The Atmospheric Infrared Sounder (AIRS) instrument aboard NASA’s Aqua satellite senses temperature using infrared wavelengths. This image shows temperature of the Earth’s surface or clouds covering it for the month of April 2003. The scale ranges from -81 degrees C (-114 F) in black/blue to 47 C (116 F) in red.

Earth is the only planet we know of that can support life. The planet is not too close or too far away from the sun. It lies in a "Goldilocks zone" that is just right — not too hot, not too cold.

The distance from Earth to the sun is one of the most important factors in making Earth habitable. The next closest planet to the sun, Venus, for example, is the hottest planet in the solar system. Temperatures there reach more than 750 degrees Fahrenheit (400 degrees Celsius), while the average temperature on Mars is minus 80 F (minus 60 C).

Earth's atmosphere also plays a vital role in regulating the temperature by providing a blanket of gases that not only protects us from excessive heat and harmful radiation from the sun, but also traps heat rising from the Earth's interior, keeping us warm.

Open to interpretation

Absolute estimates of the global average temperature are difficult to compile. Global temperature data comes from thousands of observation stations around the world, but in some regions, such as deserts and mountaintops, stations are rare. Also, different groups, analyzing the same data, use different methods for calculating the global average. These differences in methodology sometimes produce slightly different results.

Data from the observation stations are compared to historical data from a long-term period (and different groups use different time spans). The differences in temperatures, called anomalies, are plotted on a grid. Some grids may be empty because there were no observations recorded. Gaps in data are treated differently by different groups.

For example, NASA's Goddard Institute for Space Studies (GISS) assumes that temperature anomalies are about the same up to about 1,200 kilometers from a station. That way, they can estimate temperatures using a smaller number of stations, especially in the polar regions. The National Oceanic and Atmospheric Administration (NOAA), on the other hand, fills in fewer of the gaps, and produces a more conservative estimate.

The NOAA tracks anomalies relative to temperatures between 1901 and 2000. According to the NOAA's data, anomalies calculated for 2017 were 1.5 degrees F (0.83 C) higher than the average temperatures for all the years in the 20th century.

GISS measures the change in global surface temperatures relative to average temperatures from 1951 to 1980. GISS data show global average temperatures in 2017 rose 1.62 degrees Fahrenheit (0.9 degrees Celsius) above the 1951-1980 mean. According to GISS, the global mean surface air temperature for that period was estimated to be 57 F (14 C). That would put the planet's average surface temperature in 2017 at 58.62 F (14.9 C).

Temperature extremes

According to the World Meteorological Organization, the coldest place on Earth is Vostok Station in Antarctica, where it reached minus 128.6 F (minus 89.2 C) on July 21, 1983. The coldest inhabited place is Oymyakon, Russia, a small village in Siberia, where it dips down to an average of minus 49 F (minus 45 C) and once hit a low of minus 96.16 F (minus 71 C).

Which location holds the record as the hottest place on Earth is a matter of some contention. El Azizia, Libya, held the top hot spot for 90 years. Temperatures allegedly climbed to 136.4 F (58 C) on Sept. 13, 1922. But the World Meteorological Organization stripped the town southwest of Tripoli of that distinction in 2012. A committee of climate experts from nine countries concluded that the temperature had been documented in error by an inexperienced observer.

So the "new" hottest place on Earth is Greenland Ranch (Furnace Creek) in Death Valley, Calif., where it reached 134 F (56.7 C) on July 10, 1913. But even that distinction depends on what is being measured. Death Valley's record is for the highest air temperature. A higher surface temperature of 159.3 F (70.7 C) was recorded by a Landsat satellite in 2004 and 2005 in the Lut Desert in Iran.

Highest and lowest temperatures by continent

Continent Temperature Date Location North America High: 134 F (56.7 C) July 10, 1913 Furnace Creek Ranch, Death Valley, Calif. Low: -81.4 F (-63 C) Feb. 3, 1947 Snag, Yukon Territory, Canada South America High: 120 F (48.9 C) Dec. 11, 1905 Rivadavia, Argentina Low: -27 F (-32.8 C) June 1, 1907 Sarmiento, Argentina Europe High: 118.4 F (48 C) July 10, 1977 Athens and Elefsina, Greece Low: -72.6 F (-58.1 C) Dec. 31, 1978 Ust 'Schugor, Russia Asia High: 129.2 F (54 C) June 21, 1942 Tirat Zevi, Israel Low: -90 F (-67.8 C) 1) Feb. 5, 1892

2) Feb. 6, 1933 1) Verkhoyansk, Russia

2) Oymyakon, Russia Africa High: 131 F (55 C) July 7, 1931 Kebili, Tunisia Low: -11 F (-23.9 C) Feb. 11, 1935 Ifrane, Morocco Australia High: 123 F (50.7 C) Jan. 2, 1960 Oodnadatta, South Australia Low: -9.4 F (-23 C) July 21, 1983 Charlotte Pass, New South Wales Antarctica High: 67.6 F (19.8 C) Jan. 30, 1982 Signy Research Station, Antarctica Low: -129 F (-89.2 C) July 21, 1983 Vostok Station, Antarctica

Source: World Meteorological Organization

Rising temps, rising seas

There is considerable uncertainty about how warm Earth will get in the coming decades, as climate change is complex. It depends on a variety of factors, including how quickly the ice melts in the Arctic and Antarctic, how the ocean will respond to warmer temperatures, and how the atmosphere will shift wind directions. Even little changes in solar activity affect Earth's temperature — but climate change is by far the more pressing problem.

The National Oceanic and Atmospheric Administration (NOAA) says average surface temperatures on Earth rose 1.71 degrees Fahrenheit (0.95 degrees Celsius) between 1880 and 2016, and that change is accelerating in recent years. In 2017, 159 nations ratified the Paris Agreement to try to halt the warming at 2.7 degrees F (1.5 degrees C) above Earth's average temperature before the Industrial Age. Given industry's and transportation's reliance on fossil fuels, many studies say that agreement will be difficult to keep to.

For example, a 2017 study in the journal Geophysical Research Letters suggests that Earth's climate will be 1.5 degrees higher as early as 2026. This would happen if the Interdecadal Pacific Oscillation (IPO) fluctuates back to a warm period, instead of its current cool period. (IPO changes similarly to El Niño and La Niña in the Pacific).

In early 2018, the U.S. National Academies released a report called "Thriving on Our Changing Planet: A Decadal Strategy for Earth Observation from Space." The report focused on the importance of satellite observations in gaining information about Earth's climate in the coming years. Some of its suggestions include observatories that can help with forecasting air quality and weather, and others that can look at metrics such as biodiversity change, extreme weather and the ocean's ability to store heat. [10 Climate Change Myths Busted]

— Additional reporting by Elizabeth Howell, Space.com contributor