Jan 19, 20213 min
Earth's global average surface temperature in 2020 tied with 2016 as the warmest year on record
The last seven years have been the warmest seven years on record, typifying the ongoing and dramatic warming trend.
Tracking global temperature trends provides a critical indicator of the impact of human activities -- specifically, greenhouse gas emissions -- on our planet. Earth's average temperature has risen more than 2 degrees Fahrenheit (1.2 degrees Celsius) since the late 19th century.
Rising temperatures are causing phenomena such as loss of sea ice and ice sheet mass, sea-level rise, longer and more intense heatwaves, and shifts in plant and animal habitats. Understanding such long-term climate trends is essential for the safety and quality of human life, allowing humans to adapt to the changing environment in ways such as planting different crops, managing our water resources and preparing for extreme weather events.
A separate, independent analysis by the National Oceanic and Atmospheric Administration (NOAA) concluded that 2020 was the second-warmest year in their record, behind 2016. NOAA scientists use much of the same raw temperature data in their analysis but have a different baseline period (1901-2000) and methodology.
In contrast, global shutdowns related to the ongoing coronavirus (COVID-19) pandemic reduced particulate air pollution in many areas, allowing more sunlight to reach the surface and producing a small but potentially significant warming effect. These shutdowns also appear to have reduced the amount of carbon dioxide (CO2) emissions last year, but overall CO2 concentrations continued to increase, and since warming is related to cumulative emissions, the overall amount of avoided warming will be minimal.
The largest source of year-to-year variability in global temperatures typically comes from the El Nino-Southern Oscillation (ENSO), a naturally occurring cycle of heat exchange between the ocean and atmosphere. While the year has ended in a negative (cool) phase of ENSO, it started in a slightly positive (warm) phase, which marginally increased the average overall temperature. The cooling influence from the negative phase is expected to have a larger influence on 2021 than 2020.
NASA's analysis incorporates surface temperature measurements from more than 26,000 weather stations and thousands of ship- and buoy-based observations of sea surface temperatures. These raw measurements are analyzed using an algorithm that considers the varied spacing of temperature stations around the globe and urban heating effects that could skew the conclusions if not taken into account. The result of these calculations is an estimate of the global average temperature difference from a baseline period of 1951 to 1980.
Source: NASA