2020 tied with 2016 for the hottest year on record according to a press release from the NASA Goddard Institute for Space Studies.

2019 was the second hottest year on record, and the 2010s was the hottest decade ever. But what does a hotter planet mean, and how do scientists actually know that things are heating up?

“So the trend that we’re on is up,” said director of NASA’s Goddard Institute for Space Studies, Gavin Schmidt, in an interview with WAMC Northeast Public Radio, “The last seven years have been the seven warmest years, we’ve warmed about two degrees Fahrenheit a little bit more than that, since the late 19th century.”

To estimate global temperatures, NASA uses the GISS temperature analysis methods, also known as GISTEMP. The analysis began in the late 1970s under the direction of Dr. James Hansen, whose 1988 congressional testimony brought increased public awareness to the greenhouse effect. Hansen and other GISS scientists were becoming concerned about the effects of greenhouse gasses on the surface temperatures of the earth and sought to measure these effects.

In the early years, the analysis was relatively basic compared to the more advanced methods used today. Before NASA’s development of GISTEMP, estimates were largely based on the Northern Hemisphere, not digitized and not well adjusted for temperature anomalies. Since then, there have been improvements in the amount of data and the methods to accurately understand how global temperatures are changing.

NASA’s data collection includes large networks of meteorological stations, measurements from Antarctic research stations and sea surface temperatures, which are collected through the use of satellites and calibrated through the use of ships and buoys. These measurements are updated monthly, and are part of NASA’s established method which seeks to understand the surface temperature from across the earth.

According to a research article published in 2019 by Schmidt, Hansen and other scientists, the method for estimating global temperature begins with dividing the earth into 80 equal boxes arranged in bands of constant latitude. The bands are divided along polar regions, mid-latitudes, subtropics and tropics to provide a global scope to these measurements. These bands are then divided into 100 equal area sub-boxes to produce a globe broken down into 8,000 boxes.

The article outlines the method of combining thousands of measurements. Within each sub-box all measurement stations are combined into a mathematical formula which takes into account the distance from the center of the sub-box and the amount of time that station has been measuring temperatures. Then the values of the sub-boxes are averaged across the 80 bands of constant latitude, corrected for anomalies and reported.

This raw data undergoes several adjustments to correct for temperature anomalies, local warming associated with urban areas and how to properly combine the thousands of reported temperatures.

Like any estimate, the GISTEMP comes with a level of uncertainty, but it has been greatly reduced in the past couple of decades along with improved measurement methods and increased amounts of temperature measurement stations.

The research article notes that the GISTEMP estimate is similar in magnitude to estimates produced by other organizations that measure global temperatures. The National Oceanic and Atmospheric Administration’s report placed 2020 behind 2016 — instead of tied with — but the estimates were very close and different due to differences in methodology.

“Whether one year is a record or not is not really that important — the important things are long-term trends,” Schmidt said in an interview with The Mercury News.

Assistant Professor of  Environmental Science and Sustainability Matt Bethurem, who studies environmental policy, agreed.

“If (2020) had come in, say a little bit below 2016 that would still be way, way too hot for the planet,” Bethurem said, “I think the thing that I would encourage people to do is be a little bit less tied to this idea about like, ‘oh, which one is ranked number one, which one’s ranked number two,’ and recognize that all of the years now are way too hot compared to where we should be.”

“To be honest, (setting records has) kind of become the new normal,” said Ian Carbone, assistant professor of environmental science and sustainability, who works on solar power production and energy efficiency projects in Meadville.

Both Bethurem and Carbone share the view that rising global temperatures and record setting years are not a surprise, but they also find sources of positive news in the face of scientific reports that are discouraging.

Carbone finds hope for increased renewable energy production due to recent changes in the levelized cost of electricity, which is a measurement of how much a power plant costs over its lifetime divided by the total amount of energy produced by the plant.

“If you look at new plants that are coming online before 2025, the cheapest form of electricity we can build in the United States is solar energy, and the second cheapest form of electricity it is wind,” Carbone said. According to Carbone, the types of energy generation that are the worst polluters are becoming less economically viable.

“As far as I’m concerned we’ve had the technology to avoid climate change for decades now,” Carbone said. “What’s really slowed us down is not the technology or the science, it’s the social will and the priorities to implement those technologies and invest in them.”

Bethurem finds encouragement in the face of the long term trend of warming in the fact that he knows that we have the ability to make systemic changes.

“The thing that I’m always encouraged about — is that we could literally, today start the process of changing these systems that have put us in this bad position,” Bethurem said.

While Bethurem finds encouragement in the idea that we can start to make improvements immediately, he also feels a sense of urgency.

“We literally don’t have time to continue to wait at this point, we have to make changes. And that happens through enacting policy changes that are aimed at breaking down some of those systemic structures.” Bethurem said.

With 2020 capping off the hottest decade on record and the expectation that warming global temperatures is the new normal, Bethurem sees a way forward to be hopeful about.

“We’re not in a position where we have to hope and pray that some brilliant inventor out there comes up with some solution to this,” Bethurem said. “We have it, it’s right there on the table in front of us. We just have to have the willpower. And we have to have the sort of leadership on this to push those things into action,”