“Science leaves no room for doubt: Climate change is the existential threat of our time,” when the US space agency Nasa’s administrator Bill Nelson said this last Thursday, he was reiterating the bitter truth, as scientists have been warning time and again. His statement came along with the announcement that 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). Scientists at Nasa’s Goddard Institute for Space Studies in New York City produce this record using data from instruments all over the world, which is validated by satellite data. They update the record every year, maintaining one of the world’s most important datasets to study the extent, pace and causes of warming on our home planet.
Continuing the planet’s long-term warming trend, global temperatures in 2021 were 0.85 degrees Celsius (C) above the average for Nasa’s baseline period, 1951-1980. 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 1.1C warmer than the late 19th century average, the start of the industrial revolution. Nelson explained that 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 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, he observed.
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 on Nasa’s Aqua satellite. Scientists analyse 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 0.03C 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 take home point is that rising temperatures are causing ice sheets and glaciers worldwide to melt, heatwaves to be longer and more intense, and plants and animal habitats to shift as they respond to warming.
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