It’s important to realize that global temperatures and atmospheric CO2 levels have fluctuated greatly through entirely natural causes over hundreds, thousands, and millions of years.

This began long before humankind lit cave fires, ancient Romans donned cool togas and sandals, or Icelandic Vikings tended cattle, sheep and goats on previously warm southwestern coastal Greenland grasslands.

Incidentally, ice core and ocean sediment records show that those temperature changes led, rather than followed, changes in atmospheric CO2 levels — not the other way around.

No, there is certainly nothing new about cyclical, often abrupt climate changes, most particularly those that occur during relatively brief interglacial periods, such as the one we currently have the great fortune to enjoy.

Over the past 400 thousand years, much of the Northern Hemisphere has been covered by ice up to three miles thick at regular intervals lasting about 100 thousand years each. Far shorter inter-glacial cycles lasting about 12 to 18 thousand years, like our current one-have offered reprieves from the bitter cold.

So yes, from this long-term perspective, there can be no question that current temperatures are indeed abnormally warm.

The average temperature of our planet has been gradually increasing on a fairly constant basis over the past 18,000 years or so since it began thawing out of the last Ice Age. By about 12 to 15 thousand years ago, Earth had warmed enough to halt the advance of the glaciers, causing sea levels to rise about 400 feet.

A very brief review of recent history (at least according to Earth’s large calendar) may provide some much-warranted perspective.

Let’s start with a period from about 750 B.C. to 200 B.C., before the founding of Rome, when temperatures had dropped from a previously warmer time much like today. A resulting cooler, drier climate caused river and lake levels to drop in Egypt and Central Africa.

The Tiber River froze, and snow remained on the ground for previously unimaginable long periods. European glaciers advanced, trapping sufficient water to caused sea levels to slightly drop.

Then, the climate warmed up again. Grapes which were first reported in Rome about 150 BC. Italian grapes and olives were soon being cultivated in large abundance than would not have been possible during earlier centuries.

By about 350 A.D., the climate became milder in northern regions, and tropical regions became much wetter. Heavy rains in Africa caused high-level Nile floods, and Central America and the tropical Yucatan experienced similar conditions. By the late fourth century, the climate may have been warmer than now.

Conditions then began to cool again by around 800 A.D.

Ice formed once more on the Nile. But then, guess what!

In about 900 A.D., it again began to become warmer. Many castles were built in Europe.

By 1300 A.D. — thanks to longer growing seasons that enabled crop rotations with higher yields — the British population doubled to about 5.5 million.

A decline in high winds and fierce storms favored more shipping, and trade fairs began to occur in about 1000 AD.

The Norse colonized Greenland and caught codfish and seals in ice-free seas.

This time was called the Medieval Warm Period, and is also referred to by another term — the Medieval Climate Optimum, and for very good reasons. It was much like it is today.

Year-round food crop abundance during the Medieval Warm Period again supported European population growth and prosperity. In addition, mountain passes stayed open longer during summers, enabling luxury goods, such as spices from Oriental caravans, sugar from Cyprus, and Venetian glass, to be traded for English woolens and Scandinavian furs.

Once again, the warm times were global good times.

Thousands of temples were constructed in Southeast Asia, including Angkor Wat, suggests very favorable weather for food and labor.

That good fortune chilled when temperatures began to drop again around 1200 A.D.

Atlantic pack ice began to grow around 1250, and shortened growing seasons and unreliable weather patterns, including torrential rains in Northern Europe, led to the Great Famine of 1315 to 1317.

By approximately 1350, Eric the Red’s Viking descendants had abandoned their Greenland farming settlements.

Between 1550 and 1700, even colder climate shifts caused record food shortages that claimed millions of lives.

Advancing Alpine glaciers gradually engulfed farms and villages by the mid-17th century.

The Thames River and New York Harbor froze over by 1780, and sea ice closed shipping harbors in Iceland, where an estimated one-third of the population perished.

Known as the Little ice age this brutal period thankfully ended during the mid-1800s; notably before the Industrial Revolution introduced smoke stacks and SUVs.

Nevertheless, let’s not get too complacent that Mother Nature won’t change her mind again  — along with the climate — long before that next likely scheduled deep-freeze whopper Ice Age occurs in another 3,000 years or so.

At least for now, show her a little gratitude.