NASA analysis confirms 2023 as warmest year on record

Earth's average surface temperature in 2023 was the warmest on record, according to an analysis by NASA. Global temperatures last year were around 2.1 degrees Fahrenheit (1.2 degrees Celsius) above the average for NASA's baseline period (1951-1980), scientists from NASA's Goddard Institute for Space Studies (GISS) in New York reported.

"NASA and NOAA's global temperature report confirms what billions of people around the world experienced last year; we are facing a climate crisis," said NASA Administrator Bill Nelson. "From extreme heat, to wildfires, to rising sea levels, we can see our Earth is changing. There's still more work to be done, but President Biden and communities across America are taking more action than ever to reduce climate risks and help communities become more resilient -- and NASA will continue to use our vantage point of space to bring critical climate data back down to Earth that is understandable and accessible for all people. NASA and the Biden-Harris Administration are working to protect our home planet and its people, for this generation -- and the next."

In 2023, hundreds of millions of people around the world experienced extreme heat, and each month from June through December set a global record for the respective month. July was the hottest month ever recorded. Overall, Earth was about 2.5 degrees Fahrenheit (or about 1.4 degrees Celsius) warmer in 2023 than the late 19th-century average, when modern record-keeping began.

"The exceptional warming that we're experiencing is not something we've seen before in human history," said Gavin Schmidt, director of GISS. "It's driven primarily by our fossil fuel emissions, and we're seeing the impacts in heat waves, intense rainfall, and coastal flooding."

Though scientists have conclusive evidence that the planet's long-term warming trend is driven by human activity, they still examine other phenomena that can affect yearly or multi-year changes in climate such as El Niño, aerosols and pollution, and volcanic eruptions.

Typically, the largest source of year-to-year variability is the El Niño -- Southern Oscillation ocean climate pattern in the Pacific Ocean. The pattern has two phases -- El Niño and La Niña -- when sea surface temperatures along the equator switch between warmer, average, and cooler temperatures. From 2020-2022, the Pacific Ocean saw three consecutive La Niña events, which tend to cool global temperatures. In May 2023, the ocean transitioned from La Niña to El Niño, which often coincides with the hottest years on record.

However, the record temperatures in the second half of 2023 occurred before the peak of the current El Niño event. Scientists expect to see the biggest impacts of El Niño in February, March, and April.

Scientists have also investigated possible impacts from the January 2022 eruption of the Hunga Tonga-Hunga Ha'apai undersea volcano, which blasted water vapor and fine particles, or aerosols, into the stratosphere. A recent study found that the volcanic aerosols -- by reflecting sunlight away from Earth's surface -- led to an overall slight cooling of less than 0.2 degrees Fahrenheit (or about 0.1 degrees Celsius) in the Southern Hemisphere following the eruption.

"Even with occasional cooling factors like volcanoes or aerosols, we will continue to break records as long as greenhouse gas emissions keep going up," Schmidt said. "And, unfortunately, we just set a new record for greenhouse gas emissions again this past year."

"The record-setting year of 2023 underscores the significance of urgent and continued actions to address climate change," said NASA Deputy Administrator Pam Melroy. "Recent legislation has delivered the U.S. government's largest-ever climate investment, including billions to strengthen America's resilience to the increasing impacts of the climate crisis. As an agency focused on studying our changing climate, NASA's fleet of Earth observing satellites will continue to provide critical data of our home planet at scale to help all people make informed decisions."

Open Science in Action

NASA assembles its temperature record using surface air temperature data collected from tens of thousands of meteorological stations, as well as sea surface temperature data acquired by ship- and buoy-based instruments. This data is analyzed using methods that account for the varied spacing of temperature stations around the globe and for urban heating effects that could skew the calculations.

Independent analyses by NOAA and the Hadley Centre (part of the United Kingdom Met Office) concluded the global surface temperatures for 2023 were the highest since modern record-keeping began. These scientists use much of the same temperature data in their analyses but use different methodologies. Although rankings can differ slightly between the records, they are in broad agreement and show the same ongoing long-term warming in recent decades.

Building on a half century of research, observations, and models, the Biden-Harris Administration including NASA and several federal partners recently launched the U.S. Greenhouse Gas Center to make critical climate data readily available to decisionmakers and citizens. The center supports collaboration across U.S. government agencies and the non-profit and private sectors to make air-, ground-, and space-borne data and resources available online.

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Ozone hole continues shrinking in 2022, NASA and NOAA scientists say

The annual Antarctic ozone hole reached an average area of 8.9 million square miles (23.2 million square kilometers) between Sept. 7 and Oct. 13, 2022. This depleted area of the ozone layer over the South Pole was slightly smaller than last year and generally continued the overall shrinking trend of recent years.

"Over time, steady progress is being made, and the hole is getting smaller," said Paul Newman, chief scientist for Earth sciences at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "We see some wavering as weather changes and other factors make the numbers wiggle slightly from day to day and week to week. But overall, we see it decreasing through the past two decades. The elimination of ozone-depleting substances through the Montreal Protocol is shrinking the hole."

The ozone layer -- the portion of the stratosphere that protects our planet from the Sun's ultraviolet rays -- thins to form an "ozone hole" above the South Pole every September. Chemically active forms of chlorine and bromine in the atmosphere, derived from human-produced compounds, attach to high-altitude polar clouds each southern winter. The reactive chlorine and bromine then initiate ozone-destroying reactions as the Sun rises at the end of Antarctica's winter.

Researchers at NASA and NOAA detect and measure the growth and breakup of the ozone hole with instruments aboard the Aura, Suomi NPP, and NOAA-20 satellites. On Oct. 5, 2022, those satellites observed a single-day maximum ozone hole of 10.2 million square miles (26.4 million square kilometers), slightly larger than last year.

When the polar sun rises, NOAA scientists also make measurements with a Dobson Spectrophotometer, an optical instrument that records the total amount of ozone between the surface and the edge of space -- known as the total column ozone value. Globally, the total column average is about 300 Dobson Units. On Oct. 3, 2022, scientists recorded a lowest total-column ozone value of 101 Dobson Units over the South Pole. At that time, ozone was almost completely absent at altitudes between 8 and 13 miles (14 and 21 kilometers) -- a pattern very similar to last year.

Some scientists were concerned about potential stratospheric impacts from the January 2022 eruption of the Hunga Tonga-Hunga Ha'apai volcano. The 1991 Mount Pinatubo eruption released substantial amounts of sulfur dioxide that amplified ozone layer depletion. However, no direct impacts from Hunga Tonga have been detected in the Antarctic stratospheric data.

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Past eight years: Warmest since modern recordkeeping began

Earth's global average surface temperature in 2021 tied with 2018 as the sixth warmest on record, according to independent analyses done by NASA and the National Oceanic and Atmospheric Administration (NOAA).

Continuing the planet's long-term warming trend, global temperatures in 2021 were 1.5 degrees Fahrenheit (0.85 degrees Celsius) above the average for NASA's baseline period, according to scientists at NASA's Goddard Institute for Space Studies (GISS) in New York. NASA uses the period from 1951-1980 as a baseline to see how global temperature changes over time.

Collectively, the past eight years are the warmest years since modern recordkeeping began in 1880. This annual temperature data makes up the global temperature record -- which tells scientists the planet is warming.

According to NASA's temperature record, Earth in 2021 was about 1.9 degrees Fahrenheit (or about 1.1 degrees Celsius) warmer than the late 19th century average, the start of the industrial revolution.

"Science leaves no room for doubt: Climate change is the existential threat of our time," said NASA Administrator Bill Nelson. "Eight of the top 10 warmest years on our planet occurred in the last decade, an indisputable fact that underscores the need for bold action to safeguard the future of our country -- and all of humanity. NASA's scientific research about how Earth is changing and getting warmer will guide communities throughout the world, helping humanity confront climate and mitigate its devastating effects."

This warming trend around the globe is due to human activities that have increased emissions of carbon dioxide and other greenhouse gases into the atmosphere. The planet is already seeing the effects of global warming: Arctic sea ice is declining, sea levels are rising, wildfires are becoming more severe and animal migration patterns are shifting. Understanding how the planet is changing -- and how rapidly that change occurs -- is crucial for humanity to prepare for and adapt to a warmer world.

Weather stations, ships, and ocean buoys around the globe record the temperature at Earth's surface throughout the year. These ground-based measurements of surface temperature are validated with satellite data from the Atmospheric Infrared Sounder (AIRS) on NASA's Aqua satellite. Scientists analyze these measurements using computer algorithms to deal with uncertainties in the data and quality control to calculate the global average surface temperature difference for every year. NASA compares that global mean temperature to its baseline period of 1951-1980. That baseline includes climate patterns and unusually hot or cold years due to other factors, ensuring that it encompasses natural variations in Earth's temperature.

Many factors affect the average temperature any given year, such as La Nina and El Nino climate patterns in the tropical Pacific. For example, 2021 was a La Nina year and NASA scientists estimate that it may have cooled global temperatures by about 0.06 degrees Fahrenheit (0.03 degrees Celsius) from what the average would have been.

A separate, independent analysis by NOAA also concluded that the global surface temperature for 2021 was the sixth highest since record keeping began in 1880. NOAA scientists use much of the same raw temperature data in their analysis and have a different baseline period (1901-2000) and methodology.

"The complexity of the various analyses doesn't matter because the signals are so strong," said Gavin Schmidt, director of GISS, NASA's leading center for climate modeling and climate change research. "The trends are all the same because the trends are so large."

NASA's full dataset of global surface temperatures for 2021, as well as details of how NASA scientists conducted the analysis, are publicly available from GISS (https://data.giss.nasa.gov/gistemp).

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