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Evidence That Global Warming Is Being Caused by Humans

I have been studying the science of global warming with a passion since the late 1970s and earned a degree in Environmental Science in 1992.

This article will help you understand the ice age cycle and what's really causing temperatures to rise.

This article will help you understand the ice age cycle and what's really causing temperatures to rise.

Rising Temperatures

Earth’s temperatures have warmed over the past century as carbon dioxide levels have increased. There is a strong indication that implicates mankind’s release of greenhouse gases into the atmosphere as being the primary cause of global warming.

Since there is a lot of noise and misinformation in the debate regarding what the cause of rising global temperatures is, it is best to take a broader view of the cause and effect of global warming. How do we know that mankind’s emissions of greenhouse gases are the cause of the recent global warming trend? The best indication that mankind is responsible for the current global warming trend is found by taking a broad look at where the recent global temperature rise fits into the natural glaciation (ice age) and warm period (interglacial) cycle that the Earth has been going through for millions of years.

During the current interglacial warm period, the global average atmospheric temperature of Earth peaked about 7,000 years ago, then commenced on a long gradual decline to cooler temperatures until very recently.

During the current interglacial warm period, the global average atmospheric temperature of Earth peaked about 7,000 years ago, then commenced on a long gradual decline to cooler temperatures until very recently.

Since the 1980s solar radiation from the Sun has decreased, yet global temperatures increased over this same time period.

Since the 1980s solar radiation from the Sun has decreased, yet global temperatures increased over this same time period.

Why Are Global Temperatures Warming When an Ice Age Should Be Approaching?

The historical global average atmospheric temperature record shown above has been compiled by an array of scientists that study Earth’s past global temperatures by analyzing ice sheet cores and other data. The temperature record indicates that the Earth should be heading into another ice age right now at a time when Earth’s temperatures are warming.

The figure above shows the Earth’s global temperatures since it emerged from the last ice age and entered the current interglacial warm period, known as the Holocene epoch, about 11,000 years ago. As you can see, the global average atmospheric temperature of Earth peaked about 7,000 years ago and commenced a long gradual decline to cooler temperatures until they spiked higher in recent years to levels above the peak that occurred approximately 7,000 years ago.

An astronomer named Milutin Milankovitch from Serbia proposed in 1941 that ice ages are caused by changes in the Earth’s orbit around the Sun and its tilt in regards to the Sun. These changes occur in predictable cycles that, when aligned correctly, cause the amount of solar radiation reaching the Earth’s polar regions to diminish, which starts a new ice age cycle to commence.

\However, scientists determined that a lack of solar radiation was not enough to allow an ice age to progress beyond the initial stage. Scientists found that carbon dioxide levels had to reach a certain low level as ice formation during the initial cool-down removed carbon dioxide from the atmosphere in order to kick the Earth’s cooling feedback loops and subsequent ice age into high gear. As more water was frozen into ice, more carbon dioxide was removed from the Earth’s atmosphere, causing further temperature drops and a feedback loop that continued the cooling until large ice sheets grew over many of the continents and a full ice age had taken hold of Earth.

What does the glaciation (ice age) cycle have to do with looking for evidence that mankind is the cause of the recent global warming that Earth has been experiencing? To answer this question, it is important to understand the natural length of the Earth’s natural glaciation (ice age) cycle. An ice age lasts approximately 100,000 to 120,000 years, while the much briefer inter-glacial (warm) periods last approximately 10,000 to 12,000 years. With this understanding and the fact that the last ice age ended about 12,000 years ago, the Earth should be starting a new ice age right about now. The figure above clearly shows global average atmospheric temperatures gradually sliding lower until they recently spiked higher.

Why has the Earth broken its long-established ice age cycle and suddenly started warming when it appeared to be naturally ready to begin a new ice age? What is a variable that did not exist during prior interglacial periods? Mankind’s burning of fossil fuels and the subsequent increase in atmospheric carbon dioxide levels is the variable.

Looking back at the geological record and taking into consideration the glaciation cycle initially driven by the Earth and the Sun’s interaction, the global warming trend that has been evident for the past 150 years does not appear to be natural since the natural course in the Earth’s glaciation cycle is to be sliding into another ice age right now. This trend lower in temperatures has been halted and the climate has moved into a warming phase.

This graph shows global temperatures and  carbon dioxide accelerating higher in tandem in recent years.

This graph shows global temperatures and carbon dioxide accelerating higher in tandem in recent years.

Is Global Warming a Bad Thing? A Little Bit No, But if Left Unchecked, It Will Be Very Bad

It can be argued that a little man-induced global warming is a good thing since a new ice age would be very problematic for the supply of food that mankind relies upon and for life on Earth, as currently habitable land areas would become covered with ice.

However, global warming that occurs quickly will likely cause dire outcomes in the upcoming centuries for future generations of humans. Runaway global warming would cause sea levels to rise at an increasing rate, flooding the world’s population centers that are near sea level and low-lying food-producing areas. Additionally, some of the current farmable lands would become arid and unfarmable in a world that warms by several degrees Celsius.

Is it too late to stop runaway global warming? Perhaps it is. Even if the entire world switched from carbon-based fuels to non-carbon-based renewable energy next year, the buildup of carbon dioxide that has already occurred in the atmosphere would continue to increase global temperatures for many centuries into the future.

It takes natural processes a long time to remove carbon dioxide from the atmosphere. Additionally, the warming of the Earth’s atmosphere in the coming centuries will cause positive feedback loops that will increase the rate of global warming. Once the global temperature increases past a certain point, it will cause the release of large amounts of the potent greenhouse gas methane, which is currently frozen in polar regions of the Earth and under ocean floors.

If the Earth reaches the tipping point at which methane gas is liberated in increasingly large quantities from ice formations that it has been bound to for millions of years, global warming will enter a self-reinforcing positive feedback loop that will raise the average global temperature dramatically over time; a condition known as runaway warming.

Some of the world's rich farmland areas will suffer prolonged droughts in a rapidly warming world.

Some of the world's rich farmland areas will suffer prolonged droughts in a rapidly warming world.

© 2019 John Coviello