Geneva: Greenhouse gas emissions surged to a record level last year and world temperatures could rise by more than twice the globally agreed warming limit if nothing is done, a U.N. report showed on Tuesday.

The "Emissions Gap Report" is one of several studies released ahead of U.N. climate talks in Madrid next week aimed at spurring world leaders to limit climate change.

It measures the amount of emissions cuts needed to limit global temperature rises to 1.5 degrees Celsius (2.7 Fahrenheit) above pre-industrial levels, as agreed in the key 2015 Paris Agreement. The U.N. Intergovernmental Panel on Climate Change last year warned of huge global changes if that target is not met, such as the loss of nearly all coral reefs and most Arctic sea ice.

Under current national pledges to cut emissions, "temperatures can be expected to rise by 3.2C this century, bringing wide-ranging and destructive climate impacts," said a summary of the report by the U.N. Environment Programme (UNEP).

"Being a grandfather - we don't want to leave that for our grandkids," the report's lead author John Christensen told a news conference.

The report said the safest temperature threshold set in Paris - of 1.5C - was still achievable, but would require emissions cuts of 7.6% a year between 2020-2030, the report said. Limiting the rise to 2C it would mean annual cuts of 2.7%.

"We are talking about transformational change now - incremental change simply will not make it. We simply need to transform societies in the next 10 years," Christensen said.

"The longer you wait, the more difficult it becomes."

The report showed that emissions, including those from land-use change such as deforestation, had not yet peaked and rose to a record 55.3 gigatonnes of carbon dioxide equivalent in 2018.

Christensen said some of those that had met their targets comfortably, such as Turkey and Russia, should tighten them significantly.

The report named the United States as one of several large emitters alongside Brazil and Japan falling short of its own targets, or Nationally Determined Contributions (NDCs). This month, the Trump administration filed paperwork to quit the Paris Agreement in the first step of a formal withdrawal process.

Countries face a 2020 deadline to set more ambitious emissions cut pledges.

"Had we done it 10 years ago, it would have been easier," said Inger Andersen, UNEP Executive Director. "But the time is now and the opportunity is now."