Models typically simulate water vapour as rising to 15km and forming clouds, rather than updraughts of water vapour that rise only a few kilometres and pull away the cloud-forming vapour. This prediction of cloud cover is important because clouds reflect sunlight, lessening the impact of global warming.
In reality, the study found, water vapour is distributed to different heights in the atmosphere, causing fewer clouds to form as the climate warms.
In turn, this increases the amount of sunlight entering the atmosphere, making the level of warming far more sensitive to heat-trapping gases such as CO2.
As a result, the world can expect a temperature increase of "at least" 4C by 2100 if, as predicted, there is a doubling of CO2 in the atmosphere. This could then rise by more than 8C by 2200.
This is beyond the lower range of predictions and double the 2C limit, compared with pre-industrial times, agreed by countries to prevent the impact of runaway climate change. By comparison, average temperatures have risen 0.8C over the past 100 years.
"Mixing inferred from observations appears sufficiently strong to imply a climate sensitivity greater than 3C for a carbon dioxide doubling," the report states. "This is significantly higher than the currently accepted lower bound of 1.5C, thereby constraining model projections toward relatively severe future warming."
The issue of how sensitive the climate is to CO2 was a contentious one following the release of the latest climate report in September by the Intergovernmental Panel on Climate Change (IPCC). Some sceptics have claimed a so-called warming "pause" over the past 15 years shows the climate does not react strongly to high concentrations of carbon emissions, which continued to escalate to a new average high of393.1ppm in 2012.
"Climate sceptics like to criticise climate models for getting things wrong, and we are the first to admit they are not perfect, but what we are finding is that the mistakes are being made by those models which predict less warming, not those that predict more," said Professor Sherwood, lead author of the report at the UNSW centre of excellence for climate system science.
"Our research has shown climate models indicating a low temperature response to a doubling of carbon dioxide from pre-industrial times are not reproducing the correct processes that lead to cloud formation.
"When the processes are correct in the climate models the level of climate sensitivity is far higher. Previously, estimates of the sensitivity of global temperature to a doubling of carbon dioxide ranged from 1.5C to 5C," he said.
"This new research takes away the lower end of climate sensitivity estimates, meaning that global average temperatures will increase by 3C to 5C with a doubling of carbon dioxide.
"Rises in global average temperatures of this magnitude will have profound impacts on the world and the economies of many countries if we don't urgently start to curb our emissions."
The climate crisis of the 21st century has been caused largely by just 90 companies, which between them produced nearly two-thirds of the greenhouse gas emissions generated since the dawning of the industrial age, new research suggests.
The companies range from investor-owned firms – household names such as Chevron, Exxon and BP – to state-owned and government-run firms.
The analysis, which was welcomed by the former vice-president Al Goreas a "crucial step forward" found that the vast majority of the firms were in the business of producing oil, gas or coal, found the analysis, which has been accepted for publication in the journal Climatic Change.
"There are thousands of oil, gas and coal producers in the world," climate researcher and author Richard Heede at the Climate Accountability Institute in Colorado said. "But the decision makers, the CEOs, or the ministers of coal and oil if you narrow it down to just one person, they could all fit on a Greyhound bus or two."
Half of the estimated emissions were produced just in the past 25 years – well past the date when governments and corporations became aware that rising greenhouse gas emissions from the burning of coal and oil were causing dangerous climate change.
Many of the same companies are also sitting on substantial reserves of fossil fuel which – if they are burned – puts the world at even greater risk of dangerous climate change.
Climate change experts said the data set was the most ambitious effort so far to hold individual carbon producers, rather than governments, to account.
The United Nations climate change panel, the IPCC, warned in September that at current rates the world stood within 30 years of exhausting its "carbon budget" – the amount of carbon dioxide it could emit without going into the danger zone above 2C warming. The former US vice-president and environmental champion, Al Gore, said the new carbon accounting could re-set the debate about allocating blame for the climate crisis.
Leaders meeting in Warsaw for the UN climate talks this week clashed repeatedly over which countries bore the burden for solving the climate crisis – historic emitters such as America or Europe or the rising economies of India and China.
Gore in his comments said the analysis underlined that it should not fall to governments alone to act on climate change.
"This study is a crucial step forward in our understanding of the evolution of the climate crisis. The public and private sectors alike must do what is necessary to stop global warming," Gore told the Guardian. "Those who are historically responsible for polluting our atmosphere have a clear obligation to be part of the solution."
Between them, the 90 companies on the list of top emitters produced 63% of the cumulative global emissions of industrial carbon dioxide and methane between 1751 to 2010, amounting to about 914 gigatonne CO2 emissions, according to the research. All but seven of the 90 wereenergy companies producing oil, gas and coal. The remaining seven were cement manufacturers.
The list of 90 companies included 50 investor-owned firms – mainly oil companies with widely recognised names such as Chevron, Exxon, BP , and Royal Dutch Shell and coal producers such as British Coal Corp, Peabody Energy and BHP Billiton.
Some 31 of the companies that made the list were state-owned companies such as Saudi Arabia's Saudi Aramco, Russia's Gazprom and Norway's Statoil.
Nine were government run industries, producing mainly coal in countries such as China, the former Soviet Union, North Korea and Poland, the host of this week's talks.
Experts familiar with Heede's research and the politics of climate change said they hoped the analysis could help break the deadlock in international climate talks.
"It seemed like maybe this could break the logjam," said Naomi Oreskes, professor of the history of science at Harvard. "There are all kinds of countries that have produced a tremendous amount of historical emissions that we do not normally talk about. We do not normally talk about Mexico or Poland or Venezuela. So then it's not just rich v poor, it is also producers v consumers, and resource rich v resource poor."
Michael Mann, the climate scientist, said he hoped the list would bring greater scrutiny to oil and coal companies' deployment of their remaining reserves. "What I think could be a game changer here is the potential for clearly fingerprinting the sources of those future emissions," he said. "It increases the accountability for fossil fuel burning. You can't burn fossil fuels without the rest of the world knowing about it."
Others were less optimistic that a more comprehensive accounting of the sources of greenhouse gas emissions would make it easier to achieve the emissions reductions needed to avoid catastrophic climate change.
John Ashton, who served as UK's chief climate change negotiator for six years, suggested that the findings reaffirmed the central role of fossil fuel producing entities in the economy.
"The challenge we face is to move in the space of not much more than a generation from a carbon-intensive energy system to a carbonneutral energy system. If we don't do that we stand no chance of keeping climate change within the 2C threshold," Ashton said.
"By highlighting the way in which a relatively small number of large companies are at the heart of the current carbon-intensive growth model, this report highlights that fundamental challenge."
Meanwhile, Oreskes, who has written extensively about corporate-funded climate denial, noted that several of the top companies on the list had funded the climate denial movement.
"For me one of the most interesting things to think about was the overlap of large scale producers and the funding of disinformation campaigns, and how that has delayed action," she said.
The data represents eight years of exhaustive research into carbon emissions over time, as well as the ownership history of the major emitters.
The companies' operations spanned the globe, with company headquarters in 43 different countries. "These entities extract resources from every oil, natural gas and coal province in the world, and process the fuels into marketable products that are sold to consumers on every nation on Earth," Heede writes in the paper.
The largest of the investor-owned companies were responsible for an outsized share of emissions. Nearly 30% of emissions were produced just by the top 20 companies, the research found.
By Heede's calculation, government-run oil and coal companies in the former Soviet Union produced more greenhouse gas emissions than any other entity – just under 8.9% of the total produced over time. China came a close second with its government-run entities accounting for 8.6% of total global emissions.
ChevronTexaco was the leading emitter among investor-owned companies, causing 3.5% of greenhouse gas emissions to date, with Exxon not far behind at 3.2%. In third place, BP caused 2.5% of global emissions to date.
The historic emissions record was constructed using public records and data from the US department of energy's Carbon Dioxide Information and Analysis Centre, and took account of emissions all along the supply chain.
The centre put global industrial emissions since 1751 at 1,450 gigatonnes.
Global greenhouse gas emissions from burning fossil fuels reached the highest levels in human history last year, driven predominantly by Chinese growth, and are projected to surge even further in 2013.
New data from the Global Carbon Project - a team of scientists who track global emissions - finds carbon dioxide released from burning fossil fuels and making cement grew 2.2 per cent in 2012 from the previous year. In 2013 a further 2.1 per cent rise is expected.
But the latest data suggests the world's emissions could be slowing. The approximate 2 per cent growth in 2012 and 2013 falls short of the 3.1 per cent average annual rise since 2000.
CSIRO climate scientist Dr Pep Canadell - who is also executive director of the Global Carbon Project - told Fairfax Media the emissions rates of the past two years could be the tentative signs of a global slowdown.
''But it is important to understand it is only a slowdown in growth - emissions every year are still higher than the previous one. Two per cent growth is still a very large number,'' he said.
Dr Canadell said that if current emissions trends continued the world would reach 2 degrees of global warming in about 30 years, a threshold regarded by scientists as triggering the worst impact of climate change.
The data comes as countries are meeting in Warsaw in the latest round of United Nations negotiations towards a new climate change treaty. Through the UN, countries have already agreed to the aim of keeping warming below 2 degrees.
If the Global Carbon Project projections hold the world will emit 36 billion tonnes of CO2 from fossil fuels and making cement during 2013, up 61 per cent from the 1990 levels for those sources.
Fossil fuels and cement making are responsible for 92 per cent of global greenhouse gas emissions, with the rest coming from changes in land use - such as cutting down forests.
Land-change emissions are harder to calculate due to a lack of data in some countries, but the trend since the late-1990s has been improvement. The Global Carbon Project reports 3.1 billion tonnes of CO2 were emitted from land-use change in 2012, a rise on 2011.
China was found to be responsible for 71 per cent of the global rise in fossil fuel emissions in 2012. Chinese CO2 emissions grew 6 per cent in 2012, and its annual total is now almost double the next largest contributor, the United States.
But the 6 per cent rise is slower than China's growth in recent years, which hit 10 per cent in 2011.
Greenhouse gases in the atmosphere are rising at an accelerating pace to record levels, a trend that will drive climate change and endanger future generations, according to the World Meteorological Organisation Greenhouse Gas Bulletin No. 9 (pdf).
Carbon dioxide, the most important greenhouse gas linked to fossil fuel burning and deforestation, rose by an average of 2.2 parts per million (ppm) in 2012 to 393.1. That increase compared with 1.5 ppm in the 1990s and 2 ppm in the past decade, and brings atmospheric levels to 41 per cent more than pre-industrial times, the WMO said in its annual Greenhouse Gas Bulletin.
Methane emissions, 60 per cent of which come from human activities such as cattle breeding and fossil fuel extraction, also reached a new high at 1819 parts per billion (ppb) in 2012, rising by 6 ppb. The gas resumed its increase after a pause between 1999 and 2006.
Nitrous oxide, another important gas with almost 300 times the impact on climate as carbon dioxide and is linked to fertiliser use among other sources, rose 0.9 ppb to 325.1 ppb, quickening from the 0.8 ppb average increase over the previous decade.
Between 1990 and 2012 there was a 32 per cent increase in radiative forcing - the warming effect on our climate - because of the increase in these long-lived greenhouse gases, the WMO said.
Michael Raupach, a team leader in CSIRO's Marine and Atmospheric Research division, said the rise in atmospheric temperatures from the additional greenhouse gases had been temporarily limited by the oceans absorbing much of the extra heat trapped by those gases.
That pause, though, will end and "we'll see a return to significant rates of warming," he said.
While reducing carbon emissions won't stop the build-up of heat in the earth's biosphere, reductions now reduce the magnitude of the future task.
"The reduction in emissions over the [near term] is absolutely essential," Dr Raupach said. Failure to do so will mean the size of future cuts required will "become completely impossible if we are to avoid any reasonable definition of dangerous climate change."
Australia may face more intense and frequent bouts of extreme weather in the future as global warming "energises" the El Nino-Southern Oscillation (ENSO), the dominant climate system over the Pacific, according to an Australian-led team of researchers.
The research, led by Shayne McGregor at the University of NSW's Climate Change Research Centre, found that the ENSO phenomena were more active and intense during the 1979-2009 period that at any time in the past 600 years.
"Our research suggests in a warming world we are likely to see more extreme El Nino and La Nina events, which over the past decade in Australia have been related to extreme flooding, persistent droughts and dangerous fire seasons," said Dr McGregor.
An El Nino occurs when the central and eastern Pacific waters are relatively warm, weakening easterly trade winds. A reduction in clouds typically results in droughts and heatwaves for eastern Australia in particular, such as during 1982-83 and 1997-98.
La Nina years see the patterns reverse, with sea-surface temperatures to Australia's north relatively warm, with floods more common.
"In Australia we don't want El Nino to become more variable," said Matthew England, a co-author of the report published in the Climate of the Past journal, and also from the Climate Change Research Centre. "We're possibly having slightly more events, and they're becoming more intense when they do occur."
The opposite looks likely to be true, however, as humans pump more greenhouse gases into the atmosphere, driving temperatures higher.
"If we warm the planet we tend to energise El Nino," Professor England said. "We tend to excite it to become more variable, and so the events become stronger."
Karl Braganza, manager of climate monitoring at the Bureau of Meteorology, said research is ongoing to examine the link between climate change and extreme weather.
"If they can show a relationship with global temperatures [and ENSO variance], that's a pretty important result," Dr Braganza said of the latest research. (A separate study out earlier this month found that ENSO systems could have a greater impact on Australia in the future even if they did not intensify.)
Australia's extraordinary run of above-average temperatures continued in October despite ENSO being a "neutral" mode, neither El Nino or La Nina.
Sydney, for instance, recorded its second-hottest October on record by daytime and equalled the highest number of days of 32 degrees or warmer weather at five. Brisbane had its hottest October with an average maximum of 28.8 degrees.
Nationally, this month will probably be among the 10 warmest Octobers over the past century, the bureau said. That's enough to make both the past 12 months and the year-to-date periods, the hottest on record for Australia.
"A lot of climate experts are expecting the global climate to take a step up the next time an El Nino occurs," Professor England said. "Temperatures that year will break records in a significant way."