AP/Nick Ut Heat. It's here, and it's staying. Collectively, the past six months have been the hottest since humans started keeping track of global temperatures.

Last month was the warmest September humans have recorded, according to both NASA's Global Land-Ocean Temperature Index and the National Oceanic and Atmospheric Administration's National Climatic Data Center.

September came at the end of a record-breaking six months: April, May, June, and August of this year were all also the warmest on record, and July came in at fourth hottest.

According to Eric Holthaus at Slate:

Recent research shows the current warm stretch is probably the planet's warmest in at least 4,000 years. That means global temperatures may have already passed a level that human civilization has never experienced. The sheer size and depth of the world's oceans means that most of global warming's extra heat has been stored there. For the last decade or so, atmospheric warming has been playing catch up.

That means things will just keep getting warmer — and humans are doing a poor job of slowing things down. At the 2009 UN Framework Convention on Climate Change, world leaders agreed to take measures to keep global temperatures from rising more than 2 degrees Celsius (3.6 degrees Fahrenheit) above their historical levels.

Beyond that point, many experts agree that the world could see a disastrous series of climate change effects, including widespread floods, fires, storms, famines, and extinctions. Unfortunately, recent reports suggest that we're on track to miss our target by a good 2 C before the end of the century.

NASA's map below shows the difference in temperature between September 2014 and the average temperature from 1951 and 1980.

View photos NASA_September_1 More

NASA You can see that the heat is affecting some parts of the world more strongly than others. Some areas are even "abnormally cold." Temperatures can fluctuate around the world, depending on weather patterns – for instance, in August, parts of the US saw temperatures below the baseline average, and in September the entire country was at or above the baseline. But the important takeaway is that there is a general pattern of warming temperatures across the globe.

The differences becoming greater as the colors move from yellow to orange to red. Some of the greatest temperature differences were seen in the Arctic and Antarctic regions.

The NOAA chart below shows temperature anomalies between the April-to-September months and the 20th century average every year since 1880. You can see below that 2014 deviates most from the average, and is a part of a much bigger trend of increasing temperature anomalies.

View photos Global_Temperature_1 More

NOAA National Climatic Data Center September was also noteworthy for the flurry of climate change activism it saw around the world, including the People's Climate March in New York City, which spawned similar demonstrations around the world and at the UN 2014 Climate Summit, during which world leaders gathered to discuss their strategies for reducing carbon emissions and slowing down climate change.

September was also marked by a spree of climate-related events, including widespread drought in the western US and intense flooding in India.



NOW WATCH: Researchers Just Discovered 18 Mysterious Viruses In NYC's Rat Population







More From Business Insider

