EXPLAINER

The world has faced its 12th straight month of historic heat, with this summer on track to be among the hottest yet.

While summer has only just begun in the Northern Hemisphere, heatwaves have already gripped many parts of the world including across the United States, Mexico, Europe, the Middle East and South Asia.

Extreme heat has led to more than a thousand deaths, urgent health warnings and school closures.

July is historically the hottest month of the year, where in parts of the Northern Hemisphere, temperatures regularly exceed 40C (104F).

According to the UN’s World Meteorological Organization (WMO), July 2023 was the warmest month ever recorded, likely the hottest for at least the past 120,000 years, with this year already on track to be one of the hottest yet.

Axial tilt and the summer solstice

The Earth is tilted 23.5 degrees on its axis as it orbits the sun.

This results in varying amounts of sunlight at different times of the year, which creates the changing seasons.

Astronomical summer starts on the summer solstice, which is around June 20 or 21 in the Northern Hemisphere and around December 21 or 22 in the Southern Hemisphere.

This is the day when the sun reaches its highest point in the sky at noon, leading to the longest day and shortest night of the year.

The part of the Earth that receives the most amount of direct sunlight is 23.5 degrees above the equator, which is known as the Tropic of Cancer.

This line passes through Mexico, the Bahamas, Egypt, Saudi Arabia, and India among other countries, contributing to very hot summers.

Summer in the Northern Hemisphere

While half of the Earth’s land mass experiences summer from June to September, roughly 90 percent of the world’s population lives in the Northern Hemisphere, where these months coincide with more direct sunlight and longer daylight hours.

In northernmost cities around the Arctic Circle, the sun does not set between late May and late July in a phenomenon known as the midnight sun.

Conversely, during the winter months, these same locations experience a polar night, where the sun remains below the horizon between late November and late January.

Why is the afternoon hotter than noon?

During the summer months, more of the sun’s energy is absorbed into the ground, which heats up the surrounding air and leads to warmer temperatures.

The time delay between the heating and releasing is known as seasonal lag.

The Earth’s surface, especially large bodies of water like oceans, which comprise 70 percent of the Earth’s surface, takes time to absorb heat from the sun and subsequently release it.

This explains why the peak temperature of the day occurs in the afternoon, not at midday, and why July, rather than June, typically experiences the highest average temperatures.

How to stay cool this summer

As summer temperatures soar in various regions across the globe, with some even shattering all-time heatwave records, staying cool becomes crucial. Fortunately, there are effective methods to beat the heat, whether you have access to air conditioning or not.

Here are 10 tips to help minimise the risk of heat stroke: