BERLIN - U.N. talks on tackling climate change made limited progress over the past 10 days, with several issues still unresolved ahead of three key meetings later this year, officials said Thursday.

Governments wrapped up their regular meeting in Bonn, Germany, amid a record-setting heat wave in parts of Europe.

Australia, South Asia and the Middle East have also experienced extreme temperatures this year in what scientists warn could be a sign of future conditions in a warming world.

“We can no longer afford incremental progress when tackling climate change,” U.N. climate chief Patricia Espinosa said in a statement at the end of the talks.

Espinosa called for “deep, transformational and systemic change throughout society” to achieve the most ambitious target in the 2015 Paris climate accord — capping global warming at 1.5 degrees Celsius (2.7 Fahrenheit) by the end of the century.

Campaigners and vulnerable countries lamented further attempts by oil-rich countries to undermine a key scientific report on meeting that target. The effort was led by Saudi Arabia, but also received overt or tacit support from other fossil fuel exporting nations like Iran and Australia.

“To reject a report that looks at what life might be under temperature increases that we are very close to is fundamentally problematic,” said Tyrone Hall, an adviser for the Alliance of Small Island States who took part in the talks.

Average global temperatures have already increased by about 1 degree Celsius since pre-industrial times. Scientists say it’s becoming increasingly unlikely the 1.5 C goal can be achieved if current rates of greenhouse gas emissions continue.

Most countries present at the talks said the 1.5-degree report remains the benchmark for discussion.

“We think all countries should use that report as the basis for their policy making and for their action,” said Swiss diplomat Franz Xaver Perrez, wearing a t-shirt bearing the slogan “science is not negotiable.”

A growing number of countries, including major industrialized economies such as Britain, say they want to stop adding carbon — the main greenhouse gas — to the atmosphere by 2050. This goal, known as ‘net zero emissions,’ failed to get the support of all 28 European Union members earlier this month, but campaigners hope that may still happen before a Sept. 23 summit hosted by U.N. Secretary-General Antonio Guterres at which governments from around the world are expected to pledge greater ambition on tackling climate change.

A month later, countries will come together to decide how much money to give to the Green Climate Fund that helps poor nations cope with the impacts of global warming and shift to a low-carbon economy.

Among the issues left unresolved in Bonn were the rules by which countries and businesses can pay to cut greenhouse gas emissions elsewhere and count this toward their own targets.

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This is likely to become one of the main negotiating points when Chile hosts the annual U.N. climate summit in December.

“I urge governments to use the rest of this year to find solutions, allowing solid rules for carbon markets to finally take shape,” said Espinosa. “Businesses want this and they are looking for positive signals from governments that they will do this. They know it’s a good way to reduce emissions globally.”