It may be too late to cap global warming at 3.6 degrees, scientists allied with an Australian research group say, as heat-trapping emissions hit a record high.

"An immediate, large and sustained global mitigation effort" will need to begin if the world has any hope of achieving a 2009 agreement by nearly 200 nations to limit future temperature increases to 3.6 degrees Fahrenheit, or 2 degrees Celsius, biologist and Global Carbon Project Executive Director Josep Canadell said in a statement.

The 2009 agreement was reached at a U.N. Climate Change Conference in Denmark commonly known as the Copenhagen Summit.

Delegates starting a second week of negotiations at a U.N. climate conference in Doha, Qatar, are trying to find ways of reaching that target, but so far report no success.

Canadell's remarks echoed those of State of the World Forum President Jim Garrison, who told United Press International ahead of a "climate leadership" conference before Copenhagen, "If we don't completely rethink and radically accelerate the plans to reverse global warming, we will, in all likelihood, create catastrophic climate change in our lifetime."

Overall global emissions jumped 3 percent in 2011 and are predicted to jump 2.6 percent this year, researchers from the Global Carbon Project and Britain's Tyndall Center for Climate Change Research reported Sunday in the journal Nature Climate Change.

Their research data from the U.S., Australian, British, French and Norwegian scientists were also published in the journal Earth System Science Data Discussions.

This year's projected 2.6 percent rise would mean global fossil-fuel emissions are 58 percent higher than 1990 levels, the baseline year used by the United Nations' 1997 Kyoto Protocol, which set binding obligations on the industrialized countries to reduce their greenhouse gas emissions.

The protocol has been signed and ratified by 191 countries. The only country to have signed it but not ratified it is the United States.

U.N. member states that did not ratify the protocol are Afghanistan, Andorra and South Sudan. Canada withdrew from the Protocol a year ago.

The average temperature of the Earth's surface increased about 1.4 degrees Fahrenheit, or 0.8 degrees Celsius, over the past 100 years, with about two-thirds of the increase occurring since 1980, the U.S. National Research Council reported last year.

If emissions continue growing at an average annual 3.1 percent, as they have since 2000, the global mean temperature is likely to rise more than 9 degrees Fahrenheit, or more 5 degrees Celsius, by 2100, the Global Carbon Project-Tyndall Center study forecast.

The study found 2011's biggest contributors to global emissions were China at 28 percent, the United States at 16 percent, the European Union at 11 percent and India at 7 percent.

China's emissions increased 9.9 percent and India's grew 7.5 percent, the study found, while U.S. and EU emissions decreased 1.8 percent and 2.8 percent, respectively.

The U.S. decrease appears to be partly due to economic weakness and transferring some manufacturing to developing countries, The New York Times said.

The study, "The Challenge to Keep Global Warming Below 2 Degrees Celsius," said carbon dioxide emissions were slowed briefly around 2009 by the global financial crisis.

The U.S. decrease also appears to reflect conscious U.S. states' efforts to limit emissions, as well as a boom in the natural gas supply from induced hydraulic fracturing, commonly known as hydrofracking or simply fracking, the newspaper said.

Natural gas, which is mostly methane, is replacing coal at many U.S. power stations, leading to lower emissions.

At the same time, coal usage is growing fastest globally, with coal-related emissions leaping more than 5 percent in 2011 from 2010, the study said.

Coal is the most carbon-intensive fossil fuel, producing hundreds of millions of tons of solid waste a year, including various types of ash and sludge found to contain mercury, uranium, thorium, arsenic and other heavy metals.