Is climate change natural?

I. “The weather changes all the time. There are even cold spells!” True, but it’s not the same thing.

It’s easy to refer to a cold snap, as Donald Trump has done, to prove that global warming doesn’t exist.

Don't confuse weather and climate.

Weather is an instant and local phenomenon, such as temperature, rain and wind. Climate, on the other hand, is based on statistics: averages and variability of such phenomena over long periods and on a global scale. The reference period set by the World Meteorological Organization to establish averages that characterize a climate is 30 years.

The correct definition of “climate disruption.”

Climate disruption refers to sustainable modification caused by human activity on the global climate “compounded with natural climate variability observed over similar periods”.

However, it is not easy to model climate disruption given the number of phenomena and variables involved. Simple equations are not enough.

To model climate change, IPCC experts rely on numerous simulations of the atmosphere, oceans and ice sheets, landforms, vegetation, clouds, and greenhouse gases. Global analysis and forecasts are possible using a combination of climate models.

A general indicator was nevertheless chosen as a reference to symbolize and measure climate change: “global warming”.

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That’s the difference between the average temperature on the Earth’s surface at a given time and the known average temperature during the pre-industrial era, between 1850 and 1900.

II. "The climate has always changed naturally." True, but this is different.

The planet has undergone major climate changes throughout history. They are due to three astronomical parameters called the "Milankovich cycles":

• First parameter: "obliquity” - the axial tilt of the Earth which varies approximately every 41,000 years.
• Second parameter: “eccentricity” - the shape of the Earth’s orbit around the sun, which defines its distance from the sun. This trajectory oscillates between an almost perfect circle and an ellipse approximately every 100,000 years.
• Third parameter: "axial precession” - the change in the direction of the Earth’s axis of rotation, like a top. The rotation of the axis makes a circle in roughly 23,000 years.
  

These three parameters, amongst others, have contributed to global climate evolution for millions of years. They influence the quantity of solar energy received, causing hotter or cooler summers, for example.

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Scientists have observed alternation over the last million years between ice ages and interglacial periods.

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We have been in an interglacial era for 11,000 years. Theoretically, the Earth should cool down and enter a new ice age within a decade or so. So, it’s true. The climate has always changed naturally!

And yet, the climate change we are now observing is unprecedented.

The IPCC is clear in its fifth synthesis report published in 2014: “Warming of the climate system is unequivocal and, since the 1950s, many of the observed changes are without precedent over decades to millennia.”

Not only is the Earth heating up, it’s heating up very quickly. Changes that took several thousand years in the past now only take a few hundred years.

Compare the solar energy received on Earth with the average temperature on the globe’s surface. Observe the difference between the natural evolution caused by the Milankovich cycles before 1950 and changes since. The two curves correlated until 1950. They have completely digressed since. The Earth is receiving a stable amount of solar energy, but the temperature has jumped by one degree.

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This shows that current global warming is both unnatural and unprecedented. In the past, a positive or negative change of five degrees took tens of thousands of years. The temperature has already increased by a degree in less than one hundred years. It’s a first!