year in climate finance by 2020.

"Pre-2020 action can become a basis for a stronger deal in Paris, by building trust and showing leadership from developed countries," said Singh.

- Writing on the wall -

The UN's Intergovernmental Panel on Climate Change (IPCC) says a 2 C pathway requires annual greenhouse-gas cuts of 40-70 percent by 2050, compared to levels in 2010 -- and to zero or below by 2100.

"What we do between now and 2020 is crucial for developing countries," Seyni Nafo, a spokesman for the African negotiating bloc, told AFP in Bonn.

"Developing countries are saying to their developed counterparts: If you want that we take on commitments post-2020, you have to do more before 2020," added Alix Mazouni of the Climate Action Network.

France's Foreign Minister Laurent Fabius, who will head the year-end negotiations, urged delegates at Monday's opening in Bonn to "prepare a decision on pre-2020 action to be adopted in Paris."