Earth Hits 400 Straight Months of Hot

Ahira Sanchez-Lugo is a scientist at NOAA's National Centers for Environmental Information. Part of her job is to put climate data from the 21st century into historical perspective. She's also interested in the ways that climate and weather patterns have affected human societies.

NOAA publishes monthly Global Climate Reports — the most recent of which was about the trends and temperatures observed in April 2018. To make sense of these findings, we've got to understand the frame of reference. What exactly do climatologists mean when they say that a given month is higher or lower than "average?"

In an email, Sanchez-Lugo says "Higher than average means that the observed temperature ... was warmer than the reference temperature (typically computed by averaging 30 years of temperature data)." She then provided us with a helpful hypothetical. "For example, if the observed temperature for April 2018 was 72 degrees Fahrenheit [22.2 degrees Celsius], but the 30-year average April reference temperature for the place of interest was 60 degrees Fahrenheit [15.5 degrees Celsius], we would say that the April 2018 temperature was higher than average."

Please note — once again — that the temperatures mentioned above are purely hypothetical. Now let's dive into the real data, shall we?

The reference temperature used in the new NOAA report is 13.7 degrees Celsius, or 56.7 degrees Fahrenheit. That was the average April surface temperature on Earth during the 20th century. By comparison, the average recorded surface temperature in April 2018 was 0.83 degrees Celsius (1.49 degrees Fahrenheit) warmer.

That makes April 2018 the 400th month in a row to exceed the 20th century's global averages. (Likewise, March 2018 was hotter than the average 20th-century March; February 2018 was hotter than the average 20th-century February, and so on.) The streak goes all the way back to January 1985 — when Madonna's "Like A Virgin" topped the Billboard Charts and Ronald Reagan was being sworn in for his second term as president.

Imagine for a moment that humanity didn't exist and, as a consequence, no one was around to burn fossil fuels en masse. In our absence, would Earth still be going through this prolonged period of warmth?

The evidence says "no." True, there are natural forces that can prompt rises or falls in the global temperature. An example of this would be El Niño, long stretches of unusually warm water temperatures in the eastern and central Pacific that arise every two to seven years. El Niño is part of a cycle called the El Niño Southern Oscillation (or ENSO). Another phase of this is La Niña, a cold spell that grips these same Pacific waters periodically.

Due partly to the vastness of the Pacific, El Niño and La Niña years have a measurable influence on the planet's overall climate. The global surface temperature tends to rise while during El Niño and tend to drop during La Niña — something you can clearly observe in this handy graph from NOAA.

This pattern is still going on, but the goal posts have shifted. The aforementioned graph shows that from 1980 to 2017, surface temperatures climbed overall — despite the expected fluctuations induced by El Niño and La Niña. For instance, even though March 2017 was not part of an El Niño period, its average surface temperature was still higher than usual.

NOAA's Sanchez-Lugo tells us that "if we were to remove the human factor," there would still be global temperature variations in accordance with the ENSO cycle. On the other hand, the "upward trend" documented in the graph would not exist. Natural processes alone can't explain the rapidly-climbing temperatures we now face. Mankind bears most of the responsibility for those.

April 2018 was a punishing month for much of the world's population. The temperature in Nakwabash, Pakistan peaked at 122.4 degrees Fahrenheit (50.2 degrees Celsius), which could be the hottest April temp that's ever been recorded anywhere on Earth. Atypical heat was a common refrain in Europe and South America: Poland, Germany and Argentina also had their hottest Aprils on record in 2018.

"With a warmer climate, droughts and heat waves are expected to occur more frequently and [become] more intense, potentially affecting our health, agriculture, water quality and availability, etc.," writes Sanchez-Lugo. She adds that overheating is just one of the medical problems associated with rising temperatures. "You can have an increase in water-borne diseases due to flooding because of extreme precipitation." Furthermore, "air quality can be affected [by] increased wildfires due to extreme heat and dry conditions." The World Health Organization echoes her concerns. By their estimates, the 2030s and 2040s will see 250,000 climate change-related deaths per year.