Global Warming Did Not Stop Recently

Global Warming Did Not Stop Recently

The main text presented some of the evidence that temperature is rising. But, the climate is influenced by the 11-year sunspot cycle, the occasional sun-blocking influence of particles from big volcanic eruptions, and also by the sloshing of water in the tropical Pacific Ocean associated with El Nino and La Nina-when the hot waters spread along the equator in an El Nino event, some heat moves from the ocean to the air, and when the cold waters of La Nina follow, heat flows back into the ocean. An extra El Nino, or an extra-strong one, in a decade can make global warming look very fast, whereas an extra La Nina can temporarily slow the upward march of temperature from the rising CO₂. This sort of sloshing cannot ultimately change the warming of the planet, but can make it appear more variable, and control whether the air warms fast and the ocean much slower, or whether faster warming of the ocean slows the atmospheric warming a bit.

Think for a minute about a neighbor taking a very active dog for a walk. Watch the person, and you can see steady progress down the street. Watch the dog, and you may have to study carefully for a while to even know which way they are going. You may find it useful to think of the year-to-year temperature changes as the dog, and the average behavior as the person.

Animated gif demonstrating trends.

Click for a text description of Global mean temp Celsius vs year graph.

This animated GIF displays a graph of global mean temperature (°C) over time from 1960 to 2010, with temperature fluctuations shown in red. The x-axis represents the years, while the y-axis represents global mean temperature in degrees Celsius, ranging from 14°C to 15.5°C.

Frame 1 (Early 1960s to 1970s)

• The graph initially shows data only from the 1960s to late 1970s.
• The red temperature line fluctuates, but appears to decline slightly.
• A black trend line slopes downward, suggesting cooling.
• Text displayed: "Dr. Alley was born in 1957, at the start of cooling?"

Frame 2 (Extending into the 1980s)

• The graph expands, now including temperature data up to the early 1980s.
• The red line still fluctuates, but some warmer years start appearing.
• The black trend line slightly flattens, though cooling is still implied.
• Text changes to: "Oh wait... we forgot some data."

Frame 3 (More 1980s Data Appears)

• Additional data from the mid-to-late 1980s appears.
• The red temperature line rises more visibly.
• The black trend line flattens further, reducing the cooling trend.
• Text now reads: "Oops... forgot some more data."

Frame 4 (1990s Data Added)

• The timeline now extends through the 1990s<.
• The red temperature line shows a noticeable warming trend.
• The black trend line is nearly flat.
• Text changes again to: "Hmmm... looks like it's getting warmer."

Frame 5 (Early 2000s Data Appears)

• Data from the early 2000s appears, reinforcing warming.
• The red temperature line climbs further, surpassing earlier fluctuations.
• The black trend line now slopes slightly upward.
• Text now reads: "Maybe the cooling was just a fluke?"

Frame 6 (Late 2000s Data Added)

• The graph extends into the late 2000s.
• The red temperature line is now clearly trending upward, confirming warming.
• The black trend line now visibly slopes upward.
• Text changes to: "Yeah, definitely a fluke."

Frame 7 (Final Frame - Full Data to 2010)

• The graph completes the dataset, extending into 2010.
• The red temperature line reaches its highest points, solidifying the warming trend.
• The black trend line fully reverses, now clearly showing long-term warming.
• Final text displayed: "Never mind!

Credit: Richard B. Alley @ Penn State is licensed by CC-BY-NC-4.0

Next, take a look at the figures, which highlight events from Dr. Alley’s career. In each case, the jagged red line connects the temperatures from year to year, using data from NASA’s Goddard Institute for Space Studies, and the smoother black line is the best fit to the data over the interval selected. You will see that in each case, Dr. Alley has carefully picked the end points so that the best-fit line slopes downward, indicating a cooling trend. For the last 20 years, Dr. Alley has met important people in Washington, DC who declared that global warming stopped. It is very easy to do so; be quiet during a year with strong warming, and then the next year go back to claiming that global warming stopped.

Over a century ago, the Guinness brewery in Ireland hired an Oxford mathematician, W.S. Gosset, to develop ways to separate actual trends from short-term variability. The techniques were published with a pseudonym (A. Student), presumably to help people without telling competitors how valuable it was for a business to avoid self-delusion. If you apply techniques derived from that research, global warming has not stopped; all time intervals long enough to show a statistically significant trend do show warming.

By 2016, the temperature had risen enough that it barely fit in the chart above, aided by the ongoing human warming and by a strong El Nino event. This strong El Nino was warmer than the previous one, which was warmer than earlier ones, mostly because of human CO2. But, temperature was dropping a bit in late 2016 as the El Nino faded. And, some inaccurate voices were already, again, declaring that global warming had stopped.