(CNN) -- It's hot out there. But this time, it's more than idle watercooler talk, according to weather scientists.
At the same time the National Oceanic and Atmospheric Administration's National Climatic Data Center has released a report noting that this spring in the United States has been the warmest since record-keeping began in 1895, a group of scientists has published a paper in the journal Nature warning that the planet is approaching a critical tipping point because of climate and other factors.
Rampant population growth and changes to the environment caused by humans, including the burning of fossil fuels and the conversion of nearly 43% of the planet's land to farms or cities, threaten to cause an abrupt and unpredictable shift in the global ecosystem, 22 scientists from five countries said in their paper.
In its report issued Thursday, the climate data center said the average U.S. temperature between March and May was 57.1 degrees, 5.2 degrees above the long-term average from 1901 to 2000.
While May was only the second-warmest on record, it was still in the top third for monthly average temperatures, marking 12 consecutive months with temperatures in that range, said Jake Crouch, a NOAA climate scientist.
"For that to happen 12 times in a row in a random circumstance is one in 540,000," he said.
Globally, NOAA reported in May that the average temperature in April was 1.17 degrees warmer than the average from the past century, making it the fifth-warmest April since at least 1880.
It was the 326th consecutive month that global temperatures exceeded the 20th-century average, NOAA said.
The warm spring weather in the United States was partially the result of the waning La Niña, a pattern of below-average sea surface temperatures in the central Pacific that tends to help direct the high-level jet stream and influence weather patterns nationwide.
But it was also partially the result of long-term climate change, Crouch said.
"The pattern we've been in for the last 12 months is exactly what we would expect in climate change," he said.
The notion of long-term climate change -- particularly as caused by humans -- is politically controversial but generally accepted as fact by most scientists.
The Nature article, also published Thursday, said that such shifts in weather patterns and human-induced changes could have sudden and unpredictable effects on the global ecosystem, including the collapse of food supplies and other problems.
It warned that "widespread social unrest, economic instability and loss of human life could result."
The paper calls for improvements in efforts to detect critical changes in the ecosystem, as well as reduced global population growth and energy use and other measures.
A shift in the biosphere is possible by 2100 if nothing is done to better predict changes and act upon them, said Anthony D. Barnosky, professor of integrative biology at the University of California, Berkeley and lead author on the Nature article.
"If we do nothing, I personally think we hit this tipping point," Barnosky said Friday. "It means the world will be very different, losing biodiversity and (affecting where) species live in particular places."
The scientists are concerned that the biosphere has seen dramatic changes since the last Ice Age, factoring in the climate and a huge increase in global population. The current population of 7 billion is expected to increase to 9 billion within three decades.
"People have become a geological force in their own right, and we are changing the planet in ways every bit as dramatic as major geological events," Barnosky said. "We are becoming much more dominant organisms in Earth by our sheer numbers and the way we use natural resources."
Barnosky said the NOAA report buttresses his group's findings on global temperatures. The mean temperature by 2070, perhaps earlier, will be higher than it has been since the human species evolved, according to the Nature article.
When it comes to policy, Barnosky suggests that countries look at new and clean energy technologies as the world's petroleum supply draws down. Also crucial are food production and distribution, with an eye toward not letting the percentage of land disturbance worldwide -- currently 43% -- surpass 50%. The loss of rain forests, he said, is a reminder of the loss of biodiversity as humans try to meet their needs.
Nations are at a crossroads "where if we recognize these major ways we are changing the planet and actively guide how we are making those changes, we can move our biosphere in directions we want it to," Barnosky said.
"I see people are clever and resourceful when they realized there is a major global problem," he said. "My fear is that we keep our heads in the sand and we don't recognize these things going around us until it is too late."