The World Meteorological Organization says the warmest day in recorded history in terms of global average temperature was 22 July 2024, at 17.15 °C / 62.85 °F.
That same press release also gives a few previous record holder dates. All the listed dates are in July and August, i.e., Northern hemisphere summer. Is there a particular reason why the hottest day in terms of global average should be when it’s summer in the Northern rather than the Southern hemisphere? I know the Northern hemisphere has more land, and a much higher population, than the Southern one; but wouldn’t temperature anomalies be just as likely to occur South of the equator and heat up the oceans there?
The Northern Hemisphere contains about 2/3 of the earth’s total land mass. Land heats up much more quickly than water, so NH summer is going to have a more dramatic and immediate impact on global temperature. That’s likely the dominant factor. The larger population in the NH also means more localized GHG emissions and more urban heat islands, though those are much lesser factors.
Another factor is that year-by-year reduction of arctic ice cover in the NH has been rapidly increasing Arctic temperature (“Arctic amplification”) while Antarctic ice cover exhibits a more complex pattern and has sometimes actually been growing due to increased amounts of sea ice.
As noted above, the ocean tends to moderate seasonal temperature swings, so not as cold in the winter or hot in the summer. Consider the climate of the east and west coasts of the United States compared with the interior, for an example.
Overall temperature extremes tend to lag the solar cycle by about a month, so the hottest days are in late July, one month after the summer solstice, and the coldest days in late January, one month after the winter solstice. Local conditions may muddle this, but it’s true on average.
You can look at it from the standpoint that the Northern Hemisphere has twice as much land area as the South, or that the Southern Hemisphere has twice as much ocean surface as the North.
I prefer to think of it in terms of the north’s much larger land area heating up quickly, and then the infrared radiation being “trapped” (technically, absorbed and retransmitted) by greenhouse gases, whereas sea surface temperatures warm quite slowly in comparison. Oceans absolutely do moderate temperatures, but northern Australia is still tropical.
Because the Earth is closest to the sun in July and furthest in January . Oh wait, no it’s the other way around. Whatever the reason, Earth’s distance from the sun isn’t it.
Didn’t you ever stand outside next to a window air conditioner and feel all the hot air being blown out from it? Summers are hotter because people run their air conditioners during the summer.
The Earth is about 3 million miles closer to the sun in January than July, so it receives about 7% more total solar energy in southern summer than northern summer.
So you’re right that the distance isn’t the reason the higher temperatures are recorded in the north. But it points to how big an impact the difference in landmass has, that it is counteracts the increased total radiation.
. Oh wait, no it’s the other way around. Whatever the reason, Earth’s distance from the sun isn’t it.