The average temperature in July is not a single, universal number, but a dynamic, measured concept known as a climate normal. July is a significant month because it generally represents the peak of the Northern Hemisphere’s summer season, which covers the majority of the world’s landmasses and population. This climate normal serves as a reference point for meteorologists to compare current weather and forecast future conditions.
How Climatologists Calculate the Average
Climatologists rely on a standardized method to establish a reliable average temperature, known as a “climatological standard normal.” This value is not a simple yearly average, but a mean calculated from observations taken over a consistent 30-year period, a standard set by the World Meteorological Organization (WMO). The current standard period used by organizations like the National Oceanic and Atmospheric Administration (NOAA) is 1991–2020.
To determine the July average for a specific location, scientists first collect daily temperature measurements from weather stations, calculating the mean of the daily high and low temperatures for each day of the month. These daily mean temperatures are then averaged across all 31 days of July for each of the 30 years in the reference period. This process yields a stable baseline temperature that smooths out the year-to-year variability in weather.
Why July Is Globally the Warmest Month
July typically holds the record for the highest global average temperature compared to any other month, a phenomenon rooted in Earth’s geography and orbit. Paradoxically, Earth is farthest from the sun, at aphelion, during early July, receiving slightly less solar energy overall than it does in January. The dominance of the Northern Hemisphere is the primary reason for the warmth, as it contains about two-thirds of the planet’s landmass.
Land heats up and cools down much more quickly than water, which has a high heat capacity and acts as a climate moderator. Since the Northern Hemisphere is tilted toward the sun during this time, the extensive land areas rapidly absorb solar radiation, significantly raising the hemisphere’s temperature. The peak heating does not occur at the summer solstice in late June, but is delayed due to a phenomenon called seasonal lag. This lag occurs because the Earth’s surface and atmosphere continue to absorb and accumulate heat well into July, pushing the average temperature higher than the preceding months.
Temperature Extremes and Regional Variation
A single global July average is not useful for practical purposes, as the actual temperature varies drastically depending on location and climate zone. In the Northern Hemisphere’s temperate zones, July is the height of summer, resulting in high average temperatures. For example, a location like Central, South Carolina, sees July daily high temperatures averaging around 89°F (31.7°C), with lows around 70°F (21.1°C).
Equatorial and tropical regions experience far less seasonal temperature variation, meaning their July averages may not be much different from their January averages. The Southern Hemisphere, however, is experiencing its mid-winter in July, resulting in the lowest annual temperatures for that half of the globe. Southern Hemisphere cities like Buenos Aires, Argentina, have July averages with high temperatures around 57°F (14°C) and lows near 47°F (8.3°C). Sydney, Australia, similarly experiences its coldest month in July, with average maximums around 63°F (17°C) and minimums near 46°F (8°C).
Understanding Shifting Climate Normals
The concept of a fixed 30-year average is periodically updated to account for the dynamic nature of Earth’s climate, a necessity that reflects long-term warming trends. The WMO mandates that these normals be updated every decade, which means the baseline is consistently shifting to incorporate more recent, warmer years. When the standard shifted from the 1981–2010 period to the current 1991–2020 period, the resulting average temperature for July increased across most regions.
This update means that a July day once considered “above average” under the old normal might now be considered closer to the new, warmer normal. The continual need to update the baseline temperature emphasizes that the climate is not static, and the resulting averages are trending upward.