Hottest year on record an ‘unmistakable sign’ of human impact on environment

Much of the grass on Boston Common has been parched this summer amid high temperatures and a drought.John Tlumacki/Globe Staff/Globe Staff

In the 136 years scientists have been tracking global temperatures, there has never been a warmer month than this July, according a new NASA report.

It was the 10th consecutive month of record warmth, making it likely that 2016 will be the hottest year ever recorded — breaking records set the two previous years.

Climate specialists said the striking pattern is an unmistakable sign of manmade global warming and called for action to reduce greenhouse gases.

“Statistics, like all these breaking records, tell us that real change is already happening, and ultimately, it poses serious risks to us and our descendants,” said Kerry Emanuel, a professor of atmospheric science at MIT. “I wonder how many more records we have to break before we all realize how important it is to act.”

Two years ago, a report by the federal government called the National Climate Assessment found that the Northeast was already seeing the impact of climate change, from prolonged heat waves to torrential rains and increased flooding. The report attributed the impact to the burning of fossil fuels and other human activity.

It found that over the past century, average temperatures in the Northeast have risen by 2 degrees, while the region’s precipitation has climbed by more than 10 percent. The worst storms now bring far more precipitation than before.

Reto A. Ruedy, a project manager at NASA’s Goddard Institute for Space Studies who oversaw the analysis of the recent findings, said warming is primarily due to the burning of fossil fuels and the rising amount of heat-trapping carbon dioxide in the atmosphere.

“If we want to have a planet that looks similar to what we have now, one as habitable for humankind and animals as it has been for the past thousands of years, we better change our ways and stop building up CO2 concentration in the atmosphere,” he said.

This year has a 99 percent chance of being the warmest on record, said Gavin Schmidt, another climate scientist at the Goddard Institute.

Efforts to curb rising temperatures, including the historic agreement last year in Paris that requires carbon emission reductions, may help the planet avert worst-case scenarios.

But many effects of warming temperatures, such as rising sea levels, more powerful storms, and more species dying off, are already happening and will continue as the existing concentrations of carbon remain in the atmosphere, scientists say.

NASA’s report found that July was 1.51 degrees Fahrenheit warmer than the global average from 1950 to 1980, and about .18 degrees warmer than the previous records, set in July 2011 and July 2015.

July’s record temperatures were also the result of a lingering El Niño, a natural warming of portions of the Pacific Ocean that can change weather patterns elsewhere on the planet.

Scientists say the record temperatures should serve as a clarion call for the public to recognize climate change and elect leaders to address it.

“If you don’t accept the science, you can’t come up with a plan about how to address the problem,” said Raymond S. Bradley, head of the Climate System Research Center at the University of Massachusetts.

In Boston, the consequences of climate change could be calamitous. A report released by the city this year found that sea levels could rise more than 10 feet by the end of the century, plunging about 30 percent of Boston under water. If high levels of greenhouse gases continue to be released into the atmosphere, the seas could rise as much as 37 feet by 2200.

Richard Primack, a biology professor at Boston University, said climate change has altered everything from where and when flowers and plants grow to how birds migrate and when insects are born.

“There are huge consequences for us as the climate changes,” he said. “Even if it gets just a little warmer and dryer in some places, agricultural systems around the world could collapse.”