Do Milankovitch Cycles fully explain climate change?

Question

The Milankovitch Cycles is the effect on the climate caused by variations in astronomical movements by the Earth relative to the Sun.

A recent Natural News article attributes of the recent effects of climate change to Milankovitch Cycles:

For more than 60 years, the National Aeronautics and Space Administration (NASA) has known that the changes occurring to planetary weather patterns are completely natural and normal. But the space agency, for whatever reason, has chosen to let the man-made global warming hoax persist and spread, to the detriment of human freedom.

I read through the linked NASA articles but I didn't find anything corresponding to warming of the Earth whatsoever.

Another example of the claim: Hal Turner Radio Show article

Do Milankovitch Cycles fully explain the current global warming tendencies?

Answer 1

The articles try to do some sleight-of-hand poorly. It goes on at great length about the accepted Milankovitch cycles (mostly taken straight from the NASA article, the same agency which is supposed to be untrustworthy) to pad its scientific credibility. Then leaps to its conclusion while providing no evidence, instead banging on about conspiracies.

The article itself contains the central problem with their thesis.

“… orbital variations remain the most thoroughly examined mechanism of climatic change on time scales of tens of thousands of years and are by far the clearest case of a direct effect of changing insolation on the lower atmosphere of Earth.”

(Note that Milankovitch cycles' effect on long-term climate is not clear. This quote is pulled, out of context, from 1982, 37 years ago. We've gotten better at climate science since.)

Milankovitch cycles happen on a scale of tens of thousands of years. And we are indeed in an interglacial warm period. However those long-term cycles do not explain the observed temperature variations in mere decades.

Source: NASA

Furthermore, the observed changes in solar radiation, 0.05 Watts/m^2, do not match with the change necessary to produce the observed climate change of about 2.8 Watts/m^2.

Source: IPCC

These sort of "gotcha" articles come from a gross misunderstanding of how climate models work. They disingenuously expect naivety on the part of thousands of climate scientists to not have included something as obvious as Milankovitch cycles in their models while offering no models of their own.

Good climate models contain known natural and human factors. They include radiative forcing, changes in how much energy we receive and retain from the Sun. These include the very well known Milankovitch cycles. The models which exclude human factors do not match our observations. The ones which do include human factors match.

Source: Union of Concerned Scientists

As you can see, solar variability is a component of their model and does not explain the recent warming trends of the last couple decades.

The Union Of Concerned Scientists has this to say about the effect of solar radiation on climate change.

We do know with a good degree of certainty that between 1750-2011, or since the beginning of the industrial period until today, the average increase in energy hitting a given area of the atmosphere (radiative forcing, measured in a unit called watts per square meter) due to heat-trapping gases is 56 times greater (~ 2.83 watts per square meter) than the increase in radiative forcing from the small shift in the sun’s energy (~0.05 watts per square meter).

In its Fifth Assessment Report, IPCC scientists evaluated simulations of historical climate variables using a number of numerical models. They first assumed no increase in heat-trapping gases since 1750, so that the temperatures calculated were those that would have been achieved if only solar variability, volcanic eruptions, and other natural climate drivers were included.

The temperature results were similar to observed temperatures only for the first half of the century, but the models did not accurately show the general warming trend that has been recorded during the second half of the twentieth century.

When computer models include human-induced heat-trapping gases, they accurately reproduce the observed warming during the twentieth and twenty-first centuries.

The evidence shows that although fluctuations in the amount of solar energy reaching our atmosphere do influence our climate, the global warming trend of the past six decades cannot be attributed to changes in the sun.

Source: Union of Concerned Scientists

See Also

• Union Of Concerned Scientists: How Does the Sun Affect Our Climate?
• IPCC AR5 Synthesis Report

Answer 2

No, there is no proof that the Milankovitch Cycle fully explains the current global warming tendencies. The article you linked to includes a sensationalist headline which the article itself makes no attempt to support, and in fact explicitly denies. The headline states:

NASA admits that climate change occurs because of changes in Earth’s solar orbit, and NOT because of SUVs and fossil fuels

However, the article itself makes no such claim, instead merely asserting that NASA observed in 1958 that changes in the earths orbit and tilt cause warming and cooling of the climate, and published information about the Milankovitch Cycles on their website in 2000. It goes on to explain the discovery and gradual acceptance of the Milankovitch Cycle theory, which is now the accepted explanation for the glacial and interglacial cycles on earth over the past million years or so as explained here, for example.

The article contains many sensationalist statements, but they are all the words of the author, rather than anything sourced from NASA. The article directly contradicts its own headline with the statement

But NASA has thus far failed to set the record straight, and has instead chosen to sit silently back and watch as liberals freak out about the world supposedly ending in 12 years because of too much livestock, or too many plastic straws.

So clearly, NASA has not "admitted" that climate change is "...NOT because of SUVs and fossil fuels."

Milakovitch Cycles are the accepted explanation for the long-term climate changes which have caused repeating ice ages, but provides no explanation for the rapid warming that is observed today. The article contains nothing to discredit the overwhelmingly accepted explanation that current warming trends are a direct result of human-caused increases in greenhouse gases.

Answer 3

No. The problem is the unfortunate use of the weasel-worded term "climate change" when people really mean global warming, and almost always ANTHROPOGENIC global warming.

Milankovich cycles do a pretty good job of explaining past changes in climate. That climate change is a natural process driven in large part by those cycles. (Though of course there are other factors.) Global warming is the result of humans adding lots of CO2 to the atmosphere by burning fossil fuels. Not related to the Milankovitch cycles at all - indeed, IIRC the natural cycle should have the planet in a very gradual cooling trend: https://en.wikipedia.org/wiki/Milankovitch_cycles#Present_and_future_conditions

Answer 4

The relative contributions of natural and anthropogenic forcings are nicely illustrated in Figure 10.1 of the IPCC's AR5 report here. It's in Chapter 10: "Detection and Attribution of Climate Change: from Global to Regional" and I've added it below. (The caption is a separate image as they looked odd as a single image.)

The left-hand column of images shows global mean surface temperatures (GMST) with (a) both natural and anthropogenic sources of greenhouse gases, (b) natural and anthropogenic sources separated (natural: red and blue; anthropogenic: black) and (c) anthropogenic only. Solar forcings, which include the effect of the Milankovitch cycles, cannot account for the observed increase in GMST.

This text refers to the figure specifically, and I've added some links to the papers:

Figure 10.1a shows that when the effects of anthropogenic and natural external forcings are included in the CMIP5 simulations the spread of simulated GMST anomalies spans the observational estimates of GMST anomaly in almost every year whereas this is not the case for simulations in which only natural forcings are included (Figure 10.1b) (see also Jones et al., 2013; Knutson et al., 2013).

...and these (along with other statements) are from the executive summary, the first relating specifically to solar forcing:

Solar forcing is the only known natural forcing acting to warm the climate over this period but it has increased much less than GHG forcing, and the observed pattern of long-term tropospheric warming and stratospheric cooling is not consistent with the expected response to solar irradiance variations

It is extremely likely that human activities caused more than half of the observed increase in GMST from 1951 to 2010.