By Wynne Parry, LiveScience Contributor:

Global greenhouse-gas emissions already have passed the point where the worst effects of global warming could be averted, and they are still rising, according to the third annual United Nations report on the so-called emissions gap.

Some countries have made pledges to help reverse this trend by lowering their emissions. However, the report by the U.N. Environment Programme warns that the gap between these pledges and reductions necessary to cap average global warming at 2 degrees Celsius (3.6 degrees Fahrenheit) by 2020 continues to widen.

"In addition we have one year less to close it," said Niklas Höhne, one of the UNEP report's lead authors.

The report, released shortly before an annual round of climate talks set to begin on Monday (Nov. 26) in Qatar, seeks to balance a heightened sense of urgency with a positive message.

"It is technically feasible and economically feasible that the gap can be closed," Höhne, director of energy and climate policy at the independent research and consulting company Ecofys, told LiveScience.

The math

In 2009, at a meeting in Copenhagen, international negotiators agreed to the goal of capping global warming at 2 degrees C by 2020. Following the meeting, some nations submitted pledges to cut their emissions. The United States, for example, pledged to bring its emissions to about 17 percent below the 2005 level.

In the years since, nations have not made any substantial change to their pledges.

The UNEP report highlights the gap between these pledges and cuts needed put the world on a "likely" path to stay below the 2-degree target. It calculates that the annual emission rate by 2020 should be no more than  48.5 gigatons (44 metric gigatons) of carbon dioxide and other greenhouse gases. [8 Ways Global Warming Is Already Changing the World]

Using the most recent data available, for 2010, the report puts current emissions at 54 gigatons (49 metric gigatons). Extrapolate out to 2020, and the gap grows to between 8.8 and 14.3 gigatons (8 and 13 metric gigatons). Last year's report put the gap at between 6.6 and 12.1 gigatons (6 and 11 metric gigatons).

This year's report attributes the increase to faster-than-expected growth from 2009 to 2010 after the economic downturn. (More economic activity creates more greenhouse-gas emissions.) Improved accounting, taking into account situations in which two countries claim credit for the same emissions reductions, also contributed, the report stated.

(A word about these calculations: While carbon dioxide is the dominant greenhouse gas, others such as methane, which has potent warming effect but stays in the atmosphere for only a minuscule period of time compared with carbon dioxide, also contribute. The UNEP report lumps greenhouse gases together, describing them in terms of "carbon dioxide equivalent." Because of the differences among the gases, not all scientists support this approach.)  

Two sides of a story

Prior to the UNEP report, the World Bank released its assessment of a future resulting from no action, in which the average global surface temperature climbs by 3 degrees C (5.4 degrees F) or more and the world sees more extreme effects.

As emissions continue to climb, some climate scientists have said that an increase of 4 degrees C (7.2 degrees F) is a more likely scenario. 

The World Bank report, called "Turn Down the Heat," describes a future world of unprecedented heat waves, severe drought and major floods in many regions. The effects are expected to hit humans hard, particularly in the poorer parts of the world.  

Both reports attempt to convey a positive message:

"With action, a 4-degree C world can be avoided, and we can likely hold warming below 2 degrees C," the authors of the World Bank report write.  

The UNEP emissions gap report, meanwhile, lists policies that, when implemented, could help narrow the gap. These include energy-efficiency standards and labeling for equipment and lighting; improvements in building codes; transportation infrastructure focused on mass transit, walking, cycling and waterways; and forestry policies such as Brazil's increasing protection of areas in the Amazon and its investment in satellite-based monitoring to prevent illegal deforestation.

"There is certainly more action now than ever if you [look] at what is happening in different countries,” Höhne said.

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    We look at which 10 countries have the most CO2 emissions. Figure are preliminary 2010 numbers from the U.S. government's <a href="http://cdiac.ornl.gov/trends/emis/perlim_2009_2010_estimates.html" target="_hplink">Carbon Dioxide Information Analysis Center. </a> (Photo Getty Images)

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