Why is July hotter than June?

July 21, 2017

Man, it’s hot.

But that’s July for you.

One thing I’ve always wondered is this: If the Summer Solstice (June 21) is the longest day of the year, then why isn’t it the hottest? After all, we’re getting the most sunlight out of any day of the year; plain logic says it should be hot. How come it’s after June 21, when the days begin getting shorter, that things really start to heat up?

Being someone pre-disposed to think about such things, I wondered this for years.

Finally, I got an explanation thanks to a series on Netflix called “Orbit: The Earth’s Extraordinary Journey.”

“Orbit” is a BBC documentary series presented by Kate Humble and Helen Czerskiwhich which aired in 2012. But even at 5 years old, it is still worth watching.

The three-episode series follows the Earth through its 365.25-day journey around the sun over the course of a year. It examines each of the seasons, of course, but also looks at why certain regions are deserts, others are rain forests and others are tundra. We learn that the corresponding latitude to ours in the southern hemisphere is much cooler during its own summertime. We also learn about how the wind shapes our climate zones.

But back to my original question: “Why is July hotter than June?”

Well, you can thank the oceans for causing a lag of seasons.

You see, the water in the ocean takes longer to heat up than the land. In the northern hemisphere, approximately 60 percent of our surface is water and 40 percent of it is land. Of the land on earth, 68 percent of it is in the northern hemisphere. This includes all of North America, Europe and Asia, most of Africa and part of South America. Land also heats up much faster than water and much of our weather develops when the cool ocean air meets up with the hot land air.

Now, our coordinates here in Batesville are 35.7698° North, 91.6410° West. Flip that and turn the North to a South and you’ll find our corresponding spot on the southern hemisphere is in the middle of the Pacific Ocean, somewhere about 800-1,000 miles west of Chile.

So, let’s assume that we’re just going to mosey on east back onto land, to a city at the exact same latitude called Curico. Right now it is winter in the southern hemisphere and Curico’s highs are only in the mid-40s to lower-50s, not too dissimilar to what we see sometimes in January. Their average temperature will stay a little warmer than ours, though, due to the influence of the Pacific Ocean.

If you move forward to January, which would be the equivalent of July for us in the northern hemisphere, you’ll find that the average temperature is 84.6 degrees Fahrenheit. In Batesville, our average high in July is 93 degrees: Much hotter and I’m sure you can feel it.

Curico is on the narrower end of the South American continent, so it’s pretty close to both the Atlantic and Pacific oceans. This is why they seem to have such mild weather, despite being the same distance as us from the equator.

You see, the oceans not only warm up slower, but they also cool down slower. That’s why in the northern hemisphere, January and February are often colder than December. With less ocean and more land, it heats up quite quickly.

So, why the temperature difference? Well, not only does it have much less of the world’s land mass, only 32 percent, it is also mostly ocean. The surface of the southern hemisphere is approximately 81 percent water (some of it ice) and only 19 percent land. You’ll also notice that much of that land in the southern hemisphere is close to the equator, which is warmer no matter what side you’re on. South America is the only settled continent that reaches deep into that hemisphere.

Another interesting fact, South America’s winter occurs when the planet is at its furthest point from the sun, which may or may not have a big impact — that was never made clear to me. Our winter marks when the earth is closest to the sun.

Now, you may not find this information useful, but it does give you a picture of how integral the oceans are to us having a comfortable existence. With the average temperature of the oceans rising every year, we’ll find our own temperatures on land correspond.

Anyway, go watch “Orbit: The Earth’s Extraordinary Journey” on Netflix while they still have it.

Originally printed in the Batesville Daily Guard
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