Three recent reports, each a comprehensive look at the climate crisis and possible paths out of it, provide the latest evidence that the barriers to reducing greenhouse gas emissions are daunting, but not insurmountable.

One report comes from the United Nations Environment Program (UNEP); one from the World Bank; and one from a consortium that includes two United States' national laboratories. Together, they illustrate the concerted effort by various schools of climate analysis to promote a global treaty in Paris next year. All echo themes presented in the Intergovernmental Panel on Climate Change's fifth assessment report, issued over the past year.

The first of the new studies is UNEP's Emissions Gap Report for 2014, an annual exercise in which the UN agency assesses the pledges of the world's nations, and calculates how short they fall of what's needed to keep warming to 2 degrees Celsius.

The World Bank's contribution, its third in a series it calls Turn Down the Heat, warns that warming of at least 1.5 degrees Celsius is already "locked in," and that we are approaching "4°C—a frightening world of increased risks and global instability."

Finally, there's the Deep Decarbonization project's report on possibilities for dramatic action in the United States to stay within the carbon budget endorsed by scientists. Its main finding is that there are feasible pathways for the U.S. to achieve an 80 percent reduction in its greenhouse gas emissions by 2050, using technologies that are already, or nearly, at hand.

An Abrupt Course

The UNEP Gap Report comes out each year to track some nations' increasing ambition for controlling climate change. All countries are supposed to commit to targets early next year, after the Lima climate talks this December as part of the pell-mell race toward a Paris treaty.

Given the scientific conclusion that the whole world can only emit about a billion tons more carbon dioxide to stay within the 2-degree budget, the gap report concludes that zero net carbon emissions must be achieved some time between 2055 and 2070. (Total greenhouse gas emissions, including pollutants other than CO2, must then fall to zero between 2080 and 2100.)

This represents an abrupt turn of course. By 2030 emissions will have to have "already turned the corner," and be 10 percent or so below where they were in 2010. By 2050, they would have to fall by 55 percent.

The problem is that as things stand, greenhouse gas emissions "will increase hugely up to at least 2050."

In other words, despite pledges of action to date, the gap between what's needed and what nations have promised "is not becoming smaller." By 2030, the gap will reach "about 14-17 [gigatons] CO2e, but can be closed if the available global emissions reduction potential is exploited."

This year's gap report identifies energy efficiency as one key to closing the gap, but the answer is probably much more complicated than that.

'Unavoidable' Warming

The consequences of not closing the gap are laid out in the second report, prepared by the Potsdam Institute for Climate Impact Research and Climate Analysis for the World Bank.

It emphasized that "climate change impacts such as extreme heat events may now be unavoidable."

"As the planet warms, climatic conditions, heat and other weather extremes which occur once in hundreds of years, if ever, and considered highly unusual or unprecedented today would become the 'new climate normal,'" it said.

The World Bank, as a leading development agency, found the prospects especially troubling for poor nations: declining crop yields, water shortages, the spread of disease, coastal flooding.

"Ending poverty, increasing global prosperity and reducing global inequality, already difficult, will be much harder with 2°C warming, but at 4°C there is serious doubt whether these goals can be achieved at all," it said. And without swift action, the hotter climate is coming in the next century.

The report, which looked closely at several world regions, broke down its dire warnings for each:

In Latin America and the Caribbean, extreme heat and changing rain patterns would wreak havoc on agriculture and biodiversity. Two degree warming could cut Brazil's soybean yields 70 percent and wheat 50 percent.

In the Middle East and North Africa, yields could decrease by up to 30 percent at 1.5–2 degrees Celsius warming and by almost 60 percent at 3-4 degrees Celsius.

In northern Russia, "forest dieback and thawing of permafrost threaten to amplify global warming as stored carbon and methane are released into the atmosphere, giving rise to a self-amplifying feedback loop," the report said.

We Have the Know-How

The third report looked closely at the contribution the United States would have to make to reduce carbon emissions steeply, as President Obama said it would do in the coming decades.

Entitled Pathways to Deep Decarbonization in the United States, it was published by Energy and Environmental Economics in collaboration with the Lawrence Berkeley National Laboratory and the Pacific Northwest National Laboratory.

The goal it examined—a reduction of greenhouse gas emissions by 80 percent below 1990 levels by the year 2000—would be in line with global warming of no more than 2 degrees, but would require nothing less than a "transformation of the U.S. energy system."

Not only is that "technically feasible," the report found, but there are many roads to this Nirvana: "Redundant technology pathways to deep decarbonization exist."

The added cost to the nation's energy system might amount to about 1 percent of gross domestic product, the study found. However, there's a lot of uncertainty in this prediction, since it's hard to forecast the pace of innovation decades down the road, and other changes in energy markets.

Not only would it entail a wholesale switch to electricity from fossil fuels for heat and transportation, but electric supplies would have to convert almost entirely to carbon-free fuel sources. These might include renewable energy, nuclear, or the capture and sequestration of carbon dioxide from the use of coal.

Obama's commitment, in a joint announcement with China, that the U.S. would cut greenhouse gas pollution by 26 to 28 percent below 2005 levels by 2025 "is consistent with the results of this report," it said.

So is the proposed regulation of new fossil-fuel electric plants that would essentially require carbon capture and sequestration on any new coal plant.

The bottom line: "This study did not find any major technical or economic barriers to maintaining the U.S. long term commitment to reducing greenhouse gas emissions consistent with limiting global warming to less than 2 degrees Celsius."

Indeed, the breadth of the revolution is not an obstacle, but implies "significant opportunities for technology innovation and investment in all areas of the U.S. energy economy."