Americans have just endured one of the coldest winters in memory, so global warming may not be on their radar. But a new U.N. panel report has just refocused the public debate on a problem some scientists call the greatest threat facing the world.

There is trouble ahead for global agriculture, warns the influential Intergovernmental Panel on Climate Change, if measures are not taken quickly to reduce greenhouse gas emissions. The panel, which synthesizes the findings of thousands of peer-reviewed studies every seven years, has issued a report card on the state of the planet.

The report card serves as a guide to policymakers and a basis for international deliberations, including the summit on global warming and greenhouse gas emissions scheduled to be held in Paris next year. The report will be officially released on Sunday in Yokohama, Japan, but an advance copy has been leaked.

This IPCC report predicts that by the end of the century, “hundreds of millions of people will be affected by coastal flooding and displaced due to land loss,” the majority living in island nations and in southern Asia.

The report goes on to link food price increases (like the 2010 spike in wheat prices that helped spark the Arab Spring) to climate change-related droughts and floods. It forecasts that prices will continue to rise as grain yields decline by as much as 2 percent per decade for the rest of the century, while demand is projected to rise by 14 percent per decade through 2050.

Food shortages are predicted to be the new normal in vulnerable areas, according to the IPCC. Africa and Asia will be the principal losers. Monsoon rain patterns are already being disrupted on both continents and desertification is spreading in semi-arid regions of western India and China as well as north and east Africa. River basins like the Mekong, the Yangtze, the Ganges and the Brahmaputra will see larger and more frequent floods in the years ahead, followed by permanent drying trend as the Himalayan glaciers gradually melt.

The biggest news from this report, however, may be the anticipated price tag for climate change. Even a relatively modest temperature rise of 2.5 degrees Celsuis (6.25 degrees Fahrenheit), scientists say, would reduce global economic output by more than 2 percent (roughly $1.4 trillion annually).

The cost of climate change includes higher food prices, increased healthcare spending, natural disasters like hurricanes, droughts and floods, the depletion of surface and groundwater and land loss due to the inundation of coastal areas from sea-level rise.

The first installment of the three-part IPCC document, released in September, projected — rather conservatively, according to many experts — a possible 4 degrees Celsius (10 degrees Farhrenheit) rise in global temperatures (temperatures have already risen by about 0.8 degrees Celsius [2 degrees Fahrenheit]) and up to a three-foot rise in sea levels by the end of the century. Yet even these arguably lowball numbers attracted the fire of climate skeptics, who pointed to lower-than-expected global temperature increases over the past decade as evidence that global warming has “stalled.”

Today’s assessment will likely also spark controversy from both those who think it goes too far, and others who believe that it does not go far enough. The latter was the focus of a study earlier this month. A coalition of environmental groups argued that projections of the economic cost, like this IPCC report, routinely leave out many of the harder-to-quantify damages that are brought on by political unrest and the destruction of ecosystems.

These reports also fail to take into account what would happen if certain tipping points are crossed, which could potentially send the earth’s climate system into a tailspin.

For example, if the permafrost thaws, as it has already begun to do in parts of the Arctic, and releases vast amounts of trapped methane gas, a greenhouse gas 20 times as potent as CO2, the resulting temperature rise might soar off the current charts.

This uncertainty over methane gas underscores the difficulties that scientists face in devising reliable projections. This is particularly true when it comes to predicting regional climate shifts. Computer models sometimes arrive at strikingly different conclusions about how local weather patterns will change — hardly surprising given that the climate system is an immensely complex and interactive system.

In some cases, the best guide for what will happen is what is already taking place. On a recent trip to East Africa, I asked farmers how things have changed for them. They consistently told the same story: less predictable seasonal rains, maize crops withering and wells and rivers drying up. They are increasingly apprehensive about the future, as I report in Foreign Policy.

Not every place will be negatively affected, though. In the northern United States, including the upper Midwest, growing seasons are getting longer. Over the past century, they have increased by almost three weeks in North Dakota, where farmer John Nowatzki, whose family has grown cold-tolerant grains like wheat and barley for more than a hundred years, now plants warm-season crops like corn and soybeans.

In the Finger Lakes region of upstate New York, the sun-dependent wine business has been booming. Peach orchards are spreading north into lands that used to be too cold to grow the fruit.

On the other side of the continent, by contrast, California’s almonds, cherries and apricots are not getting enough critical winter-chill time for the trees to properly flower and fruit. Southern California is suffering from an historic drought. Parts of Texas are becoming too dry to cultivate and reverting to rangeland for grazing cattle.

As a rough rule of thumb, climate change will be a boon in some temperate areas, where production is more limited by cold than by heat. Warmer regions are another story, however.

“You can’t grow crops in a blast furnace,” said Bruce McCarl, a professor of agricultural economics at Texas A&M University and co-author of the current IPCC report. A blast furnace is precisely what large parts of the U.S. Southwest have become in recent summers, as successive droughts and record-breaking heat waves have scorched the region.

Though the IPPC report acknowledges the winners and losers, it insists that the damage from climate change will far outweigh the benefits. Yet McCarl, in an email interview, manages to be guardedly optimistic. “Climate change is inevitable,” he said, “and agriculture must adapt by changing planting dates, varieties, harvest dates, crop mix, livestock mix among other means.”

McCarl says that adaptation will be difficult in many parts of the globe. Like Mali, for example, where temperatures are increasing and precipitation is decreasing. He argues in his study on the West African nation that more must be done to develop heat-resistant grain varieties and more money must be spent on outreach programs that train farmers for the rigors of climate change.

The challenge for Mali and the world is to find new ways to grow the food that we need on a rapidly transforming planet. “The heat is on,” said U.N. Secretary-General Ban Ki-moon when he launched the first installment of the IPCC report in September. “Now we must act.”

The question remains whether the world will act in time.

PHOTO (TOP): A stream of water trickles on the bottom of the Almaden Reservoir near San Jose, California, January 21, 2014. REUTERS/Robert Galbraith

PHOTO (INSERT 1): A parched field that has yet to be planted is seen at a farm near Cantua Creek, California, February 14, 2014. REUTERS/Robert Galbraith

PHOTO (INSERT 3): Trees emerge from the flooded Missouri River as seen from the Council Bluffs, Iowa, side of the Bob Kerrey Pedestrian Bridge, June 21, 2011. Downtown Omaha, Nebraska, is in the background. REUTERS/Lane Hickenbottom