Global warming is natural evidence

The idea that Global Warming is a natural cycle is well understood from paleo data covering the past 1 million years. Is there a difference between current climate, and the natural cycle? For the past million years the natural climate has oscillated between warm periods and ice ages. This shifting in and out of warm periods and ice ages is correlated strongly with Milankovitch cycles. In order to understand the difference between natural cycle and human-caused/influenced global warming, one needs to consider changes in radiative forcing and how this affects systems on Earth such as the atmosphere, vegetation, ice and snow, ocean chemistry and ocean heat content overturn cycles and related effects. The current radiative forcing levels are clearly outside of the natural cycle range.

Is global warming a natural cycle? Or is global warming affected by human influence? What does the science say? Both are true. In the natural cycle, the world can warm, and cool, without any human interference. For the past million years this has occurred over and over again at approximately 100, 000 year intervals. About 80-90, 000 years of ice age with about 10-20, 000 years of warm period, give or take some thousands of years.

The difference is that in the natural cycle CO2 lags behind the warming because it is mainly due to the Milankovitch cycles. Now CO2 is leading the warming. Current warming is clearly not natural cycle.

Where are we currently in the natural cycle (Milankovitch cycle)? The warmest point of the last cycle was around 10, 000 years ago, at the peak of the Holocene. Since then, there has been an overall cooling trend, consistent with a continuation of the natural cycle, and this cooling would continue for thousands of years into the future if all else remained the same. But since 1750 however, the CO2 content of the atmosphere has deviated from the natural cycle. Instead of decreasing, it has increased because of the fossil-fuel burning. Methane and nitrous oxide have also increased unnaturally because of agricultural practices and other factors. The world has also warmed unnaturally. We are now deviating from the natural cycle.

The natural cycle is understood by examining the paleo records. The fact that the earth goes in and out of ice ages distinctly outlines the natural cycles of Earth's climate. This occurs about every 100, 000 years. We are currently in a warm period. Generally, Earth spends about 80-90, 000 years in an ice age and around 10-20, 000 years (or so) in a warm period.

12, 000 Years

The Holocene temperatures peaked around 8, 000 years ago. This temperature peak was associated with the perihelion phase of the Milankovitch cycles. That was when it is estimated that the natural cycle climate forcing was at maximum, including associated climate feedbacks. Since then the forcing levels have been slowly dropping and the temperature has been following the slope of forcing in line with the changes in the Milankovitch cycle forcing combined with system feedbacks.

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