NASA has announced that 2023 will be the hottest year on record, based on an analysis of annual global average temperatures by the Goddard Institute for Space Studies. Temperature records begin in 1880, and the scientists responsible for maintaining them calculate global temperature anomalies each year to determine how much the temperature has changed compared with temperatures from 1951 to 1980.
What makes this year so hot? Here's a breakdown of the main factors scientists consider.
Each month from June to December 2023 will be the hottest on record. July is the hottest month on record. But what makes 2023, especially the second half of the year, so hot? Scientists have asked themselves this question, too. Here are the main factors scientists believe could explain the record-breaking heat.
Long-term increases in greenhouse gases are the main driver.
For more than 100 years, humans have been burning fossil fuels like coal, natural gas, and oil to power everything from lightbulbs and cars to factories and cities. These behaviors, along with changes in land use, lead to an increase in greenhouse gases in the atmosphere. Greenhouse gases act like a blanket, trapping heat around the Earth. The more greenhouse gases are added, the thicker the blanket becomes and the planet will heat up further.
In May 2023, atmospheric carbon dioxide concentrations peaked at 424 parts per million at the National Oceanic and Atmospheric Administration's Mauna Loa Observatory in Hawaii. This annual peak has been rising steadily since measurements began in 1958. (Other global carbon measurement projects have shown similarly high values.) Carbon dioxide concentrations are at their highest levels in at least 800,000 years, according to ice core records.
"We're going to continue to have records being broken because baseline temperatures have been rising," said Gavin Schmidt, director of NASA's Goddard Institute for Space Studies in New York. "Over the past 50 or 60 years, much of this warming trend has been caused by our changes to greenhouse gases, particularly carbon dioxide and methane."
The return of El Niño is making the weather even hotter.
In addition to the long-term global warming trend, there are also natural changes in climate. One of the largest sources of this year-to-year variability is the El Niño Southern Oscillation (ENSO) that occurs in the tropical Pacific.
The El Niño/Southern Oscillation transitions between three phases: El Niño, La Niña, and neutral or average.
During El Niño, the trade winds weaken; that is, the winds that normally blow from east to west in the tropical Pacific weaken. The sea surface will also be hotter (higher) than normal in the central Pacific Ocean near South America and near the eastern equator. El Niño events tend to coincide with the years with the highest average global temperatures.
During La Niña, the opposite happens: Trade winds strengthen and sea surface temperatures in the eastern Pacific are cooler than normal. This helps offset some of the rising temperatures caused by long-term global warming.
From 2020 to 2022, the Pacific Ocean has experienced a La Niña phenomenon for three consecutive years. Subsequently, the El Niño phenomenon will return starting in May 2023. This El Niño has not yet been as strong as the 2015-2016 or 1997-1998 El Niño events, both of which caused significant spikes in global average temperatures. However, if you add this ocean warming to the long-term warming trend caused by greenhouse gases, the occurrence of El Niño is enough to help temperatures soar and set new high-temperature records.
"For the most part, it's a problem between us and El Niño," said Josh Willis, a climate scientist at NASA's Jet Propulsion Laboratory. "At the end of the day, humans are heating the planet, and El Niño is dancing on our heads."
Globally, long-term ocean warming and above-normal sea surface temperatures also play a role.
From a broader perspective, the tropical Pacific isn't the only area of water experiencing warmer-than-normal temperatures this year. Global sea surface temperatures set new records in 2023, and the North Atlantic and other seas experienced several marine heat waves.
"Like global temperatures, ocean temperatures are rising," Willis said. "Ocean temperatures have been rising for more than a century and they're not slowing down. If anything, they're accelerating."
What's behind rising ocean temperatures? Greenhouse gases warm the earth. About 90% of the heat generated by greenhouse gas warming is absorbed by the ocean. This means that as greenhouse gases continue to increase, ocean temperatures will rise as well, leading to higher global temperatures.
Aerosols are declining and therefore no longer slow the rise in temperatures.Another global trend that scientists are monitoring is changes in aerosols in the atmosphere. Aerosols are small particles in the air such as smoke, dust, volcanic gases, sea fog, air pollution or soot that can affect climate. Particles in the air can reflect sunlight, cooling the air slightly, or absorb sunlight, warming the air slightly.
As governments pass regulations to reduce air pollution and improve air quality, aerosol amounts are declining in most areas. Many of these human-generated particles are of the type that cool the climate slightly, so fewer particles in the air will have a slight warming effect. However, this effect is very small compared to the greater warming caused by increased greenhouse gases.
NASA and scientists around the world are studying how new shipping regulations that reduce aerosols might change the amount of solar energy reflected back into space. While these changes may be noticeable on a regional scale, the global impact is likely to be small, Schmidt said.
Scientists have found that the eruption of the Hungatonga-Hungahapai volcano did not significantly add to the record heat.
In January 2022, the Hunga Tonga-Hunga Apai submarine volcano erupted, ejecting an unprecedented large amount of water vapor and particles, known as aerosols, into the stratosphere. Water vapor is a greenhouse gas that has a warming effect on the atmosphere, so scientists study the impact of volcanic eruptions on global temperatures. On the other hand, sulfate aerosols produced by volcanic eruptions sometimes contribute to some global cooling events.
The January 15, 2022 eruption of the Hunga Tonga-Hunga Haʻapai volcano, recorded by NOAA's GOES-17 weather satellite. Source: Simon Proud and Simeon Schmauß/Oxford University, RAL Space CEO/NOAA
A recent study found that volcanic sulfate aerosols reflect away some sunlight from the Earth's surface, causing temperatures in the Southern Hemisphere to drop slightly after volcanic eruptions, by less than 0.1 degrees. Basically, the warming caused by the increase in water vapor in the stratosphere is offset by the cooling caused by volcanic sulfate aerosols, resulting in a slight cooling in the lower atmosphere. This means that the volcanic eruption likely did not add to the record heat in 2023.
"We're very interested in weather and weather extremes in any given year because those are the factors that influence us," Schmidt said. "But the main difference between this decade and the previous one is that temperatures continue to rise due to our activities, primarily the burning of fossil fuels." "
Compiled source: ScitechDaily