Q: Where was the annual temperature warmer or cooler than usual?
A: Colors
show where average annual temperature was above or below its 1991-2020
average. Blue areas experienced cooler-than-usual temperatures for the
year while areas shown in red were warmer than usual. The darker the
color, the larger the difference from the long-term average temperature.
Q: Where do these measurements come from?
A: Weather
stations on every continent record temperatures over land, and ocean
surface temperatures come from measurements made by ships and buoys.
NOAA scientists merge the readings from land and ocean into a single
dataset. To calculate difference-from-average temperatures—also called
temperature anomalies—scientists calculate the average annual
temperature across hundreds of small regions, and then subtract each
region’s annual average from 1991-2020. If the result is a positive
number, the region was warmer than the long-term average. A negative
result from the subtraction means the region was cooler than usual. To
generate the source images, visualizers apply a mathematical filter to
the results to produce a map that has smooth color transitions and no
gaps.
Q: What do the colors mean?
A: Shades
of red show where average annual temperature was warmer than the
average from 1991–2020. Shades of blue show where the annual average was
cooler than the long-term average. The darker the color, the larger the
difference from average temperature. White and very light areas were
close to their long-term average temperature. Gray areas near the North
and South Poles show where no data are available.
Q: Why do these data matter?
A: Over
time, these data give us a planet-wide picture of how climate varies
over years and changes over decades. Each year, some areas are cooler
than the long-term average and some areas are warmer. Though we don’t
see an increase in temperature at every location every year, the
long-term trend shows a growing portion of Earth’s surface is warmer
than it was during the base period.
Q: How did you produce these snapshots?
A: Data
Snapshots are derivatives of existing data products: to meet the needs
of a broad audience, we present the source data in a simplified visual
style. NOAA's Environmental Visualization Laboratory (NNVL) produces the
source images for the Difference from Average Temperature – Yearly
maps. To produce our images, we run a set of scripts that access the
source images, re-project them into desired projections at various
sizes, and output them with a custom color bar.
Additional information
Source images
available through NOAA's Environmental Visualization Lab (NNVL) are
interpolated from data originally provided by the National Center for
Environmental Information (NCEI) - Weather and Climate. NNVL images are
based on NOAA's Merged Land-Ocean Surface Temperature Analysis (MLOST).
* Temperature - Global Yearly, Difference from Average _NOAA Climate.gov.pdf is a screenshot of the main Climate.gov site for these snapshots (
* Cimate_gov_ Data Snapshots.pdf is a screenshot of the data download page for the full-resolution files.