I've said, and written for years, that it's the height of human hubris to assume we know what this planet's "correct" temperature range is, much less that we can influence it enough to hold it at the level we deem to be optimal. In fact, that's a question that climate scolds never seem able to answer: "What is the Earth's correct temperature range, and how do we know what that range is?"
This planet is ancient beyond our ability to easily understand. Its climate is literally planetary in scale. We know some of the influences and the vast cycles on which the climate operates, but not all of them. Now, my standard disclaimer on this issue still applies: Yes, the Earth's climate does change, in the short term and long. Yes, human activity does have some effect on that climate. No, our effect isn't worth sacrificing our modern, technological lifestyle for.
So, what is the optimal temperature range for us self-centered humans? Well, we do know a few things, and they boil down to this: Warmer is better than colder. A look at two periods in history is illustrative; the Roman Warm Period, and the Little Ice Age.
First, the Roman Warm Period, which lasted from 250 B.C. to 400 A.D.
New research shows the Roman Warm Period (≈250 BC‑300 AD) was approximately 2 °C warmer than today, with wetter conditions across Iberia and Central Europe—evident from cave records and tree‑ring and stalagmite data confirming this humid era.
Summer temperatures 2–3 °C warmer than today between 250 BC and 150 AD.
Increased precipitation; wet Iberian Roman humid period indicated by Pyrenees cave records.
A warmer, damper climate led to increased crop yields. Much of the expansion of the Roman Republic and later, the Roman Empire happened in this warm, friendly time. Food security led to the growth of cities, of trade, and of culture; some of the greatest cultural advances in early Western Civilization happened in this time. Now, this time also allowed for military adventurism; it was during this time that Caesar conquered Gaul and invaded Britain. The expansion of trade also led to the expansion of diseases; every cloud has its silver lining, after all.
Second, the Little Ice Age, which lasted into the Industrial Revolution, from the mid-13th to the mid-19th century.
Little Ice Age (LIA), climate interval that occurred from the early 14th century through the mid-19th century, when mountain glaciers expanded at several locations, including the European Alps, New Zealand, Alaska, and the southern Andes, and mean annual temperatures across the Northern Hemisphere declined by 0.6 °C (1.1 °F) relative to the average temperature between 1000 and 2000 ce.
This was a time marked by cold winters with heavy snowfalls and cool, wet summers. It was a time of widespread crop failures, especially in Europe and North America. It was a time of shortages and economic instability. Soldiers on horseback captured ships stuck in ice. People struggled to survive through cold, dark winters. The cause? The largest solar Grand Minimum in 6,000 years, and an uptick in volcanic eruptions, which filled the skies with ash.
Unfortunately, as this period lasted into the early years of the Industrial Revolution, it's too often used as a baseline in climate history assumptions; when the scolds yap about warming, they are using one of the coldest periods since the last major glaciation as their standard. That's not a time any of us should want to go back to.
So, what is that optimal range? Is it between these two? The broad strokes are these: Warmer is better for humans and human society than colder.
So, what is the optimal global temperature for humankind? This period must be a time when agriculture was productive, civilizations expanded, ecosystems were stable, extreme cold was rare, and glaciers were not advancing into farmland and villages. Historically, when were these times? Refer to figure 3 and here and we see the best times for humans were the Holocene Climatic Optimum (~8000BC to 4200BC), the Medieval Warm Period (~800AD to 1250AD), and the Modern Warm Period (~1905 to present). These were the times that civilizations grew and prospered. Table 2 lists the average temperature in these periods from all three curves in figure 3. The average shown for the Modern Warm Period is mostly from the Pages2K instrumental data after it was moved to the same reference period used for the proxies.
This planet is roughly 4.6 billion years old. Through most of that history, it's been warmer than now. Warmer is better for life than colder; we see that in the planet's history and our own history. The historical times of great human advance and prosperity have all been times when it's warmer than it is now. And yet, the climate scolds, ignoring this data, these facts, somehow think they know better than the entire expanse of human history what the Earth's correct climate is.
This is why the entire climate change issue is a political issue, not a matter of science. Yes, the study of the Earth's climate is a scientific endeavor, or at least, it should be. But the arrogant notion that the scolds and only the scolds know where Earth's thermostat should be set and that they should be the ones with their hands on the dial — that's an arrogant, baseless political concern, and that's all it is.
