Global carbon neutrality should be reached between 2055 and 2070 if the global temperature rise is to be limited to 2 degrees Celsius and head off the worst impacts of climate change, according to a UN report released here Wednesday.

The Emissions Gap Report 2014, published by the UN Environment Program (UNEP), is the fifth in a series that examines whether the pledges made by countries are on track to meet the internationally agreed target of limiting global warming to 2 degrees Celsius in this century, relative to the pre-industrial period.

It found global greenhouse gas emissions have grown by more than 45 percent since 1990 and were about 54 gigatons of carbon dioxide equivalents (Gt CO2e) in 2012.

To stay within the two-degree limit, global emissions in 2020 should not be higher than 44 Gt CO2e, but the range of expected global emissions based on national pledges is 52 to 54 Gt CO2e in 2020, a gap of 8 to 10 Gt CO2e, the report said.

"An increase in global temperature is proportional to the build- up of long-lasting greenhouse gases in the atmosphere, especially CO2," Achim Steiner, UN Under-Secretary-General and Executive Director of the UNEP, said in a statement.

"Taking more action now reduces the need for more extreme action later to stay within safe emission limits."

He said the fifth Emissions Gap Report also focused on what are required to do beyond 2020 as "countries are giving increasing attention to where they realistically need to be by 2025, 2030 and beyond."

To have a likely chance of staying below the two-degree limit, global greenhouse gas emissions should drop by about 15 percent or more by 2030 compared to 2010, and be at least 50 percent lower by 2050, the report said.

And global carbon neutrality will need to be achieved sometime between 2055 and 2070, it noted.

Global carbon neutrality means that some remaining CO2 emissions could be fully absorbed by the globe's natural infrastructure such as forests and soils so that the net input to the atmosphere due to human activity is zero.

Taking into account non-CO2 greenhouse gases, including methane, nitrous oxide and hydrofluorocarbons, total global greenhouse gas emissions need to shrink to net zero between 2080 and 2100, the UNEP report said.

Meanwhile, the report also found that five parties to the United Nations Framework Convention on Climate Change -- Brazil, China, the European Union, India and Russia -- are on track to meet their pledges.

Australia, Canada, Mexico and the USA "are likely to require further action and/or purchased offsets to meet their pledges," said the report, citing government and independent estimates of projected national emissions in 2020.

Conclusions are not drawn for Japan, the Republic of Korea, Indonesia and South Africa because of various uncertainties, nor for Argentina, Turkey and Saudi Arabia because they have not proposed pledges, it added.

"Unfortunately, the world is not currently headed in the right direction," Andrew Steer, president and CEO of the World Resources Institute, said in the UNEP statement.

"But, with the growing momentum for global climate action, we have the opportunity to close the emissions gap and keep within the limits of what the science says is needed to prevent the worst impacts of climate change." Endite