Climate change is likely to be more severe than some models have implied, according to a new study which ratchets up the possible temperature rises and subsequent climatic impacts.

The analysis by the US National Centre for Atmospheric Research (NCAR) found that climate model projections showing a greater rise in global temperature were likely to be more accurate than those showing a smaller rise. This means not only a higher level of warming, but also that the resulting problems – including floods, droughts, sea level rise and fiercer storms and other extreme weather – would be correspondingly more severe and would come sooner than expected.

Scientists at the NCAR published their study on Thursday in the leading peer-reviewed journal Science. It is based on an analysis of how well computer models estimating the future climate reproduce the humidity in the tropics and subtropics that has been observed in recent years. They found that the most accurate models were most likely to best reproduce cloud cover, which is a major influence on warming. These models were also those that showed the highest global temperature rises, in future if emissions of greenhouse gases continue to increase.

John Fasullo, one of the researchers, said: “There is a striking relationship between how well climate models simulate relative humidity in key areas and how much warming they show in response to increasing carbon dioxide. Given how fundamental these processes are to clouds and the overall global climate, our findings indicate that warming is likely to be on the high side of current projections.”

Extreme weather has been much in evidence around the globe this year, with superstorm Sandy’s devastating impact on New York the most recent example. There has also been drought across much of the US’s grain-growing area, and problems with the Indian monsoon. In the UK, one of the worst droughts on record gave way to the wettest spring recorded, damaging crop yields and pushing up food prices.

The new NCAR findings come just weeks ahead of a crucial UN conference in Doha, where ministers will discuss the future of international action on greenhouse gas emissions. The ministers will have to take the first steps to a new global climate treaty, to kick in from 2020, but so far have shown little sign of urgency.

The next comprehensive study of our knowledge of climate change and its effects will come in 2014, when the Intergovernmental Panel on Climate Change publishes its fifth assessment report. Before that, next September, the first part of the report will deal with the science of climate change and predictions of warming.

There has already been increasing evidence of a warming effect this year – the Arctic’s summer ice sank to its lowest extent and volume yet recorded, and satellite pictures showed that surface ice melting was more widespread across Greenland than ever seen in years of observations. Experts have predicted that the Arctic seas could be ice-free in winter in the next decade.

The International Energy Agency warned earlier this year that on current emissions trends the world would be in for 6C of warming – a level scientists warn would lead to chaos. Scientists have put the safety limit at 2C, beyond which warming is likely to become irreversible.

Given this year’s extreme weather, the results of the NCAR may not surprise some. But for scientists, narrowing down the uncertainties in climate models is a key activity. “The dry subtropics are a critical element in our future climate,” Fasullo says. “If we can better represent these regions in models, we can improve our predictions and provide society with a better sense of the impacts to expect in a warming world.”

Barack Obama‘s invocation of “the destructive power of a warming planet” in his victory speech has stoked expectation that he will act on climate change in his second term.

Environmental campaigners are already mobilising to hold the president to that promise.

They argued Obama’s re-election, amid the devastation of superstorm Sandy, was a clear mandate for action on climate change, in stark contrast to Mitt Romney, who turned sea-level rise into a laugh line in the biggest speech of his political career.

Campaigners put Obama on immediate notice, calling an 18 November demonstration at the White House to demand he scrap the controversial Keystone XL pipeline.

“In the wake of hurricane Sandy, as the warmest year in American history draws to a close, as the disastrous drought lingers on in the midwest, everyone is looking for ways to make a real difference in the fight to slow climate change,” said an open letter from 350.org and the Sierra Club.

But a strategic decision by the White House in 2009 to downplay climate change, and Obama’s avoidance of the issue during the campaign, makes it tricky for the president to now claim that he was elected to act on the issue.

The Republicans’ continued control of the House of Representatives will also continue to limit Obama’s scope for action.

However, environmental campaigners said Sandy – and an endorsement from New York city mayor, Michael Bloomberg, due to Obama’s position on climate change – create public space for the president to act.

“Of course president Obama certainly did not take up the cause in the way we had hoped but he has indicated in numerous events and in the New Yorker and Rolling Stone that climate will be a top priority for his second term,” said Betsy Taylor, president of the climate strategy firm Breakthrough Solutions. “There is reason to feel hope. We moved from silence to a growing mandate for action.”

A number of newly elected Democrats in the Senate and the House of Representatives also owe their victories, in part, to support from environmental campaign groups, giving greens more allies in Congress.

The president has a chance early on to show he intends to deliver on climate change.

The first big decision will be on the Keystone XL pipeline, a project designed to expand production of the Alberta tar sands by pumping crude to Texas refineries. The administration is due to make its decision early next year and many believe that Obama will approve the pipeline.

Environmental groups will also be watching whether Obama continues to fight to keep tax credits for the wind industry during the lame duck session of Congress. Their expiry at the end of the year has hurt the industry, leading to lay-offs. Obama has said he will continue to fight $46bn in subsidies to the fossil fuel industry.

Then there are appointments. Obama came to the White House in 2009 with a green “dream team” including Nobel laureate, Steve Chu, as energy secretary. Obama will have to make new appointments in his second term.

He must also decide whether to resurrect the post of White House climate adviser, which has been empty since early 2011 when Carol Browner stepped down. That could help push policies blocked by Congress.

Now that Obama has a second term, the Environmental Protection Agency is also expected to move more aggressively on tightening rules on mercury and carbon dioxide emissions.

But the environmental community will be looking for Obama to deliver the big changes that will move America towards a low-carbon future – and protect the country from the extreme weather, rising seas and other consequences of future climate change.

At its most ambitious, that would involve some kind of carbon tax – an option that is now a topic of discussion at a number of Washington thinktanks, including the conservative American Enterprise Institute.